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1
Perrotta, Gino, Frank E. Fish, Danielle S. Adams, Ariel M. Leahy, Abigal M. Downs, and Megan C. Leftwich. "Velocity Field Measurements of the California Sea Lion Propulsive Stroke Using Bubble PIV." Fluids 7, no. 1 (December 22, 2021): 3. http://dx.doi.org/10.3390/fluids7010003.
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California sea lions are among the most agile of swimming mammals. Most marine mammals swim with their hind appendages—flippers or flukes, depending on the species—whereas sea lions use their foreflippers for propulsion and maneuvering. The sea lion’s propulsive stroke generates thrust by forming a jet between the flippers and the body and by dragging a starting vortex along the suction side of the flipper. Prior experiments using robotic flippers have shown these mechanisms to be possible, but no flow measurements around live sea lions previously existed with which to compare. In this study, the flow structures around swimming sea lions were observed using an adaptation of particle imaging velocimetry. To accommodate the animals, it was necessary to use bubbles as seed particles and sunlight for illumination. Three trained adult California sea lions were guided to swim through an approximately planar sheet of bubbles in a total of 173 repetitions. The captured videos were used to calculate bubble velocities, which were processed to isolate and inspect the flow velocities caused by the swimming sea lion. The methodology will be discussed, and measured flow velocities will be presented.
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Ng, Terry Fei Fan, Wm Kirk Suedmeyer, Elizabeth Wheeler, Frances Gulland, and Mya Breitbart. "Novel anellovirus discovered from a mortality event of captive California sea lions." Journal of General Virology 90, no. 5 (May 1, 2009): 1256–61. http://dx.doi.org/10.1099/vir.0.008987-0.
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A viral metagenomic study was performed to investigate potential viral pathogens associated with a mortality event of three captive California sea lions (Zalophus californianus). This study identified a novel California sea lion anellovirus (ZcAV), with 35 % amino acid identity in the ORF1 region to feline anelloviruses. The double-stranded replicative form of ZcAV was detected in lung tissue, suggesting that ZcAV replicates in sea lion lungs. Specific PCR revealed the presence of ZcAV in the lung tissue of all three sea lions involved in the mortality event, but not in three other sea lions from the same zoo. In addition, ZcAV was detected at low frequency (11 %) in the lungs of wild sea lions. The higher prevalence of ZcAV and presence of the double-stranded replicative form in the lungs of sea lions from the mortality event suggest that ZcAV was associated with the death of these animals.
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Hückstädt, L. A., and T. Antezana. "Behaviour of the southern sea lion (Otaria flavescens) and consumption of the catch during purse-seining for jack mackerel (Trachurus symmetricus) off central Chile." ICES Journal of Marine Science 60, no. 5 (January 1, 2003): 1003–11. http://dx.doi.org/10.1016/s1054-3139(03)00100-0.
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Abstract The fishery for jack mackerel (Trachurus symmetricus) off central Chile competes for the resource with southern sea lions (Otaria flavescens), and during purse-seining makes the fish more accessible to the pinnipeds. Interactions with sea lions were recorded during 31 purse-seine sets off central Chile during October 1999. The sea lion behaviour associated with the fishing operations was distinctive. Feeding, movement, predator avoidance, and resting displays were identified. The sea lions approached the purse-seiner as soon as net-setting began. The number of sea lions per set (0–50) was seemingly unaffected by school size of jack mackerel, number of purse-seiners on the fishing ground, whether fishing was by night or by day, the presence of killer whales, or the species being targeted. However, the number of sea lions at a purse-seine differed significantly between fishing grounds. Other effects of fishing operations on O. flavescens included incidental mortality and capture. The amount of fish consumed by the sea lions at a set was as much as 0.4% of the catch. The results of the interaction are documented and discussed in the light of likely interaction with the whole sea lion population, as well as the impact of the interaction on the fishery.
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Reyes, Pablo, Rodrigo Hucke-Gaete, and Juan Pablo Torres-Florez. "First observations of operational interactions between bottom-trawling fisheries and South American sea lion, Otaria flavescens in south-central Chile." Journal of the Marine Biological Association of the United Kingdom 93, no. 2 (September 21, 2012): 489–94. http://dx.doi.org/10.1017/s0025315412001282.
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This paper presents results of a study conducted on the trawling industrial fishery fleet of Merluccius gayi in south-central Chile, and the resulting interactions with the South American sea lion (Otaria flavescens). This study is based on observations made during September 2004, when incidental sea lion catch in the trawls was 6.3 sea lions/working day (1.2 sea lions/trawl−1). A total of 82 animals were incidentally caught, of which 12 were found dead, and the 70 remaining suffered from internal bleeding and/or fractures as a result of their capture. 83.3% of the fatalities occurred during nocturnal trawls, which comprise 30% of all observed trawls. Possible mechanisms of sea lion take are discussed. This note presents the first records of sea lions incidental by-catch by the trawler fleet along the south-east Pacific coast of Chile.
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Szteren, Diana, and Enrique Páez. "Predation by southern sea lions (Otaria flavescens) on artisanal fishing catches in Uruguay." Marine and Freshwater Research 53, no. 8 (2002): 1161. http://dx.doi.org/10.1071/mf02006.
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Southern sea lions (Otaria flavescens) forage in coastal fishery grounds in shallow waters, where they interact with coastal fishing activities. The main objective of this research was to evaluate the predation of southern sea lions on artisanal fishery catches and thus determine whether interactions with sea lions affected catches. Between July 1997 and March 1998, we observed 53 fishing events onboard artisanal fishing boats in four localities. The presence and number of sea lions around the boat and the numbers of each fish species consumed by sea lions were recorded by an onboard observer. To estimate the damage caused by sea lions to fishery catches, we considered two scenarios, a conservative scenario and a maximized scenario. Predation on catches was observed in 50.9% of all the fishing events and up to four sea lions were sighted in 67.9% of fishing events. Considering a conservative scenario, predation varied from 0.8 to 9.1% of the catch per unit effort (CPUE) depending on the location. Considering the maximized scenario, predation varied from 3.4 to 46.2%. However, no significant relationship was found between CPUE and the number of sea lions in any locality or with either type of fishing gear. Furthermore, CPUE did not differ in the presence or absence of sea lion interactions and predation per unit effort did not vary between localities or seasons. It was concluded that neither the presence of sea lions nor the damage they cause were responsible for variations in CPUE.
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Sigler, Michael F., Jamie N. Womble, and Johanna J. Vollenweider. "Availability to Steller sea lions (Eumetopias jubatus) of a seasonal prey resource: a prespawning aggregation of eulachon (Thaleichthys pacificus)." Canadian Journal of Fisheries and Aquatic Sciences 61, no. 8 (August 1, 2004): 1475–84. http://dx.doi.org/10.1139/f04-086.
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The availability of seasonally abundant energy-rich prey can be a significant factor for the survival and reproductive success of predator populations. Large numbers of Steller sea lions (Eumetopias jubatus) were attracted to a prespawning aggregation of eulachon (Thaleichthys pacificus) in Berners Bay in southeast Alaska during AprilMay in 2002 and 2003. Sea lion abundance increased as eulachon gathered in Berners Bay, peaked as eulachon abundance peaked, and decreased as the eulachon moved up-river. As sea lion abundance increased in Berners Bay, sea lion abundance decreased at Benjamin Island, a sea lion haulout located 22 km away. The eulachon provided an abundant, energy-rich, predictable prey source for the Steller sea lions: (i) eulachon energy density was 9.70 ± 0.24 kJ·g1, much higher than that of any forage species reported in the North Pacific Ocean except northern lampfish (Stenobrachius leucopsarus); (ii) a large surplus of prey was available per sea lion while the eulachon aggregation was present; and (iii) the spawning run usually begins between late April and early May. The eulachon pulse may be critical to Steller sea lions during a period of high energetic demands.
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Miller, C. N., L. K. Polasek, A. C. M. Oliveira, C. J. Frost, and J. M. Maniscalco. "Milk fatty acid composition of perinatal and foraging Steller sea lions (Eumetopias jubatus): examination from pup stomachs." Canadian Journal of Zoology 96, no. 2 (February 2018): 153–62. http://dx.doi.org/10.1139/cjz-2016-0015.
