Setting the net lower: A potential low-cost mitigation method to reduce cetacean bycatch in drift gillnet fisheries

1. Bycatch is the most significant threat to marine megafauna (sea turtles, marine mammals, elasmobranchs, seabirds) worldwide, and the leading cause of the decline of several cetacean species. The bycatch issue in the Indian Ocean is poorly understood, but high bycatch levels in gillnet fisheries have been documented for the past two decades, in both small-scale and semi-industrial fisheries. Unfortunately, methods to reduce bycatch are often unavailable, financially non-viable or socially unacceptable to fishermen.
2. Using a network of trained boat captains in the tuna drift gillnet fishery in the Arabian Sea, targeted catch and bycatch data were collected from 2013 to 2017 off the coast of Pakistan (northern Indian Ocean). Two fishing methods using multifilament gillnets were used: surface deployment and subsurface deployment (i.e. headline of net set below 2 m depth).
3. Predicted catch rates for targeted species did not differ significantly between the two fishing practices, although a drop in tuna (6.2%) and tuna-like (10.9%) species captures was recorded in subsurface sets. The probability of cetacean bycatch, however, was 78.5% lower in subsurface than in surface sets.
4. Cetacean bycatch in tuna drift gillnet fisheries has the potential to be significantly reduced at a relatively low cost for fishers. However, further research with an appropriate sampling design and a large sample size is required to confirm the efficacy of the proposed mitigation method. The acceptability and adoption of subsurface setting by fishers also needs to be further investigated. Despite some limitations, this preliminary study also highlights the importance of crew-based observer data as an alternative source of data when observers cannot be deployed on fishing vessels.

     

Potential bycatch of seabirds and turtles in hook-and-line fisheries of the Itaipava Fleet, Brazil

The decline of populations of certain seabirds and sea turtles around the world is partly related to their incidental capture in large-scale fisheries. However, the impacts of small-scale fisheries on endangered seabirds and sea turtles, being carried out in many places around the world, have been largely neglected by scientists and governments. We monitored 178 fishing days and described a range of poorly known hook-and-line commercial fisheries carried out by the Itaipava fleet, southeastern Brazil, composed by 497 vessels and deploying hooks from 18°S to 35°S. Seven fisheries were defined: fast trolling for tuna and tuna-like species, slow trolling for Bigeye tuna, handlining, surface longline for Dolphinfish, pelagic longline for Swordfish, bottom dropline, and pole-and-line with live bait. We observed bycatch of 47 seabirds of six species and 45 turtles of four species. Capture rates were higher for the surface longline for Dolphinfish (0.15 birds/1000 hooks and 1.08 turtles/1000 hooks), slow trolling for Bigeye tuna (0.41 birds/day) and handlining targeting Yellowfin tuna (0.61 birds/day). Endangered Spectacled petrel (Procellaria conspicillata), Atlantic Yellow-nosed (Thalassarche chlororhynchos), and Black-browed (T. melanophris) albatrosses were the main seabirds caught. Immature Loggerhead turtles (Caretta caretta) and immature or adult Leatherback turtles (Dermochelys coriacea) were the main sea turtles affected by the surface longline for Dolphinfish. Monitoring the fleet and bycatch levels, development of mitigation measures, establishment of educational programs, government control over the fleet, and enforcement, are urgently required for the hook-and-line fisheries described in the present study.     

Effects of circle versus J-style hooks on target and non-target species in a pelagic longline fishery

The U.S. Atlantic coastal pelagic longline fishery that targets tunas and swordfish also interacts with a wide range of non-target species including billfishes and sea turtles. Preliminary studies indicate that a change in terminal gear from J-style hooks to circle hooks may reduce bycatch mortality, but the effects of this change on catch rates of target species are unclear. To evaluate this, we monitored catch composition, catch rates, hooking location, and number of fish alive at haulback during 85 sets in the fall and spring seasonal fisheries from a commercial vessel operating in the western North Atlantic. Circle (size 16/0, 0° offset) and J-style (size 9/0, 10° offset) hooks were deployed in an alternating fashion. Hook–time recorders were used to assess time at hooking and temperature–depth recorders to measure gear behavior. Catch rates for most species categories were not significantly different between hook types (P < 0.05), although circle hooks generally had higher tuna catch rates in the fall and lower swordfish catch rates in the spring. In the fall, both total catches and catches of pelagic rays were significantly higher on J-style hooks. Yellowfin tuna in the fall and dolphinfish in the spring caught on circle hooks were significantly larger than those caught on J-style hooks. In both seasonal fisheries, circle hooks caught fishes in the mouth more frequently than J-style hooks, which hooked more often in the throat or gut, although these differences between hook types were not statistically significant. Yellowfin tuna in the fall fishery were over four times more likely to be hooked in the mouth with circle hooks than with J-style hooks. Several target and bycatch species showed higher rates of survival at haulback with circle hooks, although only for dolphinfish in the fall fishery was this difference statistically significant. Our results suggest that the use of 0° offset circle hooks in the coastal pelagic longline fishery will increase the survival of bycatch species at haulback with minimal effects on the catches of target species.     

