Auswahl der wissenschaftlichen Literatur zum Thema „Trawl Shrimp Fishery“

Abstract In the deep sea trawl fishery targeting shrimp (Pandalus borealis) and other cold-water shrimp species, fishers often use a Nordmöre sorting grid ahead of a small mesh codend to avoid bycatch. However, small fish can pass through the grid and are subsequently retained in the codend. This makes shrimp size selection complex and the size-dependent curve for both the shrimp and the bycatch species often exhibits a bell-shaped signature. In this study we developed a new model and method to estimate size selection in this fishery, conducted fishing trials in the Northeast Barents Sea, and applied the new method to quantify the individual and combined size selection of the Nordmöre grid and codend for deep water shrimp and two bycatch species. The size selectivity for both bycatch species showed the expected bell-shaped signature with low retention probability of very small and larger fish. The Nordmöre grid had high passage probability for all sizes, although it decreased slightly for the largest shrimps. The smallest shrimps were released by the codend.

Discards of small northern shrimp (Pandalus borealis) are a problem in the Skagerrak northern shrimp trawl fishery. To reduce catches of small shrimp, we studied the effect of trawl belly length on size selectivity in November 2017 and June 2018 onboard 15 and 27 m double-rigged shrimp trawlers. The selectivity of the vessels’ standard trawl was compared with a trawl differing only in the belly length, being 37% shorter. The trawls had 40 mm bottom panels and cod ends of 35 mm mesh sizes. Eleven and 14 hauls were made, respectively, in 2017 aboard the 15 m vessel and in 2018 aboard the 27 m vessel. The trawls fished shrimp above 19 mm carapace length equally, while catch rates of shrimp below 15.5–16 mm carapace length in the shorter trawl were more than halved. The results were consistent between the two vessels. In short, modifying trawl length is a simple design modification that can reduce catches of small shrimp. Bycatch of Norway pout (Trisopterus esmarkii) was slightly reduced in the shorter trawl, unrelated to fish length.

Shrimp trawl bycatch is a significant source of fishery induced mortality for managed species including red snapper (Lutjanus campechanus Poey), Spanish mackerel (Scomberomorus maculatus MitcheU), and weakfish (Cynoscion regalis Baloch, Schneider) in the southeastern United States. These species have been overfished and are under both state and federal management plans which include regulations mandating reduction of shrimp trawl bycatch mortality. In 1990 the U.S. Congress passed amendments to the Magnuson Fishery Conservation and Management Act (16 U.S.C. 1854) which called for a research program that included the design and evaluation of approaches for reducing shrimp trawl bycatch mortality. A strategic planning initiative addressing finfish bycatch in the Gulf of Mexico and southeastern Atlantic shrimp fisheries was developed by the Gulf and South Atlantic Fisheries Foundation through funding and guidance provided by the National Marine Fisheries Service. A cooperative research plan was developed in 1992 which included the identification, development, and evaluation of gear options for reducing bycatch in the Gulf of Mexico and southeastern Atlantic shrimp fisheries. Between 1990 and 1996 one hundred and forty five bycatch reduction conceptual gear designs contributed by fishers, net shops, gear technicians, and biologists were evaluated. Sixteen of these designs were tested on cooperative commercial shrimp vessels by observers under the southeast regional cooperative bycatch program. Analyses of data from commercial vessel testing indicates that two bycatch reduction designs have potential to significantly reduce shrimp trawl bycatch for weakfish and Spanish mackerel in the southeastern Atlantic and two designs have the potential to significantly reduce red snapper bycatch in the Gulf of Mexico. The fisheye and the extended funnel bycatch reduction devices have been mandated for use in the southeastern Atlantic shrimp fishery and the fisheye and Jones/Davis bycatch reduction devices have been mandated for use in the Gulf of Mexico shrimp trawl fishery.

Studies of the bycatch associated to the shrimp trawling fishery in the Pacific coast of Costa Rica do not assess small organisms (< 10 cm TL) and non-dominant species (< 0.1% of total catch). There is a void in assessing the maintenance of the ecology and ecosystem on which the fishery depends. Furthermore, the Constitutional Court of Costa Rica prohibited the renewal of existing and the issuing of new shrimp bottom-trawl licenses, indicating the necessity of more scientific information on the impacts of this fishery. We present the results of a 23-month study of the shrimp bottom-trawl fishery performed between 50 and 350 m deep in the Pacific coast of Costa Rica. A total of 109 hermit crabs were collected (six species and two families). Paguristes cf. holmesi was the most common species. Zone II presented the highest species richness and abundance. Most specimens (81.8 %) were caught in shallower waters (50-149 m). More than 45% of the trawls presented hermit crabs. It is imperative to further assess the trawling effects on non-commercial benthic fauna and changes on predator-prey relationships before issuing new shrimp licenses

Abstract We examined how catches of ocean shrimp (Pandalus jordani), eulachon (Thaleichthys pacificus), and juvenile groundfish could be affected by altering the level of artificial illumination along the fishing line of an ocean shrimp trawl. In the ocean shrimp trawl fishery, catches of eulachon are of special concern, as the species’ southern Distinct Population Segment is listed as “threatened” under the US Endangered Species Act. Using a double-rigged trawl vessel, with one trawl illuminated and the other unilluminated, we compared the catch efficiencies for ocean shrimp, eulachon, and juvenile groundfish between an unilluminated trawl and trawls illuminated with 5, 10, and 20 LED fishing lights along their fishing line. The addition of artificial illumination along the trawl fishing line significantly affected the average catch efficiency for eulachon, rockfish (Sebastes spp.), and flatfish, with the three LED configurations each catching significantly fewer individuals than the unilluminated trawl without impacting ocean shrimp catches. For Pacific hake (Merluccius productus), the ten LED-configured trawl caught significantly more fish than the unilluminated trawl. For the five and 20 LED configurations, mean Pacific hake catches did not differ from the unilluminated trawl. This study contributes new data on how artificial illumination can affect eulachon catches (and other fish) and contribute to their conservation.

