Longline Fleet Research Articles

Monitoring socioeconomic impacts of Hawai‘i's 2010 bigeye tuna closure: Complexities of local management in a global fishery

This paper presents the results of a study to monitor the socioeconomic impacts of the first extended closure of the western and central Pacific Ocean (WCPO) bigeye tuna (bigeye) fishery to US longliners from the state of Hawai‘i. We applied qualitative and quantitative approaches to examine how diverse members of Hawai‘i's bigeye fishery community, including fishermen, a large fish auction, dealers, processors, retailers, consumers, and support industries, perceived and were affected by the constraints of the 40-day closure of the WCPO bigeye fishery at the end of 2010. Our analysis found that there was reduced supply and reduced quality of bigeye landed along with increased prices for bigeye during the closure period. In addition, Hawai‘i longliners were forced to travel longer distances to fish during the closure. These factors contributed to increased stress and in some cases lost revenue for a variety of individuals and businesses connected to the fishery. We also found that different stakeholder groups responded to the closure in different ways and fish dealers were among those most affected by the closure. However, overall impacts to the bigeye community were not as severe as what had been anticipated at the outset. Several mitigating factors meant this was not a true closure, as US boats could continue to fish for bigeye in the Eastern Pacific Ocean and foreign and dual permitted vessels could still fish in the WCPO. Hawai‘i's longline fleet has since benefited from US legislation and federal rules that have prevented any subsequent closures of the fishery. While this relief from closures could stall short term socioeconomic impacts to Hawai‘i bigeye community, some worry that it could set back global efforts towards sustainable management of the fishery. This study highlights the challenges and equity considerations inherent in efforts to achieve meaningful conservation benefits from localized management actions within a global fishery. It also demonstrates the importance of interdisciplinary socioeconomic monitoring to examine how global fisheries policies scale down to individual fishing communities.

Analysis of marine mammal bycatch in the Uruguayan pelagic longline fishery operating in the Southwestern Atlantic Ocean

Abstract Bycatch is one of the main causes of human-caused mortality and population decline of many marine mammals. Monitoring bycatch is the first step to understand the impact of the fisheries on the species affected. Understanding how the interaction between marine mammals and fishing operations varies in space and time, and how it is influenced by environmental variables, is essential for designing mitigation strategies to reduce bycatch mortality. In this paper, we use data gathered by scientific observers and a fishing skipper to analyse marine mammals bycatch by the Uruguayan pelagic longline fishery operating in the Southwestern Atlantic Ocean from 1996 to 2007. The total bycatch per unit effort (Bcpue) was 0.0150 marine mammals/1000 hooks and the highest values (∼0.2) were recorded between 37°–38°S and 49°–51°W. Total cetacean Bcpue during the study period was low (0.0051 cetacean/1000 hooks) and occurred between 32°–37°S and 46°–54°W. Generalized additive models showed that cetaceans' bycatch was mainly affected by the depth, sea surface temperature, and season. Although cetaceans were captured year-round, the highest values were registered in spring months, most bycatch events occurred over the continental slope (median = 619 m) and in waters with a median temperature of 19.7°C. The bycatch of pinnipeds was influenced by depth, location, and season. Pinniped bycatch occurred mainly in winter, in waters ranging from 80 to 5000 m of depth (median = 2366 m) between 34°–37°S (median = 35.9°S) and 54°–49°W (median = 51.8°W). The spatial analysis showed that most bycatch events occurred within the Brazil–Malvinas Confluence zone, an area of high productivity where the pelagic longline fleet concentrates its fishing effort and where marine mammals probably concentrate to feed.

