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Journal articles on the topic 'Hooker's sea lion'

Author: Grafiati

Published: 4 June 2021

Last updated: 12 February 2022

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1

BEDDARD, FRANK E. "XV. On the Structure of Hooker's Sea-Lion (Arctocephalus hookeri)." Transactions of the Zoological Society of London 12, no. 10 (July 7, 2010): 369–80. http://dx.doi.org/10.1111/j.1096-3642.1890.tb00004.x.

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2

Roe, WD, PJ Duignan, L. Meynier, GW de Lisle, and DV Cousins. "Tuberculosis in a New Zealand (Hooker's) sea lion." New Zealand Veterinary Journal 54, no. 1 (February 2006): 51. http://dx.doi.org/10.1080/00480169.2006.36610.

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3

Woodley, Thomas H., and David M. Lavigne. "Potential effects of incidental mortalities on the Hooker's sea lion (Phocarctos hookeri) population." Aquatic Conservation: Marine and Freshwater Ecosystems 3, no. 2 (June 1993): 139–48. http://dx.doi.org/10.1002/aqc.3270030206.

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4

Hawke, D. J. "Observations of Hooker's sea lion,Phocarctos hookeri, at a hauling ground on Otago Peninsula, New Zealand." New Zealand Journal of Marine and Freshwater Research 20, no. 3 (September 1986): 333–37. http://dx.doi.org/10.1080/00288330.1986.9516154.

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5

BEENTJES, MICHAEL P. "Comparative terrestrial locomotion of the Hooker's sea lion (Phocarctos hookeri) and the New Zealand fur seal (Arctocephalus forsteri): evolutionary and ecological implications." Zoological Journal of the Linnean Society 98, no. 4 (April 1990): 307–25. http://dx.doi.org/10.1111/j.1096-3642.1990.tb01204.x.

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6

Robinson, S., L. Wynen, and S. Goldsworthy. "PREDATION BY A HOOKER'S SEA LION (PHOCARCTOS HOOKERI) ON A SMALL POPULATION OF FUR SEALS (ARCTOCEPHALUS SPP.) AT MACQUARIE ISLAND." Marine Mammal Science 15, no. 3 (July 1999): 888–93. http://dx.doi.org/10.1111/j.1748-7692.1999.tb00855.x.

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7

Slooten, Elisabeth, and Stephen M. Dawson. "Conservation of marine mammals in New Zealand." Pacific Conservation Biology 2, no. 1 (1995): 64. http://dx.doi.org/10.1071/pc950064.

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New Zealand has a diverse fauna of marine mammals, comprising 35 cetacean and six pinniped species. None of these is hunted within the 200 mile Exclusive Economic Zone, but several species are killed incidentally in coastal or deep-water fisheries. Particularly affected are Hector's Dolphin, Hooker's Sea Lion, and the New Zealand Fur Seal. Detailed information on the nature and magnitude of incidental catches is patchy at best, and inadequate to assess nationally the impact on any one species. Other species are known to be caught, but a quantitative assessment of how many are caught per year is impossible. The impact of whale watching on sperm whales has attracted more attention, and impacts of tourism on other marine mammals are just beginning to be studied. We critically review the nature and management of the potential threats facing New Zealand marine mammals, including bycatch, entanglement in plastic debris, chemical pollution, and tourism. We discuss research needs and management recommendations for each conservation problem in turn.

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8

McMahon, Clive R., Dave Holley, and Susan Robinson. "The diet of itinerant male Hooker's sea lions, Phocarctos hookeri, at sub-Antarctic Macquarie Island." Wildlife Research 26, no. 6 (1999): 839. http://dx.doi.org/10.1071/wr98079.

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Scats were collected from itinerant male Hooker's sea lions, Phocarctos hookeri, at Macquarie Island and the uneroded faunal remains used to assess the diet. Uneroded sagittal otoliths were used to identify teleost fish and to calculate fish size. Prey items included 14 taxa of teleost fish, cephalopods, gastropods, crustaceans and fur seals. Fish constituted the primary component of the diet. Prey species previously uncommon in the diet of seals and penguins around Macquarie Island were commonly eaten by Hooker's sea lions. The sub-Antarctic horse fish (Zanclorhynchus spinifer) and the Patagonian tooth fish (Dissostichus eleginoides) were the two most abundant species and occurred in 62.5% and 41.7% of all scats respectively. There were no age-specific and individual differences in the diet of sea lions. Seasonal variances in diet were absent. Small plastic fragments (diameter ∼1 mm) were found only in association with otoliths of Electrona subaspera. Some overlap was seen between the diet of itinerant male Hooker's sea lions and the commercial fisheries that currently operate around Macquarie Island.