Broadbill swordfish: status of established fisheries and lessons for developing fisheries

Guidelines for the assessment and management of developing swordfish fisheries are derived through an examination of five swordfish fisheries. As they develop, swordfish fisheries may be inclined to local depletion around underwater features, such as seamounts and banks. Few nations have applied the precautionary approach in managing their developing swordfish fisheries. Without controls, swordfish fisheries expand geographically and fishing effort increases, often overshooting optimum levels. However, it is difficult to distinguish clear evidence of fishery collapse; modern longliners harvest widely distributed tuna and swordfish and they are able to relocate to distant areas or switch between target species in response to fluctuations in species abundance and price. Furthermore, the wide distribution of swordfish combined with year‐round spawning and high growth rates amongst juveniles probably contribute to the apparent resilience of swordfish stocks to intensive harvesting. Over half the world’s swordfish catch is taken as an incidental catch of longliners fishing for tuna. In several areas, such as the North Atlantic, catch quotas have sometimes caused tuna longline fishers to discard swordfish. Minimum size limits have also resulted in discarding of swordfish in tuna fisheries and in dedicated swordfish fisheries. In addition to weakening the effectiveness of those management measures, bycatch and discarding add to the complexities of managing swordfish fisheries and to uncertainties in assessing the stocks. Longliners that target swordfish often fish at high latitudes where interactions with marine wildlife, such as seabird, are generally more frequent than at low latitudes. Concern over incidental catches of marine wildlife and other species is becoming a driving force in the management of several swordfish fisheries. Fishery management organisations will need to implement management measures to protect non‐target species and gather reliable data and information on the situation by placing observers on boats fishing for swordfish.     

Policy and transparency gaps for oceanic shark and rays in high seas tuna fisheries

The incidental capture by marine fisheries as bycatch poses a global threat to pelagic sharks and rays. In large, industrialized fisheries that often operate in areas beyond national jurisdiction, at least 22 threatened species of pelagic elasmobranchs are caught as bycatch, representing the majority of megafauna bycatch in tuna fisheries. Here, we investigate (1) the efficacy of the current policies of the five tuna-related Regional Fisheries Management Organizations (tRFMOs) in mitigating elasmobranch bycatch, (2) data needed to better assess the amount and impact of elasmobranch bycatch and (3) the research necessary for the adoption of new policies. We found that tRFMOs have adopted 34 active policies that address pelagic elasmobranch bycatch. However, most policies (~76%, n = 26) are unlikely to avoid or minimize elasmobranch bycatch. Instead, most policies focus on mitigating post-capture mortality via remediation and requiring or encouraging research and data collection. Despite the emphasis on research mandates, we find that the existence of research was not related to policy adoption, suggesting that lack of research has not historically prohibited policymaking. Overall, we suggest that current research and data transparency, though perhaps not necessary for policy adoption, are not sufficient to adequately evaluate the population-level impacts of bycatch on many elasmobranch species in tRFMO-managed fisheries. Given these results, we recommend a precautionary approach that involves reforms in tRFMO voting processes to facilitate the adoption of binding requirements for elasmobranch catch limits, bycatch avoidance, pre- and post-capture handling and release modifications and protection of areas important to threatened pelagic elasmobranchs.     