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To investigate the milk fatty acid composition of female Steller sea lions (Eumetopias jubatus (Schreber, 1776)) between and within maternal states (i.e., perinatal or foraging), milk samples were collected in 2010 and 2011 via gastric intubation from Steller sea lion pups on a small rookery in the central Gulf of Alaska. Maternal states of lactating females were determined upon reuniting with their sampled pups via remotely operated video cameras on the rookery. Milk fatty acid composition between Steller sea lion maternal states was significantly different, and thus can be utilized to distinguish between perinatal and foraging Steller sea lions of the same geographic region in the absence of direct observation. However, milk fatty acid composition remained relatively constant within perinatal Steller sea lions, suggesting steady mobilization of fatty acids from blubber to milk, and within foraging Steller sea lions, implying females forage on similar prey species within several days after their perinatal period. Differences in milk fatty acid composition between maternal states, including differences in the relative percentages of polyunsaturated fatty acids, may have important implications for growth and development of offspring.
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Harcourt, Robert. "Individual variation in predation on fur seals by southern sea lions (Otaria byronia) in Peru." Canadian Journal of Zoology 71, no. 9 (September 1, 1993): 1908–11. http://dx.doi.org/10.1139/z93-273.
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Southern sea lions (Otaria byronia) were observed to prey on juvenile and adult female South American fur seals (Arctocephalus australis) at Punta San Juan, Peru (15°22′S, 75°12′W) between October 1987 and December 1988. Over the course of the study there were 165 attacks on fur seals with 33 seals killed. While both adult male and subadult male sea lions captured and killed fur seals, adult female and juvenile sea lions never acted aggressively towards fur seals. Adult males attacked fur seals on 82.4% of the occasions when they were present at the rookery, subadults on 52% of occasions. Distinctive pelage characteristics allowed some of the male sea lions to be individually identified, and differences in hunting success were observed between adults and subadults, and between five identifiable adults who hunted on at least five occasions. Motivation for attacks differed for subadults and adults, with subadult males using captured fur seals as female sea lion substitutes, guarding them from others and copulating with them, whilst adult sea lions hunted fur seals as food. However, only a small proportion of adult sea lions hunted fur seals, and with differing rates of success.
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Jefferson, Thomas A., Mari A. Smultea, and Eric J. Ward. "Distribution and Abundance of California (Zalophus californianus) and Steller (Eumetopias jubatus) Sea Lions in the Inshore Waters of Washington, 2013-2016." Aquatic Mammals 49, no. 4 (July 15, 2023): 366–81. http://dx.doi.org/10.1578/am.49.4.2023.366.
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Two species of sea lions occur in the in387land waters of Washington State: the California sea lion (Zalophus californianus) and the Steller sea lion (Eumetopias jubatus). Both species breed elsewhere, but they typically move into Puget Sound and adjacent waters of the Salish Sea from autumn through spring. There is a need for information on their current abundance and seasonal use patterns as both species prey heavily on threatened/endangered stocks of salmon and steelhead trout (Oncorhynchus spp.), and empirical abundance estimates of these species are lacking for inland Washington waters. From 2013 to 2016, we conducted 39,399 km of aerial surveys for marine mammals in this area, sighting 255 groups of sea lions. We used a subset of 7,841 km of effort and 165 sea lion sightings made during surveys in good sighting conditions to estimate in-water abundance using line-transect methods. Historical tagging data collected in Pacific Northwest waters were used to evaluate the proportions of time that each species spent on land and conducting dives, and then to develop correction factors to derive total abundance for both sea lion species, providing the first empirical abundance estimates for these waters. We estimated that between 33 and 442 California sea lions were found in Puget Sound/Hood Canal in different seasons, with nearly 3,000 being found in the broader inland Washington waters in the peak season (spring). Steller sea lions occurred in much smaller numbers, with a peak of 219 animals in Puget Sound/Hood Canal/Strait of Juan de Fuca in autumn (and possibly as many as 600 to 700 in the entire study area). While some estimates suffer from low precision, this study demonstrates that substantial numbers of sea lions use waters of the study area throughout much of the year. Our results provide an important step toward a better understanding of these two species in the inland waters of Washington, as well as their potential effects on protected salmonid prey species.
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Dennis, T. E., and P. D. Shaughnessy. "Seal survey in the Great Australian Bight region of Western Australia." Wildlife Research 26, no. 3 (1999): 383. http://dx.doi.org/10.1071/wr98047.
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In December 1996, a survey by helicopter of the Baxter Cliffs region of the Great Australian Bight in Western Australia did not locate any previously unreported colonies of the Australian sea lion or New Zealand fur seal. Although geologically contiguous with the Bunda Cliffs in South Australia (where sea lions have a scattered distribution), the Baxter Cliffs appeared generally more weathered and stable, with fewer collapsed sections of cliff forming platforms and providing habitat for seals. In total, 29 Australian sea lions were observed during the survey. Most were at a previously surveyed site approximately 2 km west of Twilight Cove. Ten other sites were recorded as potentially providing haul- out opportunity for sea lions; they were mainly caves and deep overhangs with access from the sea. No fur seals were seen. From this survey and from other records, we estimate the Australian sea lion population along the Baxter Cliffs in the Great Australian Bight region of Western Australia at less than 100 animals.
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Lorden, Rosanne, Richard Sambrook, and Robert W. Mitchell. "Residents’ and Tourists’ Knowledge of Sea Lions in the Galápagos." Society & Animals 20, no. 4 (2012): 342–63. http://dx.doi.org/10.1163/15685306-12341278.
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Abstract This study examined knowledge of sea lions (Zalophus wollebaeki) for both residents and tourists on San Cristóbal Island in the Galápagos, a famous nature tourism destination. Participants (N = 281) obtained through convenience and snowball sampling answered questionnaires about their knowledge of sea lions. Participants with higher education received higher overall scores, but participants’ education and age influenced answers on only a few questions. Residents and tourists obtained comparable overall scores, exhibiting extensive knowledge of sea lion behavior and life history. Whether participants were residents or tourists influenced answers to several questions, but when only participants with 13 years of education or more were examined, few differences in answers remained between residents or tourists. Participants’ broad knowledge of sea lions may be attributed to the items of knowledge tested, participants’ motivations for travel to the Galápagos, and the fact that sea lions are an engaging and ubiquitous animal.
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Ryazanov, Sergey D., Olga A. Belonovich, Evgeny G. Mamaev, Victor S. Nikulin, Sergey V. Fomin, and Vladimir N. Burkanov. "Establishing of local population, population dynamics and current abundance of Steller sea lion ( Eumetopias jubatus) in the Commander Islands." Izvestiya TINRO 176, no. 1 (March 30, 2014): 100–114. http://dx.doi.org/10.26428/1606-9919-2014-176-100-114.
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The time course of the establishment of a local population of Steller sea lions in the Commander Islands, population dynamics and current abundance were studied using literature published since the 1930s and the author’s observations conducted during breeding seasons 2008-2011. The local population of Steller sea lions started formation in the early 1960s, when mature females first began to populate the islands and the population was fully established in the early 1990s. The whole process of development the Commander Islands Steller sea lion sub-population took about three decades. Abundance of adult and juvenile sea lions fluctuated highly in 1991-2011 without any statistically significant trend, but numbers of pups had a pronounced negative slope mostly due to three sharp declines in pup production in 2000, 2009, and 2011. A total of about 700 animals of age 1+ inhabit the islands during the breeding season and about 200 pups are born annually at the present time. This total number of Steller sea lions is close to the mean value for the period after 1990s. Nevertheless, occasional sharp declines in pup production cause some anxiety, so far as they could lead to extinction of the Steller sea lion sub-population in this area as had occurred in the middle of the 19th century.
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Merrick, Richard L., and Thomas R. Loughlin. "Foraging behavior of adult female and young-of-the-year Steller sea lions in Alaskan waters." Canadian Journal of Zoology 75, no. 5 (May 1, 1997): 776–86. http://dx.doi.org/10.1139/z97-099.
