Bycatch Mortality Research Articles

Connecting fishers to conserve a transpacific ambassador: A trinational fisheries learning exchange

Fisheries learning exchanges (FLE) can be useful for enhancing fisheries management. Reversing the decline of the North Pacific loggerhead turtle is a priority articulated in US, Japanese, and Mexican natural resources policy. However, by 2005, while nesting beach protection was strong in Japan and bycatch reduction had been achieved in U.S. Hawaii-based longline fisheries, bycatch mortality was very high in Mexican artisanal fisheries and believed to be problematic in Japanese coastal fisheries. Efforts to conserve the population were hindered by lack of understanding and cooperation by and between fishers, conservation practitioners, scientists, and managers of all three countries. The authors produced a trinational FLE with participants from Japan, Mexico, and Hawaii to share bycatch challenges and develop solutions. The trinational FLE gave fishers and other participants new, otherwise unattainable knowledge, perspectives, and experiences that empowered them as leaders among their peers, resulting in unexpectedly strong cultural and conservation outcomes that included: a) understanding of the myriad threats to loggerheads throughout their ranges and lifetimes, b) development of a transpacific conservation partnerships to undertake coordinated recovery efforts, c) participatory research to develop and test bycatch reduction technological and practical solutions for Japan and Mexico, and d) hundreds of juvenile loggerheads spared per yr from bycatch mortality via changes in fishing practices by FLE participants. The authors conclude that the reciprocal FLE can serve as a practical tool with potential for broad application for empowering fishers and other fisheries stakeholders to improve fisheries.

Genetic stock composition of marine bycatch reveals disproportional impacts on depleted river herring genetic stocks

Bycatch of mid-trophic-level anadromous fishes that connect marine and freshwater ecosystems is a growing conservation concern. Anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) are important components of coastal freshwater and marine food webs, but have experienced dramatic declines in the abundances of spawning adults. Freshwater-focused restoration efforts have yielded few consistent signs of recovery, raising concerns that bycatch in Northwest Atlantic commercial fisheries may be negating these conservation actions. Using data from 15 microsatellites genotyped for baseline populations and bycatch, we conducted genetic stock identification to understand how bycatch was partitioned among previously identified regional genetic stocks. We then combined this information with fishery observer data to estimate genetic stock-specific bycatch mortality for the southern New England Atlantic herring fishery (2012–2013). Bycatch overall, but especially in the Atlantic herring fishery, was disproportionately assigned to the most severely depleted genetic stocks (alewife southern New England stock — 70% of assignments; blueback herring mid-Atlantic stock — 78% of assignments). These genetic stocks overlap in the region surrounding Long Island Sound, suggesting that bycatch taken from this area in recent years may be negatively impacting recovery efforts in this region. Our study suggests that mitigating bycatch on the southern New England fishing grounds may benefit recovery efforts for alewife and blueback herring genetic stocks that have experienced the greatest declines in spawning adult abundances.

Quantification of the indirect effects of scallop dredge fisheries on a brown crab fishery

This study aimed to describe the characteristics of the by-catch of Cancer pagurus in king scallop dredges in the Isle of Man, and to determine the damage, immediate mortality and estimated mortality during fishing seasons associated with scallop dredges. Based on dredge surveys, spatial and seasonal variations were observed, with the highest number of crabs found off the west coast of the Isle of Man in the autumn when berried females crabs were most frequently caught. In general, female crabs comprised 84% of the catch. The damage levels of crabs was high with 45% of crabs recorded as crushed or dead or with severe damage, whilst 24% of crabs exhibited missing limbs. Estimates of the potential mortality associated with scallop dredging led to a lower and upper estimate of possible crab by-catch mortality of 15t and 24t respectively which represented 3.0–4.8% of the commercial landings of brown crab for the Isle of Man. Heaviest mortalities of crabs occurred in autumn to the west of the Isle of Man when female berried crabs move offshore into deeper water. The use of a temporary and spatially restricted scallop dredging closure could provide a simple solution to mitigate additional crab mortality in the event that scallop dredging increased beyond current levels in the future.