Reducing sea turtle by-catch in pelagic longline fisheries

Reducing by‐catch of sea turtles in pelagic longline fisheries, in concert with activities to reduce other anthropogenic sources of mortality, may contribute to the recovery of marine turtle populations. Here, we review research on strategies to reduce sea turtle by‐catch. Due to the state of management regimes in most longline fisheries, strategies to reduce turtle interactions must not only be effective but also must be commercially viable. Because most research has been initiated only recently, many results are not yet peer‐reviewed, published or readily accessible. Moreover, most experiments have small sample sizes and have been conducted over only a few seasons in a small number of fisheries; many study designs preclude drawing conclusions about the independent effect of single factors on turtle by‐catch and target catch rates; and few studies consider effects on other by‐catch species. In the US North Atlantic longline swordfish fishery, 4.9‐cm wide circle hooks with fish bait significantly reduced sea turtle by‐catch rates and the proportion of hard‐shell turtles that swallowed hooks vs. being hooked in the mouth compared to 4.0‐cm wide J hooks with squid bait without compromising commercial viability for some target species. But these large circle hooks might not be effective or economically viable in other longline fisheries. The effectiveness and commercial viability of a turtle avoidance strategy may be fishery‐specific, depending on the size and species of turtles and target fish and other differences between fleets. Testing of turtle avoidance methods in individual fleets may therefore be necessary. It is a priority to conduct trials in longline fleets that set gear shallow, those overlapping the most threatened turtle populations and fleets overlapping high densities of turtles such as those fishing near breeding colonies. In addition to trials using large 4.9‐cm wide circle hooks in place of smaller J and Japan tuna hooks, other fishing strategies are under assessment. These include: (i) using small circle hooks (≤ 4.6‐cm narrowest width) in place of smaller J and Japan tuna hooks; (ii) setting gear below turtle‐abundant depths; (iii) single hooking fish bait vs. multiple hook threading; (iv) reducing gear soak time and retrieval during daytime; and (v) avoiding by‐catch hotspots through fleet communication programmes and area and seasonal closures.     

Standardized catch and survival rates,and effect of a ban on shark retention,Palau pelagic longline fishery

相似文献   

Evaluation of observer‐ and industry‐based catch data in a recreational charter fishery

There is international recognition for greater inclusion of recreational fisheries catch data in species, fisheries and ecosystem assessments. Recreational charter fisheries provide important social services and contribute to total species catches. This study compares and validates industry logbook catch and effort data (1,357 trips) against observer data (154 trips) across six ports in a recreational charter fishery in eastern Australia. The mean numbers of clients and fishing effort (hours) per trip varied inconsistently between data sources and among ports. Logbooks did not adequately report released catches, and the mean number of species retained per trip was consistently underestimated in logbooks compared to observer data. For both data sources, catch rates of total individuals and key species displayed similar trends across different units of effort; catch per hour, client, client/hour and trip. The mean catch rates of total individuals and most key species, except those retained for bait, were similar across data sources, as were estimates of total fleet harvests. The length compositions of retained catches of some key species displayed truncation of larger organisms in the observer data whereas other species did not. Despite the shortcomings of the logbook data, future fishery and species monitoring strategies could include industry and observer data sources.     

中东太平洋公海金枪鱼延绳钓误捕海龟的观察和分析

根据2006年2－11月科学观察员对热带东太平洋公海海域(05°N～10°S,134° W~173°W)金枪鱼延绳钓渔业的调查,期间共投钩223次(天),误捕到绿海龟、蠵龟、丽龟、玳瑁和棱皮龟5种共22尾,死亡海龟13尾。从海龟误捕率看,平均每次尾数为0.098 65。平均每千钩尾数0.037 40。从海龟的钩获部位看,喙(嘴)上钩占41.0%,躯干部位上钩占13.6%,喉部上钩占13.6%,前肢上钩占18.2%,主绳缠绕被捕获占13.6%。海龟的误捕区域位于04°S以北海域,几乎可全年捕获。此外分析了不同钩位误捕海龟的数量,探讨了影响误捕率和死亡率的因素,提出保护对策。     

A comparison of methods to spatially represent pelagic longline fishing effort in catch and bycatch studies

Bycatch in fisheries has been recognized as a threat to many endangered populations of sea turtles, sea birds and marine mammals. Interactions between pelagic longline fisheries and critically endangered populations of leatherback sea turtles (Dermochelys coriacea) have led to temporary closures of the Hawaiian pelagic longline swordfish fishery and severe bycatch quotas. The negative impact of these events on both the populations of certain endangered species and the economic livelihood of the fishermen has resulted in a strong push from all sides to better understand bycatch events. Typically, analyses of longline catch and bycatch have examined fishing effort summarized over large areas (≥1°). Although aggregation of effort to this level may be necessary to account for uncertainty, confidentiality concerns, or to make comparisons across regions, it specifically limits the researcher's ability to characterize the local oceanographic factors that may drive individual bycatch events. Higher resolution analyses must be undertaken to identify such features. However, for these higher resolution analyses, the methods currently used to spatially represent pelagic longline fishing effort may significantly affect researcher's results. Here, we look at different methods to represent this fishing effort (i.e., points, centroids, polylines and polygons) at various resolutions (2 km to 5°) to better understand which method and spatial resolution are most appropriate. Our results validate the use of point features to represent fishing effort in previous low resolution studies of the Hawaiian pelagic longline fishery by showing that the set point method is suitable for studies with resolutions lower than 15 km. However, at higher resolutions (≤15 km) and in areas with more sparsely distributed fishing, aggregated effort values differed significantly between spatial representation methods. We demonstrate that the use of polygons to describe pelagic longline fishing effort is more representative and necessary for such high resolution analyses.     

