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On bycatch
Abstract
This paper attempts to provide a synthesis of several issues relevant to the study and management of bycatches. It includes a proposed set of definitions for the different fractions of the harvest (catch, bycatch, release) and for other impacts of the fishing process, either at sea or in port. It also provides a system for the classification of bycatches that shows some basic similarities and differences among fisheries.
The classifications are based on different criteria, including the degree of spatial or temporal ‘aggregation’ of bycatches, the degree of control that the fishers have, the frequency of occurrence, its predictability, its ecological or random origin, the level of impact of bycatches, and whether bycatches are the result of market conditions or regulations.
One of the main issues to address in plans to deal with bycatches is defining the objectives to be pursued. These objectives can include ecological or socio-economic goals, and some of the possible goals are briefly discussed. Once the targets are set, it is necessary to find the strategies to achieve them. The bycatch process is quite simple because it has only two controls: the average impact per unit of effort and the total level of effort. The definition of effort used is not always equivalent to the one used in fisheries models.
If a decision is made to reduce the ecological impacts of a fishery, three sets of tools are available to achieve it, acting over the two controls mentioned above: technology, training of fishers, and management measures. Five possible lines of defence are available to reduce bycatches: (1) increasing the selectivity of the fishery by choices of gear, areas, or seasons; (2) modifying deployment conditions; (3) increasing the fraction released alive either from the gear, or (4) later, from the deck; or (5) increasing the utilization to make catches out of the incidental captures.
One of the options more commonly used to manage fisheries problems is the development of incentive/disincentive programmes, with both positive and negative responses applied to the fishers in accordance to their level of performance. Some examples are mentioned.
Some of the challenges facing scientists, managers, the fishing industry and the environmental community to tackle the bycatch problems in coming years are also presented.
The catch and discard of non-target species could have detrimental effects on bycatch, species due, among others, to the increase in mortality and prevalence of injuries. In Argentina, the southern king crab (SKC), Lithodes santolla, supports a profitable trap fishery but is also caught as bycatch in trawl fisheries. The aims of this work were: i) to quantify the mortality and injuries in SKC caught as bycatch in the hake fishery in San Jorge Gulf (southwestern Atlantic Ocean), ii) to assess the factors that affect their mortality and injury occurrence, and iii) to estimate their postdiscard mortality.Immediate mortality (IM) and injuries in SKC were recorded in hauls of the hake fishery, and then related to operational and biological variables. SKC vitality was assessed using the reflex action mortality predictor (RAMP) test. Postdiscard mortality was analyzed in aquaria and wild (sea cages) conditions. The IM of SKC in the common hake fishery was 31%. The IM, as well as increased injuries and decreased vitality, were directly associated with the time and conditions of air exposure. Both the IM and injury occurrence were also affected by biological variables such as the sex,size and molt stage. Postdiscard mortality was lower in wild conditions than in the aquaria (1%). Our results suggest that SKC could have high resistance to handling and high recovery capacity after its return to the sea. In consequence, the quick return of SKC to the sea may have a positive effect on SKC survival.
Fisheries bycatch is considered the largest threat to sea turtle populations globally. However, it has been challenging to assess the impact of bycatch on sea turtles in some regions such as Northwest Africa (i.e. Cabo Verde, Guinea, Guinea–Bissau, Mauritania, Senegal, Sierra Leone and The Gambia) owing to large data gaps. This hampers effective management actions and interferes with conservation efforts in the region.
Five sea turtle species occur in Northwest Africa (i.e. green turtle Chelonia mydas , hawksbill Eretmochelys imbricata , leatherback Dermochelys coriacea , loggerhead Caretta caretta and olive ridley Lepidochelys olivacea ). The region has regionally and globally important sea turtle nesting and foraging habitats and is a global fishing hotspot, with high and increasing fishing pressure.
Available information on sea turtle bycatch in Northwest Africa was compiled from peer‐reviewed and grey literature from 2010 onwards to determine the impact of artisanal and industrial fisheries (by gear type) on regional sea turtle populations and assess the level of threat to individual species.