Sharks caught by the Brazilian tuna longline fleet: an overview

Large pelagic sharks are distributed throughout all of the oceans and are caught as bycatch in pelagic longline fisheries worldwide. In the southern Atlantic Ocean, more than a dozen shark species are caught by the Brazilian tuna longline fleet. This study compiles information of the main shark species caught by the Brazilian tuna longline fishery in the southwestern and equatorial Atlantic Ocean. Catch and effort data of 14,860 longline sets from the Brazilian chartered tuna longline fleet, between 2004 and 2010, were analyzed. The blue shark Prionace glauca was the main shark species captured by this fishery. Shark catches showed contrasting trends during the study period: the silky (Carcharhinus falciformis) and the oceanic whitetip (C. longimanus) sharks catch increased up to 2008 and then declined, while mako sharks (Isurus spp.) showed an opposite trend. Effort for the Brazilian longline fishery had a higher concentration from 10°N to 30°S and from 20°W to 40°W. High values of catch per unit effort of southwestern and equatorial Atlantic Ocean sharks were heterogeneously distributed and, although elasmobranchs were caught over most of the longline fishing range, only blue sharks were caught in all areas. In the southern Atlantic Ocean, high fishing effort zones overlap significantly with some nursery areas, especially for the oceanic whitetip shark, indicating that these areas are at a direct risk from the industrial longline fishery.

热带大西洋黄鳍金枪鱼垂直分布空间分析

PDF HTML阅读 XML下载 导出引用 引用提醒 热带大西洋黄鳍金枪鱼垂直分布空间分析 DOI: 10.5846/stxb201401060036 作者: 作者单位: 中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海;农业部东海与远洋渔业资源开发利用重点实验室;同济大学法学院/知识产权学院;卫星海洋环境动力学国家重点实验室,同济大学法学院/知识产权学院,卫星海洋环境动力学国家重点实验室,中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海,中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海,中国水产科学研究院渔业资源与遥感信息技术重点开放实验室 上海 作者简介: 通讯作者: 中图分类号: S931.3 基金项目: 上海市自然科学基金(14ZR1449900);科技支撑计划项目(2013BAD13B01);上海市科技创新行动计划(12231203901) Spatial analysis of the horizontal and vertical distribution of yellowfin tuna Thunnus albacares in the tropical Atlantic Ocean Author: Affiliation: Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences;China;Key Laboratory of East China Sea Oceanic Fishery Resources Exploitation and Utilization,Ministry of Agriculture,PRChina;China;School of Law School of Intellectural Property,Tongji University;China,School of Law School of Intellectural Property,Tongji University,,Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences,Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences,Key and Open Laboratory of Remote Sensing Information Technology in Fishing Resource,Chinese Academy of Fishery Sciences Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了解热带大西洋黄鳍金枪鱼(Thunnus albacares)延绳钓适宜渔获水温的等温线时空分布,分析黄鳍适宜的垂直和水平空间分布范围,采用Argo浮标剖面温度数据重构热带大西洋13 ℃和距海洋表层水温8℃(Δ8 ℃)的月平均等温线场,网格化计算了13 ℃和Δ8 ℃等温线深度值和温跃层下界深度差,并结合大西洋金枪鱼会委员(International Commission for the Conservation of Atlantic Tunas ICCAT)的黄鳍金枪鱼延绳钓渔业数据,绘制了13 ℃和Δ8 ℃等温线深度与月平均CPUE的空间叠加图,用于分析热带大西洋黄鳍金枪鱼中心渔场单位捕捞努力渔获量(Catch per unit effort CPUE)时空分布和次表层环境季节性变化关系。结果表明,13 ℃等温线,在高值CPUE出现的海域深度值大多小于250 m,主要在170-249 m,深度值超过250 m的海域CPUE普遍较小。5° S-9° N区域,Δ8 ℃等温线高值CPUE出现的海域深度值大多小于150 m,主要在50-139 m;7-10月份在南半球的非洲西海岸,在Δ8 ℃等温线深度值为150-350 m的海域也会出现中心渔场。全年在低纬度区域,高渔获率的垂直分布深度更加集中。13 ℃等温线影响热带大西洋黄鳍金枪鱼的空间分布,温跃层下界温度影响黄鳍金枪鱼的垂直分布。采用频次分析和经验累积分布函数计算其适宜次表层环境因子分布,13 ℃等温线180-240 m;Δ8 ℃等温线50-139 m;与下界深度差:13 ℃等温线-70-29 m;海表以下8 ℃等温线30-149 m。文章初步得出热带大西洋黄鳍金枪鱼适宜的水平、垂直深度分布区间。结果可以辅助渔情预报,为热带大西洋黄鳍金枪鱼实际生产作业和资源管理提供参考依据。 Abstract:In order to investigate the distribution of the yellowfin tuna (Thunnus albacares) in the fishing grounds in the tropical Atlantic Ocean, the isothermal distribution of subsurface temperatures in the yellowfin tuna fishing grounds was evaluated. The depths of 13℃ and 8℃ isotherm from the sea surface temperature (SST) (Delta 8℃), were plotted on spatial overlay maps using data collected on a monthly basis from Argo buoys and monthly CPUE data (catch per unit effort) from Thunnus albacares long-lines supplied by the International Commission for the Conservation of Atlantic Tunas (ICCAT). In addition, the differences in depth between the 13℃ and delta 8℃ isolines at the lower boundary of the thermocline were computed to determine the relationship between Thunnus albacares vertical distribution and thermocline depth. The overlay maps suggest that the delta 8℃ isothermal depth distribution showed obvious seasonal variation, roughly in the zonal striped distribution on the annual mode. The spatial distribution of the delta 8℃ isothermal depth is deep in winter and shallow in summer. The delta 8℃ isothermal depth is shallow, lying at 150 m in the low latitude area throughout the year. The topography of the 13℃ isothermal depth showed little seasonal variation. The 13℃ isothermal depth was greater than 250 m to the north of the slope, which started 15°N of West Africa and ended 10°N of South America, and to the south of the slope, which started from 10°S of South America and ended 30°S of West Africa. In the triangular area between these two slopes, the 13℃ isothermal depth distribution ranged from 150 m to 200 m. The CPUE is highest in areas where the 13℃ isothermal depth was shallower than 250 m (mode: 170-249 m). Conversely, if the depth is greater than 250 m, the CPUE tends to be low. Similarly, the highest CPUEs were observed in areas where the delta 8℃ isothermal depth was shallower than 150 m (mode: 50-139 m) in the latitude area between 5°S and 10°N throughout the year, whereas the delta 8℃ isothermal depth reached 150-350 m offshore of the west coast of Africa in the southern hemisphere from July to October. The vertical distribution of high hook rates was concentrated in the area between 5°S and 10°N. The horizontal distribution of Thunnus albacares in the tropical Atlantic Ocean was affected by the 13℃ isothermal depth, and the vertical distribution of Thunnus albacares was affected by the low boundary temperature and depth of the thermocline. Frequency analysis and the empirical cumulative distribution function were used to compute the optimum range of subsurface factors. The optimum ranges for 13℃ and delta 8℃ isothermal depths were 180-240 m and 50-139 m, respectively. The optimum depth difference ranges were 70-29 m for 13℃ isothermal depths and 30-149 m for delta 8℃ isothermal depths. The results were confirmed by using the Kolmogorov-Smirnov test. The distribution interval and vertical depth range for the central fishing ground of Thunnus albacares was documented, and the results provide a reference for improving the efficiency of long-line fleet and resource management. 参考文献 相似文献 引证文献

