TL;DR: Balanced fishing across a range of species, stocks, and sizes could mitigate adverse effects and address food security better than increased selectivity and challenges present management paradigms.
Abstract: Concern about the impact of fishing on ecosystems and fisheries production is increasing ( 1 , 2 ). Strategies to reduce these impacts while addressing the growing need for food security ( 3 ) include increasing selectivity ( 1 , 2 ): capturing species, sexes, and sizes in proportions that differ from their occurrence in the ecosystem. Increasing evidence suggests that more selective fishing neither maximizes production nor minimizes impacts ( 4 – 7 ). Balanced harvesting would more effectively mitigate adverse ecological effects of fishing while supporting sustainable fisheries. This strategy, which challenges present management paradigms, distributes a moderate mortality from fishing across the widest possible range of species, stocks, and sizes in an ecosystem, in proportion to their natural productivity ( 8 ), so that the relative size and species composition is maintained.
TL;DR: In this paper, the authors discuss some of the key capture technologies and identifies gaps, constraints, and opportunities that facilitate the development and adoption of Low Impact and Fuel Efficient (LIFE) Fishing.
TL;DR: This dataset contains 631 fish species and 3,529 records, making it the most complete demersal fish fauna and their temporal and spatial distributional data on the soft marine habitat in Taiwan.
Abstract: Bottom trawl fishery is one of the most important coastal fisheries in Taiwan both in production and economic values. However, its annual production started to decline due to overfishing since the 1980s. Its bycatch problem also damages the fishery resource seriously. Thus, the government banned the bottom fishery within 3 nautical miles along the shoreline in 1989. To evaluate the effectiveness of this policy, a four year survey was conducted from 2000–2003, in the waters around Taiwan and Penghu (Pescadore) Islands, one region each year respectively. All fish specimens collected from trawling were brought back to lab for identification, individual number count and body weight measurement. These raw data have been integrated and established in Taiwan Fish Database (http://fishdb.sinica.edu.tw). They have also been published through TaiBIF (http://taibif.tw), FishBase and GBIF (website see below). This dataset contains 631 fish species and 3,529 records, making it the most complete demersal fish fauna and their temporal and spatial distributional data on the soft marine habitat in Taiwan.
TL;DR: There is an urgent need to explore the issue of shark bycatch globally which is problematic given that such a synthesis could inform conservation actions and identify pressing research gaps, and this would be best achieved through interdisciplinary research that spans field, laboratory, and modeling realms.
Abstract: Over the last few decades, much effort has been devoted towards quantifying and reducing bycatch in marine fisheries. Of late, there has been a particular focus on sharks given that bycatch is a frequently listed threat for sharks on the International Union for the Conservation of Nature Red List. However, currently there are no quantitative reviews or syntheses that explore the issue of shark bycatch globally which is problematic given that such a synthesis could inform conservation actions and identify pressing research gaps. We performed a qualitative and quantitative survey of the peer-reviewed literature to characterize trends in shark bycatch research with a particular goal of identifying research needs and opportunities. Using a structured literature review we identified 103 papers that met our search criteria, with the first one published in 1993. Early research efforts focused on documenting the scope of bycatch (i.e., determining that sharks were indeed captured as bycatch), but more recently there have been increased efforts devoted to developing and evaluating bycatch reduction strategies for sharks. Research activity was most common in the North Atlantic (~40 % of the total articles analysed) with comparatively less research in other areas such as the Indo-Pacific region where shark bycatch is regarded as particularly common and problematic. Most studies were observational with comparatively fewer experimental and modeling studies, and even fewer that combined research approaches. Gear modifications (e.g., hook size and type for long lines, net size and mesh design for nets) were the most commonly evaluated strategy for reducing shark bycatch; however, development and use of techniques like repellents, or seasonal area closures, or a combination of strategies, offer interesting possibilities that require further study. In addition, although many sharks are discarded, little is known about post-release survival or sub-lethal consequences of fisheries interactions, or evaluations of different fish handling strategies, making it difficult to quantify the true cost of bycatch or to recommend handling strategies to fishers. Although there are some inherent challenges with developing and testing shark bycatch reduction strategies, there is an urgent need to do so and this would be best achieved through interdisciplinary research that spans field, laboratory, and modeling realms.