In the United States, interactions between the shrimp trawl fishery and bottlenose dolphins are known to exist; however, the level of mortality is largely unknown, and has not been studied in South Carolina, USA. The current study attempted to determine if interactions between bottlenose dolphins and the South Carolina commercial shrimp trawl fishery pose a significant threat to dolphin populations and if fishery related mortality is underreported. Onboard observations were made during a 25 day (August–December 2010) field study. No dolphin takes occurred during the observational period. These observations focused on direct physical interactions with the gear and depredation behaviours. Additionally, a subsample of the shrimp fishery in South Carolina was asked to participate in a mailed survey. The survey included questions related to gear, dolphin observations, and the status of the shrimp fishery. This paper also examines historical dolphin stranding data from the NOAA/CCEHBR MMIS database for signs of shrimp fishery interactions. A three-tiered flow diagram was developed to characterise each stranding case according to the likelihood that mortality resulted from trawler interaction. Field results point to significant dolphin presence around commercial trawlers (x2 = 23.406, p < 0.001). Survey results showed 12 unreported incidents of shrimp trawl fishery mortality of dolphins. Finally, stranding records revealed several more cases with signs of possible trawler interaction. The current US National Marine Fisheries Service (NOAA) designation of the fishery as a Category II fishery is correct. Increased observer coverage and improved communication with the fishery on the importance of reporting takes is warranted.

This study examined the extent that eulachon (Thaleichthys pacificus) and groundfishes escape trawl entrainment in response to artificial illumination along an ocean shrimp (Pandalus jordani) trawl fishing line. Using a double-rigged trawler, we compared the catch efficiencies for ocean shrimp, eulachon, and groundfishes between an unilluminated trawl and a trawl illuminated with five green LEDs along its fishing line. Results showed a significant reduction in the bycatch of eulachon and yellowtail rockfish (Sebastes flavidus) in the presence of illumination. As eulachon are a species listed in the Endangered Species Act, this finding provides valuable information for fishery managers implementing recovery plans and evaluating potential fishery impacts on their recovery and conservation. For other rockfishes (Sebastes spp.) and flatfishes, however, we did not see the same effect as the illuminated trawl caught similarly or significantly more fishes than did the unilluminated trawl. Prior to this research, the extent that eulachon and groundfishes escape trawl capture in response to illumination along an ocean shrimp trawl fishing line was unclear. Our study has provided results to fill that data gap.

The purpose of this study was to better understand the life cycle of brown shrimp along the Amazon Continental Shelf by using spatial and temporal trawl fleet activities. A total of 208,121 specimens and 1281 trawls were studied throughout the course of 13 years of shrimp size composition. To investigate differences in length composition between fishing grounds, months, and depth, a PERMANOVA analysis was employed. A geographic information system was developed for environmental characterisation and spatiotemporal trawl fleet distribution. Our findings show that the industrial trawl shrimp fleet has a close relationship with shrimp biological characteristics, following shrimp migration patterns in different months, locations, and depths during different stages of their life cycle, and that this fleet acts on two-yearly cohorts. The management measures of limiting effort (number of vessels) appear enough to avoid overcapitalisation, but the closed period and a proposed no-take fishing zone appear insufficient for what was originally proposed. Ecosystem-based management strategies should be addressed immediately because they would be far more effective than traditional fishery-based management measures in promoting sustainable fishing.

The introduction of the Nordmøre grid in shrimp trawls has reduced the bycatch of non-target species. In the Norwegian Northern shrimp (Pandalus borealis) fishery, the mandatory selective gear consists of a Nordmøre grid with 19 mm bar spacing combined with a 35 mm mesh size diamond mesh codend. However, fish bycatch in shrimp trawls remains a challenge and further modifications of the gear that can improve selectivity are still sought. Therefore, this study estimated and compared the size selectivity of Nordmøre grids with bar spacings of 17 and 21 mm. Further, the effect of applying these two grids on trawl size selectivity was predicted and compared to the legislated gear configuration. Experimental fishing trials were conducted in the Barents Sea where the bottom trawl fleet targets Northern shrimp. Results were obtained for the target species and two by-catch species: cod (Gadus morhua) and American plaice (Hippoglossoides platessoides). This study demonstrated that reducing bar spacing can significantly reduce fish bycatch while only marginally affecting catch efficiency of Northern shrimp. This is a potentially important finding from a management perspective that could be applicable to other shrimp fisheries where flexibility in the use of different grid bar spacings may be beneficial to maximize the reduction of unwanted bycatch while minimizing the loss of target species.

Data on productivity of pot fishery on humpback shrimp at the coast of Primorye are presented, actual in conditions of its trawl fishery ban in the northwestern Japan Sea. Biological parameters of the shrimp in the fishing season are considered, and dynamics of the catches is analyzed for one of the major fishing grounds. Species composition and abundance of by-catch in the shrimp pots are discussed. Dependence of the shrimp catch on options of the bite preparation is determined.

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.
Title from electronic title page (viewed Oct. 10, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Marine Sciences." Discipline: Marine Sciences; Department/School: Marine Sciences.