Influence of model misspecification, temporal changes, and data weighting in stock assessment models: Application to swordfish (Xiphias gladius) in the Indian Ocean

Results from stock assessment modelling are often highly sensitive to model assumptions. It is therefore important that models are correctly specified and sensitivity analyses are conducted to evaluate the impact of model uncertainty. Model misspecification, changes in parameters over time, and data weighting are common issues that arise when developing stock assessment models. We conducted a stock assessment for swordfish Xiphias gladius in the Indian Ocean, using an integrated age-structured model, and evaluated estimates of management quantities under alternative assumptions about (1) changes in catchability for CPUE-based indices of abundance, (2) changes in gear selectivity, (3) weighting of abundance indices, and (4) the impact of sex-specific growth. The results indicated that assuming time-blocks for both catchability and selectivity may be appropriate to reflect the changes in fishing operations of Japanese and Taiwanese longline fleets. This assumption also provided better model performance and more optimistic assessment results because it implied that the decline in indices of abundance resulted from changes in catchability rather than depletion of biomass. Inappropriate choices for selectivity curves can deleteriously affect model performance, and attempting to account for model misspecification through downweighting of data may not be appropriate. Care must be taken when modelling changes in selectivity because selectivity can be distorted to accommodate changes in catchability. More generally, substantial changes in catchability (e.g., due to changes in targeting) may not be fully addressed in CPUE standardization and may require modelling changes over time in catchability within the stock assessment model. Finally, we found that misspecification of growth is at least as influential, if not more so, than misspecification of catchability and selectivity, or data weighting.