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One explanation for recent declines in the Alaskan Steller sea lion (Eumetopias jubatus) population is that the availability of preferred prey has changed. Part of our evaluation of this hypothesis involved the use of conventional radio and satellite-linked time–depth recorder transmitters to compare summer and winter foraging of adult female and young-of-the-year Steller sea lions in Alaska waters. Foraging effort was not significantly different seasonally for postpartum adult females, though females with dependent young in winter may increase their foraging effort. In winter, all adult females made longer trips over larger home ranges and dove deeper. Young sea lions exerted less foraging effort, had the shallowest and briefest dives, and had home ranges intermediate in size to the two groups of adult females. Their foraging ability appears to develop throughout the first year. We conclude that adult female sea lions can exploit prey throughout the Gulf of Alaska and Bering Sea, and are constrained only by their reproductive status and seasonal changes in prey availability. Young sea lions' diving is more limited because their physiological and behavioral development constrains them from diving like an adult. Perhaps most important, dives remain shallow through the first year. Consequently, young sea lions could be more easily food-limited by changes in prey distribution.
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Berry, E. S., D. E. Skilling, J. E. Barlough, N. A. Vedros, L. J. Gage, and A. W. Smith. "New marine calicivirus serotype infective for swine." American Journal of Veterinary Research 51, no. 8 (August 1, 1990): 1184–87. http://dx.doi.org/10.2460/ajvr.1990.51.08.1184.
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SUMMARY A new serotype of calicivirus was isolated from California sea lions (Zalophus californianus) with severe vesicular disease. Neutralizing antibodies were found in 27 of 82 (32.9%) serum samples from California sea lions and in 15 of 146 (10.3%) serum samples from Steller sea lions (Eumetopias jubatus) tested. The seropositive animals were widely dispersed along the margins of the eastern Pacific basin, from the Bering Sea to the Santa Barbara Channel. Seropositive samples were found from as early as 1976 through the present time. This new calicivirus serotype, San Miguel sea lion virus type 13, was inoculated into weaned pigs, resulting in induction of severe vesicular disease, which spread to all pigs, including uninoculated pen contacts. Virus was continually shed by most of the pigs throughout the 2-week duration of the experiment.
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Orr, Anthony J., and James T. Harvey. "Quantifying errors associated with using fecal samples to determine the diet of the California sea lion (Zalophus californianus)." Canadian Journal of Zoology 79, no. 6 (June 1, 2001): 1080–87. http://dx.doi.org/10.1139/z01-078.
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The purpose of this study was to quantify the errors associated with using fecal samples to determine the diet of the California sea lion (Zalophus californianus). Fishes and squids of known size and number were fed to five sea lions held in enclosures with seawater-filled pools. Enclosures were washed and pools were drained periodically so that sea lion feces could be collected using a 0.5 mm mesh bag. Fish otoliths and squid beaks were collected from feces and used to estimate number and size of prey eaten. An average of 50.7% (SE = 6.4%) of 430 fishes and 73.5% (SE = 12.0%) of 49 cephalopods fed to sea lions were represented by otoliths and beaks in feces, respectively. Estimated lengths of fish from feces were less than lengths of fish fed to sea lions by an average of 30.1% (SE = 2.8%). Beaks were not digested significantly; estimated lengths of squid were underestimated by an average of only 3.3% (SE = 1.5%) relative to actual lengths. Passage rates of otoliths varied, but more than 70% were recovered within 48 h after the fish was consumed. Passage rates of beaks were generally less than those of otoliths; six beaks (11%) were collected in feces 4 days after the squid were eaten. Correction factors were created to more reliably estimate the number and size of fishes and cephalopods eaten by California sea lions.
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Deming, Alissa C., James F. X. Wellehan, Kathleen M. Colegrove, Ailsa Hall, Jennifer Luff, Linda Lowenstine, Pádraig Duignan, Galaxia Cortés-Hinojosa, and Frances M. D. Gulland. "Unlocking the Role of a Genital Herpesvirus, Otarine Herpesvirus 1, in California Sea Lion Cervical Cancer." Animals 11, no. 2 (February 13, 2021): 491. http://dx.doi.org/10.3390/ani11020491.
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Urogenital carcinoma in California sea lions (Zalophus californianus) is the most common cancer of marine mammals. Primary tumors occur in the cervix, vagina, penis, or prepuce and aggressively metastasize resulting in death. This cancer has been strongly associated with a sexually transmitted herpesvirus, otarine herpesvirus 1 (OtHV1), but the virus has been detected in genital tracts of sea lions without cancer and a causative link has not been established. To determine if OtHV1 has a role in causing urogenital carcinoma we sequenced the viral genome, quantified viral load from cervical tissue from sea lions with (n = 95) and without (n = 163) urogenital carcinoma, and measured viral mRNA expression using in situ mRNA hybridization (Basescope®) to quantify and identify the location of OtHV1 mRNA expression. Of the 95 sea lions diagnosed with urogenital carcinoma, 100% were qPCR positive for OtHV1, and 36% of the sea lions with a normal cervix were positive for the virus. The non-cancer OtHV1 positive cases had significantly lower viral loads in their cervix compared to the cervices from sea lions with urogenital carcinoma. The OtHV1 genome had several genes similar to the known oncogenes, and RNA in situ hybridization demonstrated high OtHV1 mRNA expression within the carcinoma lesions but not in normal cervical epithelium. The high viral loads, high mRNA expression of OtHV1 in the cervical tumors, and the presence of suspected OtHV1 oncogenes support the hypothesis that OtHV1 plays a significant role in the development of sea lion urogenital carcinoma.
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Chilvers, B. Louise, and Ian S. Wilkinson. "Philopatry and site fidelity of New Zealand sea lions (Phocarctos hookeri)." Wildlife Research 35, no. 5 (2008): 463. http://dx.doi.org/10.1071/wr07053.
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The New Zealand sea lion (NZ sea lion), Phocarctos hookeri, is New Zealand’s only endemic pinniped, and one of the worlds rarest otariids. It is classified as ‘Threatened’ based primarily on the low number of breeding sites and restricted distribution. In New Zealand, a species listed as ‘threatened’ is required to be managed to allow its recovery and removal from the list within 20 years. For NZ sea lions this is dependant on the establishment of new breeding areas. However, understanding the recolonisation processes for pinnipeds is still in its infancy with factors such as philopatry needing more research to understand individual dispersal and the recolonisation process. This paper presents the first quantitative investigation into the level of site fidelity and philopatry to breeding beaches in NZ sea lions. Data from resights of NZ sea lions marked as pups from the northern Auckland Island breeding area suggest that both site fidelity and philopatry are important characteristics of this species. Our results show that overall: (1) females have a higher resighting rate than males, particularly at natal sites; (2) female non-natal resightings are predominantly restricted to locations within the northern Auckland Island breeding area (an area of ~10 km2), whereas male resightings are more widely dispersed (up to 700 km to NZ mainland); and (3) philopatry occurs for both sexes, but is more predominant in females than males, with males displaying delay related to sexual and social maturity. The colonisation of new breeding habitats rarely occurs when philopatry is strong and population density is low, stable or declining such as seen for NZ sea lions. Therefore, this research indicates that management of NZ sea lions needs to minimise anthropogenic mortality and encourage population growth to maximise density at breeding sites and encourage females to disperse to establish new breeding areas.
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Ridgway, S. H., and C. C. Robison. "Homing by released captive California sea lions, Zalophus californianus, following release on distant islands." Canadian Journal of Zoology 63, no. 9 (September 1, 1985): 2162–64. http://dx.doi.org/10.1139/z85-317.
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Captive male California sea lions were twice flown to offshore breeding islands and released. Three animals returned to their pen in San Diego Bay after discharge on San Clemente Island, about 115 km away. Two of four returned to the same facility from San Nicolas Island, about 240 km away. The fastest sea lion returned in 2 days from San Clemente and in 4 days from San Nicolas. This is the first evidence for such specific east–west navigation by sea lions and suggests that these animals are good navigators.
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Dellinger, Thomas, and Fritz Trillmich. "Fish prey of the sympatric Galápagos fur seals and sea lions: seasonal variation and niche separation." Canadian Journal of Zoology 77, no. 8 (November 1, 1999): 1204–16. http://dx.doi.org/10.1139/z99-095.