Shrimp are the most economically valuable internationally-traded seafood commodity, and wild-caught, trawled shrimp make up almost half of the ~6.6 million metric tons of annual global production. Shrimp trawling is responsible for one-third of the world’s total fisheries bycatch, leading many to consider shrimp trawling to be the single most destructive fishing practice in the world. Though the bycatch of large marine animals can be significantly reduced by use of turtle excluder devices (TEDs) on shrimp trawls, current TED designs are ineffective at reducing the capture of smaller organisms which represent a large portion of the total bycatch. To further reduce bycatch in the United States Gulf of Mexico shrimp trawl fleet, a variety of bycatch reduction devices (BRDs) are currently being used in conjunction with TEDs. I evaluated the efficiency of a new TED design, intended to reduce bycatch and maintain target shrimp catch. The new TED model is characterized by 5-cm spacing between flat bars, as opposed to the current industry standard of 10-cm spacing between round bars. Comparative towing experiments under standard commercial shrimp trawling operations in waters off of Georgia, Texas and Mississippi during the summer of 2012 demonstrated shrimp losses or gains of -4.32%, +6.07%, -1.58% respectively and an overall reduction in the capture weight of sharks (41.1-99.9%), rays and skates (76.5-93.4%) and horseshoe crabs (100%). These experiments were limited in time and space, and therefore not fully representative of fishing conditions throughout the year, but this study demonstrates the new TED’s effect on the catch rates of target shrimp and bycatch. This thesis research should lead to a broader understanding of the benefits of using reduced spacing flat bar TEDs in the U.S. shrimp trawl industry.

In the southeastern United States, skimmer trawls, pusher-head trawls, wing nets, and small try nets (headrope length less than 12-ft (3.66-m)) are exempt from using a turtle excluder device (TED) and instead must adhere to tow time restrictions as a mode to mitigate sea turtle bycatch. However, observer and stranding data indicate that these tow times may often be exceeded and result in mortality of sea turtles. The National Marine Fisheries Service (NMFS) published a notice of proposed rulemaking in December 2016 to extend TED requirements to other trawl types, however there has been limited development of specialized TEDs for these smaller trawls. In anticipation of a regulatory change, we developed and identified multiple versions of a top-opening TED with a minimum width of 28-in (71-cm) and height of 24-in (61-cm) as the best option for small trawl gears. Prototypes were initially equipped within small try nets and tested for gear performance and sea turtle exclusion in Panama City, Florida. The final designs were then tested for target shrimp retention, bycatch reduction, and general usability of TEDs in the commercial fisheries. A paired comparison test was conducted in 8-ft (2.44-m) and 10-ft (3.05-m) try nets aboard the NMFS R/V Caretta, three commercial skimmer trawls in vesselsFarfantepenaeus duorarum) fishery. There was a general reduction of shrimp and bycatch averaging from a minimum loss of 3.31% in the Miami wing net fishery (FV FL-01) to 22.07% in the skimmer trawl fishery (FV LA-01). This dissertation research indicates that TEDs can function properly in small trawl types, however additional studies are recommended to minimize the shrimp loss and improve the overall TED effectiveness specific to each fishery and trawl type evaluated.

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The primary production represented by agriculture, livestock and fishing is the basis for establishment of attitudes towards the quality in this area. A raw material obtained with excellence standards is the first step to providing a safe product for consumer. The implementation of quality management system is a factor of growth and business success. A shrimp fishery trawl is a shipping company for capture and storage shrimps, thus necessitating the systems implementation ensure shrimp?s quality and safety, because it?s perishable, high commercial value and export. The objective in this work was to implement a management quality organized, represented by Manual of good handling practices to ensure safety of hygienical-sanitary for shrimp. Used a case study holistic and descriptive in a shrimp fishery trawl. The evidence collection is given through intensive direct observation and documentation. Used as research tools a check-list of Good Manufacturing Practices in establishments products/food suppliers from Sanitary Surveillance National Agency. After the first evaluation, elaborated the Manual of Good Practices on Handling of Fish and guided improvement actions, defining the basic situations that involve the capture and transport with measures to ensure the safe and sanitary quality and the instructions theoretical and practical training to develop operational techniques. Good results was achieved with the Manual as speed in providing service with a reduction in average time of work execution on board around 37,5%, higher prodution volume and profit improvement by reducing the loss by errors in manipulation, and these losses have increased from 0,5% for 0,15% considered a virtually total flow of production. With Manual of Good Practice for Handling Fish observed benefits to shrimp fishery trawl, shaping the quality and indicating ways to control production.
A produ??o prim?ria representada pela agricultura, pecu?ria e pesca ? a base para o estabelecimento de atitudes em prol da qualidade na ?rea dos alimentos. Uma mat?ria-prima obtida com padr?es de qualidade de excel?ncia ? o primeiro passo para disponibiliza??o de um produto in?cuo para o consumidor. A aplica??o de sistema de gest?o da qualidade ? um fator de crescimento e sucesso empresarial. Camaroneiro ? uma empresa mar?tima destinada ? captura e armazenagem de camar?es, necessitando, portanto da implementa??o de sistemas que garantam a qualidade higi?nico-sanit?rio e a seguran?a dos camar?es, por ser produto perec?vel, de alto valor comercial e de exporta??o. O objetivo dessa pesquisa, baseando-se no Ciclo de Deming, como pressuposto de diretriz para documenta??o de sistema de gest?o da qualidade, foi elaborar o Manual de Boas Pr?ticas de Manipula??o para barco camaroneiro com orienta??o de a??es t?cnicas de processo como forma de valorizar a mercadoria frente ao mercado competitivo. A metodologia utilizada foi o estudo de caso hol?stico e descritivo em um barco camaroneiro. A coleta de evid?ncias se deu por meio da observa??o direta intensiva e da documenta??o. Usou-se como instrumental de pesquisa o check-list de Boas Pr?ticas de Fabrica??o em estabelecimentos produtos/comercializadores de alimentos da Ag?ncia Nacional de Vigil?ncia Sanit?ria. Ap?s a primeira avalia??o, elaborou-se o Manual de Boas Pr?ticas de Manipula??o do Pescado e orientou-se a??es de melhoria, definindo as situa??es b?sicas que envolvem a captura e transporte com medidas que garantam as condi??es de seguran?a higi?nico-sanit?rias e as instru??es de ensino te?rico e pr?tico para desenvolver as t?cnicas operacionais. Obteve-se bons resultados com o Manual com agilidade na presta??o do servi?o com diminui??o do tempo m?dio de execu??o do trabalho a bordo em torno de 37,5 %, maior volume de produ??o e melhoria dos lucros pela diminui??o das perdas do produto por manipula??o incorreta, sendo que estas perdas passaram de 0,5% para 0,15% considerado um escoamento praticamente total da produ??o. Com a introdu??o do Manual de Boas Pr?ticas de Manipula??o do Pescado no local observou-se benef?cios para a embarca??o, modelando a qualidade e indicando formas de controle da produ??o.