Evaluating the impact of individual fishing quotas (IFQs) on the technical efficiency and composition of the US Gulf of Mexico red snapper commercial fishing fleet

This study examines the impact of individual fishing quotas (IFQs) on the technical efficiency (TE) and composition of the Gulf of Mexico red snapper commercial fishing fleet. Employing a parametric stochastic distance frontier framework we find that IFQs improved the TE of the vertical line and bottom longline fleets. Our results suggest that the observed TE gains were mainly driven by the retirement of less efficient vessels and, to a lesser extent, by efficiency gains of the remaining vessels. We also document changes in output and input distance elasticities and in returns to scale following the introduction of IFQs. The paper also investigates the impact of regulations and weather on productivity and the effect of crowding on TE. Policy implications stemming from these results are also discussed.

Estimates of reproductive potential of Greenland halibut (Reinhardtius hippoglossoides) in East Greenland based on an update of maturity status

When estimating reproductive potential (RP), correct interpretation of the maturity status is essential. It has now become apparent the presence of vitellogenic oocytes within the ovary of Greenland halibut (Reinhardtius hippoglossoides) does not necessarily indicate they will spawn within the next twelve months. This has led to a revision of the interpretation of the maturity scale where fish which contain only a developing cohort (DC) of oocytes are considered immature. Comparisons were made of estimates of L50 of female Greenland halibut in East Greenland using the previous interpretation of maturity status where the leading cohort (LC) and DC oocytes are not differentiated with the new interpretation where they are. Differentiation led to an increase from 63.8 to 80.2cm and from 61.2 to 74.1cm for the northern (between 63°40′N and 67°00′N) and southern area (between 61°45′N and 62°40′N), respectively. Combining the maturity data with abundance data of Greenland halibut in East Greenland, spawning stock biomass (SSB) and total egg production (TEP) was estimated in four quadrants between 1998 and 2012 using both the previous and current interpretation of the maturity scale. Using the new interpretation of the scale led to a decrease in SSB estimates of 28–92% in specific areas and years, with an average of 56%. Estimates of TEP were directly proportional to SSB so this approach did not offer any advantages over SSB as a measure of reproductive potential. Length composition of Greenland halibut caught by Norwegian fishing vessels fishing in East Greenland indicate that 85 and 57% of the females caught by the trawl and longline fleet respectively in the northern area and 46% caught by the longline fleet in the southern area were immature.

Foraging zones of the two sibling species of giant petrels in the Indian Ocean throughout the annual cycle: implication for their conservation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 499:233-248 (2014) - DOI: https://doi.org/10.3354/meps10620 Foraging zones of the two sibling species of giant petrels in the Indian Ocean throughout the annual cycle: implication for their conservation Laurie Thiers1,*, Karine Delord1, Christophe Barbraud1, Richard A. Phillips2, David Pinaud1, Henri Weimerskirch1 1Centre d’Études Biologiques de Chizé, Centre National de la Recherche Scientifique, 79360 Villiers en Bois, France 2British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK *Corresponding author: thiers@cebc.cnrs.fr ABSTRACT: We studied the year-round distribution and at-sea activity patterns of the sibling species, northern giant petrel Macronectes halli and southern giant petrel M. giganteus. Loggers combining light-based geolocators and immersion sensors were used to provide year-long data on large-scale distribution and activity of both species from the Crozet Islands (46°25’S, 51°51’E) and northern giant petrels from the Kerguelen Islands (49°19’S, 69°15’E) in the southern Indian Ocean. Argos platform transmitter terminals (PTTs) were used to track fine-scale movements of breeding adults and juveniles. Overall, adults remained within the Indian Ocean during and outside the breeding season, whereas juveniles dispersed throughout the Southern Ocean. In accordance with previous studies, differences in adult distribution and behaviour were greater between sexes than species: females dispersed more widely than males and also spent more time sitting on the water, particularly during the winter. Observed differences in distribution have important conservation implications: adults, especially males, overlap to a large extent with longline fisheries for Patagonian toothfish Dissostichus eleginoides in shelf areas within national Exclusive Economic Zones (EEZs), whereas adult females and juveniles are more likely to encounter high-sea longline fleets targeting tuna in subtropical waters. The circumpolar wide ranging behavior of naïve juvenile birds makes them particularly susceptible to interaction with a wide range of longline fisheries. KEY WORDS: Year-round distribution · Giant petrels · Telemetry · Global location sensing · Longliners Full text in pdf format Supplementary material PreviousNextCite this article as: Thiers L, Delord K, Barbraud C, Phillips RA, Pinaud D, Weimerskirch H (2014) Foraging zones of the two sibling species of giant petrels in the Indian Ocean throughout the annual cycle: implication for their conservation. Mar Ecol Prog Ser 499:233-248. https://doi.org/10.3354/meps10620 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 499. Online publication date: March 03, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Killer Whale Depredation and Associated Costs to Alaskan Sablefish, Pacific Halibut and Greenland Turbot Longliners