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9

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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10

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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11

Ponganis, Paul J., Edward P. Ponganis, Katherine V. Ponganis, Gerald L. Kooyman, Roger L. Gentry, and Fritz Trillmich. "Swimming velocities in otariids." Canadian Journal of Zoology 68, no. 10 (October 1, 1990): 2105–12. http://dx.doi.org/10.1139/z90-293.

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Velocities during surface swimming and diving were measured with microprocessor recorders in four otariid species: northern fur seals (Callorhinus ursinus), Galapagos sea lions (Zalophus californianus wollebaeki), Galapagos fur seals (Arctocephalus galapagoensis), and Hooker's sea lions (Phocarctos hookeri). Mean surface swimming velocities ranged from 0.6 to 1.9 m/s. Transit distances to feeding sites (1.2–90 km) were calculated using these velocities. Dive velocities, recorded every 15 s, ranged from 0.9 to 1.9 m/s. These velocities were consistent with calculated minimal cost of transport velocities in the smaller species. Using time partitioning, the metabolic cost of a northern fur seal foraging trip is estimated on the basis of recorded velocities and their calculated energy costs. This value is within 6% of that previously made with doubly labeled water techniques.

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12

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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13

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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14

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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15

Gales, N. J., and R. H. Mattlin. "Summer diving behaviour of lactating New Zealand sea lions, Phocarctos hookeri." Canadian Journal of Zoology 75, no. 10 (October 1, 1997): 1695–706. http://dx.doi.org/10.1139/z97-796.

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The diving behaviour of 14 female New Zealand sea lions (Phocarctos hookeri) was recorded during early lactation in January and February 1995 on the Auckland Islands, New Zealand. During 73 trips to sea, 19 720 dives were recorded. The average duration of a foraging cycle was 2.9 days (range 1.4–4.8 days), of which 1.7 days (57%) (range 1.1–3.4 days) were spent at sea and 1.2 days (43%) (range 0.8–2.3 days) ashore. At sea the sea lions dived almost continuously at a rate of 7.5 dives/h and spent a mean of 45% of the time submerged (≥ 2 m). Dive behaviour varied among individuals but showed no diel pattern overall. The dive depth for all dives ≥ 6 m was 123 ± 87 m (mean ± SD) (median 124 m, maximum 474 m) and ranged among individuals from 79 ± 85 to 187 ± 166 m. About half of the dives were in the 101- to 180-m range. The duration of all dives was 3.9 ± 1.8 min (median 4.33 min, maximum 11.3 min); about half (51%) of the dive durations were between 4 and 6 min. Surface interval was 4.5 ± 15.8 min (median 1.9 min). Almost half (44%) of all dives exceeded the calculated aerobic dive limit of each sea lion (range 16–73% for individuals). Most dive profiles were flat bottomed and, we believe, are to the benthos. A mean of 51.5% of all dive time was spent in the deepest 85% of the dive. Prey remains found during this study were primarily of benthic and demersal organisms. Phocarctos hookeri is the deepest and longest diving of any of the otariids recorded to date. We suggest that the dive behaviour may reflect either successful physiological adaptation to exploiting benthic prey and (or) a marginal foraging environment in which diving behaviour is close to physiological limits.

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16

Breen, Paul A., Ray Hilborn, Mark N. Maunder, and Susan W. Kim. "Effects of alternative control rules on the conflict between a fishery and a threatened sea lion (Phocarctos hookeri)." Canadian Journal of Fisheries and Aquatic Sciences 60, no. 5 (May 1, 2003): 527–41. http://dx.doi.org/10.1139/f03-046.