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Analysis of fish otoliths in scats and vomits of Galápagos fur seals (Arctocephalus galapagoensis) and Galápagos sea lions (Zalophus californianus wollebaeki) was used to determine the numerical composition of the diets for the post-El Niño year 1983, the cold seasons in 1984 and 1985, and the warm season in 1986. Between 84 and 99% of all otoliths in fur seal scats were from myctophids and bathylagids. The fur seals' diet included 26 species. Only 3 species contributed more than 1% of otoliths. No seasonal differences in diet were found. Sea lion samples contained a mean of 14 otoliths. Sardines (Sardinops sagax) contributed 75-85% of otoliths. Sea lions preyed on 24 species, but only 3 surpassed 1% abundance. Seasonality was not reflected in the sea lions' diet. After the 1982-1983 El Niño, the diets of both species deviated from those in all other years of the study. Food-niche overlap between the two sympatric species was almost non-existent. This is hard to understand, based on our knowledge of the diving capabilities of the two species, but reflects the fact that Galápagos fur seals are nighttime foragers and sea lions are daytime foragers.
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Rosen, David A. S., and Andrew W. Trites. "Satiation and compensation for short-term changes in food quality and availability in young Steller sea lions (Eumetopias jubatus)." Canadian Journal of Zoology 82, no. 7 (July 1, 2004): 1061–69. http://dx.doi.org/10.1139/z04-082.
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Foraging theory predicts that animals should proportionately increase their food intake to compensate for reduced food energy content and (or) prey availability. However, the theoretical intake levels will, at some point, exceed the digestive capacity of the predator. We tested the ability of Steller sea lions, Eumetopias jubatus (Schreber, 1776), to compensate for short-term changes in prey energy density and availability, and quantified the maximum amount of food a young sea lion could consume. Five 1–2-year-old captive Steller sea lions were offered either herring (high energy) or capelin (low energy) each day or every second day. When prey were available on a daily basis, the sea lions compensated for differences in the energy content of herring and capelin by consuming sufficient quantities of each (8.3 vs. 14.0 kg·d–1, respectively) to maintain equivalent gross energy intakes. When herring was available only on alternate days, the sea lions increased their consumption by 52% to 11.5 kg·d–1, which was not sufficient to maintain an average gross intake equal to that maintained when herring was available every day. When capelin was available only on alternate days, some animals increased their intake for a few days, but average intake (15.2 kg·d–1) was far below levels observed during daily feeding. Generally, the sea lions appeared to reach their digestive limit at a level equivalent to 14%–16% of their body mass. Our findings suggest that Steller sea lions can alter their food intake in response to short-term changes in prey quality or availability, but that these variables can quickly combine to necessitate food intake levels that exceed the physiological digestive capacities of young animals.
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Lowther, A. D., R. G. Harcourt, and S. D. Goldsworthy. "Regional variation in trophic ecology of adult female Australian sea lions inferred from stable isotopes in whiskers." Wildlife Research 40, no. 4 (2013): 303. http://dx.doi.org/10.1071/wr12181.
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Context The primary selective forces responsible for shaping life-history traits come from the physical and biological environment in which a species resides. Consequently, the limits of a species range may provide a useful measure of adaptive potential to environmental change. The proximity of foraging grounds to terrestrial nursing habitat constrains central-place foragers such as otariid seals in selecting breeding locations. The Australian sea lion (Neophoca cinerea) is an endangered otariid endemic to Australia, whose northern-range extent occurs at a temperate–tropical transition zone on the western coast of Western Australia (WA). Aims Currently, there is a complete absence of data on the foraging ecology of Australian sea lions in WA. We sought to address this critical knowledge gap and provide data on the foraging ecology of adult female Australian sea lions at three isolated breeding colonies in western WA. Methods We used stable-isotope ratios of carbon (δ13C) and nitrogen (δ15N) in the whiskers of pups as proxies to characterise feeding behaviour of 10–28% of all adult female Australian sea lions at each colony. We then compared these geographic data to (1) conspecifics at similar latitude in South Australia (SA) and (2) isotopic data collated from other studies on seabirds that inhabit the region, to place foraging behaviour of adult female Australian sea lions into context. Key results At the southernmost colonies in WA, individual animals were members of one of two distinct isotopic clusters that could be described by differences in δ15N and δ13C values. Individuals at the northernmost colony displayed δ15N values similar to those of seabirds in the same region. Across the study, isotope ratios of adult female Australian sea lions in western WA were between 3‰ and 5‰ lower than those observed at a colony at similar latitude in SA. Conclusions Gross differences in the physical oceanography between WA and SA may in part explain the differences in isotope ratios of individuals between the regions, with lower δ15N and δ13C values in WA probably reflecting the relatively depauperate conditions of the Leeuwin Current. Implications Potential regional differences in trophic structure should be considered when developing appropriate management plans for Australian sea lions and regional variation in the diet of Australian sea lion warrants further investigation.
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Campagna, Claudio. "Southern Sea Lions." Marine Mammal Science 1, no. 4 (October 1985): 340. http://dx.doi.org/10.1111/j.1748-7692.1985.tb00021.x.
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Guénette, Sylvie, Sheila JJ Heymans, Villy Christensen, and Andrew W. Trites. "Ecosystem models show combined effects of fishing, predation, competition, and ocean productivity on Steller sea lions (Eumetopias jubatus) in Alaska." Canadian Journal of Fisheries and Aquatic Sciences 63, no. 11 (November 1, 2006): 2495–517. http://dx.doi.org/10.1139/f06-136.
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Steller sea lions (Eumetopias jubatus) increased in the eastern portion of their range while declining in the Gulf of Alaska and Aleutian Islands from the late 1970s to late 1990s. We constructed ecosystem models of the central and western Aleutians and of southeast Alaska to simultaneously evaluate four hypotheses explaining sea lion dynamics: killer whale (Orcinus orca) predation, ocean productivity, fisheries, and competition with other species. Comparisons of model predictions with historical time series data indicate that all four factors likely contributed to the trends observed in sea lion numbers in both ecosystems. Changes in ocean productivity conveyed by the Pacific Decadal Oscillation influenced the abundance trajectory of several species. Fishing could have affected the ecosystem structure by influencing the abundance of Atka mackerel (Pleurogrammus monopterygius) in the Aleutians and Pacific herring (Clupea pallasii) in southeast Alaska. Pacific halibut (Hippoglossus stenolepis) in the Aleutians and arrowtooth flounder (Atheresthes stomias) in southeast Alaska appear to impede sea lion population growth through competitive interactions. Predation by killer whales was important when sea lions were less abundant in the 1990s in the Aleutians and in the 1960s in Southeast Alaska, but appear to have little effect when sea lion numbers were high.
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Dennis, TE, and PD Shaughnessy. "Stautus of the Australian sea lion, Neophoca cinerea, in the Great Australian Bight." Wildlife Research 23, no. 6 (1996): 741. http://dx.doi.org/10.1071/wr9960741.
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In August 1994, a systematic survey of potential haulout sites of the Australian sea lion, Neophoca cinerea, was conducted along the coastline of the Great Australian Bight from Twin Rocks to Wilson Bluff, a distance of 206 km. A total of 289 Australian sea lions was recorded at 23 sites widely dispersed at the base of the Bunda Cliffs, hauled out on perched platforms formed by collapsed sections of cliff at various levels above the sea. Of these, 37 sea lions were recorded in a deep cave accessed from the sea. The total included 86 pups aged under 12 months, which were probably born in the region; six of these had almost completed moulting their natal pelage and were estimated to be near four months old. Only 12 New Zealand fur seals, Arctocephalus forsteri, were recorded. The Australian sea lion sites located in 1994 were surveyed again in August-September 1995, during a predicted breeding season. In this survey, a total of 284 sea lions was recorded at nine sites in South Australia and one site in Western Australia. This included 90 pups under six months of age, of which 44 were still in lanugo. Overall, we recorded 10 breeding sites and 14 haulout sites. Breeding events were recorded at one colony over three seasons and were consistent with an 18-month cycle. By extrapolating from the number of sea lion pups found in 1994, the population for the Great Australian Bight region in South Australia is estimated to be 613-774. This addition increases the previous estimate for South Australia by 9.3% and the previous total population estimate by 6.6%.
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Childerhouse, Simon, Bruce Dix, and Nick Gales. "Diet of New Zealand sea lions (Phocarctos hookeri) at the Auckland Islands." Wildlife Research 28, no. 3 (2001): 291. http://dx.doi.org/10.1071/wr00063.