The Australian continental shelf is one of the few remaining areas of the world where sea turtle populations have been subject to relatively small levels of direct harvest and where nesting- and feeding-ground habitats remain essentially intact. The area supports six of the world’s seven sea turtle species (i.e., Chelonia mydas, Caretta caretta, Eretmochelys imbricata, Natator depressus, Lepidochelys olivacea and Dermochelys coriacea), contains significant nesting populations of three species (i.e., Chelonia mydas, Caretta caretta, Eretmochelys imbricata), the world’s only nesting populations of N. depressus and is the main feeding-grounds area of Natator depressus. The incidental capture of sea turtles in the trawl fisheries of northern Australia was a significant threat to sea turtle populations of Australia. Trawl by-catch mortality of Caretta caretta is considered to have contributed to the 80% decline in numbers of nesting sea turtles in eastern Australia, but this speculation is based on limited or unpublished data relating to mortality associated with trawl fisheries. There is limited information on the potential impact of trawl fisheries on other sea turtle species that occur in Australian waters. Turtle Excluder Devices (TEDs) were legislated for use in trawl fisheries of northern Australia in 1999. TEDs allow sea turtles to escape from trawl nets whilst enabling the trawl fishery to continue to operate and catch prawns. TEDs can be an effective solution to sea turtle by-catch, but the adoption and use of TEDs in a fishery needs to be monitored to ensure that the devices are having the desired outcome i.e., sea turtle exclusion. The scale and geographic extent of Australian trawl fisheries have the potential to result in a poor capacity to monitor the effective use of TEDs by fishers. TED compliance strategies (i.e., monitoring and enforcement) should be focused in areas where the effective use of TEDs would have the greatest benefit to sea turtle conservation i.e., areas where sea turtle by-catch or mortality is greatest. The present study adopted a comprehensive approach to understanding the interaction between trawling and endangered sea turtle species in waters adjacent to the Queensland east coast, by collecting and utilising baseline data on the size and distribution of sea turtle by-catch. Aspects of compliance strategies for TEDs that would contribute to the sustainable management of sea turtle by-catch in trawl fisheries are also considered. In this context, the following objectives are addressed in this thesis: (i) To estimate the number and species composition of sea turtles caught and killed in a multiple sector trawl fishery using spatial stratification; (ii) To examine the behavioural responses of sea turtles to trawl capture in order to investigate the potential for post-trawl mortality; (iii) To investigate the factors that influence the distribution pattern of sea turtles, and from this analysis, predict the relative in-water densities of sea turtles at broad spatial scales; and (iv) To develop a spatially explicit strategy for TED compliance (i.e., monitoring and enforcement), based on an assessment of the interaction between sea turtles and fishing effort. The thesis concentrates on sea turtle by-catch in the Queensland East Coast Trawl Fishery, but has broader implications for the management of sea turtles in their feeding-grounds. Baseline information on sea turtle by-catch was collected from select commercial fishers who voluntarily reported information on sea turtles caught in the Queensland East Coast Trawl Fishery. About 1,500 sea turtles were reported caught during ~24,000 days of trawling by 105 fishers who participated in a voluntary program to monitor sea turtle by-catch between 1991 and 1996. Stratified, weighted analysis of the data resulted in an annual estimated sea turtle catch of about 5,900 for the Queensland East Coast Trawl Fishery, given a mean annual total fleet effort of about 85,000 days fished per year. The catch was comprised of Caretta caretta (~50%), Chelonia mydas (27%), Natator depressus (16%) and Lepidochelys olivacea (6)%. The fishery had minimal catches of Eretmochelys imbricata and Dermochelys coriacea. Sea turtle by-catch was dominated by immature individuals, with between 60 and 80% of individuals caught being immature, based on approximate size-at-maturity for each species. Estimates of total mortality were based on observed rates as well as published mortality rates from USA shrimp trawl fisheries. In general, mortality rates of sea turtles caught in the Queensland East Coast Trawl Fishery were lower than mortality rates reported for other trawl fisheries in northern Australia and the USA. Lower mortality rates were probably a function of the tow duration associated with various sectors of the Queensland East Coast Trawl Fishery. However, the combined by-catch of sea turtles in the three major trawl fisheries of northern Australia (i.e., the Queensland East Coast Trawl Fishery, the Northern Prawn Fishery and Torres Strait Prawn Fishery) was estimated to be of sufficient magnitude to have contributed to the observed declines in nesting numbers of east Australian Caretta caretta. Estimates of the mortality of sea turtles in the trawl fisheries of northern Australia raise concerns about the likely impacts of these fisheries on other species of sea turtle, particularly Australian sub-populations of Natator depressus and Lepidochelys olivacea. These species frequent feeding-ground habitats typical of trawl grounds and are poorly monitored through nesting-ground surveys. The scale of impact estimated in this thesis indicates that the use of TEDs in the trawl fisheries of northern Australia is warranted. Mortality rates of trawl-caught sea turtles could be higher than currently estimated if sea turtles die after release as a consequence of the delayed effects of capture or secondary mortality resulting from changes in diving behaviour. Six trawl-caught sea turtles were monitored post-release using ultrasonic transmitters and Temperature Depth Recorders in order to assess their diving patterns for signs of modified behaviour. Two rodeo-caught sea turtles were monitored post-release as controls to the trawl-caught individuals. All sea turtles swam rapidly away from the point of release and displayed a period of frequent surfacing behaviour that was speculated to represent swimming and hyperventilation. The sea turtles then settled into a steady pattern where dive intervals were long and regular. This was speculated to represent recovery behaviour. ‘Normal’ activity patterns, as documented in the literature, were not apparent in the dive profiles of the trawl-caught sea turtles within the post-release monitoring period (i.e., 66 hours). Rodeo-caught sea turtles displayed ‘normal’ activity patterns at about 85 and 111 hours post-release. There was no evidence of delayed post-release mortality in the limited number of individuals monitored. However, the trawl-caught sea turtles displayed modified diving patterns that potentially made them more susceptible to secondary mortality such as boat strike or predation. Recovering sea turtles did not appear to undertake normal feeding activities, suggesting that sea turtles exposed to non-lethal interactions with human activities on a frequent basis may have lower growth rates. The results suggest that sea turtles are affected by interactions with humans to a much greater extent than previously thought and that the recovery period of such interactions can take several days The relative spatial distribution of sea turtles is poorly known and is insufficient for developing management plans, such as monitoring and enforcement strategies for TEDs. Sea turtle catch per unit effort from trawl captures and sea turtle sightings from aerial surveys were used to estimate the relative density of sea turtles in the waters adjacent to the Queensland east coast. As expected, sea turtles were not evenly distributed, with several areas having exceptionally high relative densities. In trawled areas, the relative density of sea turtles was significantly correlated with the benthic species trawled (e.g., species of prawn) as well as water-depth. Natator depressus and Lepidochelys olivacea had high relative densities in inshore, tropical waters less than 40 m deep, where tiger prawns (Penaeus esculentus, P. semisulcatus) and endeavour prawns (Metapenaeus endeavouri, M. ensis) were caught most commonly. Caretta caretta had high relative densities in inshore, sub-tropical waters less than 30 m deep, where banana prawns (Fenneropenaeus merguiensis) or bay prawns (Metapenaeus bennettae i.e., Moreton Bay) were caught most commonly. The relative density of sea turtles was predicted for the majority of waters adjacent to the Queensland east coast based on the mean sea turtle CPUE and information on target species caught most commonly and mean-depth trawled. The relative distribution of sea turtle density developed in this thesis provides the first broad scale maps that quantitatively identify areas that appear to be important as sea turtle habitat. This information could be used to assist the conservation management of sea turtles populations of eastern Australia. Sea turtle by-catch in northern Australia has been addressed through the mandatory use of Turtle Excluder Devices (TEDs) in otter trawl fisheries. However, the use of TEDs in a fishery needs to be supported by monitoring or enforcement to ensure that TEDs are used effectively, but this is difficult in fishery that operates over a large geographic scale. A pragmatic solution would be to target the monitoring and enforcement of TEDs in critical areas where reductions in sea turtle by-catch will make the greatest contribution to recovery of impacted populations of sea turtles. The spatial distribution of effort for the Queensland East Coast Trawl Fishery in the year 2001 was integrated with the relative density of sea turtles to identify critical areas for sea turtle by-catch. Critical areas for sea turtle by-catch were similar despite the use of qualitative or quantitative methods. The results suggest that effective TED use is most critical in the inshore waters of the Queensland east coast. Monitoring and enforcing TEDs in these critical areas would enable fisheries managers to measure progress towards the stated target of the 95% reduction in sea turtle by-catch and contribute to the sustainable management of the fishery. The use of TEDs in non-critical areas should also be monitored, but because of the lower contribution of these areas to sea turtle by-catch, monitoring and enforcement could take place with less intensity. Critical areas for monitoring the effective use of TEDs may change if the intensity of fishing effort changes and may become unnecessary should it be demonstrated that most fishers comply fully with TED regulations.