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In New Zealand, a fishery for squid (Nototodarus sloanii) incidentally catches a threatened sea lion, Phocarctos hookeri. Bycatch is managed with an annual limit designed to ensure rebuilding of the sea lion population. We explore the conservation and cost effects of the current limit and two simple alternative rules, comparing them with no fishing and unrestricted fishing. We fitted an age-structured Bayesian model to sea lion pup estimates to obtain samples of the joint posterior distribution of parameters; from these we made 100-year simulations with five harvest control rules under six different sets of environmental conditions. The base-case fit suggests that the current sea lion population may be near its carrying capacity, although this may be sensitive to modelling choices. The fishery bycatch constitutes little risk to the sea lion population in the absence of catastrophes and generates small marginal risks when catastrophes are simulated. The current management rule does not minimise the marginal risk of extinction, is much more costly to the fishery than simple alternative rules, and incurs greatest cost when risk is smallest. The model appears to be a good tool for evaluating alternative management strategies against predefined objectives.

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17

Geschke, Katja, and B. Louise Chilvers. "Managing big boys: a case study on remote anaesthesia and satellite tracking of adult male New Zealand sea lions (Phocarctos hookeri)." Wildlife Research 36, no. 8 (2009): 666. http://dx.doi.org/10.1071/wr09133.

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Context. Handling animals is essential for many applications in wildlife management. However, currently there are limited techniques to safely handle and move large mobile pinnipeds, particularly when they cannot be physically restrained first. Such animals can be the cause of many land-based wildlife–human conflicts. The New Zealand (NZ) sea lion (Phocarctos hookeri) is the world’s rarest and second largest otariid, and is in severe decline. Although most NZ sea lions live on uninhabited NZ subantarctic islands, a small population is recolonising the coastline of Otago, NZ and this close proximity with humans can cause conflict. Aims. The aim of this research was to assess a method of remote chemical anaesthesia for its ability to safely and practically immobilise large pinnipeds to allow attachment of satellite tracking equipment and to handle and potentially move animals if in situations of conflict. Methods. The chemical anaesthetic Zoletil® was remotely applied to immobilise adult male NZ sea lions at Enderby Island, Auckland Islands, to allow handling and the application of satellite tracking equipment. Key results. Six adult males weighing up to 330 kg were successfully anaesthetised, weighed and measured. Two of these had satellite location tags attached, which showed two very different post-breeding movement patterns by adult males and indicated minimum overlap with local fisheries activities. Conclusions. This remote anaesthesia technique was successful for adult male NZ sea lions and could be used for the immobilisation and management of other large mobile pinnipeds. Implications. The ability to anaesthetise and safely handle large adult male pinnipeds will provide better management in areas where animals come in close contact with human populations with possible lethal interactions or where attachment of monitoring equipment is required to investigate population parameters or possible lethal interactions.

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18

Duignan, PJ, I. Wilkinson, and MR Alley. "New Zealand sea lion (Phocarctos hookeri) epidemic 2002." New Zealand Veterinary Journal 51, no. 1 (February 2003): 45–46. http://dx.doi.org/10.1080/00480169.2003.36339.

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19

Kahui, Viktoria. "A bioeconomic model for Hooker’s sea lion bycatch in New Zealand*." Australian Journal of Agricultural and Resource Economics 56, no. 1 (August 22, 2011): 22–41. http://dx.doi.org/10.1111/j.1467-8489.2011.00566.x.

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20

Meyer, Stefan, Bruce C. Robertson, B. Louise Chilvers, and Martin Krkošek. "Marine mammal population decline linked to obscured by-catch." Proceedings of the National Academy of Sciences 114, no. 44 (October 9, 2017): 11781–86. http://dx.doi.org/10.1073/pnas.1703165114.

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Declines of marine megafauna due to fisheries by-catch are thought to be mitigated by exclusion devices that release nontarget species. However, exclusion devices may instead conceal negative effects associated with by-catch caused by fisheries (i.e., unobserved or discarded by-catch with low postrelease survival or reproduction). We show that the decline of the endangered New Zealand (NZ) sea lion (Phocarctos hookeri) is linked to latent levels of by-catch occurring in sub-Antarctic trawl fisheries. Exclusion devices have been used since 2001 but have not slowed or reversed population decline. However, 35% of the variability in NZ sea lion pup production is explained by latent by-catch, and the population would increase without this factor. Our results indicate that exclusion devices can obscure rather than alleviate fishery impacts on marine megafauna.