Selective commercial line fishing and biodiversity conservation co-exist on seamounts in a deepwater marine reserve

Enhanced socio-economic and conservation outcomes for both an existing fishery and a new deep-water marine reserve off eastern Australia were achieved by research that identified additional options for conservation managers. Commercial power hand-line fishing was permitted to continue on productive seamount fishing grounds within the reserve because new information enabled boundaries and zoning proposed in the reserve’s draft Management Plan to be revised and consistent fisheries regulations to be formulated. The draft plan would have removed access to fishing grounds that provide approximately 25% of the annual regional Australian total allowable catch of the premium fishery species, Blue-eye Trevalla (Hyperoglyphe antarctica). Day-time power handline fishing in 280–550m depths on Taupo and Barcoo Seamounts avoided Harrisson’s Dogfish (Centrophorus harrissoni) – the primary species of conservation concern – because the shark is a diel vertical migrator, residing deeper than Blue-eye during the day before ascending to shallower depths at night to feed on micronekton. Harrisson’s Dogfish occurs on several other seamounts where it was previously unrecorded. These results, together with expectation of low mortality of any incidental dogfish bycatch and low impacts on benthic habitats, supported changes to management arrangements which preserve the seamount Blue-eye fishery worth approximately A$1M annually whilst protecting more seamounts and greater areas of benthic habitat in the restricted 200–700m depth range. Research uptake was facilitated by clarifying policy options at a critical stage in the planning process. This required having clearly articulated management objectives that aligned conservation and fishery imperatives, involving knowledgeable fishers in making robust field observations to address specific knowledge gaps and management needs, and identifying the requirements for ongoing fishery monitoring that addresses remaining management uncertainties. This potential to identify win-win outcomes in the Australian marine planning process provides some general signposts for future policy decisions as marine reserve networks are implemented and reviewed, and for scientists wanting to effectively engage in decision-making processes.

Moving from Measuring to Predicting Bycatch Mortality: Predicting the Capture Condition of a Longline-Caught Pelagic Shark

Incidental fisheries capture has been identified as having a major effect on shark populations throughout the world. However, factors that contribute to the mortality of shark bycatch during fisheries capture are not fully understood. Here, we investigated the effects of capture duration, sea surface temperature, and shark total length (snout to the tip of the upper caudal lobe) on the physiology and condition of longline-caught bronze whalers, Carcharhinus brachyurus. Plasma lactate and potassium concentration had a positive linear relationship with capture duration, indicating that this species experiences increasing physiological challenges while on fishing gear. Additionally, we used stereotype logistic regression models to determine variables that could predict the capture condition of sharks (categorized as “healthy”, “sluggish”, or “moribund or dead”). In these models, elevated plasma lactate concentration, plasma potassium concentration, and capture duration increased the likelihood of C. brachyurus being captured in a “sluggish” condition or in a “moribund or dead” condition. After plasma lactate concentration exceeded 27.4 mmol/L, plasma potassium concentration exceeded 8.3 mmol/L, or capture durations exceeded 293 minutes, the majority of captured sharks (>50%) were predicted to be “moribund or dead.” We recommend that a reduction in the amount of time longlines are left fishing (soak time) will reduce immediate and post-release mortality in C. brachyurus bycatch and that our methods could be applied to identify causes of fisheries-induced mortality in future studies. The identification of operational, environmental, and biological variables contributing to poor condition will be necessary to implement conservation strategies that reduce mortality during capture.

Harbour Porpoises, Phocoena phocoena, in the Mediterranean Sea and Adjacent Regions: Biogeographic Relicts of the Last Glacial Period.