The Australian continental shelf is one of the few remaining areas of the world where sea turtle populations have been subject to relatively small levels of direct harvest and where nesting- and feeding-ground habitats remain essentially intact. The area supports six of the world’s seven sea turtle species (i.e., Chelonia mydas, Caretta caretta, Eretmochelys imbricata, Natator depressus, Lepidochelys olivacea and Dermochelys coriacea), contains significant nesting populations of three species (i.e., Chelonia mydas, Caretta caretta, Eretmochelys imbricata), the world’s only nesting populations of N. depressus and is the main feeding-grounds area of Natator depressus. The incidental capture of sea turtles in the trawl fisheries of northern Australia was a significant threat to sea turtle populations of Australia. Trawl by-catch mortality of Caretta caretta is considered to have contributed to the 80% decline in numbers of nesting sea turtles in eastern Australia, but this speculation is based on limited or unpublished data relating to mortality associated with trawl fisheries. There is limited information on the potential impact of trawl fisheries on other sea turtle species that occur in Australian waters. Turtle Excluder Devices (TEDs) were legislated for use in trawl fisheries of northern Australia in 1999. TEDs allow sea turtles to escape from trawl nets whilst enabling the trawl fishery to continue to operate and catch prawns. TEDs can be an effective solution to sea turtle by-catch, but the adoption and use of TEDs in a fishery needs to be monitored to ensure that the devices are having the desired outcome i.e., sea turtle exclusion. The scale and geographic extent of Australian trawl fisheries have the potential to result in a poor capacity to monitor the effective use of TEDs by fishers. TED compliance strategies (i.e., monitoring and enforcement) should be focused in areas where the effective use of TEDs would have the greatest benefit to sea turtle conservation i.e., areas where sea turtle by-catch or mortality is greatest. The present study adopted a comprehensive approach to understanding the interaction between trawling and endangered sea turtle species in waters adjacent to the Queensland east coast, by collecting and utilising baseline data on the size and distribution of sea turtle by-catch. Aspects of compliance strategies for TEDs that would contribute to the sustainable management of sea turtle by-catch in trawl fisheries are also considered. In this context, the following objectives are addressed in this thesis: (i) To estimate the number and species composition of sea turtles caught and killed in a multiple sector trawl fishery using spatial stratification; (ii) To examine the behavioural responses of sea turtles to trawl capture in order to investigate the potential for post-trawl mortality; (iii) To investigate the factors that influence the distribution pattern of sea turtles, and from this analysis, predict the relative in-water densities of sea turtles at broad spatial scales; and (iv) To develop a spatially explicit strategy for TED compliance (i.e., monitoring and enforcement), based on an assessment of the interaction between sea turtles and fishing effort. The thesis concentrates on sea turtle by-catch in the Queensland East Coast Trawl Fishery, but has broader implications for the management of sea turtles in their feeding-grounds. Baseline information on sea turtle by-catch was collected from select commercial fishers who voluntarily reported information on sea turtles caught in the Queensland East Coast Trawl Fishery. About 1,500 sea turtles were reported caught during ~24,000 days of trawling by 105 fishers who participated in a voluntary program to monitor sea turtle by-catch between 1991 and 1996. Stratified, weighted analysis of the data resulted in an annual estimated sea turtle catch of about 5,900 for the Queensland East Coast Trawl Fishery, given a mean annual total fleet effort of about 85,000 days fished per year. The catch was comprised of Caretta caretta (~50%), Chelonia mydas (27%), Natator depressus (16%) and Lepidochelys olivacea (6)%. The fishery had minimal catches of Eretmochelys imbricata and Dermochelys coriacea. Sea turtle by-catch was dominated by immature individuals, with between 60 and 80% of individuals caught being immature, based on approximate size-at-maturity for each species. Estimates of total mortality were based on observed rates as well as published mortality rates from USA shrimp trawl fisheries. In general, mortality rates of sea turtles caught in the Queensland East Coast Trawl Fishery were lower than mortality rates reported for other trawl fisheries in northern Australia and the USA. Lower mortality rates were probably a function of the tow duration associated with various sectors of the Queensland East Coast Trawl Fishery. However, the combined by-catch of sea turtles in the three major trawl fisheries of northern Australia (i.e., the Queensland East Coast Trawl Fishery, the Northern Prawn Fishery and Torres Strait Prawn Fishery) was estimated to be of sufficient magnitude to have contributed to the observed declines in nesting numbers of east Australian Caretta caretta. Estimates of the mortality of sea turtles in the trawl fisheries of northern Australia raise concerns about the likely impacts of these fisheries on other species of sea turtle, particularly Australian sub-populations of Natator depressus and Lepidochelys olivacea. These species frequent feeding-ground habitats typical of trawl grounds and are poorly monitored through nesting-ground surveys. The scale of impact estimated in this thesis indicates that the use of TEDs in the trawl fisheries of northern Australia is warranted. Mortality rates of trawl-caught sea turtles could be higher than currently estimated if sea turtles die after release as a consequence of the delayed effects of capture or secondary mortality resulting from changes in diving behaviour. Six trawl-caught sea turtles were monitored post-release using ultrasonic transmitters and Temperature Depth Recorders in order to assess their diving patterns for signs of modified behaviour. Two rodeo-caught sea turtles were monitored post-release as controls to the trawl-caught individuals. All sea turtles swam rapidly away from the point of release and displayed a period of frequent surfacing behaviour that was speculated to represent swimming and hyperventilation. The sea turtles then settled into a steady pattern where dive intervals were long and regular. This was speculated to represent recovery behaviour. ‘Normal’ activity patterns, as documented in the literature, were not apparent in the dive profiles of the trawl-caught sea turtles within the post-release monitoring period (i.e., 66 hours). Rodeo-caught sea turtles displayed ‘normal’ activity patterns at about 85 and 111 hours post-release. There was no evidence of delayed post-release mortality in the limited number of individuals monitored. However, the trawl-caught sea turtles displayed modified diving patterns that potentially made them more susceptible to secondary mortality such as boat strike or predation. Recovering sea turtles did not appear to undertake normal feeding activities, suggesting that sea turtles exposed to non-lethal interactions with human activities on a frequent basis may have lower growth rates. The results suggest that sea turtles are affected by interactions with humans to a much greater extent than previously thought and that the recovery period of such interactions can take several days The relative spatial distribution of sea turtles is poorly known and is insufficient for developing management plans, such as monitoring and enforcement strategies for TEDs. Sea turtle catch per unit effort from trawl captures and sea turtle sightings from aerial surveys were used to estimate the relative density of sea turtles in the waters adjacent to the Queensland east coast. As expected, sea turtles were not evenly distributed, with several areas having exceptionally high relative densities. In trawled areas, the relative density of sea turtles was significantly correlated with the benthic species trawled (e.g., species of prawn) as well as water-depth. Natator depressus and Lepidochelys olivacea had high relative densities in inshore, tropical waters less than 40 m deep, where tiger prawns (Penaeus esculentus, P. semisulcatus) and endeavour prawns (Metapenaeus endeavouri, M. ensis) were caught most commonly. Caretta caretta had high relative densities in inshore, sub-tropical waters less than 30 m deep, where banana prawns (Fenneropenaeus merguiensis) or bay prawns (Metapenaeus bennettae i.e., Moreton Bay) were caught most commonly. The relative density of sea turtles was predicted for the majority of waters adjacent to the Queensland east coast based on the mean sea turtle CPUE and information on target species caught most commonly and mean-depth trawled. The relative distribution of sea turtle density developed in this thesis provides the first broad scale maps that quantitatively identify areas that appear to be important as sea turtle habitat. This information could be used to assist the conservation management of sea turtles populations of eastern Australia. Sea turtle by-catch in northern Australia has been addressed through the mandatory use of Turtle Excluder Devices (TEDs) in otter trawl fisheries. However, the use of TEDs in a fishery needs to be supported by monitoring or enforcement to ensure that TEDs are used effectively, but this is difficult in fishery that operates over a large geographic scale. A pragmatic solution would be to target the monitoring and enforcement of TEDs in critical areas where reductions in sea turtle by-catch will make the greatest contribution to recovery of impacted populations of sea turtles. The spatial distribution of effort for the Queensland East Coast Trawl Fishery in the year 2001 was integrated with the relative density of sea turtles to identify critical areas for sea turtle by-catch. Critical areas for sea turtle by-catch were similar despite the use of qualitative or quantitative methods. The results suggest that effective TED use is most critical in the inshore waters of the Queensland east coast. Monitoring and enforcing TEDs in these critical areas would enable fisheries managers to measure progress towards the stated target of the 95% reduction in sea turtle by-catch and contribute to the sustainable management of the fishery. The use of TEDs in non-critical areas should also be monitored, but because of the lower contribution of these areas to sea turtle by-catch, monitoring and enforcement could take place with less intensity. Critical areas for monitoring the effective use of TEDs may change if the intensity of fishing effort changes and may become unnecessary should it be demonstrated that most fishers comply fully with TED regulations.