All sea turtle species occurring in the region are impacted by bycatch. Reports suggest that green turtles and loggerheads have the highest bycatch rates, probably owing to their regional abundance and widespread distribution. Some of the potentially highest reported global bycatch rates (14,000–90,000 turtles/year/country) are noted, particularly in gillnets, longlines and handlines. However, further research is needed to understand mortality levels from artisanal fisheries and assess the impact of trawl fisheries operating in the region. Additional sources of mortality include deliberate capture for consumption or trade.
To strengthen regional sea turtle conservation and reduce sea turtle bycatch and mortality, urgent action is needed to implement and enforce national protection, establish a bycatch reduction framework (including gear modifications and spatio‐temporal closures), improve fisheries data collection and build capacity.
Bycatch is a significant concern in the global fisheries that catch the undersized and uneconomically important fishes in the fishing gears and question the sustainability of fishery resources for the future. The present study investigated the temporal patterns of bycatch landed from the trawlers operated off Thoothukudi Coast, Gulf of Mannar, India. The results revealed that bycatch was constituted by 184 species belonging to 12 orders, 68 families and 128 genera. Among the bycatch, Perciformes and Clupeiformes constituted the major number of fishes. The most common finfish bycatch in the trawlers was Parupeneus indicus, Zebrias quagga, Selaroides leptolepis, Odonus niger and Leiognathus elongatus. Analysis of temporal patterns of bycatch revealed that the maximum numbers of species were found to be in the post-monsoon of 2018. Considering the trophic level, top predators (38.04%) were contributed most of the catch. The bycatch of small-sized fishes and juveniles of significant growing fishes are playing a prominent role in the food chain. The large catch of these fishes adversely affects the fishery resources and thereby affects fishers' livelihoods. It is time to enforce strict implementation of bycatch reduction devices and mesh-size regulations to conserve the fishery resources.
Fisheries bycatch is the greatest threat to migratory, long‐lived marine animals.
Addressing bycatch ultimately requires changing fisher behaviour, yet social and behavioural sciences are rarely applied to bycatch mitigation, with an absence of theory‐informed behaviour change interventions. Moreover, mitigating bycatch is particularly challenging in small‐scale mixed‐species fisheries (SSFs), where perceptions of target and non‐target vary widely, and all catches have economic or subsistence value. Such fisheries are ubiquitous throughout the world's oceans, and bycatch mitigation in these contexts necessitates a people‐centred approach.
We seek to address this gap, drawing on well‐established theories from behavioural and social sciences. We first typify bycatch as a spectrum rather than a clearly delineated component of catch, where the position of a species on this spectrum depends on fishers' beliefs regarding the outcomes of bycatch‐relevant behaviour. We then outline an approach to ‘diagnose’ fishers' underlying beliefs about bycatch, using the theory of planned behaviour (TPB): a widely applied and empirically tested theory for predicting and changing behaviour. Finally, we illustrate the approach using an empirical case study, exploring fishers' beliefs regarding bycatch‐relevant behaviour for three endangered elasmobranch species in a small‐scale gill net fishery in Indonesia.
Our findings show how the TPB can help to understand fishers' underlying beliefs regarding bycatch, and facilitators/inhibitors of bycatch mitigation, to inform behaviour change interventions. We emphasize the need to understand the human dimensions of bycatch, especially in SSFs, where technical fixes alone will be insufficient to change behaviour. Rather, interdisciplinary approaches are needed to align fishers' needs with conservation objectives.
Our bycatch spectrum and the TPB could be widely applied for disentangling drivers of bycatch in other SSFs and designing interventions which support more effective and socially just marine conservation.