The harbour porpoise, Phocoena phocoena, is one of the best studied cetacean species owing to its common distribution along the coastal waters of the Northern Hemisphere. In European waters, strandings are common and bycatch mortalities in commercial fisheries reach alarming numbers. Lethal interactions resulting from human activities together with ongoing environmental changes raise serious concerns about population viability throughout the species' range. These concerns foster the need to fill critical gaps in knowledge of harbour porpoise biology, including population structure, feeding ecology, habitat preference and evolutionary history, that are critical information for planning effective management and conservation efforts. While the species is distributed fairly continuously in the North Atlantic Ocean, it becomes fragmented in the south-eastern part with isolated populations occurring along the Atlantic coasts of the Iberian Peninsula, Northwest Africa and the Black Sea. The latter population is separated from Atlantic populations by the Mediterranean Sea, where the species is almost entirely absent. Understanding the evolutionary history of these populations occurring in marginal habitats holds the potential to reveal fundamental aspects of the species' biology such as the factors determining its distribution, ecological niche, and how past and recent environmental variation have shaped the current population structure. This information can be critical for understanding the future evolution of the species in consideration of ongoing environmental changes. This chapter summarizes the recent advances in our knowledge regarding the populations bordering the Mediterranean Sea with a special emphasis on their ecological and evolutionary history, which has recently been reconstructed from genetic analyses.

Reducing bycatch mortality in crustacean traps: Effect of trap design on platypus and yabby retention rates

The platypus (Ornithorhynchus anatinus) is known to be vulnerable to drowning in enclosed traps used to capture freshwater crayfish such as yabbies (Cherax spp.). To help quantify the degree of risk posed by such traps, we carried out 113 trials in Victorian streams and larger New South Wales rivers to assess the platypus’s ability to escape from standard opera house traps (OH), a second commercially available enclosed trap design (closed-top pyramid traps, CTP), and opera house traps that had been modified by adding an opening in the roof (MOH). All 10 of the animals tested in OH failed to find an exit in the period allowed. In contrast, 82% of subjects tested in CTP (n=45) and 83% of those tested in MOH (n=58) escaped from traps within 2min. Victorian animals took significantly less time to escape from traps (CTP, mean=31s; MOH, 33s) than those tested in New South Wales (CTP, mean=55s; MOH, 53s). In addition, juveniles were less likely than adults to escape from CTP and MOH in a timely manner. The results of trials comparing the number and size of yabbies captured in Victorian farm ponds indicate that MOH should at least equal and potentially exceed the performance of OH when used to harvest yabbies for human consumption.

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

Abstract Manta and devil rays of the subfamily Mobulinae (mobulids) are rarely studied, large, pelagic elasmobranchs, with all eight of well‐evaluated species listed on the IUCN Red List as threatened or near threatened. Mobulids have life history characteristics (matrotrophic reproduction, extremely low fecundity, and delayed age of first reproduction) that make them exceptionally susceptible to overexploitation. Targeted and bycatch mortality from fisheries is a globally important and increasing threat, and targeted fisheries are incentivized by the high value of the global trade in mobulid gill plates. Fisheries bycatch of mobulids is substantial in tuna purse seine fisheries. Thirteen fisheries in 12 countries specifically targeting mobulids, and 30 fisheries in 23 countries with mobulid bycatch were identified. Aside from a few recently enacted national restrictions on capture, there is no comprehensive monitoring, assessment or control of mobulid fisheries or bycatch. Recent listing through the Convention on the International Trade in Endangered Species (CITES) may benefit mobulids of the genus Manta (manta rays), but none of the mobulids in the genus Mobula (devil rays) are protected. The relative economic costs of catch mitigation are minimal, particularly compared with a broad range of other, more complicated, marine conservation issues. Copyright © 2015 John Wiley & Sons, Ltd.

An evaluation of implementing long-term MSY in ecosystem-based fisheries management: Incorporating trophic interaction, bycatch and uncertainty