Deep-water trawling (>200 m deep) for crustaceans in the South West Indian Ocean (SWIO) yields catches of several species, including prawns (Haliporoides triarthrus, Aristaeomorpha foliacea, Aristeus antennatus and Aristeus virilis), langoustine (Metanephrops mozambicus), spiny lobster (Palinurus delagoae) and geryonid crab (Chaceon macphersoni). Infrequent deep-water trawling takes place off Tanzania, Kenya and Madagascar; however, well-established fisheries operate off Mozambique and South Africa. Regular trawling off South Africa started in the 1970’s, mainly targeting M .mozambicus and H. triarthrus. Catch and effort data for the South African fishery were regularly recorded in skipper logbooks over a 23 year period (1988 – 2010); this database was obtained from the Department of Agriculture, Forestry and Fisheries (DAFF) in order to assess abundance trends of M. mozambicus and H. triarthrus. Generalized linear models (GLM) were used to quantify the effects of year, month, depth and vessel on catch per unit effort (CPUE). By year, the standardized CPUE of M. mozambicus increased, and three factors (or a combination of them) could explain the trend: reduced effort saturation, improved gear and technology, or an increase in abundance. By month, CPUE peaked in July and was highest between depths of 300 and 399 m. The standardized CPUE of H. triarthrus fluctuated more by year than for M. mozambicus, possibly because it is a shorter-lived and faster growing species. The monthly CPUE peaked in March, and was highest between depths of 400 and 499 m. Totals of 2 033 M. mozambicus (1 041 males and 992 females) and 5 927 H. triarthrus (2 938 males and 2 989 females) were sampled at sea between December 2010 and March 2012, during quarterly trips on-board a fishing trawler. A GLM framework was used to explore their size composition, sex ratio variability, size at maturity and reproductive cycles. Male and female M. mozambicus size distributions were similar, but varied by month and decreased as depth increased. Female H. triarthrus were significant larger than males; size structure varied by month, but showed no change over depth. The sex ratio of M. mozambicus favoured males (1 : 0.89), but was close to parity in all months, except November when males predominated. H. triarthrus exhibited parity (1 : 1.002) with no significant variations in sex ratios by month. The proportion of egg-bearing M. mozambicus in the population declined between March and August (hatching period) and then increased until December (spawning period). The L₅₀ (length at 50% maturity) of M. mozambicus was estimated to be 49.4 mm carapace length (CL), and the smallest and largest observed egg-bearing females were 33.5 and 68.6 mm, respectively. No reproductively active female H. triarthrus were recorded during the sampling period. Growth parameter estimates for M. mozambicus (male and female combined) using Fabens method were K = 0.48 yearˉ¹ and L∞ = 76.4 mm CL. Estimates for the von Bertalanffy growth formula (VBGF) were: K = 0.45 yearˉ¹ and L∞ = 76.4 mm CL. H. triarthrus male and female growth parameter were estimated separately. For males they were K = 0.5 yearˉ¹ and L∞ = 46.6 mm CL using Fabens method, and K = 0.76 yearˉ¹ and L∞ = 46.6 mm CL using the VBGF. For females they were K = 0.3 yearˉ¹ and L∞ = 62.9 mm CL using Fabens method, and K = 0.47 yearˉ¹ and L∞ = 62.9 mm CL using the VBGF. CL to total weight regressions were calculated for both species; no significant differences were found between male and female M. mozambicus, although H. triarthrus females became larger and heavier than males. Comparisons with three earlier studies (Berry, 1969; Berry et al., 1975; Tomalin et al., 1997) revealed no major changes in the biology of either species off eastern South Africa. Stocks appear to be stable at current levels of fishing pressure, although some factors are not yet fully understood. Disturbance caused by continual trawling over a spatially limited fishing ground may affect distribution and abundance patterns, especially in M. mozambicus, which was less abundant in the depth range trawled most frequently. The absence of reproductive H. triarthrus in samples suggests that they occur elsewhere, and there is some evidence of a possible spawning migration northwards to Mozambique; this suggests that H. triarthrus is a shared stock between South Africa and Mozambique. The results from this thesis will add to the knowledge of M. mozambicus and H. triarthrus in the SWIO, and provide a basis for developing sustainable management strategies for the deep-water crustacean trawl fishery off eastern South Africa.
Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2013.