Fisheries bycatch is the foremost threat to the conservation of many marine species. Evaluation of alternative bycatch management strategies can account for the relative strength of evidence, contribution to achieving objectives, costs to commercial viability, likelihood of compliance and tradeoffs from multispecies conflicts. This study describes benefits and limitations of a complementary approach of applying a sequential mitigation hierarchy to develop evidence-informed bycatch policy. Measures that avoid bycatch are considered before those that minimize catch risk. These are then followed by remediation interventions that reduce fishing mortality and sublethal impacts. Finally, direct, compensatory banking or in lieu fee-based offsets of residual impacts that were not possible to avoid, minimize and remediate can be implemented as a last resort. However, offset activities can be socioeconomically unjust, and some bycatch impacts are irreversible and cannot be offset. Air-breathing bycatch are exposed to a wide range of anthropogenic hazards across ontogenetic stages, presenting more options for offset conservation activities than fishes. Averted loss offsets, which avoid foregone losses predicted to occur had an intervention not occurred, implemented in combination with true offsets can achieve at least an equivalent gain and contribute to meeting broad, population-and species-level conservation objectives. Robust metrics are needed to determine equivalency, such as in relative reproductive value and population viability, between residual impacts and in-kind versus out-of-kind and on-site versus offsite offsets. Bycatch management strategies guided by a sequential mitigation hierarchy promise to achieve ecological and socioeconomic objectives , including going bycatch-neutral or bycatch-negative through a net biodiversity gain.
Despite the importance of Rapana fisheries in the Black Sea region, few studies have focused on the non-target species, and determined discard rates from hauls on the deck, with no data on organisms that entered and subsequently escaped the fishing net during the dredge fishing. Rapana venosa is harvested along the entire coast of the Black Sea using dredging or beam-trawl fishing. This study adopted the cover net method to assess the composition and proportion of non-target escapees in Rapana fisheries by dredging along the western coast of the Black Sea. In this method, the dredge net bag (codend net) is covered with a second net bag that has a smaller mesh size to retain those individuals escaping from the dredge net bag. Up to 87% of the total ∼1.4×10⁶ individuals per km (ind. km⁻²) cover net catches belonged to non-target species. Overall, 24 non-target species were caught in the cover net, with 46% of species belonging to the Teleostei (mostly flatfishes), 21% Malacostraca, 17% Bivalvia, 8% Gastropoda, 4% Amphibia, and 4% Ascidiacea. On the other hand, up to 6.8% of the total ∼0.16×10⁶ ind. km⁻² catches of the codend net (dredge net) belonged to non-target species. Compared to the cover net, a total of seven non-target species were retained in the codend net, and six of them belonged to Bivalvia. This study demonstrated an apparent negative impact of Rapana fisheries, particularly on escapees that often go unaccounted for their vulnerability to stress and physical damage.
Considerable by-catch problems have been occurred during deep water pink shrimp targeted commercial beam trawl fishery in the Sea of Marmara. In the study, grid systems were used in order to reduce the untargeted catch and improve the species selectivity. By-catch reduction ratios of beam trawls deployed with and without grid were compared by parallel hauling method. Selectivity values of 20 mm bar spacing grid and 24 mm mesh size cod-end were also analysed by SELNET programme. In general, by-catch reduction ratios of grid beam trawl were determined to be 50.6% and 56.9% in terms of number and weight, respectively. Reduction of target catch (Parapenaeus longirostris) in the same gear was found to 23.1% in terms number and 23.2% in terms of weight. In the model for rose shrimp which was obtained according to the lowest AIC value, selectivity parameters of the grid for L50 was 13.51 cm and for SR 4.76 cm. Selectivity parameters of the same species for 24 mm mesh size cod-end were; L50 = 8.99 cm and SR = 5.56 cm. These results indicated that grid usage benefits and contributes to sustainable fishery in the target catch oriented fishing applications.
Sharks and rays are among the most threatened vertebrates, mostly due to commercial fisheries. Data on incidental capture is sparse, but it is estimated that about 50% of reported global catches of elasmobranchs are from bycatch. Elasmobranchs are captured in a variety of fishing gear throughout the world. One promising strategy to minimize incidental catches is the release of live sharks and rays. However, so far, no critical analysis had been carried out to assess the importance of release as a measure to mitigate the impacts of bycatch. Results indicated that despite onboard releases being cited in Plans of Action (along ZEEs) and recommendations/regulations of Regional Fisheries Management Commissions (in international waters), this measure is treated as secondary and has voluntary adherence, which can significantly reduce its efficiency. Moreover, among the Best Fishing Practice Manuals currently available, although release is cited as a priority, most of them do not consider the dynamics of the location/fishing modality for which it was developed. A change on how release is perceived is needed to prioritize this conservation strategy, as well as its potential as a social tool to reduce the impacts of bycatch on sharks and rays.