Trawl catch composition in relation to Norway lobster (Nephrops norvegicus L.) abundance on the Farn Deeps grounds, NE England

Management of fisheries directed at a particular species (the target) is often complicated by the capture of other species (the bycatch), each of which may be subject to competing management objectives. Optimal management depends upon a good understanding of how catches of the target species vary in relation to bycatch of other species of commercial and conservation concern. This paper considers the composition of trawl catches taken on a Norway lobster (Nephrops norvegicus) ground off the NE coast of England, examining the factors that determine catch rates of Nephrops and various commercial finfish species taken as bycatch. We describe the results of a trawl survey undertaken using four commercial vessels deploying standard commercial gear. Only about 19% of the variance in Nephrops catch rates could be accounted for by variations in local density, as measured independently by underwater television survey of Nephrops burrows. Variations in Nephrops catch rates were dominated by changes over time, particularly in relation to tidal state. Five commercial bycatch species were taken alongside Nephrops in significant quantities. Catch rates of haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus) and lemon sole (Microstomus kitt) varied independently of Nephrops, whereas catches of cod (Gadus morhua) and plaice (Pleuronectes platessa) were inversely related to Nephrops. We conclude that it is possible for the commercial Nephrops fishery to use spatial and temporal targeting to maximise catches of N. norvegicus whilst minimising the bycatch of some fish species. If catch statistics are used to identify Nephrops-directed fishing métiers for fishery management purposes it is vital that data are examined at the level of individual hauls or fishing trips. Aggregation of data at a higher level risks obscuring the effectiveness with which the fishery is targeted at Nephrops.     

Use of remote sensing tools to predict focal areas for sea turtle conservation in the south-western Atlantic

1. Fisheries bycatch of non-target species in the commercial fleet is a major source of anthropogenic injury and mortality for sea turtles and marine megafauna.
2. The Río de la Plata maritime front (RLPMF) and its adjacent international waters – comprising part of the Argentine and Uruguayan exclusive economic zones, is a highly important fishing ground in the south-western Atlantic Ocean as well as feeding and development grounds for sea turtles.
3. This paper analyses the distribution of the bottom and pelagic trawling fishery within the RLPMF using information from Vessel Satellite Monitoring System. With this information, areas of highest trawling intensity were defined and further evaluated their overlap with sea turtle habitat-use areas from available sea turtle satellite tracking information.
4. Results besides identifying high-susceptibility areas for sea turtle bycatch by the commercial trawler fleet along the RLPMF, provide predictive tools to identify vulnerable areas to interaction of sea turtles and the commercial fishing fleet.
5. Implementation of bycatch mitigation measures, such as reduced fishing effort areas by the Argentine and Uruguayan fisheries management agencies has the potential to benefit the fisheries as well as marine megafauna. Furthermore, there is a need for additional research on the impact that this fleet can have on sea turtles present in the area.

     

Hawaii longline tuna fishery temporal trends in standardized catch rates and length distributions and effects on pelagic and seamount ecosystems

相似文献   

Vulnerabilities and fisheries impacts: the uncertain future of manta and devil rays

相似文献   

Effects of 17/0 circle hooks and bait on sea turtles bycatch in a Southern Atlantic swordfish longline fishery

相似文献   

Characterizing environmental and spatial variables associated with the incidental catch of olive ridley (Lepidochelys olivacea) in the Eastern Tropical Pacific purse‐seine fishery

In the Eastern Tropical Pacific (ETP), a region of high fishing activity, olive ridley (Lepidochelis olivacea) and other sea turtles are accidentally caught in fishing nets with tuna and other animals. To date, the interaction between fishing activity, ocean conditions and sea turtle incidental catch in the ETP has been described and quantified, but the factors leading to the interaction of olive ridleys and fishing activity are not well understood. This information is essential for the development of future management strategies that avoid bycatch and incidental captures of sea turtles. We used Generalized additive models (GAM) to analyze the relationship between olive ridley incidental catch per unit effort (iCPUE) in the ETP purse‐seine fisheries and environmental conditions, geographic extent and fishing set type (associated with dolphins, floating objects or in free‐swimming tuna schools). Our results suggest that water temperature, set type and geographic location (latitude, longitude and distance to nesting beaches) are the most important predictor variables to describe the probability of a capture event, with the highest iCPUE observed in sets made over floating objects. With the environmental predictors used, sea surface temperatures (SST) of 26–30°C and chlorophyll‐a (chl‐a) concentrations <0.36 mg m^?3 were associated with the highest probability of an incidental catch. Temporally, the highest probability of an incidental catch was observed in the second half of the year (June to December). Four regions were observed as high incidental catch hotspots: North and south of the equator between 0–10°N; 0–10°S and from 120 to 140°W; and along the Colombian coast and surrounding regions.     