<em>Abstract.</em>—We examined the swimming performance and behavior of red snapper, <em>Lutjanus campechanus. </em>Our intention was to use this information toward developing a more efficient bycatch reduction device for use in the Gulf of Mexico shrimp trawl fishery. Using a Brett type swim tunnel, we found a significant effect of fish size and season on red snapper critical swimming speeds. For fish ranging between 6 and 17 cm standard length, critical swimming speeds ranged from about 35–70 cm/s, depending upon season. However, critical swimming speeds did not differ between day and night. This was an important observation since the majority of shrimp trawling in the Gulf occurs at night. We constructed and tested in the laboratory, a Vortex Generating Bycatch Reduction Device (VGBRD) that may prove useful in the shrimp trawl fishery. During behavioral tests during daylight, 79.2% of red snapper exited the VGBRD in an average of 4.1 min. However, during night-time tests, only 17.6% of red snapper exited the VGBRD in an average of 5.0 min. Behavioral tests revealed a strong negative phototactic response in dark adapted red snapper. We found that, during night-time tests when the VGBRD was illuminated with LED lights placed downstream of the exit, 96% of red snapper exited the device in 7.1 min. In color/ contrast choice experiments, red snapper unerringly associated with the dark colored (black or dark green) panel placed on the bottom of the experimental tank. In another set of experiments, we found that snapper displayed a strong optomotor response, i.e. the tendency to following and match speeds with a moving pattern. Illumination, color/contrast, and/or the optomotor response may improve bycatch reduction device performance.