Killer whale (Orcinus orca) depredation (whales stealing or damaging fish caught on fishing gear) adversely impacts demersal longline fisheries for sablefish (Anoplopoma fimbria), Pacific halibut (Hippoglossus stenolepis) and Greenland turbot (Reinhardtius hippoglossoides) in the Bering Sea, Aleutian Islands and Western Gulf of Alaska. These interactions increase direct costs and opportunity costs associated with catching fish and reduce the profitability of longline fishing in western Alaska. This study synthesizes National Marine Fisheries Service observer data, National Marine Fisheries Service sablefish longline survey and fishermen-collected depredation data to: 1) estimate the frequency of killer whale depredation on longline fisheries in Alaska; 2) estimate depredation-related catch per unit effort reductions; and 3) assess direct costs and opportunity costs incurred by longliners in western Alaska as a result of killer whale interactions. The percentage of commercial fishery sets affected by killer whales was highest in the Bering Sea fisheries for: sablefish (21.4%), Greenland turbot (9.9%), and Pacific halibut (6.9%). Average catch per unit effort reductions on depredated sets ranged from 35.1–69.3% for the observed longline fleet in all three management areas from 1998–2012 (p<0.001). To compensate for depredation, fishermen set additional gear to catch the same amount of fish, and this increased fuel costs by an additional 82% per depredated set (average $433 additional fuel per depredated set). In a separate analysis with six longline vessels in 2011and 2012, killer whale depredation avoidance measures resulted in an average additional cost of $494 per depredated vessel-day for fuel and crew food. Opportunity costs of time lost by fishermen averaged $522 per additional vessel-day on the grounds. This assessment of killer whale depredation costs represents the most extensive economic evaluation of this issue in Alaska to date and will help longline fishermen and managers consider the costs and benefits of depredation avoidance and alternative policy solutions.

Cory’s shearwater by-catch in the Mediterranean Spanish commercial longline fishery: implications for management

Cory’s shearwater Calonectris diomedea is the main seabird species by-caught by the Spanish longline fleet operating in the western Mediterranean Sea. Identification of the principal factors that determine this by-catch and understanding how they could be controlled is fundamental for improving the management of fisheries and so carry out a better conservation of Cory’s shearwater populations in the Mediterranean. The aim of this paper was to model the longline by-catch of Mediterranean Cory’s shearwater in the Spanish Mediterranean longline fishery as a function of time of the year, technical characteristics of the fishing operation, and geographical location. We used data recorded by an onboard observer program monitoring commercial longline fisheries. During the 10 years covered in this study, 80 birds were captured in 30 fishing operations out of a total of 2,587 observed fishing sets. We used favourability functions and Random Forest analyses to relate the presence of Cory’s shearwater in the by-catch with the explanatory factors. The most explanatory factor in relation to incidence of by-catch was the geographical location (longitude and fishing over the continental shelf) and then the technical characteristics of the fishing operation (number of hooks and fishing during non-working days). Our conclusion is clear, because seabirds are more likely to approach longline vessels when trawlers are not allowed to operate (i.e. non-working days), activity of longliners should be limited to working days, and closing longliners activity during the month of October could reduce greatly reducing seabird bycatch.

Interannual differences for sea turtles bycatch in Spanish longliners from Western Mediterranean Sea.