Maximum sustainable yield (MSY), often defined in relation to a single species considered in isolation, has long been considered a cornerstone in fisheries management. It is difficult to expand the concept of MSY for the purpose of ecosystem-based fisheries management (EBFM). Here we consider MSY for a fishery in a multispecies fish community by addressing issues of trophic interaction and bycatch, along with parameter uncertainty. A size-spectrum model, which fully considers trophic interactions within the fish community, was used for simulating various fisheries scenarios including a single species fishery, a multispecies stow-net fishery, and a multispecies trawl fishery. Population biomasses, yields, and ecological indicators were used to assess the dynamics of the fishery and fish community status. The single species fishery with no bycatch resulted in a low impact on non-target stocks, but led to the collapse of the target stock at low fishing mortality rates. The stow-net and trawl fisheries had broader ecosystem impacts, but allowed target stocks to be fished at much higher fishing mortality rates with higher yields. Ecological indicators were related non-linearly to fishing mortality, possibly diminishing their effectiveness as management tools. Background resource carrying capacity was found to be a greater source of uncertainty than reproductive efficiency. This study demonstrates that bycatch mortality can play an important role in trophic interactions likely via predation release and depensation, and thus influence the resilience of fisheries to fishing pressure. The study indicates that the combination of mixed fisheries and multispecies effects lead to complex fish community dynamics that may present additional challenges for fisheries management.

Mechanisms to explain purse seine bycatch mortality of coho salmon.

Research on fisheries bycatch and discards frequently involves the assessment of reflex impairment, injury, or blood physiology as means of quantifying vitality and predicting post-release mortality, but exceptionally few studies have used all three metrics concurrently. We conducted an experimental purse seine fishery for Pacific salmon in the Juan de Fuca Strait, with a focus on understanding the relationships between different sublethal indicators and whether mortality could be predicted in coho salmon (Oncorhynchus kisutch) bycatch. We monitored mortality using a ~24-h net pen experiment (N = 118) and acoustic telemetry (N = 50), two approaches commonly used to assess bycatch mortality that have rarely been directly compared. Short-term mortality was 21% in the net pen experiment (~24 h) and estimated at 20% for telemetry-tagged fish (~48-96 h). Mortality was predicted by injury and reflex impairment, but only in the net pen experiment. Higher reflex impairment was mirrored by perturbations to plasma ions and lactate, supporting the notion that reflex impairment can be used as a proxy for departure from physiological homeostasis. Reflex impairment also significantly correlated with injury scores, while injury scores were significantly correlated with plasma ion concentrations. The higher time-specific mortality rate in the net pen and the fact that reflexes and injury corresponded with mortality in that experiment, but not in the telemetry-tagged fish released into the wild could be explained partly by confinement stress. While holding experiments offer the potential to provide insights into the underlying causes of mortality, chronic confinement stress can complicate the interpretation of patterns and ultimately affect mortality rates. Collectively, these results help refine our understanding of the different sublethal metrics used to assess bycatch and the mechanisms that can lead to mortality.

Morphometrics, body condition, and growth of the ringed seal (Pusa hispida saimensis) in Lake Saimaa: Implications for conservation

AbstractMorphometrics and growth of the critically endangered Saimaa ringed seal (Pusa hispida saimensis), which inhabits a freshwater lake in Finland were studied using data from 344 carcasses. This study presents the first detailed information on ringed seal pup growth and body condition from birth to the age of one year. Newborn pups were on average 68 cm long and weighed 5 kg. Pups attained the majority of their first year growth during the nursing period. Body condition and growth declined after weaning, but pups recovered from postweaning nutritional deprivation at the age of 8 mo. The seals achieved their maximum body length, girth, and mandible size around the age of 4 yr, and asymptotic body mass two years later. Baculum growth indicated that males reached sexual maturity at age 5–6 yr. The Saimaa ringed seals' asymptotic body length and mass were 132 cm and 59 kg, respectively, which is similar to medium sized marine ringed seals. Saimaa ringed seals' survival to adulthood is extremely low due to high bycatch mortality; furthermore climate change may hamper pup growth and elevate mortality. Therefore we recommend continuation of fishing closures to improve pup survival.

The phylogenetic position of the giant devil ray Mobula mobular (Bonnaterre, 1788) (Myliobatiformes, Myliobatidae) inferred from the mitochondrial genome

The giant devil ray, Mobula mobular, is a member of one of the most distinct groups of cartilaginous fishes, the Mobulidae (manta and devil rays), and is the only mobulid assessed as Endangered due its restricted distribution, high bycatch mortality and suspected population decline. The complete mitochondrial genome is 18 913 base pairs in length and comprises 2 rRNAs, 13 protein-coding genes, 22 tRNAs and 2 non-coding regions. Comparison with the partial mitogenome of M. japanica suggests a sister-cryptic species complex and two different taxonomic units. However, the limited divergence within the species (>99.9% genetic identity) may be the result of a geographically and numerically restricted population of M. mobular within the Mediterranean Sea.