TL;DR: Assessing the composition of gannet nests could provide a useful index of the prevalence of fishing debris and could be used to assess entanglement risk of other animals in the marine environment over decadal scales.
TL;DR: Amande et al. as discussed by the authors proposed an approach for oceanographic oceanographic research based on the idea of oceanography, which can be found in the work of Monin J. Amande and Nicolas M. Bez.
Abstract: Monin J. Amande1*, Emmanuel Chassot1, Pierre Chavance1, Hilario Murua2, Alicia Delgado de Molina3, and Nicolas Bez1 Institut de Recherche pour le Developpement, UMR EME 212 (IRD, Ifremer, Universite Montpellier 2) Avenue Jean Monnet, BP 171, 34203 Sete Cedex, France AZTI-Tecnalia, Herrera Kaia, Portualde z/g, 20110 Pasaia (Gipuzkoa), Spain Instituto Espanol de Oceanografia, Apdo. Correos 1373, 38080 Santa Cruz de Tenerife, Canary Islands, Spain *Corresponding Author: tel: +33 499 573 252; fax: +33 499 573 295; e-mail: monin-justin.amande@ird.fr
TL;DR: Hooking (or "at-haulback") fishing mortality was analysed in elasmobranchs captured by Portuguese long- liners targeting swordfish in the Atlantic Ocean, and new information can be used to evaluate the impact of recent recommendations prohibiting the retention of some vulnerable elasmo- branch species.
TL;DR: The approach provided indicators of the status and trajectory of the common dolphin population in the eastern North Atlantic and therefore proved to be a valuable tool for management, applicable to other dolphin populations.
Abstract: Fisheries interactions have been implicated in the decline of many marine vertebrates worldwide. In the eastern North Atlantic, at least 1000 common dolphins (Delphinus delphis) are bycaught each year, particularly in pelagic pair-trawls. We have assessed the resulting impact of bycatch on this population using a demographic modeling approach. We relied on a sample of females stranded along the French Atlantic and western Channel coasts. Strandings represent an extensive source of demographic information to monitor our study population. Necropsy analysis provided an estimate of individual age and reproductive state. Then we estimated effective survivorship (including natural and human-induced mortality), age at first reproduction and pregnancy rates. Reproductive parameters were consistent with literature, but effective survivorship was unexpectedly low. Demographic parameters were then used as inputs in two models. A constant parameter matrix proposed an effective growth rate of −5.5±0.5%, corresponding to the current situation (including bycatch mortality). Subsequently, deterministic projections suggested that the population would be reduced to 20% of its current size in 30 years and would be extinct in 100 years. The demographic invariant model suggested a maximum growth rate of +4.5±0.09%, corresponding to the optimal demographic situation. Then, a risk analysis incorporating Potential Biological Removal (PBR), based on two plausible scenarii for stock structure suggested that bycatch level was unsustainable for the neritic population of the Bay of Biscay under a two-stock scenario. In depth assessment of stock structure and improved observer programs to provide scientifically robust bycatch estimates are needed. Effective conservation measures would be reducing bycatch to less than 50% of the current level in the neritic stock to reach PBR. Our approach provided indicators of the status and trajectory of the common dolphin population in the eastern North Atlantic and therefore proved to be a valuable tool for management, applicable to other dolphin populations.
TL;DR: Results suggest that using circle hooks on pelagic longlines do not have a major effect on shark catch rates, but do reduce at-vessel mortality compared to J-hooks, so circle hooks should be seen as one potential tool to help reduce bycatch mortality of sharks in longline fisheries.
Abstract: Circle hooks have gained recent attention as a cost-effective bycatch mitigation tool in pelagic longline fisheries, particularly for marine turtles. Over the last few years, a growing number of studies have investigated the use of circle hooks and their effects on other species, including elasmobranchs. To elucidate the potential value of circle hook use as a tool for shark conservation and management in pelagic longline fisheries, we conducted a quantitative review of all available studies to date. We compiled 15 published and eight gray literature studies and where possible used random effects meta-analysis and analysis of covariance to test the effects of circle hooks on catchability and at-vessel mortality rates. Overall, results suggest that using circle hooks on pelagic longlines do not have a major effect on shark catch rates, but do reduce at-vessel mortality compared to J-hooks. Thus circle hooks should be seen as one potential tool to help reduce bycatch mortality of sharks in longline fisheries. However, the high level of heterogeneity found between studies highlights the need for shark-specific controlled experiments to provide more definitive results.