Recent studies showed that regional abundance of loggerhead and leatherback turtles could oscillate interannually according to oceanographic and climatic conditions. The Western Mediterranean is an important fishing area for the Spanish drifting longline fleet, which mainly targets swordfish, bluefin tuna, and albacore. Due to the spatial overlapping in fishing activity and turtle distribution, there is an increasing sea turtle conservation concern. The main goal of this study is to analyse the interannual bycatch of loggerhead and leatherback turtles by the Spanish Mediterranean longline fishery and to test the relationship between the total turtle by-catch of this fishery and the North Atlantic Oscillation (NAO). During the 14 years covered in this study, the number of sea turtle bycatches was 3,940 loggerhead turtles and 8 leatherback turtles, 0.499 loggerhead turtles/1000 hooks and 0.001014 leatherback turtles/1000 hooks. In the case of the loggerhead turtle the positive phase of the NAO favours an increase of loggerhead turtles in the Western Mediterranean Sea. However, in the case of leatherback turtle the negative phase of the NAO favours the presence of leatherback turtle. This contraposition could be related to the different ecophysiological response of both species during their migration cycle.

Estimated bycatch of marine mammals and sea turtles in the U.S. Atlantic Pelagic Longline Fleet during 2013

Estimated bycatch of marine mammals and sea turtles in the U.S. Atlantic Pelagic Longline Fleet during 2013

Catch share programs in the Western Pacific—A solution in search of a problem?

The movement toward catch shares by NOAA Fisheries and fisheries managers worldwide responds to dysfunctional fisheries plagued by a host of interrelated problems including radically shortened seasons, a race to fish, supply gluts, lowered product quality, increased bycatch, safety issues, excess capacity, and lack of profitability. However, the NOAA Catch Shares Policy recognizes that catch shares are not appropriate for every fishery, and others have agreed that the success of catch shares programs depends on their fit with ecological, economic, and social characteristics. This article describes the characteristics of the Hawaii-based deep-set longline fleet, identified by NOAA Fisheries as a possible candidate for catch shares because it operates under a bigeye tuna quota instituted by the Western and Central Pacific Fisheries Commission. One of the main concerns in the fishery is the potential for closing during the holiday season, a culturally important time for fish consumption in Hawaii. An evaluation of the fishery suggests that many of the problems leading to development of catch shares programs in other fisheries are not present, but that some warning signs exist which could be addressed by catch share programs or other management alternatives.

Full retention in tuna fisheries: Benefits, costs and unintended consequences

Several tuna regional fisheries management organizations (t-RFMOs) have adopted retention requirements for skipjack, bigeye and yellowfin tunas caught by purse seine vessels to reduce discards, create disincentives to catch small fish, and incentivize the development and adoption of more selective technologies. Although retention policies in the t-RFMOs have been limited to target tunas in purse seine fisheries, some have advocated for an expansion of those policies, and t-RFMOs could consider expanding retention policies to a greater number of species and/or to other gear types. This paper discusses the benefits and costs of broader retention policies for purse seine and longline tuna fisheries in the western and central Pacific Ocean (WCPO). Using bycatch data from observers and logbooks from the U.S. purse seine and longline fleets operating in the WCPO, this paper documents the types and magnitude of fish discarded. For the purse seine fishery, this information was used to estimate direct impacts of having to off-load at the initial point of landing in key Pacific Island ports. For the longline fishery, estimates of direct impacts were limited to Honolulu and Pago Pago, American Samoa, the two primary ports where U.S. catch is landed. Expanding retention policies beyond the target tunas and to other gear types would further reduce discarding and possibly provide stronger incentives to develop and use more selective techniques. Beyond impacts to the ecosystem and fisher behavior, adopting broader retention policies may have other implications, and this paper explores those implications on vessels, processors, and communities. In general, as is the case with most direct interventions on fishing operations, there will be both benefits and costs, and the magnitude of those impacts will depend on the scope and extent of any expanded retention policy.

