Mortalities due to interactions between loggerhead (Caretta caretta) turtles and commercial bottom trawl fisheries impede the recovery of loggerhead populations worldwide. In the U.S. Mid-Atlantic, several hundred loggerheads interact with commercial bottom trawl gear each year despite the implementation of temporal and spatial conservation measures. In this analysis a Generalized Additive Model (GAM) is developed using fisheries observer data to estimate the magnitude of loggerhead interactions and mortalities in U.S. Mid-Atlantic bottom trawl gear from 2009 to 2013. Based on the results, the potential conservation benefits of hypothetical spatial closures or turtle excluder device (TED) requirements in times and areas of high estimated interactions is then evaluated. Loggerhead interaction rates were modeled as a function of retained catch, depth, latitude, and sea surface temperature. From 2009–2013, a total of 1156 (CV = 0.13, 908–1488) loggerheads were estimated to have interacted with bottom trawl gear in the U.S. Mid-Atlantic, of which 479 resulted in mortality. The total number of estimated interactions was equivalent to 166 adults, of which 68 resulted in mortality. The trawl fishery targeting Atlantic croaker (Micropogonias undulatus) in the southern Mid-Atlantic had the highest turtle interactions among fisheries investigated; this may be due to larger mesh sizes in the mouth of the trawl and high headline height of the gear. The potential conservation benefit of hypothetical spatial closures or TEDs differs depending on the metric used to define “benefit”, and further depends on factors such as the spatial and temporal design of the closure, the magnitude and distribution of effort displacement, the spatial distribution of observed loggerhead life stages, and the assumed survival rate of animals passing through TEDs.
Reports from the fishing industry suggest that seal depredation in Irish bottom-set gillnets and entangling net fisheries has increased substantially in recent years. A dedicated observer program was conducted in a range of such fisheries off the southwest and west coasts of Ireland to provide the first quantitative estimates of seal depredation. Zero inflated negative binomial and Poisson regression models found positive correlations between depredation and factors such as latitude, depth, timing of a haul within a trip and quantities of gear hauled. Soak time was significant in the inshore gillnet fishery for pollack species (Pollachius spp.) but not significant in the deeper more offshore gillnet fishery for hake (Merluccius merluccius). Results suggest that soak times should be kept short in shallow areas while faster hauling speeds, and systems which actively deter seals from the vicinity of Vessels operating in deep water should be explored.
The Nephrops fishery in the Bay of Biscay is an important commercial fishery which generates large amounts of discards owing to the use of small mesh trawls. To reduce discards, French trawlers were equipped with a variety of selective devices, from 2005 onwards. This study examines their efficacy using data from the French on-board observer programme, 2003–2010. Generalized linear models were built for catches, discards, and landings of Nephrops and hake, controlling for the other factors which drive the variability in these variables. A dorsal square-mesh panel meant to let small hake escape did not affect hake catch, but was found to decrease Nephrops catches and discards. Among the devices intended to reduce Nephrops discards, the flexible grid was the most efficient, as it decreased catches and discards in large proportions while increasing landings but this result was supported by a small number of observations; a larger mesh size in the codend (80 mm instead of 70) slightly decreased Nephrops discards; and a ventral square-mesh panel was not found to affect catch or discards of either species. The design of the on-board observer programme was meant to estimate discard amounts, which limited their utilization to investigate factors for discarding.
Due to global declines, skates and sharks have become a focus of marine conservation in recent years. Despite protective measures, they remain vulnerable to bycatch by fisheries, especially bottom-trawls and pose a problem for fisheries management measures that aim to eliminate discards in the future. In the mixed-species bottom-trawl fisheries of the North Atlantic catches can be increased by fitting a length of chain known as a “tickler” in front of the groundgear of the trawl. It was hypothesized that the tickler is especially effective at catching skates and rays that may otherwise escape beneath the net. A trial was undertaken with paired tows with and without the tickler chain. The trial demonstrated that the catch rate of skates and sharks can be significantly lowered by removing the tickler. A set of secondary nets (groundgear bags) attached behind the groundgear of the main net allowed the number of fish escaping under the net to be estimated and showed that the reduction of skates and sharks in the main net was accompanied by an increase in number in the groundgear bags. This suggests that prohibition of the use of tickler chains in areas that are known to be especially important to skates and sharks could have conservation benefits. The removal of the tickler chain had little effect on catch rates of haddock, whiting, and flatfish, but caused a marked decrease in the catch rate of commercially valuable anglerfish.
Denmark was the first nation in Europe to promote the use of Fully Documented Fisheries (FDF) through Remote Electronic Monitoring (REM) and CCTV camera systems, with pilot schemes in place since 2008. In theory, such a scheme could supplement and even potentially replace expensive control and monitoring programmes; and when associated with a catch quota management (CQM) system, incentivize positive changes in fishing patterns in a results-based management approach. New data flows are, however, required to ensure the practical implementation of such a scheme. This paper reviews the quality of the FDF data collected during 2008–2014 and their potential in strengthening information on cod discards. The analyses demonstrate the improved reporting of discards in logbooks and overall discard reductions, but they also show that some uncertainties around the absolute estimates of discard quantities have remained. Regular validation of weight estimation methods and close collaboration between scientific monitoring and control are important to support the use of reported discards as a reliable source of information. We discuss the potential of electronic monitoring in the context of the EU landing obligation.