TL;DR: The need for understanding the role of every longline component in gear performance analysis is highlighted, with significant differences in blue shark catch rate between leader types was found in J-hook treatments only and higher proportions of live sharks were found on wire leaders.
TL;DR: In this paper, the authors present an empirical analysis of bycatch risk that informs several issues of risk pool design including which bycatch species to include, pools size, and how to evaluate and mitigate adverse selection and moral hazard problems.
TL;DR: Significant differences in standardized catch rates and length distributions at a shallow seamount vs. the open ocean confirms the aggregating effect of seamounts on pelagic predators, including juvenile market species of pelagic fish and species groups relatively vulnerable to overexploitation.
Abstract: Declines in absolute abundance and altered size distributions from size-selective removals of market species of pelagic apex predators in tuna fisheries alters evolutionary characteristics of populations and ecosystem processes and stability. Pelagic fishing at seamounts, where hyperstability of pelagic predators may occur, can exacerbate declining abundance and have high bycatch of species groups that are highly vulnerable to overexploitation. Generalized additive mixed Poisson regression models (GAMMs) were fitted to Hawaii longline tuna fishery observer data to determine temporal trends in standardized catch rates, an index for local, relative abundance. Temporal trends in expectile length distributions were determined through geoadditive expectile GAMMs. Significant declining trends in relative abundance in this fishery were observed for tunas, sharks and billfish. A decline in seabird standardized catch rate occurred concurrently with the uptake of seabird bycatch mitigation technology. Changed spatial distribution of fishing effort and increased use of wider circle hooks likely contributed to a declining sea turtle standardized catch rate. Tuna and billfish mean lengths significantly increased over the time series due to entire distributions of length classes having shifted towards larger fish. Larger tunas comprised a larger proportion of the catch due to fewer small tunas being caught, and to a lesser extent because mean lengths of larger size classes increased. Conversely, billfish largest length classes experienced the largest increases in average lengths. Changes in spatial and seasonal distributions of fishing effort, increased use of wider circle hooks, and possibly increasing purse seine selective removals of juvenile tunas, may have contributed to increased selectivity for larger fish. Significant differences in standardized catch rates and length distributions at a shallow seamount vs. the open ocean confirms the aggregating effect of seamounts on pelagic predators, including juvenile market species of pelagic fish and species groups relatively vulnerable to overexploitation. Wider circle hooks significantly improved valuable tuna standardized catch rates, but also increased unwanted shark and reduced valuable billfish standardized catch rates.
TL;DR: The effects of different hook style and bait type combinations on the catches of targeted, bycatch, and discarded fishes in equatorial atlantic waters indicated that the effects of hook Style and bait on the cpuEs were species-specific.
Abstract: We examined the effects of different hook style and bait type combinations on the catches of targeted, bycatch, and discarded fishes in equatorial atlantic waters. in total, 221 longline sets (>305,000 hooks) were deployed from portuguese pelagic longline vessels (sElEct-pal project) during the february-october fishing season. Three different hook styles and two bait types were tested: the traditional J-hook was compared to two circle hooks (one non-offset and one with 10° offset), and squid bait was compared to mackerel. catch per unit effort (cpuEs) were calculated and compared between the different hook style and bait type combinations, which indicated that the effects of hook style and bait on the cpuEs were species-specific. for example, swordfish cpuEs were higher with J-hooks baited with squid, while for targeted tunas and blue shark only the bait effect was significant, but with opposite effect (i.e., higher catches of tuna with squid bait and higher catches of blue shark with mackerel bait). for the discarded species, at-haulback mortality was also species-specific. proportions of alive vs dead specimens at time of fishing gear retrieval did not vary significantly by hook style or bait type combinations. The total retained catch was analyzed in value per unit effort (VpuE), and indicated losses in fishery revenue when mackerel was used instead of squid, but not when circle hooks were used instead of J-hooks.