Assessing incidental bycatch of seabirds in Norwegian coastal commercial fisheries: Empirical and methodological lessons

With diminishing seabird populations and little knowledge on incidental bycatch in fisheries in the Northeast Atlantic, this study aimed to screen seabird bycatch in Norwegian coastal fisheries in 2009. The purpose was to 1) quantify magnitude of seabird bycatch rates and estimate total bycatch from the entire fleet by different estimators 2) evaluate data from an access point survey against monitoring data from a reference fleet as methods for collecting data on bycatch mortality of seabirds and 3) give advice on further bycatch studies. The study focused on three small-vessel fisheries (<15 m LOA) outside Northern Norway; the coastal cod (gillnet and manual longline) and lumpfish (gillnet) fisheries and the more offshore Greenland halibut longline fishery. We found no correlation between landed catch and bycatch and upscaling was made based on number of fishing trips. In these fisheries, northern fulmars Fulmarus glacialis outnumbered the other species and constituted almost half of the overall bycatch, totalling about 5500 (mostly on longlines) of the >11 000 birds estimated caught. The black guillemot Cepphus gryllealso stood out as a numerous victim, constituting almost two thirds of the >3000 birds estimated to have drowned in lumpfish gillnets. The two methods were both considered to hold merit and yielded approximately similar estimates of the bycatch in the coastal cod fisheries, however BPUE differs. Further studies are recommended especially on the lumpfish gillnet and Greenland halibut longline fisheries and on temporal and spatial variations in bycatch. More studies are also needed to model effects on seabirds at the population level.

Effects of Climate Change and Fisheries Bycatch on Shy Albatross (Thalassarche cauta) in Southern Australia.

The impacts of climate change on marine species are often compounded by other stressors that make direct attribution and prediction difficult. Shy albatrosses (Thalassarche cauta) breeding on Albatross Island, Tasmania, show an unusually restricted foraging range, allowing easier discrimination between the influence of non-climate stressors (fisheries bycatch) and environmental variation. Local environmental conditions (rainfall, air temperature, and sea-surface height, an indicator of upwelling) during the vulnerable chick-rearing stage, have been correlated with breeding success of shy albatrosses. We use an age-, stage- and sex-structured population model to explore potential relationships between local environmental factors and albatross breeding success while accounting for fisheries bycatch by trawl and longline fisheries. The model uses time-series of observed breeding population counts, breeding success, adult and juvenile survival rates and a bycatch mortality observation for trawl fishing to estimate fisheries catchability, environmental influence, natural mortality rate, density dependence, and productivity. Observed at-sea distributions for adult and juvenile birds were coupled with reported fishing effort to estimate vulnerability to incidental bycatch. The inclusion of rainfall, temperature and sea-surface height as explanatory variables for annual chick mortality rate was statistically significant. Global climate models predict little change in future local average rainfall, however, increases are forecast in both temperatures and upwelling, which are predicted to have detrimental and beneficial effects, respectively, on breeding success. The model shows that mitigation of at least 50% of present bycatch is required to offset losses due to future temperature changes, even if upwelling increases substantially. Our results highlight the benefits of using an integrated modeling approach, which uses available demographic as well as environmental data within a single estimation framework, to provide future predictions. Such predictions inform the development of management options in the face of climate change.

Sex-specific foraging behavior in response to fishing activities in a threatened seabird.