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Scat and regurgitate samples (n = 206) from New Zealand sea lions (Phocarctos hookeri) were collected at the Auckland Islands between December 1994 and February 1997. Most (82%) samples were collected during three summer seasons while the remainder (18%) were collected during a single winter season. Thirty-three taxa were identified from 3523 prey items. The six most abundant prey species accounted for 90% of all prey items. The two most numerically abundant prey species, octopus (Enteroctopus zelandicus) and opalfish (Hemerocoetes species) made up almost 50% of total prey items. Other important prey species included lobster krill (Munida gregaria), hoki (Macruronus novaezelandiae), oblique-banded rattail (Coelorhynchus aspercephalus), and salps (Pyrosoma atlanticum). New Zealand fur seals (Arctocephalus forsteri) and seabirds were also identified in samples. New Zealand sea lions are generalist feeders utilising a wide variety of prey items, with fish comprising the most common taxa (59%) numerically and both cephalopods (21%) and crustacea (15%) forming lesser, but still important, parts of the diet. Prey taxa identified indicate that New Zealand sea lions are utilising a wide variety of benthic, demersal and pelagic species ranging from the inter-tidal zone to waters deeper than 300 m. New Zealand sea lions at the Auckland Islands target different prey species to New Zealand sea lions at other locations although they have broadly consistent prey types, with fish as the major taxa. There is only a small overlap of New Zealand sea lion prey species with commercially targeted species on the Auckland Islands Shelf in the months sampled.
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McClatchie, Sam, John Field, Andrew R. Thompson, Tim Gerrodette, Mark Lowry, Paul C. Fiedler, William Watson, Karen M. Nieto, and Russell D. Vetter. "Food limitation of sea lion pups and the decline of forage off central and southern California." Royal Society Open Science 3, no. 3 (March 2016): 150628. http://dx.doi.org/10.1098/rsos.150628.
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California sea lions increased from approximately 50 000 to 340 000 animals in the last 40 years, and their pups are starving and stranding on beaches in southern California, raising questions about the adequacy of their food supply. We investigated whether the declining sea lion pup weight at San Miguel rookery was associated with changes in abundance and quality of sardine, anchovy, rockfish and market squid forage. In the last decade off central California, where breeding female sea lions from San Miguel rookery feed, sardine and anchovy greatly decreased in biomass, whereas market squid and rockfish abundance increased. Pup weights fell as forage food quality declined associated with changes in the relative abundances of forage species. A model explained 67% of the variance in pup weights using forage from central and southern California and 81% of the variance in pup weights using forage from the female sea lion foraging range. A shift from high to poor quality forage for breeding females results in food limitation of the pups, ultimately flooding animal rescue centres with starving sea lion pups. Our study is unusual in using a long-term, fishery-independent dataset to directly address an important consequence of forage decline on the productivity of a large marine predator. Whether forage declines are environmentally driven, are due to a combination of environmental drivers and fishing removals, or are due to density-dependent interactions between forage and sea lions is uncertain. However, declining forage abundance and quality was coherent over a large area (32.5–38° N) for a decade, suggesting that trends in forage are environmentally driven.
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O’Corry-Crowe, G., B. L. Taylor, T. Gelatt, T. R. Loughlin, J. Bickham, M. Basterretche, K. W. Pitcher, and D. P. DeMaster. "Demographic independence along ecosystem boundaries in Steller sea lions revealed by mtDNA analysis: implications for management of an endangered species." Canadian Journal of Zoology 84, no. 12 (December 2006): 1796–809. http://dx.doi.org/10.1139/z06-167.
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Previous genetic studies indicate Steller sea lions ( Eumetopias jubatus (Schreber, 1776)) comprise three phylogeographically distinct populations. However, differences in population trends and ecology and the limited extent of recorded dispersal suggest structure may be present at smaller scales. We examined sequence variation within a longer segment (531 bp) of the mtDNA control region in greater numbers (n = 1654) of sea lions from across Alaska than earlier investigations to investigate fine-scale dispersal patterns in Steller sea lions. We detected high levels of haplotypic diversity (h = 0.934) and confirmed phylogeographic differentiation between southeastern and western Alaska (Φst = 0.23, P < 0.0001), but also found significant differentiation at regional and local scales. Rookeries in the Gulf of Alaska, eastern Bering Sea, and eastern Aleutians were distinct from rookeries in the central and western Aleutians (Fst = 0.021, P < 0.0001; Φst = 0.017, P < 0.0001). The location of this split coincides with an oceanographic divergence between continental shelf and ocean basin waters and with differences in sea lion foraging ecology and population trends. A number of rookeries were also significantly differentiated from nearby rookeries (Fst = 0.02–0.025, P < 0.05), signifying substantial female-mediated philopatry, in some cases, at local scales. These findings have important implications for understanding the ecology of Steller sea lions in relation to marine ecosystems and the causes of population declines, and they provide guidance for management, including the identification of management stocks.
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Collins, Catherine J., B. Louise Chilvers, Matthew Taylor, and Bruce C. Robertson. "Historical population size of the threatened New Zealand sea lion Phocarctos hookeri." Journal of Mammalogy 97, no. 2 (December 29, 2015): 436–43. http://dx.doi.org/10.1093/jmammal/gyv187.
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Abstract Marine mammal species were exploited worldwide during periods of commercial sealing in the 18th and 19th centuries. For many of these species, an estimate of the pre-exploitation abundance of the species is lacking, as historical catch records are generally scarce and inaccurate. Genetic estimates of long-term effective population size provide a means to estimate the pre-exploitation abundance. Here, we apply genetic methods to estimate the long-term effective population size of the subantarctic lineage of the New Zealand sea lion (NZ sea lion), Phocarctos hookeri . This species is predominantly restricted to the subantarctic islands, south of mainland New Zealand, following commercial sealing in the 19th century. Today, the population consists of ~9,880 animals and population growth is slow. Auckland Island breeding colonies of NZ sea lion are currently impacted by commercial trawl fisheries via regular sea lion deaths as bycatch. In order to estimate sustainable levels of bycatch, an estimate of the population’s carrying capacity ( K ) is required. We apply the genetically estimated long-term effective population size of NZ sea lions as a proxy for the estimated historical carrying capacity of the subantarctic population. The historical abundance of subantarctic NZ sea lions was significantly higher than the target values of K employed by the contemporary management. The current management strategy may allow unsustainable bycatch levels, thereby limiting the recovery of the NZ sea lion population toward historical carrying capacity.
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Barragán-Vargas, Cecilia, Jorge Montano-Frías, Germán Ávila Rosales, Carlos R. Godínez-Reyes, and Karina Acevedo-Whitehouse. "Transformation of the genital epithelial tract occurs early in California sea lion development." Royal Society Open Science 3, no. 3 (March 2016): 150419. http://dx.doi.org/10.1098/rsos.150419.
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An unusually high prevalence of metastatic urogenital carcinoma has been observed in free-ranging California sea lions stranded off the coast of California in the past two decades. No cases have been reported for sea lions in the relatively unpolluted Gulf of California. We investigated occurrence of genital epithelial transformation in 60 sea lions ( n =57 pups and 3 adult females) from the Gulf of California and examined whether infection by a viral pathogen previously found to be associated with urogenital carcinoma accounted for such alterations. We also explored the contribution of MHC class II gene expression on transformation. Cellular alterations, such as squamous cell atypia (ASC), atypical squamous cells of undetermined significance (ASCUS) and low-grade squamous intraepithelial lesions were observed in 42% of the pups and in 67% of the adult females. Normal genital epithelium was more common in male than female pups. ASC was five times more likely to occur in older pups. Epithelial alterations were unrelated to infection by the potentially oncogenic otarine type I gammaherpesvirus (OtHV-1), but ASCUS was more common in pups with marked and severe inflammation. Expression of MHC class II DRB loci ( Zaca DRB-D ) by peripheral antigen-presenting leucocytes showed a slightly ‘protective’ effect for ASC. We propose that transformation of the California sea lion genital epithelium is relatively common in young animals, increases with age and is probably the result of infection by an unidentified pathogen. Expression of a specific MHC class II gene, suggestive of presentation of specific antigenic peptides to immune effectors, appears to lower the risk of transformation. Our study provides the first evidence that epithelial transformation of the California sea lion genital tract is relatively common, even from an early age, and raises questions regarding differences in sea lion cancer-detection and -repair success between geographical regions.