Shrimp are a much desired and nutritious food product with a high economic value: capture-biomass ratio. The most important shrimp fisheries take place in marine habitats and are dominated by estuary-dependent “warm-water” species of penaeid and sergestid shrimps. Fishing with otter and beam trawls accounts for the major part of shrimp production, as these gears target species that form large schools over relatively level open ocean bottoms. Bycatch and discard of nontarget species are a particular problem of shrimp trawling, which disrupts bottom communities and removes juveniles of ecologically and commercially important finfish. The destructive effect of heavy trawls on the open soft-bottom habitats of most important species is not as severe as in other fisheries, given the rapid recovery of soft-bottom communities. Management of shrimp fisheries to prevent both growth and recruitment overfishing is based on models incorporating variables such as measures of growth, mortality, and climatic factors. Fishing efforts can be controlled by limiting access (e.g., number of fishers, vessels) and regulating seasonal closures of fishing grounds. Although there are signs of overfishing in some shrimp populations, the short life cycle (one to two years) with the rapid growth of major shrimp species makes them relatively resilient to overfishing. Conflicts between aquaculture and shrimp fisheries include economic competition and the biological impacts of shrimp aquaculture on natural shrimp populations. Protection and restoration of coastal wetlands, which serve as shrimp nurseries, are vital to the future of shrimp fisheries.

Much of the biological and other research efforts on crustaceans have been driven by their importance to humans as a food source. Production comes from a diverse array of methods and scales of extraction, from small recreational or subsistence fisheries to industrial-scale operations. Most crustacean catch comes from shrimp fisheries, with over two million tons taken in 2014, mainly by trawl. The genera Acetes, Fenneropenaeus, and Pandalus account for around three quarters of this catch. Crab, krill, and lobster are the other main crustacean products (around 600,000 t crab, 380,000 t krill, and 300,000 t lobster in 2014). Trends in crustacean fisheries are broadly similar to those of other seafood, although crustaceans often target different market segments and receive higher prices than fish. Crustacean fisheries management faces many challenges with management of bycatch from trawl gears especially significant. Fortunately, crustaceans tend to be easily handled with low discard mortality, and this has enabled widespread use of regulations based on size, maturity, or sex (e.g., male-only fisheries). Total allowable catch (TAC) limits are widely used and highly effective for ensuring sustainable harvests when set responsibly using good information. TAC systems are often combined with catch share or individual transferable quota systems, which had a mixed history in crustaceans, sometimes reducing overall community benefit. This parallels the challenge facing fisheries globally of ensuring that harvests are not only sustainable but also deliver benefits to the wider community beyond the commercial fishers; management of some crustacean fisheries is at the forefront of these developments.

In order to simulate the bottom trawl fishery in Ise Bay, a typical semi-enclosed bay in Japan, a fishery simulator has been developed that consists of a fish behavioral model and a fishing operations model. The fish behavioral models are developed for two major target species, conger eel and mantis shrimp, which consider the fish migration as well as the growth and the population change. The fish behavioral models are combined with a fishing operation model, which predicts the behavior of trawling boats based on economic conditions and resource distribution as well as the fish catch amount by each boat. The model is applied to evaluate the effects of fishery management, and it is investigated that how the control of fishing efforts or number of owned fishing boats affects the profit of the target fishery. The mesh size of the trawling net which maximizes the total catch is estimated considering both conger eel and mantis shrimp. At the target ports, reduction of boats number will increase the profit because the effect of fixed cost change exceeds the impact of fish catch decrease. However, the optimum reduction rate is different in each port and interactive effect should be also considered.