Reducing the capture of non-target species and juvenile fishes through a variety of gear modifications and bycatch reduction devices are presumed to provide long-term biological and socioeconomic benefits and improve the reputation of fisheries. The adoption of these technologies by fisheries, however, has been low compared to research and development efforts. Research has focused on technical design and catch rate responses to these technological interventions with a limited focus on assessing fishers’ attitudes towards these technologies. This essay gives a personal reflection, based on an extensive collaboration with fishers, of the perspectives and barriers that may affect their responses. I also provide suggestions on how to genuinely engage fishers in the process that could lead to agreeable solutions. Above all, change should be approached from the perspective of those whose behavior one is seeking to influence, acknowledging the heterogeneity among fisheries and fishers. The essential element for the success is fishers’ motivation and readiness to the change. Fishers need a clear vision of what the changes mean for their livelihood and evidence that the technology to minimize bycatch performs sufficiently well in various conditions.
Estimates of dolphin mortality incidental to fishing operations of the E Pacific Ocean tuna fleet in 1994 are presented. Mortality estimates were computed, using data collected by observers aboard 388 trips of tuna vessels from the international fleet. Total dolphin mortality for 1994 was 4096 animals, particularly Stenella attenuata, S. longirostris and Delphinus delphis a 14% increase in the level of incidental mortality in this fishery relative to the estimated level in 1993.
Total dolphin mortality for 1993 was 3601 animals, a 97% decrease in the level of incidental mortality in this fishery relative to the estimated level in 1986. Most of this decrease is attributable to improvements to dolphin safety gear and in the performance of vessel captains and crew members; between 1986-1993, the average mortality of dolphins per set decreased by 96%. -from Authors
Large-scale research vessel surveys were conducted annually from 1986 through 1990 by the US National Marine Fisheries Service to monitor the abundance of dolphin populations in the E tropical Pacific (ETP). Distribution maps are presented for all 29 species. Data from all five surveys were pooled to give single estimates of abundance in the EPT for 24 stocks of cetaceans. Abundance estimates totaled 9.6 million animals for all dolphin species (subfamilies Delphininae and Steninae), 292 800 for all species in the subfamily Globicephalinae, 45 300 for all species in the family Ziphiidae (beaked whales), 33 881 for all species in the superfamily Physeteroidea, and 14 431 for two species in the family Balaenopteridae (rorquals). -from Authors
-The eastern Pa cific purse-seine tuna fishery has historically been very productive, yielding up to 400,000 metric tons (t) per year of primarily yellowfin, Thunnus albacares, and skipjack, Katsuwonuspelamis. However, ef forts to minimize,dolphin (prima rily spotted dolphin, Stenella attenuata, spinner dolphin, S. longirostris, and common dolphin, Delphinus delphis) mortality inci dental to tuna seining in the east ern Pacific ocean,have been,in creasing. Therefore, predictions of what,the tuna catches will be in the future, if there is a ban or moratorium,on catching dolphin associated tuna, are useful. Based on recruitment levels, age-specific catchability coefficients for yellow fin tuna caught without dolphins, and average,fishing effort ob served during 1980-88, we pre dicted that yellowfin,catches would be reduced by an average of about,25%. These results were verified by Monte Carlo simula
In 1979 an assistance program was established for inshore fishermen in Newfoundland and Labrador who caught large whales and sharks in their fishing gear. The widely advertised program allowed fishermen to call toll-free for assistance and receive help from a trained crew in releasing the animal from the gear. Mortality has varied according to the species entrapped and the duration of the entrapment. Distribution of the whales, variability of bait, fishing effort, numbers of animals in a population, and species characteristics each contribute to the relative frequency of incidental entrapments of large cetaceans. -from Authors
Review of development of surround net fishing. World's Purse Seine (PS) fisheries; theory of PS; Purse seiners; Deck equipment; Pursed seines and auxiliary gear (principal types of PS designs: Mediterranean, Scandinavian, California, Japanese, Salmon PS, Brazilian sardine PS, Hybrid PS Ringnets, Practical instruction on PS design and construction; PS fishing - operation; Terms Glossary; References.