TL;DR: The combination of 18/0 circle hooks with mackerel bait was even more effective for loggerhead sea turtles and had a significant increase in swordfish catch by weight, compared to the industry standard 9/0 J-hooks with squid bait.
Abstract: Research was conducted in 2002 and 2003 by noaa's national Marine fisheries service, southeast fisheries science center, to investigate changes in hook design and bait type to reduce the bycatch of sea turtles on pelagic longlines in the western north atlantic ocean. The effectiveness of 18/0-20/0 circle hooks and 10/0 Japanese tuna hooks with squid (Illex spp.) and mackerel bait (Scomber scombrus linnaeus, 1758) was evaluated against the industry standard 9/0 J-hooks with squid bait with respect to reducing sea turtle and shark interactions while maintaining swordfish (Xiphias gladius linnaeus, 1758) and tuna (Thunnus spp.) catch rates. In total, 973,734 hooks were deployed during the study. Individually, circle hooks and mackerel bait significantly reduced both loggerhead [Caretta caretta (linnaeus, 1758)] and leatherback [Dermochelys coriacea (vandelli, 1761)] sea turtle bycatch. The combination of 18/0 circle hooks with mackerel bait was even more effective for loggerhead sea turtles and had a significant increase in swordfish catch by weight. The combination 18/0 circle hooks with squid bait resulted in a significant decrease in the swordfish catch and a significant increase in the catch rate of blue shark [Prionace glauca (linnaeus, 1758)] , bluefin tuna [Thunnus thynnus (linnaeus, 1758)], and albacore tuna [Thunnus alalunga (bonnaterre, 1788)]. With all hook types, mackerel bait resulted in a significant decrease in blue shark, bigeye tuna [Thunnus obesus (lowe, 1839)], and albacore tuna, but significantly increased the catch of porbeagle [Lamna nasus (bonnaterre, 1788)] and shortfin mako (Isurus oxyrinchus rafinesque, 1810).
TL;DR: In this article, the authors describe the current management of the fisheries of San Jorge Gulf, which consists primarily of spatial and temporal closures for the Argentine red shrimp and zoning by stratum of the fleet for hake.
Abstract: In San Jorge Gulf, several important economic activities are developed, including two industrial fisheries: hake ( Merluccius hubbsi Marini, 1933) and Argentine red shrimp ( Pleoticus muelleri Bate, 1888). Both overlap spatially and temporally. The San Jorge Gulf hake fishery consists of a high-seas ice trawler fleet (n = 20 fishing vessels) and a coastal fleet (n = 30 fishing vessels). These fisheries capture about 10% of the catch of the southern hake stock. The Argentine red shrimp fishery consists of a double-beam trawler fleet with 80 freezer vessels, responsible for more than 75% of shrimp landings in Argentina. The main problem of both fisheries is the bycatch of hake in one of its principle nursery areas. The present work describes the current management of the fisheries of San Jorge Gulf, which consists primarily of spatial and temporal closures for the Argentine red shrimp and zoning by stratum of the fleet for hake. Neither of these two fisheries has taken measures that effectively reduce bycatch.
TL;DR: Comparisons between REM results and fishers' logbooks showed that the REM system gave more reliable results, since fishers, in many cases, did not observe the bycatch while working on the deck because the by Catch had already dropped out of the net before coming on board.
Abstract: Quantification of marine mammal bycatch is important in the context of conservation and management of protected species. Hitherto, using on-board observers has been the most reli- able and accurate method; however, observer programs can be prohibitively expensive. To inves- tigate the potential of closed-circuit television cameras to document bycatch of marine mammals, 6 Danish commercial gillnetters (10 to15 m in length) operating under the Danish catch quota management system were equipped with remote electronic monitoring (REM) systems. The REM systems provided video footage, time and position of all net hauls and bycatches of marine mam- mals. Comparisons between REM results and fishers' logbooks showed that the REM system gave more reliable results, since fishers, in many cases, did not observe the bycatch while working on the deck because the bycatch had already dropped out of the net before coming on board. Fur- thermore, very high coverage percentages at low cost, compared to on-board observers, could be obtained with REM. Alternative means of conducting the video analysis were tested; they were, however, not found to be very efficient.