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Lisitsyna, O. I., O. Kudlai, T. R. Spraker, and T. A. Kuzmina. "New Records on Acanthocephalans from California Sea Lions Zalophus californianus (Pinnipedia, Otariidae) from California, USA." Vestnik Zoologii 52, no. 3 (June 1, 2018): 181–92. http://dx.doi.org/10.2478/vzoo-2018-0019.
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Abstract To increase the currently limited knowledge addressing acanthocephalans parasitizing California sea lions (Zalophus californianus), 33 animals including pups, juvenile and adult males and females from the Marine Mammal Center (TMMC), Sausalito, California, USA were examined. Totally, 2,268 specimens of acanthocephalans representing five species from the genera Andracantha (A. phalacrocoracis and Andracantha sp.), Corynosoma (C. strumosum and C. obtuscens) and Profilicollis (P. altmani) were found. Profilicollis altmani and A. phalacrocoracis, predominantly parasitize fish-eating birds; they were registered in Z. californianus for the first time. Prevalence and intensity of California sea lion infection and transmission of acanthocephalans in these hosts of different age groups were analyzed and discussed. We provide brief morphological descriptions of the five species of acanthocephalan found in California sea lions.
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Baylis, M. M., R. A. Orben, J. P. Y. Arnould, F. Christiansen, G. C. Hays, and I. J. Staniland. "Decline of Sea Lions." Bulletin of the Ecological Society of America 96, no. 4 (October 2015): 635–38. http://dx.doi.org/10.1890/0012-9623-96.4.635.
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Costa, D. P., and N. J. Gales. "Foraging energetics and diving behavior of lactating New Zealand sea lions, Phocarctos hookeri." Journal of Experimental Biology 203, no. 23 (December 1, 2000): 3655–65. http://dx.doi.org/10.1242/jeb.203.23.3655.
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The New Zealand sea lion, Phocarctos hookeri, is the deepest- and longest-diving sea lion. We were interested in whether the diving ability of this animal was related to changes in its at-sea and diving metabolic rates. We measured the metabolic rate, water turnover and diving behavior of 12 lactating New Zealand sea lions at Sandy Bay, Enderby Island, Auckland Islands Group, New Zealand (50 degrees 30′S, 166 degrees 17′E), during January and February 1997 when their pups were between 1 and 2 months old. Metabolic rate (rate of CO(2) production) and water turnover were measured using the (18)O doubly-labeled water technique, and diving behavior was measured with time/depth recorders (TDRs). Mean total body water was 66.0+/−1.1 % (mean +/− s.d.) and mean rate of CO(2) production was 0. 835+/−0.114 ml g(−)(1)h(−)(1), which provides an estimated mass-specific field metabolic rate (FMR) of 5.47+/−0.75 W kg(−)(1). After correction for time on shore, the at-sea FMR was estimated to be 6.65+/−1.09 W kg(−)(1), a value 5.8 times the predicted standard metabolic rate of a terrestrial animal of equal size. The mean maximum dive depth was 353+/−164 m, with a mean diving depth of 124+/−36 m. The mean maximum dive duration was 8.3+/−1.7 min, with an average duration of 3.4+/−0.6 min. The deepest, 550 m, and longest, 11.5 min, dives were made by the largest animal (155 kg). Our results indicate that the deep and long-duration diving ability of New Zealand sea lions is not due to a decreased diving metabolic rate. Individual sea lions that performed deeper dives had lower FMRs, which may result from the use of energetically efficient burst-and-glide locomotion. There are differences in the foraging patterns of deep and shallow divers that may reflect differences in surface swimming, time spent on the surface and/or diet. Our data indicate that, although New Zealand sea lions have increased their O(2) storage capacity, they do not, or cannot, significantly reduce their at-sea metabolic rates and are therefore likely to be operating near their physiological maximum.
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Stelle, L. L., R. W. Blake, and A. W. Trites. "Hydrodynamic drag in steller sea lions (Eumetopias jubatus)." Journal of Experimental Biology 203, no. 12 (June 15, 2000): 1915–23. http://dx.doi.org/10.1242/jeb.203.12.1915.
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Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from ‘deceleration during glide’ measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5×10(6). The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a ‘laminar’ profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4 m s(−)(1) or 1.2-1.5 body lengths s(−)(1). These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s(−)(1) based on the minimum cost of transport for California sea lions.
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Tsuzuku, Nahoko, and Naoki Kohno. "The oldest record of the Steller sea lion Eumetopias jubatus (Schreber, 1776) from the early Pleistocene of the North Pacific." PeerJ 8 (August 27, 2020): e9709. http://dx.doi.org/10.7717/peerj.9709.
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The extant genera of fur seals and sea lions of the family Otariidae (Carnivora: Pinnipedia) are thought to have emerged in the Pliocene or the early Pleistocene in the North Pacific. Among them, the Steller sea lion (Eumetopias jubatus) is the largest and distributed both in the western and eastern North Pacific. In contrast to the limited distribution of the current population around the Japanese Islands that is now only along the coast of Hokkaido, their fossil records have been known from the middle and late Pleistocene of Honshu Island. One such important fossil specimen has been recorded from the upper lower Pleistocene Omma Formation (ca. 1.36–0.83 Ma) in Kanazawa, Ishikawa Prefecture, Japan, which now bears the institutional number GKZ-N 00001. Because GKZ-N 00001 is the earliest fossil having been identified as a species of the sea lion genus Eumetopias, it is of importance to elucidate the evolutionary history of that genus. The morphometric comparisons were made among 51 mandibles of fur seals and sea lions with GKZ-N 00001. As results of bivariate analyses and PCA based on 39 measurements for external morphologies with internal structures by CT scan data, there is almost no difference between GKZ-N 00001 and extant male individuals of E. jubatus. In this regard, GKZ-N 00001 is identified specifically as the Steller sea lion E. jubatus. Consequently, it is recognized as the oldest Steller sea lion in the North Pacific. About 0.8 Ma, the distribution of the Steller sea lion had been already established at least in the Japan Sea side of the western North Pacific.
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Seco Pon, Juan Pablo, and Marco Favero. "South American sea lions (Otaria flavescens) and killer whales (Orcinus orca) attending chub mackerel (Scomber japonicus) commercial trawl fisheries over the Patagonian Shelf: a first report." Latin American Journal of Aquatic Mammals 10, no. 1 (August 24, 2015): 48–51. http://dx.doi.org/10.5597/lajam00193.
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Killer whale-seal interactions have been reported for almost all pinniped species globally. However the literature on offshore interactions between killer whales and sea lions is rare for the South Atlantic, particularly in Argentine waters. Here we report for the first time the harassment of a South American sea lion (Otaria flavescens) by killer whales (Ornicus orca) while attending commercial fishing vessels in offshore national waters and describe a novel sea lion antipredator behaviour. These observations were made during an ongoing survey to assess seabird-fisheries interactions in the commercial trawl fishery off Argentina.
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Antonelis, George A., Brent S. Stewart, and Wayne F. Perryman. "Foraging characteristics of female northern fur seals (Callorhinus ursinus) and California sea lions (Zalophus californianus)." Canadian Journal of Zoology 68, no. 1 (January 1, 1990): 150–58. http://dx.doi.org/10.1139/z90-022.
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The foraging characteristics of northern fur seals (Callorhinus ursinus) and California sea lions (Zalophus californianus) from San Miguel Island, California, were studied during the 1985 summer breeding season. A radio transmitter was attached to 25 postpartum females of each species and used to determine their locations at sea and the frequency and duration of their feeding trips. Northern fur seals usually foraged in the oceanic zone where the mean water depth was 933 m (n = 12). California sea lions principally were found in the neritic zone, where water depth averaged 323 m (n = 9). Most fur seals (92%) were found northwest of San Miguel Island, whereas the sea lions were commonly found to the northwest (55%) or in areas south (22%) of the island. Although both species evidently foraged at similar distances from the island, foraging trips of fur seals [Formula: see text] were over twice as long as those of sea lions [Formula: see text]. Fur seals were ashore less time [Formula: see text] than were sea lions [Formula: see text] between foraging trips. Analysis of scats revealed that fur seals and sea lions ate similar prey (northern anchovy, Engraulis mordax; Pacific whiting, Merluccius productus; juvenile rockfish, Sebastes spp.; market squid, Loligo opalescens; and nail squid, Onychoteuthis borealijaponicas), although the relative proportions of these prey differed. Factors influencing the observed foraging characteristics probably were availability of prey and phylogenetic constraints associated with life-history traits of northern fur seals and California sea lions.