Bycatch and discarding in the South African demersal trawl fishery

Observers aboard commercial trawlers collected data on the total catch composition of 614 and 479 hauls made by vessels operating off the south and west coasts of South Africa, respectively. On the south coast, four fishing areas were identified on the basis of target species and fishing depth. On the west coast, hauls were separated into those targeting hake Merluccius spp. in four depth ranges (0–300, 301–400, 401–500, and >500 m) and those targeting monkfish Lophius vomerinus. For each area, the catch composition was calculated and the species assemblages were investigated using cluster analysis and multi-dimensional scaling. Finally, for each coast, the weight of fish discarded annually was estimated. On the south coast, although hake dominated, between 21% and 47% of the catch was not hake, depending on the fishing area. In comparison, hake dominated west coast catches, the proportion of hake increasing with depth. For each fishery investigated, approximately 90% of the catch was processed and landed. However, estimates of annual discards indicate that the south and west coast fisheries may annually discard 9000 or 10,000 t and 17,000 or 25,000 t, of undersized and unutilizable fish and offal, respectively, depending on the estimation method used. When developing strategies to limit or enhance utilization of bycatch, cognisance should be taken of the differences in catch composition between the south and west coasts and of the importance of bycatch revenue to south coast fishing companies.     

Results of a short study on by-catches and discards in pelagic fisheries in Scotland (UK)

Observers were placed on pelagic vessels in the Scottish fisheries for mackerel (Scomber scombrus), herring (Clupea harengus), “maatje” herring (herring caught just before their first spawning) and argentines (Argentina silus) to monitor by-catch composition and discarding practices. A total of 67 days was spent at sea, 11 on the argentine fleet, 28 on the herring fleet, 12 on the “maatje” herring fleet and 16 on the mackerel fleet. The level of by-catch generally ranged from <1% to around 2.5% of the total catch. The argentine fishery took a significant proportion of blue whiting (Micromesistius poutassou) (approx. 10% of the overall catch) but this was landed and sold in the market. The greatest range of by-catch species was found in the argentine fishery, including 11 species of fish and one species of squid. Discarding rates in the fisheries varied, with herring and argentine fisheries showing no discards, the mackerel fishery a discard rate of around 4% and the “maatje” herring fishery a discard rate of around 11%. By-catches included small numbers of gannets (Morus bassanus) but no marine mammals. If the sampled trips were representative, results indicate that marine mammal by-catch events typically occur during less than one in 20 hauls in the fisheries studied. A larger scale study is needed to confirm this. Cetaceans were sighted in the vicinity of the fishing boats during 4% of observed fishing activities.     

Enhancing the TurtleWatch product for leatherback sea turtles,a dynamic habitat model for ecosystem‐based management

Fishery management measures to reduce interactions between fisheries and endangered or threatened species have typically relied on static time‐area closures. While these efforts have reduced interactions, they can be costly and inefficient for managing highly migratory species such as sea turtles. The NOAA TurtleWatch product was created in 2006 as a tool to reduce the rates of interactions of loggerhead sea turtles with shallow‐set longline gear deployed by the Hawaii‐based pelagic longline fishery targeting swordfish. TurtleWatch provides information on loggerhead habitat and can be used by managers and industry to make dynamic management decisions to potentially reduce incidentally capturing turtles during fishing operations. TurtleWatch is expanded here to include information on endangered leatherback turtles to help reduce incidental capture rates in the central North Pacific. Fishery‐dependent data were combined with fishing effort, bycatch and satellite tracking data of leatherbacks to characterize sea surface temperature (SST) relationships that identify habitat or interaction ‘hotspots’. Analysis of SST identified two zones, centered at 17.2° and 22.9°C, occupied by leatherbacks on fishing grounds of the Hawaii‐based swordfish fishery. This new information was used to expand the TurtleWatch product to provide managers and industry near real‐time habitat information for both loggerheads and leatherbacks. The updated TurtleWatch product provides a tool for dynamic management of the Hawaii‐based shallow‐set fishery to aid in the bycatch reduction of both species. Updating the management strategy to dynamically adapt to shifts in multi‐species habitat use through time is a step towards an ecosystem‐based approach to fisheries management in pelagic ecosystems.