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BEENTJES, MICHAEL P. "HAUL-OUT PATTERNS, SITE FIDELITY AND ACTIVITY BUDGETS OF MALE HOOKER'S SEA LIONS (PHOCARCTOS HOOKERI) ON THE NEW ZEALAND MAINLAND." Marine Mammal Science 5, no. 3 (July 1989): 281–97. http://dx.doi.org/10.1111/j.1748-7692.1989.tb00341.x.

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22

Beentjes, Michael P. "BEHAVIORAL THERMOREGULATION OF THE NEW ZEALAND SEA LION (PHOCARCTOS HOOKERI)." Marine Mammal Science 22, no. 2 (April 2006): 311–25. http://dx.doi.org/10.1111/j.1748-7692.2006.00022.x.

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23

Ling, JK. "Impact Of Colonial Sealing On Seal Stocks Around Australia, New Zealand And Subantarctic Islands Between 150 And 170 Degrees East." Australian Mammalogy 24, no. 1 (2002): 117. http://dx.doi.org/10.1071/am02117.

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Details of southern elephant seal oil and fur seal and sea lion skin cargoes have been extracted from a large number of secondary sources dealing with Australian and New Zealand maritime history, which in turn referred to numerous primary sources of information. The data were collated and analysed for ten areas in the south-west Pacific region and published recently in two separate larger works. This review is a synthesis and analysis of the impact of the colonial sealing industry on seal stocks in the region, based on those papers, with some minor revisions and reference to works by other authors. Colonial sealing lasted from the late 18th to the mid- 19th century and was followed by sporadic hunting until the late 1940s. Southern elephant seals (Mirounga leonina) were hunted for their oil; and Australian fur seals (Arctocephalus pusillus doriferus), New Zealand fur seals (Arctocephalus forsteri), Australian sea lions (Neophoca cinerea) and New Zealand sea lions (Phocarctos hookeri) were targeted for their skins and some oil. At least 1,081 tons of elephant seal oil were shipped from King Is. between 1802 and 1819, while 8,380 tons were shipped from Macquarie Is. between 1810 and 1919. More than 1.4 million skins of both species of fur seals were harvested between 1792 and 1949, but only 4,000 Neophoca and 5,700 Phocarctos pelts are recorded as having been shipped by 1840. The Antipodes Islands yielded more than a quarter of the total fur seal skin harvest, and New Zealand and southern Australia each delivered a quarter of the total. Current numbers of the two species of fur seals combined are about a tenth of the crudely estimated size (1.5 million) of the original population. The exploited fur seals and sea lions were probably the same species as occur today at the original sealing localities, apart from Macquarie Is. where the identity of the exploited fur seals remains in doubt. There is some evidence that Maoris and Australian Aborigines hunted seals in pre-European times, resulting in reduced ranges and depleted stocks that were exploited later by colonial sealers.

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Chilvers, B. L., I. S. Wilkinson, and S. Childerhouse. "New Zealand sea lion,Phocarctos hookeri, pup production—1995 to 2006." New Zealand Journal of Marine and Freshwater Research 41, no. 2 (June 2007): 205–13. http://dx.doi.org/10.1080/00288330709509909.

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25

Wilkinson, I. S., S. J. Childerhouse, P. J. Duignan, and F. M. D. Gulland. "INFANTICIDE AND CANNIBALISM IN THE NEW ZEALAND SEA LION, PHOCARCTOS HOOKERI." Marine Mammal Science 16, no. 2 (April 2000): 494–500. http://dx.doi.org/10.1111/j.1748-7692.2000.tb00942.x.

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26

Chilvers, B. Louise, and Stefan Meyer. "Conservation needs for the endangered New Zealand sea lion,Phocarctos hookeri." Aquatic Conservation: Marine and Freshwater Ecosystems 27, no. 4 (February 3, 2017): 846–55. http://dx.doi.org/10.1002/aqc.2742.

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27

Gales, Nicholas J., and David J. Fletcher. "Abundance, distribution and status of the New Zealand sea lion, Phocarctos hookeri." Wildlife Research 26, no. 1 (1999): 35. http://dx.doi.org/10.1071/wr98022.