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Kastelein, Ronald A., Lean Helder-Hoek, Laura Van Acoleyen, Linde N. Defillet, and John M. Terhune. "Temporary Hearing Threshold Shift in California Sea Lions (Zalophus californianus) Due to a Noise Band Centered at 32 kHz." Aquatic Mammals 50, no. 2 (March 15, 2024): 107–21. http://dx.doi.org/10.1578/am.50.2.2024.107.
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To determine their frequency-dependent susceptibility to noise-induced temporary hearing threshold shift (TTS), two California sea lions (Zalophus californianus) were exposed for 60 min to a continuous one-sixth-octave noise band (NB) centered at 32 kHz as the fatiguing sound, at sound pressure levels of 132 to 156 dB re 1 µPa (sound exposure levels [SELs] of 168 to 192 dB re 1 µPa2s). Using a psychoacoustic technique, TTSs were quantified at the center frequency of the fatiguing sound and at half an octave and one octave above the center frequency (at 32, 44.8, and 63 kHz). When significant TTS occurred, higher SELs resulted in greater TTSs. TTSs and hearing recovery patterns were similar in both sea lions. The mean onset of TTS1-4 min (defined as 6 dB TTS) in sea lion F01 is estimated to occur after exposure to an SEL of 179 dB re 1 µPa2s (at hearing test frequency 44.8 kHz). After exposure to an SEL of 180 dB re 1 µPa2s, a mean TTS1-4 min of 6.7 dB was measured at hearing test frequency 44.8 kHz. In California sea lions, TTS onset levels are not as closely related (especially at the lower and higher frequencies) to the unmasked hearing thresholds (audiograms) as was previously assumed.
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Hirons, Amy C., Donald M. Schell, and David J. St. Aubin. "Growth rates of vibrissae of harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus)." Canadian Journal of Zoology 79, no. 6 (June 1, 2001): 1053–61. http://dx.doi.org/10.1139/z01-055.
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Growth rates of vibrissae (whiskers), which act as a temporal record of feeding in harbor seals (Phoca vitulina) and Steller sea lions (Eumetopias jubatus), were estimated using 13C- and 15N-labeled glycine followed by stable-isotope analysis. The labeled glycine was incorporated into keratin and served as a temporal marker for growth-rate calculation. One captive harbor seal received two doses 147 days apart, while a second seal received one dose; vibrissae were analyzed after 86 and 154 days. The peak positions indicated that growth began in the fall, continued into spring, but ceased in June, with active growth rates of 0.33 mm/day. Two adult captive Steller sea lions each received two labeled doses during a 308-day period. After 427 days vibrissae in both sea lions showed two peaks corresponding to the markers; growth rates were calculated as 0.050.07 mm/day. Growth rates in captive juvenile and wild adult Steller sea lions, 0.100.17 mm/day, supported the assumption that major isotopic oscillations in vibrissae of wild sea lions were annual. The multiyear records imply that Steller sea lions retain their vibrissae; harbor seal vibrissae, in contrast, have periods of rapid growth and appear to be shed, at least in part, annually.
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Shaughnessy, Peter D., Simon D. Goldsworthy, Paul Burch, and Terry E. Dennis. "Pup numbers of the Australian sea lion (Neophoca cinerea) at The Pages Islands, South Australia, over two decades." Australian Journal of Zoology 61, no. 2 (2013): 112. http://dx.doi.org/10.1071/zo13015.
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The Australian sea lion is an Australian endemic, restricted to South Australia and Western Australia, with 86% of the population in South Australia. It was listed under the Commonwealth Environment Protection and Biodiversity Conservation Act as Vulnerable in February 2005, and the International Union for the Conservation of Nature has listed it as Endangered. Sea lions are taken as bycatch in the gill-net fishery for school shark and gummy shark, and the risk of extinction of breeding colonies is high even from low levels of bycatch. We assessed trends in pup population size at The Pages Islands, a large breeding colony in South Australia. Pup abundance was estimated by direct counting of live and dead pups; the maximum count in each breeding season was used for trend analysis. The average of direct counts of pups in 14 breeding seasons between 1989–90 and 2009–10 was 473 (s.d. = 58.4). There was no trend in pup numbers, contrasting with two other large colonies: Seal Bay, Kangaroo Island (decreasing), and Dangerous Reef (increasing since 2000). The Australian Sea Lion Management Strategy of the Australian Fisheries Management Authority aims to reduce sea lion bycatch in the shark fishery; a key item is a fishery closure around each breeding colony in South Australia. Implementation of the closure around The Pages should lower the risk of bycatch of its sea lions with foraging areas that previously overlapped with the fishery and should allow the colony’s population size to increase.
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Michael, S. A., B. L. Chilvers, W. D. Roe, and B. D. Gartrell. "Long-term survival and reproductive success of New Zealand sea lions (Phocarctos hookeri) treated with ivermectin as pups." Wildlife Research 42, no. 8 (2015): 660. http://dx.doi.org/10.1071/wr15120.
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Context Hookworms (Uncinaria spp.) are a common parasite of neonatal fur seals and sea lions around the world and may contribute to decreased pup growth and survival. Removal of these parasitic burdens by administration of the anthelmintic ivermectin has been trialled in New Zealand (NZ) sea lion (Phocarctos hookeri) pups at Sandy Bay, Enderby Island, with initial benefits in growth and survival reported. Long-term effects, however, are not known. Aims To determine the impact of ivermectin treatment administered in the first month of life, on long-term survival and fecundity in a sample of NZ sea lion pups. Methods For a sample of treated and control pups born between 2002 and 2004, resighting data to 2012 was assessed with the Cox proportional hazards analysis to evaluate survival to maturity and fecundity. Key results Sample size was a limiting factor as juvenile survival was very low, but a trend of improved survival was observed in the ivermectin-treated group. Year of birth was significant due to the effects of a bacterial epizootic in the first year of the trial. Reproductive rate was not significantly different between groups. Conclusions The effect of disease and parasitism on the survival of NZ sea lions is apparent, contributing to early pup mortality, with potentially wider-ranging implications for juvenile survival and beyond. Implications Further research is warranted to investigate anthelmintic treatment of NZ sea lion pups as a safe and effective management tool to improve survival and recruitment in declining populations.
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Maravilla-Chávez, M. Octavio, Alfredo Zavala-González, and Alfredo Ortega-Rubio. "Four seasons abundance changes of Zalophus californianus californianus (Lesson 1828), Allen, 1880, in the Gulf of California, Mexico." Brazilian Archives of Biology and Technology 49, no. 1 (January 2006): 111–16. http://dx.doi.org/10.1590/s1516-89132006000100013.
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This paper describes for the first time the relative abundance, population structure and numeric variation of California sea lions in the Gulf of California, Mexico, during four different seasons. The relative abundance estimates varied from the highest 17,162 sea lions in July of 1990 (summer) to a minimum 7,470 in February of 1992 (winter), representing a reduction of 10,000 sea lions. Hypotheses about the migration of part of the population to the Pacific Ocean were compared and discussed against their residency inside the Gulf, and seasonal dispersion of individuals along this inner sea.
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Damir, Mihelić, Smodlaka Hrvoje, Tkalčić Suzana, Palmer Lauren, Mršić Gordan, Špiranec Katarina, Špoljarić Daniel, Popović Maja, and Mihelić Draga. "Creation Nerves of the Lumbar and Sacral Plexus in California Sea Lions (Zalophus Californianus) and Northern Elephant Seals (Mirounga Angustirostris)/Formiranje Nerava Iz Lumbalnog I Sakralnog Pleksusa Kod Kalifornijskog Morskog Lava (Zalophus Californianus) I Severnomorskog Slona (Mirounga Angustirostris)." Acta Veterinaria 64, no. 3 (September 1, 2014): 293–306. http://dx.doi.org/10.2478/acve-2014-0028.