TL;DR: From a veterinarian's point of view, the lesions caused by hooks in different locations in capturedSea turtles, and their possible effects are discussed, combining information gathered from personal experience, long-term studies on captive sea turtles, post-mortem analysis of stranded sea turtle, and results of satellite tagging studies.
Abstract: Six out of seven species of marine turtles are endangered, with longline bycatch considered one of the main causes for the decrease of their populations. Recently, the use of large circle hooks has been shown to reduce the impact of longline fishing on sea turtles, both decreasing the number of sea turtles captured, and shifting the number of hookings to the mouth, as opposed to other anatomical locations. However, little is known about the true post-release mortality of captured turtles in relation to hook location and associated lesions, essential information to adequately determine gear impacts. Here i discuss, from a veterinarian's point of view, the lesions caused by hooks in different locations in captured sea turtles, and their possible effects, combining information gathered from personal experience, long-term studies on captive sea turtles, post-mortem analysis of stranded sea turtles, and results of satellite tagging studies. Although hooks in the mouth are generally considered low risk, there are sensitive structures in this area, such as the glottis or the jaw joint, which should be carefully considered. On the other hand, the esophagus has a strong muscular wall and is somewhat resistant to lesions, unless the hook lodges close to the heart or large blood vessels. Lines left trailing are by far the most dangerous part of the gear, and have very high chance of causing mortality. Adequate training of fishermen by experienced researchers is essential to reduce sea turtle mortality, and more research is urgently needed to confirm the effectiveness of circle hooks.
TL;DR: In this paper, the authors hypothesized that the Atlantic sturgeon that occur in Minas Basin in the Bay of Fundy are of local Saint John River, New Brunswick origin with little or no U.S. contribution.
Abstract: Five distinct population segments of Atlantic sturgeon Acipenser oxyrinchus were recently listed (April 2012) as endangered or threatened under the U.S. Endangered Species Act. Atlantic sturgeon are anadromous, spawning occurs in rivers from the St. Lawrence River, Quebec, to the Satilla River, Georgia, and subadults and adults undertake extensive coastal migrations. Bycatch of Atlantic sturgeon in coastal fisheries may have resulted in the slowed or failed rebuilding of many populations despite the imposition of a U.S. federal moratorium on their harvest in 1998. Canada's Bay of Fundy hosts weir and trawl fisheries which bycatch Atlantic sturgeon of unknown origin. Additionally, tidal power development projects for the Bay of Fundy have been proposed which could detrimentally impact migratory sturgeon. We hypothesized that the Atlantic sturgeon that occur in Minas Basin in the Bay of Fundy are of local Saint John River, New Brunswick, origin with little or no U.S. contribution. We used microsate...
TL;DR: It was found that hook was one of the most important variables in predicting anatomical hooking location, and that soak time and hook and/or anatomicalhooking location were important in predicting the odds of observing a dead animal boatside.
Abstract: Experiments were conducted on the grand Banks of the north Atlantic ocean during 2002-2003 to evaluate the effect of circle hooks and mackerel bait on pelagic longline catches and bycatch, and compare the treatments to the industry standards at the time. Circle hooks were 18/0, and both non-offset and 10° offset were used as separate treatments and compared to the 9/0 J-hook control hooks with 10°-30° offset. Bait treatment was mackerel (Scomber scombrus linnaeus, 1758), which was compared to the squid control (Illex spp.). We analyzed the effects of hook (one J- and two circle hooks), bait (mackerel and squid), temperature, soak time, and animal length on anatomical hooking location for seven fish species and two sea turtle species. We also analyzed the effects of the same variables, inclusive and exclusive of hooking location, on the odds of boating a dead fish. We found that hook was one of the most important variables in predicting anatomical hooking location, and that soak time and hook and/or anatomical hooking location were important in predicting the odds of observing a dead animal boatside. The importance of the other variables differed by species, and for several species no models were significant for predicting hooking location or for predicting observed mortality.