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The abundance of the New Zealand sea lion, Phocarctos hookeri, was estimated using a model that incorporated estimated pup production. Pups are born at only five sites, four of which are at the sub-Antarctic Auckland Islands, which lie to the south of New Zealand. The remaining breeding site is at Campbell Island in the same region. Pup production was estimated during the 1994/95 and 1995/96 breeding seasons from mark–recapture studies at the two largest sea lion rookeries, at the Auckland Islands (Sandy Bay and Dundas Island), which account for almost 90% of total pup production for the species. Pup production for the other sites was estimated from direct counts or, in the case of Campbell Island, from recent tagging data. Total pup production estimates for all sites during the 1994/95 and 1995/96 breeding seasons are 2640 and 2807 respectively. During the four-week pupping season, pup mortality at most sites was estimated to be about 10%. The estimates of absolute abundance based on pup production for the two breeding seasons were 11 700 (95% confidence interval (CI): 10 500–13 100) and 12 500 (95% CI: 11 100–14 000) respectively. This population abundance is among the smallest reported for a species within the Otariidae. The highly localised, and historically reduced distribution make this species vulnerable to impact and warrants particular attention from conservation managers. In particular, the potential impact of the annual bycatch of P. hookeri in a trawl fishery requires close monitoring and, ideally, some mitigation action.

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Augé, Amélie A., B. Louise Chilvers, Lloyd S. Davis, and Antoni B. Moore. "In the shallow end: diving behaviour of recolonising female New Zealand sea lions (Phocarctos hookeri) around the Otago Peninsula." Canadian Journal of Zoology 89, no. 12 (December 2011): 1195–205. http://dx.doi.org/10.1139/z11-098.

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Female New Zealand sea lions ( Phocarctos hookeri (Gray, 1844)) at the Auckland Islands (remnant populations) are the deepest and longest diving otariids. These remnant populations are found at the margin of the historical range of the species. We hypothesized that diving behaviours of animals in the core of their historical range is less extreme owing to a better marine habitat. All female New Zealand sea lions (n = 13, aged 2–14 years) born on the Otago Peninsula (initial recolonising population) were equipped with time–depth recorders during April and May 2008, 2009, and 2010. The mean dive depth was 20.2 ± 24.5 m and mean dive duration was 1.8 ± 1.1 min, some of the lowest values reported for otariids. Otago female New Zealand sea lions did not exhibit two distinct diving specialisations as reported at the Auckland Islands. Otago adult females exceeded calculated aerobic dive limits in 7.1% of dives compared with 68.7% at the Auckland Islands. The contrasting differences in diving behaviour between Otago and the Auckland Islands suggest that Otago represents a better marine habitat for New Zealand sea lions, with food easily accessible to animals of all ages.

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Mcconkey, SD, H. Mcconnell, C. Lalas, S. Heinrich, A. Ludmerer, N. Mcnally, E. Parker, C. Borofsky, K. Schimanski, and G. Mcintosh. "A Northward Spread In The Breeding Distribution Of The New Zealand Sea Lion (Phocartos Hooeri)." Australian Mammalogy 24, no. 1 (2002): 97. http://dx.doi.org/10.1071/am02097.

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The primary objective of the population management plan for New Zealand sea lions, Phocarctos hookeri, is to move the species from its current conservation status of ‘Threatened’ to ‘Non-threatened’. The mechanism by which this will occur is through the establishment of new breeding colonies away from the only existing colonies at Auckland Islands and Campbell Island. Otago, on the southeast coast of the South Island of New Zealand, is one of only three locations where breeding has been recorded away from these islands in modern times. We found only one female at the initiation of our surveys here in 1991, an individual that had been tagged as a pup at Auckland Islands. This female has remained resident at Otago and is now breeding. Her first live birth, in the 1993/94 breeding season, represented the first record of a P. hookeri pup on the New Zealand mainland since the elimination of the species here by humans c. 150 years ago. Up to and including the 2000/01 breeding season she had produced six pups. Her surviving pups have remained at Otago and her eldest two daughters have started breeding, producing a further three pups. From this total of nine live births, two pups have died. Although 6 - 8 other migrant females have been recorded, to our knowledge none have bred at Otago. We conclude that the initiation of breeding by P. hookeri at Otago has been a serendipitous event attributable to atypical behaviour by a single female.