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Abstract The lumbosacral plexus was investigated in the California sea lion and Northern elephant seal. In 9 California sea lions and 2 Northern elephant seals the femoral nerve rises from the ventral branches of the 3rd and 4th lumbar nerves, whilst in one male and two specimens of the Northern elephant seal the 5th lumbar nerve was also involved. Ventral branches of the 3rd and 4th lumbar nerves comprised the obturatorius nerve in 7 specimens; in 3 specimens the 5th lumbar nerve additionally supplements the obturatorius nerve. In Northern elephant seals the obturatorius nerve originates from the ventral branches of the 3rd, 4th and 5th lumbar nerves. The ischiadic nerve originates from the ventral branches of the 4th, 5th lumbar and 1st sacral nerves in 8 specimens California sea lions and in 2 North elephant seals. In 2 specimens of both species the 2nd sacral nerve also participates. The gluteal nerve created ventral branches of the 5th lumbar and 1st sacral nerves in three specimens; however in one specimen the 4th and 5th lumbar nerves gave rise to the same nerve in the Northern elephant seal. In California sea lions the gluteal nerve originates from the ventral branches of the 5th lumbar nerve in seven specimens, nonetheless in 3 specimens the 4th lumbar nerve also participates in its formation.
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Aznar, F. J., J. Hernández-Orts, A. A. Suárez, M. García-Varela, J. A. Raga, and H. L. Cappozzo. "Assessing host–parasite specificity through coprological analysis: a case study with species of Corynosoma (Acanthocephala: Polymorphidae) from marine mammals." Journal of Helminthology 86, no. 2 (April 18, 2011): 156–64. http://dx.doi.org/10.1017/s0022149x11000149.
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AbstractIn this paper we report an investigation of the utility of coprological analysis as an alternative technique to study parasite specificity whenever host sampling is problematic; acanthocephalans from marine mammals were used as a model. A total of 252 scats from the South American sea lion, Otaria flavescens, and rectal faeces from 43 franciscanas, Pontoporia blainvillei, from Buenos Aires Province, were examined for acanthocephalans. Specimens of two species, i.e. Corynosoma australe and C. cetaceum, were collected from both host species. In sea lions, 78 out of 145 (37.9%) females of C. australe were gravid and the sex ratio was strongly female-biased. However, none of the 168 females of C. cetaceum collected was gravid and the sex ratio was not female-biased. Conversely, in franciscanas, 14 out of 17 (82.4%) females of C. cetaceum were gravid, but none of 139 females of C. australe was, and the sex ratio of C. cetaceum, but not that of C. australe, was female-biased. In putative non-hosts, the size of worms was similar to that from specimens collected from prey. Results suggest that both acanthocephalans contact sea lions and franciscanas regularly. However, C. australe and C. cetaceum cannot apparently reproduce, nor even grow, in franciscanas and sea lions, respectively. Coprological analysis may represent a useful supplementary method to investigate parasite specificity, particularly when host carcasses are difficult to obtain.
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Vilata, Juan, Doris Oliva, and Maritza Sepúlveda. "The predation of farmed salmon by South American sea lions (Otaria flavescens) in southern Chile." ICES Journal of Marine Science 67, no. 3 (November 6, 2009): 475–82. http://dx.doi.org/10.1093/icesjms/fsp250.
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Abstract Vilata, J., Oliva, D., and Sepúlveda, M. 2010. The predation of farmed salmon by South American sea lions (Otaria flavescens) in southern Chile. – ICES Journal of Marine Science, 67: 475–482. The South American sea lion Otaria flavescens is abundant off southern Chile. Because Chilean salmon farming has experienced an explosive growth in the past two decades, interactions between O. flavescens and this industry have increased. Fieldwork, including in situ behavioural observations, was carried out at three salmon farms off southern Chile from May to July 2008. The aim was to analyse possible patterns in the interactions and to evaluate whether they were influenced by the endogenous circa-rhythms of the species, prey size, tidal flux, and the use of an acoustic harassment device (AHD). The results showed that the attacks by O. flavescens followed seasonal patterns, with salmon predated more in autumn and winter, and daily patterns, with more interactions at night. In addition, attacks were more frequent on larger salmon, suggesting the existence of a prey-size preference. More sea lions were sighted at the ebb and flow tide peaks, when currents are stronger, suggesting that currents linked to tidal flux might facilitate the access of the sea lions to the farmed salmon. Although the use of AHDs appeared positive at one site, there is a strong suspicion that their efficacy may be site-specific.
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Rehberg, M. J., L. D. Rea, and C. A. Eischens. "Overwintering Steller sea lion (Eumetopias jubatus) pup growth and behavior prior to weaning." Canadian Journal of Zoology 96, no. 2 (February 2018): 97–106. http://dx.doi.org/10.1139/cjz-2016-0296.
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We measured individual growth, looked for evidence of weaning, and examined the interaction of these changes with diving behavior in young-of-year Steller sea lion (Eumetopias jubatus (Schreber, 1776)) pups in Alaska, USA, during their first winter. Steller sea lions employ an income breeding strategy, in which females provision their young over an individually variable period of months to years. Thus, we set out to identify whether these young sea lions showed evidence of weaning during the challenging winter months, describe the nature of their growth during this time, and examine their behaviors in light of these changes. Between 2005 and 2008, we captured 71 pups during early winter and recaptured 33 of these pups in early spring. Mark–resight and stable nitrogen isotope ratios in vibrissae indicated most pups remained nutritionally dependent on adult females throughout the winter. All pups increased both mass and lipid mass, with half of growth contributed by lipid mass. Changes in behavior were not correlated with growth excepting a weak but significant effect on rate of vertical travel. This study demonstrated that capture–recapture of Steller sea lion pups is possible, provided seasonal timing, locations, and age classes are carefully considered for their likelihood of capture success.
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Schakner, Zachary A., Michael G. Buhnerkempe, Mathew J. Tennis, Robert J. Stansell, Bjorn K. van der Leeuw, James O. Lloyd-Smith, and Daniel T. Blumstein. "Epidemiological models to control the spread of information in marine mammals." Proceedings of the Royal Society B: Biological Sciences 283, no. 1844 (December 14, 2016): 20162037. http://dx.doi.org/10.1098/rspb.2016.2037.
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Socially transmitted wildlife behaviours that create human–wildlife conflict are an emerging problem for conservation efforts, but also provide a unique opportunity to apply principles of infectious disease control to wildlife management. As an example, California sea lions ( Zalophus californianus ) have learned to exploit concentrations of migratory adult salmonids below the fish ladders at Bonneville Dam, impeding endangered salmonid recovery. Proliferation of this foraging behaviour in the sea lion population has resulted in a controversial culling programme of individual sea lions at the dam, but the impact of such culling remains unclear. To evaluate the effectiveness of current and alternative culling strategies, we used network-based diffusion analysis on a long-term dataset to demonstrate that social transmission is implicated in the increase in dam-foraging behaviour and then studied different culling strategies within an epidemiological model of the behavioural transmission data. We show that current levels of lethal control have substantially reduced the rate of social transmission, but failed to effectively reduce overall sea lion recruitment. Earlier implementation of culling could have substantially reduced the extent of behavioural transmission and, ultimately, resulted in fewer animals being culled. Epidemiological analyses offer a promising tool to understand and control socially transmissible behaviours.
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Blackburn, L. "SEA LIONS DIVE FOR DINNER." Journal of Experimental Biology 210, no. 2 (January 15, 2007): i. http://dx.doi.org/10.1242/jeb.02686.
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Barinaga, Marcia. "US sea lions join casualties." Nature 336, no. 6194 (November 1988): 8. http://dx.doi.org/10.1038/336008a0.
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Kirkman, Stephen P. "Fur Seals and Sea Lions." African Journal of Marine Science 36, no. 4 (October 2, 2014): 529–30. http://dx.doi.org/10.2989/1814232x.2014.990923.
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Stirling, Ian. "Sea Lions of the World." Marine Mammal Science 23, no. 4 (October 2007): 987–88. http://dx.doi.org/10.1111/j.1748-7692.2007.00139.x.
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