Trophic ecology of sharks in the mid-east Pacific ocean inferred from stable isotopes

As apex predators, sharks are of ecological and conservation importance in marine ecosystems. In this study, trophic positions of sharks were estimated using stable isotope ratios of carbon and nitrogen for five representative species caught by the Chinese longline fleet in the mid-east Pacific, i.e., the blue shark (Prionace glauca), the bigeye thresher shark (Alopias superciliosus), the silky shark (Carcharhinus falciformis), the scalloped hammerhead (Sphyrna lewini), and the oceanic whitetip shark (Carcharhinus longimanus). Of these species, oceanic whitetip shark has the lowest trophic level and mean δ15N value (3.9 and 14.93‰ ± 0.84‰), whereas bigeye thresher shark has the highest level/values (4.5 and 17.02‰ ± 1.21‰, respectively). The bigeye thresher shark has significantly higher δ15N value than other shark species, indicating its higher trophic position. The blue shark and oceanic whitetip shark has significantly higher δ13C values than bigeye thresher shark, silky shark and scalloped hammerhead, possibly due to different diets and/or living habitats. The stable isotope data and stomach content data are highly consistent, suggesting that stable isotope analysis supplements traditional feeding ecology study of sharks, and thus contributes to understanding their trophic linkage.

Mortality rates in by-caught loggerhead turtle Caretta caretta in the Mediterranean Sea and implications for the Atlantic populations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 489:225-234 (2013) - DOI: https://doi.org/10.3354/meps10411 Mortality rates in by-caught loggerhead turtle Caretta caretta in the Mediterranean Sea and implications for the Atlantic populations I. Álvarez de Quevedo1,*, M. San Félix2, L. Cardona1 1Department of Animal Biology and Institut de Recerca de la Biodivesitat (IRBio), Faculty of Biology, University of Barcelona, 08028 Barcelona, Spain 2Vellmarí Formentera, 07870 Formentera, Spain *Email: alvarezdequevedo@ub.edu ABSTRACT: Reliable estimates of the post-release mortality probability of marine turtles after incidental by-catch are essential for assessing the impact of longline fishing on these species. Large numbers of loggerhead turtles Caretta caretta from rookeries in the northwestern Atlantic Ocean have been by-caught annually in the southwestern Mediterranean Sea since the 1980s, but nothing is known about their post-release mortality probability under natural conditions. Pop-up archival transmitting tags were attached to 26 loggerhead turtles following incidental capture by Spanish longliners. Hooks were not removed, and 40 cm of line was left in place. The post-release mortality probability during the 90 d following release ranged from 0.308 to 0.365, and was independent of hook location. When the post-release mortality probability was combined with previously reported estimates of the mortality probability before hauling, the aggregated by-catch mortality probability ranged from 0.321 to 0.378. Assuming a total annual by-catch of 10656 loggerhead turtles by the Spanish longline fleet operating in the southwestern Mediterranean, by-catch results in 3421 to 4028 turtle deaths annually. This range is equivalent to 8.5-10.1% of the approximately 40000 turtles inhabiting the fishing grounds used by Spanish longliners, most of them from rookeries in the northwestern Atlantic. As a consequence, the accumulated mortality during the oceanic stage is expected to be larger for those loggerhead turtles of Atlantic origin that spend several years in the Mediterranean Sea than for turtles of the same cohort that remain in the Atlantic. For this reason, the Mediterranean can be considered a dead end for loggerhead turtle populations nesting in the Atlantic, although the actual demographic relevance of by-catch mortality of loggerhead turtles in the Mediterranean remains unknown. KEY WORDS: Caretta caretta · By-catch · Mortality · Longlines · Mediterranean · Satellite tags Full text in pdf format See Comment and Reply Comment on this article PreviousNextCite this article as: Àlvarez de Quevedo I, San Félix M, Cardona L (2013) Mortality rates in by-caught loggerhead turtle Caretta caretta in the Mediterranean Sea and implications for the Atlantic populations. Mar Ecol Prog Ser 489:225-234. https://doi.org/10.3354/meps10411 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 489. Online publication date: August 28, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Reproduction and growth of Aphanopus carbo and A. intermedius (Teleostei: Trichiuridae) in the northeastern Atlantic

Summary Commercial fishery landings of the black scabbardfish, Aphanopus carbo, from the Madeira mid-water drifting longline fleet (northeastern Atlantic) were studied for 2 years within a Portuguese government programme for fishing management. The process noted that 20% of the total catch corresponded to the intermediate scabbardfish, Aphanopus intermedius. Length-frequency distribution, and age, growth and reproduction of both species were analysed and compared. The results revealed significant differences in age and growth in influencing the length-frequency distributions. Intermediate scabbardfish attained the largest size (148 cm TL) and age (15 years). However, the two species had similar reproductive strategies. According to data published on A. carbo in this region, it is thought to be very likely that previous studies unintentionally mixed both species together in their analyses.