Some seabird species have learnt to efficiently exploit fishing discards from trawling activities. However, a discard ban has been proposed as necessary in Europe to ensure the sustainability of the seas. It is of crucial importance for the management and conservation purposes to study the potential consequences of a discard ban on the foraging ecology of threatened seabirds. We assessed the influence of fishing activities on the feeding habits of 22 male and 15 female Audouin's gulls (Larus audouinii) from the Ebro Delta (Mediterranean Sea) during the breeding period using GPS loggers together with Stable Isotope Analysis (SIA), which provided new insights into their foraging behavior and trophic ecology, respectively. GPS data revealed different sex-specific foraging patterns between workdays and weekends. Females were highly consistent in that they foraged at sea throughout the week even though discarding stops at weekends. In contrast, males switched from foraging at sea during the week (when discards are produced) to an increased use of rice field habitats at weekends (when fishermen do not work). This sex-specific foraging behavior could be related to specific nutritional requirements associated with previous egg production, an energetically demanding period for females. However, on a broader time scale integrated by the SIA, both sexes showed a high degree of individual specialization in their trophic ecology. The need to obtain detailed information on the dependence and response of seabirds to fishing activities is crucial in conservation sciences. In this regard, sex-specific foraging behavior in relation to fisheries has been overlooked, despite the ecological and conservation implications. For instance, this situation may lead to sex differentiation in bycatch mortality in longlines when trawlers do not operate. Moreover, any new fisheries policy will need to be implemented gradually to facilitate the adaptation of a specialized species to a discard ban scenario.

A novel tool to mitigate by-catch mortality of baltic seals in coastal fyke net fishery.

Developing methods to reduce the incidental catch of non-target species is important, as by-catch mortality poses threats especially to large aquatic predators. We examined the effectiveness of a novel device, a “seal sock”, in mitigating the by-catch mortality of seals in coastal fyke net fisheries in the Baltic Sea. The seal sock developed and tested in this study was a cylindrical net attached to the fyke net, allowing the seals access to the surface to breathe while trapped inside fishing gear. The number of dead and live seals caught in fyke nets without a seal sock (years 2008–2010) and with a sock (years 2011–2013) was recorded. The seals caught in fyke nets were mainly juveniles. Of ringed seals (Phoca hispida botnica) both sexes were equally represented, while of grey seals (Halichoerus grypus) the ratio was biased (71%) towards males. All the by-caught seals were dead in the fyke nets without a seal sock, whereas 70% of ringed seals and 11% of grey seals survived when the seal sock was used. The seal sock proved to be effective in reducing the by-catch mortality of ringed seals, but did not perform as well with grey seals.

Facing the river gauntlet: understanding the effects of fisheries capture and water temperature on the physiology of coho salmon.

An improved understanding of bycatch mortality can be achieved by complementing field studies with laboratory experiments that use physiological assessments. This study examined the effects of water temperature and the duration of net entanglement on physiological disturbance and recovery in coho salmon (Oncorhynchus kisutch) after release from a simulated beach seine capture. Heart rate was monitored using implanted electrocardiogram biologgers that allowed fish to swim freely before and after release. A subset of fish was recovered in respirometers to monitor metabolic recovery, and separate groups of fish were sacrificed at different times to assess blood and white muscle biochemistry. One hour after release, fish had elevated lactate in muscle and blood plasma, depleted tissue energy stores, and altered osmoregulatory status, particularly in warmer (15 vs. 10°C) and longer (15 vs. 2 min) capture treatments. A significant effect of entanglement duration on blood and muscle metabolites remained after 4 h. Oxygen consumption rate recovered to baseline within 7–10 h. However, recovery of heart rate to routine levels was longer and more variable, with most fish taking over 10 h, and 33% of fish failing to recover within 24 h. There were no significant treatment effects on either oxygen consumption or heart rate recovery. Our results indicate that fishers should minimize handling time for bycatch and maximize oxygen supply during crowding, especially when temperatures are elevated. Physiological data, such as those presented here, can be used to understand mechanisms that underlie bycatch impairment and mortality, and thus inform best practices that ensure the welfare and conservation of affected species.