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Mcconkey, SD, S. Heinrich, C. Lalas, H. Mcconnell, and N. Mcnally. "Pattern Of Immigration Of New Zealand Sea Lions Phocarctos Hookeri To Otago, New Zealand: Implications For Management." Australian Mammalogy 24, no. 1 (2002): 107. http://dx.doi.org/10.1071/am02107.

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The present management strategy for New Zealand sea lions Phocarctos hookeri assumes that kills in a squid trawl fishery around Auckland Islands, the species population base, have prevented an increase in abundance of sea lions. This strategy also assumes that emigration will be initiated as the population reaches carrying capacity, and that emigration rates will be density dependent. We used the combination of photographic identification of individuals and diagnostic features of age classes to estimate immigration rates of P. hookeri to Otago, South Island, New Zealand. Most immigrants were males = 2 years old at arrival, and included animals tagged as pups at Auckland Islands. Estimates for total numbers of immigrants to Otago from four consecutive cohorts, 1991/92 - 1994/95, varied three-fold through a period of constant annual pup production at Auckland Islands. The greatest influx was from the 1993/94 cohort, a breeding season that predated the enforcement of early closures of the squid fishery. We suggest published records from the Auckland Islands indicate that this population is already at carrying capacity. If so, then factors other than, or in addition to, pup production and fishery mortality have an impact on emigration rates.

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Costa, Daniel P., Nicholas J. Gales, and Daniel E. Crocker. "Blood Volume and Diving Ability of the New Zealand Sea Lion,Phocarctos hookeri." Physiological Zoology 71, no. 2 (March 1998): 208–13. http://dx.doi.org/10.1086/515911.

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Collins, CJ, NJ Rawlence, TH Worthy, RP Scofield, AJD Tennyson, I. Smith, M. Knapp, and JM Waters. "Pre-human New Zealand sea lion (Phocarctos hookeri) rookeries on mainland New Zealand." Journal of the Royal Society of New Zealand 44, no. 1 (October 15, 2013): 1–16. http://dx.doi.org/10.1080/03036758.2013.828761.

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Roe, WD, S. Michael, J. Fyfe, E. Burrows, SA Hunter, and L. Howe. "First report of systemic toxoplasmosis in a New Zealand sea lion (Phocarctos hookeri)." New Zealand Veterinary Journal 65, no. 1 (September 21, 2016): 46–50. http://dx.doi.org/10.1080/00480169.2016.1230526.

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Robertson, Bruce C. "Is management limiting the recovery of the New Zealand sea lion Phocarctos hookeri?" Polar Biology 38, no. 4 (November 11, 2014): 539–46. http://dx.doi.org/10.1007/s00300-014-1619-2.

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35

Hamilton, Sheryl, and G. Barry Baker. "Population growth of an endangered pinniped—the New Zealand sea lion (Phocarctos hookeri)—is limited more by high pup mortality than fisheries bycatch." ICES Journal of Marine Science 76, no. 6 (March 28, 2019): 1794–806. http://dx.doi.org/10.1093/icesjms/fsz039.

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Abstract The endangered New Zealand sea lion, Phocarctos hookeri is killed as incidental bycatch in a trawl fishery operating near their second largest population on Campbell Island in New Zealand’s sub-Antarctic. Using the Potential Biological Removal (PBR) procedure to assess the sustainability of this bycatch for the sea lion population on Campbell Island indicated that annual bycatch estimates, particularly following the implementation of bycatch mitigation measures, are below the PBR threshold of 25 (derived using a precautionary approach). Preliminary Population Viability Analysis (PVA) modelling supported the finding that current bycatch levels, especially given a strong male bias (98%) in bycatch, are sustainable for this population. Models showed that reducing pup mortality through management actions, such as installing ramps in wallows where large numbers of pups drown, would lead to increased population growth. While obtaining more accurate data on population status and demographic parameters for the Campbell Island population should be a priority, this will take many years of research. The PBR and PVA tools demonstrate that contemporary conservation management should continue to focus on increasing pup survival while maintaining mitigation approaches that have reduced bycatch to low levels, together with high observer coverage to sustain confidence in annual bycatch estimates.

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Saprtza, F. G. Riet, N. Lopez‐Villalobos, D. D. S. Mackenzie, P. J. Duignan, A. MacGibbon, B. L. Chilvers, and I. S. Wilkinson. "Comparison of methods for the analysis of New Zealand sea lion,Phocarctos hookeri, milk." New Zealand Journal of Marine and Freshwater Research 43, no. 4 (December 2009): 997–1006. http://dx.doi.org/10.1080/00288330909510056.