TL;DR: The authors in this paper estimate the species' incidental mortality on the Southern coast of Buenos Aires province through interviews with the captains of artisanal fishing vessels, in the period 2006-2009.
Abstract: In Argentina, the franciscana dolphin is one of the most vulnerable cetaceans regularly entangled in coastal artisanal fishery nets. The aim of this paper is to estimate the species' incidental mortality on the Southern coast of Buenos Aires province through interviews with the captains of artisanal fishing vessels, in the period 2006-2009. Franciscana bycatch was reported for gillnets and shrimper gear all year round but it occurred more frequently between October and February, at 5 km offshore and 10-20 m depth. The estimated mean annual incidental mortality was 107 dolphins (CI 95% = 87-129), 92 caught in gillnets (CI 95% = 73-112) and 15 in shrimpers' gear (CI 95% = 8-25) with a capture per unit effort of 0.029 dolphins per km of gillnet (CI 95% = 0.023-0.036) and 0.022 per shrimpe r's net (CI 95% = 0.012-0.035). Annual fluctuations were due to differences in the number of gillnetting fishing days. If mortality estimates for the Northern coast are also taken into account, values attain a maximum of 360-539 dolphins bycaught in the entire Buenos Aires province, representing 2.5-3.7% of the species' abundance in Argentina. This will inevitably lead to the decline of franciscana dolphin populations in the near future unless alternative fishing grounds are identified and alternative gearadopted.
TL;DR: Results were not statistically significant, but length-based analyses indicated that the grid rejection likelihood for particularly smaller Norway pout was higher when fishing with the forwards-leaning grid during the night; this might be explained by behavioural and visual aspects of the fish-grid encounter process for Norway pouts.
TL;DR: Although hook location was species-specific and only bait appeared to be driving bycatch rate differences, most sea turtles were caught in the mouth, except for leatherbacks, and only hook type contributed significantly to haulback mortality, with J-hooks associated with slightly higher mortality rates.
Abstract: Here we report a component of the results of the sElEct-pal project, namely marine turtle bycatch composition and rates, hooking location, and status at haulback and at release for several hook-bait combinations in a portuguese commercial longline fishery targeting swordfish in the atlantic equatorial region. In total, 221 longline sets were deployed during the fishing season (february-october) by the portuguese fleet operating in the area. Three different hook types were tested, traditional J-hook (9/0) and two 17/0 circle hooks (non-offset and 10° offset), but only one bait type was used in each set (Scomber spp. or Illex spp.). Four species of sea turtle were caught, most consisting of the olive ridley, Lepidochelys olivacea (Eschscholtz, 1829), and leatherback, Dermochelys coriacea (Vandelli, 1761). The highest mean bycatch per unit effort (bpuE) values for both species combined and for the individual species occurred with the J-hook. The 10° offset circle hook baited with mackerel provided a reduction of 88% and 85% on the bycatch rates, for all turtles combined and olive ridleys, respectively. Although hook location was species-specific and only bait appeared to be driving bycatch rate differences, most sea turtles were caught in the mouth, except for leatherbacks. Only hook type contributed significantly to haulback mortality, with J-hooks associated with slightly higher mortality rates.
TL;DR: The performance of circle hooks for other target species, such as swordfish, Xiphias gladius (Linnaeus, 1758), and sharks, and for bycatch species including sea turtles and seabirds remains unclear and requires further research.
Abstract: Circle hooks have been promoted as an alternative to traditional J-hooks in pelagic longline fisheries to minimize bycatch mortality and injury to sea turtles and other marine wildlife. We evaluated the effect of hook type (circle hook vs J-hook) on the catch and length composition of target and non-target species in the Uruguayan pelagic longline fishery, for both American- and Spanish-style longlines. The sample unit used for comparing catches was two consecutive sections of the longline, each with a different hook type. For the American-style longline 39,822 hooks were deployed in 108 paired sections, and for the Spanish-style 45,142 hooks were deployed in 238 paired sections. The catch of albacore tuna, Thunnus alalunga (Bonnaterre, 1788), was higher with circle hooks with both gears. The catch of shortfin mako shark, Isurus oxyrinchus (Rafinesque, 1810), also increased with the use of circle hooks, but only with the American-style longline. A decrease was observed in the catch of pelagic stingray, Pteroplatytrygon violacea (Bonaparte, 1832), with both gears, though it was significant only with the Spanish-style longline. The performance of circle hooks for other target species, such as swordfish, Xiphias gladius (Linnaeus, 1758), and sharks, and for bycatch species including sea turtles and seabirds remains unclear and requires further research.