Whale interactions with Alaskan sablefish and Pacific halibut fisheries: Surveying fishermen perception, changing fishing practices and mitigation

Whale depredation occurs when whales steal fish, damage fish or damage fishing gear. In Alaska, killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus) primarily depredate on demersal sablefish (Anoplopoma fimbria) and Pacific halibut (Hippoglossus stenolepis) longline fisheries. Quantitative data on whale depredation in Alaska is limited due to low fishery observer coverage and minimal depredation evidence left on longline fishing gear. This study utilized semidirected interviews (n=70) and written questionnaires (n=95) with longline fishermen to examine: (1) perceptions and experiences of whale–fishery interactions in Alaska, (2) effects of depredation on fishing practices, and (3) potential depredation mitigation measures. Eighty-seven percent of fishermen surveyed agreed that whale depredation became worse between 1990 and 2010. Respondents reported changing their fishing practices in response to depredating whales in several ways, including: traveling up to 50 nautical miles and ceasing hauling operations up to 24h until the whales left the fishing grounds. Respondents fishing in western Alaska, primarily encountering killer whales, were forced to wait longer and travel greater distances than fishermen operating in central and southeast Alaska, regions more affected by sperm whales. Deterrent research, gear modifications and real-time tracking of depredating whales were solutions favored by study participants. Survey respondent answers varied based on areas fished, quota owned, years involved in the fishery and vessel size. This study presents the first statewide evaluation of fishermen's perception and knowledge of whale interactions with the Alaskan longline fleet and is a critical step toward developing baseline data and feasible depredation mitigation strategies.

Hook selectivity as a mitigating measure in the catches of the stingray Pteroplatytrygon violacea (Bonaparte, 1832) (Elasmobranchii, Dasyatidae)

Hook selectivity, sex ratio of catches and relative abundance (Catch Per Unit Effort – CPUE) were assessed for the pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1872), caught by longline gear in the southwestern Atlantic Ocean over the continental slope and adjacent oceanic area. The catches were carried out at depths of 200–4000 m by research cruises in 2002 and 2003, from Cabo Frio (22°52′S) to Laguna (28°28′S); and by hook selectivity experiments from 2004 to 2008, from Itajaí (26°54′S) to Tramandaí (29°59′S). Hook selectivity experiments indicated higher catches of stingrays with ‘J’ hooks (9/0, 10° offset) commonly used by the pelagic longline fleet than with ‘circle’ hooks (18/0, 10° offset). ‘circle’ hooks reduce the longline by-catches of this species. Most of the stingrays caught were males (6 : 1). One female aborted mid-term embryos at the time of capture. CPUE was highest between spring and autumn and lowest during winter.

Size, distribution and catch rates of the oceanic whitetip shark caught by the Brazilian tuna longline fleet

Catch and effort data from 14,835 longline sets conducted by foreign tuna longline vessels chartered by Brazil, from 2004 to 2010, were analyzed aiming at assessing the size, distribution and the relative abundance of the oceanic whitetip shark (Carcharhinus longimanus) in the southwestern and equatorial Atlantic Ocean. The nominal catch per unit of effort (CPUE) exhibited a gradual increase, from 0.04 sharks/1000 hooks, in 2004, the first year of the time series, up to 0.13, in 2007. In 2008, however, the CPUE increased sharply, reaching 0.43, dropping, then, back to 0.15, in 2010. A CPUE standardization was performed using a delta-GLM approach, but the standardized index of abundance did not differ significantly from the nominal CPUE. The models indicated that the catches of oceanic whitetip sharks are higher for the Spanish fishing strategy, which is characterized by the deployment of hooks at shallower depths. These results indicate that the use of deep longline hooks (>100m) may help to mitigate the bycatch of this species.