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Meyer, Stefan, Bruce C. Robertson, B. Louise Chilvers, and Martin Krkošek. "Population dynamics reveal conservation priorities of the threatened New Zealand sea lion Phocarctos hookeri." Marine Biology 162, no. 8 (July 19, 2015): 1587–96. http://dx.doi.org/10.1007/s00227-015-2695-8.

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Chilvers, BL, IS Wilkinson, PJ Duignan, and NJ Gemmell. "Summer foraging areas for lactating New Zealand sea lions Phocarctos hookeri." Marine Ecology Progress Series 304 (2005): 235–47. http://dx.doi.org/10.3354/meps304235.

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Chilvers, BL, SJ Childerhouse, and NJ Gales. "Winter foraging behaviour of lactating New Zealand sea lions (Phocarctos hookeri)." New Zealand Journal of Marine and Freshwater Research 47, no. 2 (June 2013): 125–38. http://dx.doi.org/10.1080/00288330.2012.752755.

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Crocker, D. E., N. J. Gales, and D. P. Costa. "Swimming speed and foraging strategies of New Zealand sea lions (Phocarctos hookeri)." Journal of Zoology 254, no. 2 (June 2001): 267–77. http://dx.doi.org/10.1017/s0952836901000784.

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Childerhouse, S., G. Dickie, and G. Hessel. "Ageing live New Zealand sea lions (Phocarctos hookeri) using the first post-canine tooth." Wildlife Research 31, no. 2 (2004): 177. http://dx.doi.org/10.1071/wr03006.

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Live New Zealand sea lions (Phocarctos hookeri) were aged from growth layer groups (GLGs) in the cementum of a lower first post-canine tooth. A single post-canine (PC1) was removed from individuals of known-age (n = 74) between 1997 and 2001 while under a full anaesthetic. Teeth were decalcified, sectioned on a cryostat, stained and then mounted on glass slides. Age was estimated by counting GLGs in the cementum multiple times. Age estimates were calibrated with known-aged individuals and confirmed the annual formation of cementum annuli in PC1 tooth. While there is some variation in assigning exact age to individuals, it was possible to age 94% of teeth to the exact year or to within 1 year of actual age. There was no significant difference in the slope of regression lines associated with actual and estimated age using this technique (t-test, t = 0.309, d.f. = 144, P < 0.05). Accuracy in ageing was improved by discarding sets of readings with low precision and re-reading the tooth until a precise set of estimates was made. GLGs in the cementum were more accurate and robust for age estimation than using GLGs in the dentine. This paper describes a reliable method for the preparation and ageing of the first post-canine tooth (PC1) from live New Zealand sea lions.

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Wilkinson, I. S., B. L. Chilvers, P. J. Duignan, and P. A. Pistorius. "An evaluation of hot-iron branding as a permanent marking method for adult New Zealand sea lions, Phocarctos hookeri." Wildlife Research 38, no. 1 (2011): 51. http://dx.doi.org/10.1071/wr10077.

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Context Studies of the population and behavioural ecology of pinnipeds require the ability to identify individuals over periods ranging from a single season to an entire lifetime. Aims The aims of this research were to examine the efficacy of hot-iron branding as a permanent marking technique including the legibility of marks over time and comparing estimates of survival for animals marked with brands versus flipper tags. Methods Adult female New Zealand sea lions (n = 135) aged between 4 and 24 years of age were hot-iron branded with four-digit numbers during the austral summer of 2000. Key results Ten years on, 100% of animals still alive could be identified from these brands. Over the 10-year research period, it was observed that the skin of fully healed individual brands could, on occasion, become lacerated due to injuries received from shark bites and/or bites from other sea lions, removing or temporarily reducing the legibility of single characters of some brands. However, these animals were still identifiable when all digits were considered – and scars could become an identifying mark in their own right. Key conclusions Survival estimates derived from branded versus tagged-only individuals were similar, although the variance associated with tagged-only survival estimates was higher, giving less robust estimates. This is likely a result of higher resight probabilities observed for branded individuals. Resighting of tags requires a close approach with a high associated level of disturbance to both the marked animal and those associated with it, especially when considered over the lifetime of the animal, while brands can be read from a considerable distance with little or no disturbance. Implications Thus, hot-iron branding can be an effective method for permanently identifying sea lions that provides robust parameter estimates, causes low disturbance in the resighting process, and does not compromise survival.