TL;DR: The size-dimorphism and niche divergence hypotheses are examined as potential explanations for sexual segregation in the New Zealand sea lion (Phocarctos hookeri), a nationally critical, declining species impacted by trawl fisheries and support the predictions of the niche divergence hypothesis.
Abstract: Sexual segregation (sex differences in spatial organisation and resource use) is observed in a large range of taxa. Investigating causes for sexual segregation is vital for understanding population dynamics and has important conservation implications, as sex differences in foraging ecology may affect vulnerability to area-specific human activities. Although behavioural ecologists have proposed numerous hypotheses for this phenomenon, the underlying causes of sexual segregation are poorly understood. We examined the size-dimorphism and niche divergence hypotheses as potential explanations for sexual segregation in the New Zealand (NZ) sea lion (Phocarctos hookeri), a nationally critical, declining species impacted by trawl fisheries. We used satellite telemetry and linear mixed effects models to investigate sex differences in the foraging ranges of juvenile NZ sea lions. Male trip distances and durations were almost twice as long as female trips, with males foraging over the Auckland Island shelf and in further locations than females. Sex was the most important variable in trip distance, maximum distance travelled from study site, foraging cycle duration and percent time at sea whereas mass and age had small effects on these characteristics. Our findings support the predictions of the niche divergence hypothesis, which suggests that sexual segregation acts to decrease intraspecific resource competition. As a consequence of sexual segregation in foraging ranges, female foraging grounds had proportionally double the overlap with fisheries operations than males. This distribution exposes female juvenile NZ sea lions to a greater risk of resource competition and bycatch from fisheries than males, which can result in higher female mortality. Such sex-biased mortality could impact population dynamics, because female population decline can lead to decreased population fecundity. Thus, effective conservation and management strategies must take into account sex differences in foraging behaviour, as well as differential threat-risk to external impacts such as fisheries bycatch.
TL;DR: Indonesia, the Philippines, and Papua New Guinea, all part of a regional subgroup known as the Coral Triangle, have sizeable skipjack, yellowfin and bigeye tuna fisheries as mentioned in this paper.
TL;DR: In this paper, the authors addressed the issue of bird bycatch in set-nets in the southern Baltic Sea by assessing the vulnerability of diving birds to drowning by developing a vulnerability index based on weighted bird abundance, providing information on set-net fishing activities, and using a spatial overlap approach to indicate the potential conflicts between diving birds and fishing activities.
Abstract: We addressed the issue of bird bycatch in set-nets in the southern Baltic Sea by (i) assessing the vulnerability of diving birds to drowning by developing a vulnerability index based on weighted bird abundance, (ii) providing information on set-net fishing activities, and (iii) using a spatial overlap approach to indicate the potential conflicts between diving birds and fishing activities. Birds and fisheries concentrated in the same areas. Vulnerability and potential conflict were highest during winter and spring in coastal waters and around shallow offshore grounds. Local bycatch studies validated the usefulness of our approach, which can provide a valuable tool for conservation purposes. Although the conflict analysis outlined the current extent of overlap between birds and fisheries, the vulnerability index indicated important areas and periods in terms of diving bird abundance, irrespective of fisheries, and enabled the development of appropriate conservation and management options. A suite of measures including temporal or spatial restrictions can be derived, despite a scarcity of real data for bycatch rates. This approach is particularly useful for assessing impacts that are difficult to monitor and where mortality cannot be properly addressed, as in artisanal gillnet fisheries. It is also generally applicable to any marine area or species worldwide.
TL;DR: In this paper, the authors analyzed catches and fishery dynamics before and after the 2006 trawl ban in the Malindi-Ungwana Bay fishery, showing that the fishery was faced with numerous resource use conflicts and a decline in catches.