Hooking mortality of scalloped hammerhead Sphyrna lewini and great hammerhead Sphyrna mokarran sharks caught on bottom longlines

The scalloped hammerhead Sphyrna lewini and the great hammerhead S. mokarran are typically caught as bycatch in a variety of fisheries and are listed as globally Endangered by the International Union for the Conservation of Nature. Due to very high at-vessel mortality for these species, research is needed on fishing methods to reduce mortality for longline-captured sharks. A series of fishing experiments were conducted employing hook timers and temperature–depth recorders on contracted commercial vessels fishing with bottom-longline gear to assess factors related to mortality. A total of 273 sets were deployed with 54 485 hook timers. Scalloped and great hammerheads had at-vessel mortality rates of 62.9% and 56.0%, respectively. Median hooking times for scalloped and great hammerheads were 3.5 h and 3.4 h, respectively, and 50% mortality was predicted at 3.5 h and 3.8 h. When these data are considered for potential management strategies to reduce the mortality of hammerhead sharks, a limitation on gear soak time would probably improve hammerhead shark survivorship. However, it may prove to be difficult for a fishery to remain economically viable if the soak time is limited to less than the median hooking time for the target species. Additional management options, such as time/area closures, may need to be explored to reduce bycatch mortality of scalloped and great hammerheads.

Controlling stochastic externalities with penalty threats: the case of bycatch

Previous literature has shown that when there is a deterministic relationship between abatement choices and outcomes, policies with penalty threats can be designed to induce polluting firms to undertake efficient abatement measures voluntarily. We develop a game theoretic model to investigate whether a similar policy can be designed and applied to reduce stochastic bycatch. The policy design would involve a penalty threat that would induce fishers to undertake efficient avoidance measures voluntarily to reduce interactions between fishing vessels and bycatch species. Our findings indicate that both individual and group performance standards (a threshold of allowable bycatch mortalities per fishing season) can be designed such that the penalty threat is sufficient in inducing risk-neutral agents to undertake the first-best level of avoidance activity voluntarily. The optimal threshold depends on the degree of variability in the bycatch level and the discount factor. The net impact of environmental uncertainty on the optimal threshold is ambiguous and depends on the underlying distribution of bycatch mortalities, given the efficient level of avoidance measures. The paper identifies and emphasizes the information requirements that arise when environmental policies involving penalty threats are applied to mitigate stochastic externalities by inducement of efficient (voluntary) abatement behavior.

A Comparison of Alternative Circle Hook (Kahle Hook) and J Style Hook Performance in Experimental Pelagic Longline Fishery in Turkey

In recent years, circle hooks have been encouraged as an alternative to traditional J-hooks in pelagic longline fisheries to minimize by-catch mortality and injury to sea turtles and other marine wildlife. Prior to this study, circle hooks had not been used by domestic commercial pelagic longliners in Turkey. The main objective of the study was to evaluate the efficiency of kahle hook comparing with J-style hook baited with sardine (Sardina pilchardus) in pelagic longline fishery in the Aegean coast of Turkey (Kuşadası Bay).We used conventional J-style hooks (Mustad 2315DT-4/0) and kahle hooks (Eagle Claw142A-6/0) for each fishing operation and compared catch rates, catch compositions of target and non-target species. The relative performance of kahle and traditional J-style hooks was tested during 22 valid pelagic longline fishing operations between August 2010 and December 2012. A total of 2200 hooks were used equally amongkahle and J-style hooks consecutively. Captured fish were identified, total and fork lengths were measured,weighed, the time of haulback, and hook type as well as by-catch fish were recorded. A total of 78 fish were caught belonging to 13 species during the samplings. The overall CPUE was 4.73 fishes per 100 hooks for kahle hooks and 2.46 fishes for J-style hooks. For the CPUE of all fishes, the difference was statistically significant (Z = -1.977; P&lt;0.05), in favour of the kahle hook being almost two times greater than the J-style hook. Likewise CPUE was 17007.69 g per 100 hooks for kahle style hooks and 4807.27 g for J-style hooks (Z = -1.997; P&lt;0.05). While no difference was found between two hook models on by-catch species, kahle hooks were more efficient in comparison to J hooks on discard species. Swordfish (Xiphiasgladius) had the highest CPUE (2.82) among all species for kahle hooks followed by silver scabbard fish (Lepidopuscaudatus), 0.64. For J-style hooks, silver scabbard fish catch had the highest CPUE (0.64) followed by swordfish (0.55).