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Parga M.L.,SUBMON | Pons M.,Research Center y Conservacion Marina | Andraka S.,WWF | Mituhasi T.,Overseas Fishery Cooperation Foundation of Japan | And 5 more authors.
Fisheries Research | Year: 2015

Bycatch by longline fisheries, especially by artisanal small-scale fisheries, is one of the main conservation problems for some sea turtle populations around the world. Since 2004, a network of professionals under the "Eastern Pacific Regional Sea Turtle Bycatch Program" have been working with artisanal longline fishers in the Eastern Pacific Ocean (EPO) to reduce sea turtle bycatch and related mortality. Trials assessing circle hooks of different sizes and shapes, and different baits, have been conducted to determine the effectiveness in the reduction of sea turtle bycatch and changes in hooking location. In this paper, information from 1823 olive ridley sea turtles incidentally captured in the EPO were analyzed to assess how hook type (J, tuna hooks or circle hooks), hook size, bait type (squid or fish), turtle size and target species (tunas, sharks or mahi-mahi) affect hooking location on sea turtles. This were modeled with a Classification and Regression Tree using hooking location as a multinomial variable response (for 6 categories of hooking locations); and also as a binomial response (swallowed vs. non-swallowed) using a Generalized Linear Mixed Model (GLMM). Hook type and size, plus bait type, were the most important factors affecting hooking location, while turtle size and target species did not have any significant effect. J-hooks and tuna hooks had a much greater probability of being swallowed than circle hooks. In addition, as the hook size increased, the likelihood of swallowing it decreased. The use of fish bait in combination with larger circle hooks tended to produce higher proportions of external hookings. An increase in external or lower mandible hookings is preferred since these locations are assumed to be less dangerous for the animal's post-release survival, and because hooks and attached gear are easier to remove by well-trained fishermen. © 2014 Elsevier B.V.

Andraka S.,WWF | Mug M.,WWF | Hall M.,Inter American Tropical Tuna Commission IATTC | Pons M.,Research Center y Conservacion Marina | And 13 more authors.
Biological Conservation | Year: 2013

Since 2004, governments and non-governmental organizations, together with the fishing communities from nine countries, from Mexico to Peru, have implemented joint efforts to reduce incidental mortality of sea turtles in artisanal longline fisheries of the Eastern Pacific Ocean (EPO). These countries are involved in a Regional Sea Turtle Bycatch Program to achieve this goal. Circle hooks have been proposed as a way to mitigate incidental mortality of sea turtles. Thus, we analyze the performance of circle hooks in relation to J-style and tuna hooks on the hooking rates of target and non-target species in the artisanal surface longline fisheries of three of the participating countries with the largest sample sizes (Ecuador, Panama and Costa Rica). These fisheries target mahi-mahi, Coryphaena hippurus, or a combination of tunas, billfishes and sharks (TBS), and use different techniques and gear configurations to catch their targets. For the TBS fishery we presented the results of comparisons between tuna hooks and 16/0 circle hooks from Ecuador, Panama and Costa Rica, and between tuna hooks and 18/0 circle hooks in Costa Rica. For the mahi-mahi fishery, we analyzed the performance of 14/0 and 15/0 circle hooks in Ecuadorian vessels and 16/0 circle hooks in Costa Rican vessels vs. the traditional J-style hooks. A total of 730,362 hooks were observed in 3126 sets. Hooking rates for target and non-target species were not consistent for all fisheries and countries analyzed. However, circle hooks reduced sea turtle hooking rates in most of the comparisons. © 2013 Elsevier Ltd.

Kobayashi T.,Kinki University | Honryo T.,Kinki University | Agawa Y.,Kinki University | Sawada Y.,Kinki University | And 6 more authors.
Reproductive Biology | Year: 2015

To develop techniques for seedling production of yellowfin tuna, the behavior of primordial germ cells (PGCs) and gonadogenesis were examined at 1-30 days post hatching (dph) using morphometric analysis, histological examination, and in situ hybridization. Immediately after hatching, PGCs were located on the dorsal side of the posterior end of the rectum under the peritoneum of the larvae, and at 3 dph they came into contact with stromal cells. PGCs and stromal cells gradually moved forward from the anus prior to 5 dph At 7-10 dph, germ cells were surrounded by stromal cells and the gonadal primordia were formed. In individuals collected at 12 dph, PGCs were detected by in situ hybridization using a vasa mRNA probe that is a germ-cell-specific detection marker. The proliferation of germ cells in the gonadal primordia began at 7-10 dph. We observed double the number of germ cells at 30 dph (22 ± 3.2 cells), compared to that at 1 dph (11 ± 2.1 cells). Therefore, based on our data and previous reports, the initial germ cell proliferation of yellowfin tuna is relatively slower than that of other fish species. © 2015 Society for Biology of Reproduction & the Institute of Animal Reproduction and Food Research of Polish Academy of Sciences in Olsztyn.

Vandeperre F.,University Of The Azoresrua Prof Dr Frederico Machado 4Horta Portugal | Aires-da-Silva A.,Inter American Tropical Tuna Commission IATTC | Lennert-Cody C.,Inter American Tropical Tuna Commission IATTC | Serrao Santos R.,University Of The Azoresrua Prof Dr Frederico Machado 4Horta Portugal | Afonso P.,University Of The Azoresrua Prof Dr Frederico Machado 4Horta Portugal
Limnology and Oceanography | Year: 2016

Knowledge on the distribution and habitat use of species is an important precondition for their appropriate management and conservation. This is particularly challenging for highly mobile marine predators such as blue shark that migrate between dynamic and transient oceanic habitats. In addition, blue shark populations have complex spatial structures due to age and sexual segregation, and accurately identifying oceanic nursery habitat is vital to ensure population growth via survival of juveniles. In this study, long-term satellite telemetry data (up to 950 d) was used to estimate the broad-scale habitat utilization of juvenile blue shark and predict their distribution in the North Atlantic. Habitat utilization models were fitted separately for three juvenile life stages that recruit to the pelagic longline fishery (small juvenile males and females, large juvenile and sub-adult females and large juvenile males), and subsequently validated using fisheries data. The models demonstrated that the patterns of spatiotemporal distribution and segregation are shaped to a large extent by differential habitat preferences, notably for distinct ranges of sea surface temperature. For the first time, this modeling approach provides a unifying framework to understand the essential pelagic habitat and dynamic spatial structuring of blue shark at the scale of an entire ocean basin. It represents an important contribution to our understanding of the spatial ecology of pelagic sharks by presenting novel clues to their behavioral strategies in exploiting the most productive oceanic habitats, and offers a promising tool for their management in the face of current intensive shark exploitation. © 2016 Association for the Sciences of Limnology and Oceanography.

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