Abstract: The Malindi–Ungwana Bay fishery Kenya is one of the most important marine fisheries of the Western Indian Ocean. There are two fishing grounds: Formosa and Malindi, with a designated 5-nM no-trawl zone offshore. However, the fishery was faced with numerous resource use conflicts and a decline in catches, culminating in a trawl ban in 2006. This study analyses catches and fishery dynamics before and after the 2006 trawl ban. Results show that artisanal landings declined before the ban, but rapidly recovered within 2 years after the ban was imposed. However, shrimp landings in the artisanal fishery remain low. Commercial shrimp landings gradually declined before the ban: ~550 t in 2001 to 250 t in 2006, and the shrimp: fish bycatch ratio was 1:1.5 compared to early reports of 1:7 in 1999. SIMPER analyses shows that 6 and 16 families (groups) accounted for 91.0 and 90.2% of the similarity in catch within the Formosa and Malindi fishing grounds, respectively. Formosa was important for Claridae, Cichlidae and Protopteridae, while Malindi recorded Carangidae, Siganidae, Carcharhinidae and Lethrinidae as the main families. Future studies should therefore embark on analyses of the factors driving the spatio-temporal distributions of the species and assess the impacts of bottom trawling on fishery dynamics before the trawl ban can be lifted.
TL;DR: By-catch-to-shrimp ratio, CPUE index and catch percentage of species (based on Wt %) were computed and it’s estimated that 283.4 tonnes of By-catches are taken annually in Bushehr coastal waters by 12 steel trawlers.
Abstract: This paper is a comprehensive study of the shrimp trawl by- catch from Bushehr coastal waters (N. Persian Gulf). Sampling operation was carried out in two shrimp fishing seasons using the (Saber and Jahanara) commercial trawlers Generally, 87.5% of the total catch was by-catch and 12.5% was target species (shrimp). The catch composition included: 114 species from 45 teleostei families, 13 species from 7 elasmobranchs families and 13 species from 13 invertebrate families. Species composition of By-catch included: 72% teleosts, 14% elasmobranchs and 13.9% invertebrates. By-catch-to-shrimp ratio, CPUE index and catch percentage of species (based on Wt %) were computed. On average By-catch-to-shrimp ratio was estimated 7:1. It’s estimated that 283.4 tonnes of By-catches are taken annually in Bushehr coastal waters by 12 steel trawlers.
TL;DR: The results suggest that both the incidental bycatch associated with longline fisheries and high sea surface temperatures (indirectly linked to food availability; SST) increased mortality rates during the long breeding season, and shearwater survival was also negatively affected during the short non-breeding season by positive episodes of the Southern Oscillation Index.
Abstract: Predicting the impact of human activities and their derivable consequences, such as global warming or direct wildlife mortality, is increasingly relevant in our changing world. Due to their particular life history traits, long-lived migrants are amongst the most endangered and sensitive group of animals to these harming effects. Our ability to identify and quantify such anthropogenic threats in both breeding and wintering grounds is, therefore, of key importance in the field of conservation biology. Using long-term capture-recapture data (34 years, 4557 individuals) and year-round tracking data (4 years, 100 individuals) of a trans-equatorial migrant, the Cory’s shearwater (Calonectris diomedea), we investigated the impact of longline fisheries and climatic variables in both breeding and wintering areas on the most important demographic trait of this seabird, i.e. adult survival. Annual adult survival probability was estimated at 0.914±0.022 on average, declining throughout 1978–1999 but recovering during the last decade (2005–2011). Our results suggest that both the incidental bycatch associated with longline fisheries and high sea surface temperatures (indirectly linked to food availability; SST) increased mortality rates during the long breeding season (March-October). Shearwater survival was also negatively affected during the short non-breeding season (December-February) by positive episodes of the Southern Oscillation Index (SOI). Indirect negative effects of climate at both breeding (SST) and wintering grounds (SOI) had a greater impact on survival than longliner activity, and indeed these climatic factors are those which are expected to present more unfavourable trends in the future. Our work underlines the importance of considering both breeding and wintering habitats as well as precise schedules/phenology when assessing the global role of the local impacts on the dynamics of migratory species.