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ROBERTSON, Bruce C., and B. Louise CHILVERS. "The population decline of the New Zealand sea lion Phocarctos hookeri: a review of possible causes." Mammal Review 41, no. 4 (March 14, 2011): 253–75. http://dx.doi.org/10.1111/j.1365-2907.2011.00186.x.

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Michael, SA, L. Howe, BL Chilvers, PCH Morel, and WD Roe. "Seroprevalence of Toxoplasma gondii in mainland and sub-Antarctic New Zealand sea lion (Phocarctos hookeri) populations." New Zealand Veterinary Journal 64, no. 5 (June 7, 2016): 293–97. http://dx.doi.org/10.1080/00480169.2016.1191974.

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Roberts, J., and C. Lalas. "Diet of New Zealand sea lions (Phocarctos hookeri) at their southern breeding limits." Polar Biology 38, no. 9 (June 4, 2015): 1483–91. http://dx.doi.org/10.1007/s00300-015-1710-3.

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Chilvers, B. L. "Stable isotope signatures of whisker and blood serum confirm foraging strategies for female New Zealand sea lions (Phocarctos hookeri) derived from telemetry." Canadian Journal of Zoology 95, no. 12 (December 2017): 955–63. http://dx.doi.org/10.1139/cjz-2016-0299.

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Recognizing the individual variability of foraging behaviour of marine predators is important for understanding their role in the marine ecosystem and identifying how species may respond to environmental variability or human impacts. This research examines stable isotope signatures (δ13C and δ15N) of blood serum and whiskers from 22 female New Zealand sea lions (Phocarctos hookeri (Gray, 1844)) to determine if the isotopic composition of serum reflects foraging strategy, and whether serum and proximal whisker growth have similar signatures, therefore indicating the isotopic composition of whiskers also reflects the foraging strategy diet at the time of their growth. Female New Zealand sea lions are known to have two distinct foraging strategies (mesopelagic or benthic ecotypes), shown to be habitual within and between years. Females who are known to be mesopelagic foragers have higher overlap and are at greater risk of harmful interactions with fisheries. This research found that the two foraging strategies identified from telemetry are also associated with different δ13C and δ15N isotopic values from blood serum and whiskers. Therefore, stable isotope analysis could be used to determine the proportion of the female population that are likely to be exposed to the detrimental direct and indirect interactions with fisheries.

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Osborne, Amy J., Sandra S. Negro, B. Louise Chilvers, Bruce C. Robertson, Martin A. Kennedy, and Neil J. Gemmell. "Genetic Evidence of a Population Bottleneck and Inbreeding in the Endangered New Zealand Sea Lion,Phocarctos hookeri." Journal of Heredity 107, no. 5 (March 19, 2016): 392–402. http://dx.doi.org/10.1093/jhered/esw015.

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Meynier, Laureline, Duncan D. S. Mackenzie, Pádraig J. Duignan, B. Louise Chilvers, and Patrick C. H. Morel. "Variability in the diet of New Zealand sea lion (Phocarctos hookeri) at the Auckland Islands, New Zealand." Marine Mammal Science 25, no. 2 (April 2009): 302–26. http://dx.doi.org/10.1111/j.1748-7692.2008.00252.x.

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Hamilton, Sheryl, and G. Barry Baker. "Review of research and assessments on the efficacy of sea lion exclusion devices in reducing the incidental mortality of New Zealand sea lions Phocarctos hookeri in the Auckland Islands squid trawl fishery." Fisheries Research 161 (January 2015): 200–206. http://dx.doi.org/10.1016/j.fishres.2014.07.010.

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Lenting, B., B. Gartrell, A. Kokosinska, P. J. Duignan, S. Michael, S. Hunter, and W. D. Roe. "Causes of adult mortality in two populations of New Zealand sea lions (Phocarctos hookeri)." Veterinary and Animal Science 7 (June 2019): 100057. http://dx.doi.org/10.1016/j.vas.2019.100057.

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