Conservation concerns and new management policies such as the implementation of ecosystem-based approaches to fisheries management are motivating an increasing need for estimates of mortality associated with commercial fishery discards and released fish from recreational fisheries. Traditional containment studies and emerging techniques using electronic tags on fish released to the wild are producing longitudinal mortality-time data from which discard or release mortalities can be estimated, but where there may also be a need to account analytically for other sources of mortality. In this study, we present theoretical and empirical arguments for a parametric mixture-distribution model for discard mortality data. We show, analytically and using case studies for Atlantic cod (Gadus morhua), American plaice (Hippoglossoides platessoides), and winter skate (Leucoraja ocellata), how this model can easily be generalized to incorporate different characteristics of discard mortality data such as distinct capture, post-release and natural mortalities, and delayed mortality onset. In simulations over a range of conditions, the model provided reliable parameter estimates for cases involving both discard and natural mortality. These results support this modelling approach, indicating that it is well suited for data from studies in which fish are released to their natural environment. The model was found to be less reliable in simulations when there was a delay in discard mortality onset, though such an effect appears only in a minority of existing discard mortality studies. Overall, the model provides a flexible framework in which to analyse discard mortality data and to produce reliable scientific advice on discard mortality rates and possibilities for mitigation.
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.
Regulations to reduce bycatch of non-marketed marine species often impose gear restrictions, reductions in harvest of the target species, and/or spatial and temporal closures of the fishing ground. These regulations can exact significant social costs in commercial fisheries. We evaluate performance of a cap-and-trade bycatch management policy. Harvest of a target fish species, costly avoidance of the bycatch species, and harvesting efficiency are examined in a stochastic production environment with and without at-sea observability of bycatch, and with and without trade in harvest quotas and bycatch caps. Our results suggest that precise implementation of a socially optimal management plan is possible only if bycatch is observable and trade in fish quotas and bycatch cap is frictionless. Conditions exist in which quota/permit trading raises bycatch relative to a no-trade environment. The results offer useful guidance for designing cap-and-trade bycatch management programs.
Population declines of Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus prompted initial fisheries closures and an eventual endangered or threatened species listing across the U.S. portion of their range in 2012. Atlantic Sturgeon aggregations and migration routes along the coast of Long Island overlap with commercial fishing activities that may lead to incidental take in nondirected fisheries. Thus, understanding the distribution and movement of Atlantic Sturgeon in relation to commercial fisheries can help management agencies determine impacts and develop bycatch mitigation measures. Stratified random sampling and targeted bottom trawl surveys were used to identify the temporal and spatial use of marine habitat in New York waters. The majority of survey captures were restricted to depths of less than 15 m and known aggregation areas. During the aggregation periods (May, June, September, and October) in known aggregation areas, catches were an order of magnitude higher than in other areas and months of the year. Northeast Fisheries Observer Program bycatch data from 1989 to 2013 was analyzed for the New York region and suggested that bycatch occurs within two main gear types: otter bottom trawls and sink gill nets. Trawling bycatch contained primarily subadult Atlantic Sturgeon and is highest during the Summer Flounder Paralichthys dentatus fishery in New York State waters. Trawling overlaps spatially and temporally with identified Atlantic Sturgeon aggregation areas, while bycatch in gill nets targeted adult fish farther offshore in federal waters. Bycatch in these fisheries may be a regional threat to recovery, and spatial and temporal closures, gear modifications, or other bycatch reduction techniques are suggested to protect aggregating and migrating fish.
Odontocete bycatch on and depredation from tropical pelagic longlines is globally widespread, having negative impacts on the economic viability of affected fisheries and on the conservation of affected odontocete populations. Reports by fishers that depredating odontocetes avoid gear tangles has underpinned the development of simulated structures to physically deter depredating odontocetes. This study assessed the efficacy of two such devices developed to mitigate odontocete depredation and associated bycatch. Of particular interest was their impact on (i) soak depth and (ii) sink rate using truncated trials, before determining their impact under full operational conditions on rates of (iii) catch of the five most economically important fish, and (iv) odontocete depredation and bycatch, on changes in (v) fish survival and size, and (vi) setting and hauling speed. The results indicated that the inclusion of devices on longlines had negligible impact on soak depth, thus were unlikely to impact on the suite of fish specifically targeted and caught. The sink rate was slowed, perhaps by drag, trapped air, or propeller wash, although the addition of weight might remedy this if the devices were to be used in areas where seabird bycatch could occur. Most importantly, trials conducted in Australian and in Fijian waters indicated that pooled fish catch rates (i.e. albacore, yellowfin, bigeye, mahi mahi, and wahoo) increased in the presence of the devices, possibly because more fish were attracted by them or because more depredators were deterred. Catch rates on control gear next to gear with devices attached were higher than more distant control gear, suggesting the influences of the devices may have extended to adjacent branchlines. The size of caught fish was mostly unaffected, although the survival of yellowfin and bigeye increased significantly in the presence of the devices. Hauling was slowed by the use of the devices and the need for an extra crewmember during setting and hauling, which could be cost prohibitive in some fisheries, especially if economic benefits from their use are not obvious. Despite the small sample size, odontocete bycatch only occurred on unprotected fishing gear and all individuals were released alive, although their fate was uncertain; there was evidence of injuries sustained from the event. The outcomes are positive and should motivate stakeholders to view such devices as a potentially effective tool for mitigating odontocete bycatch and depredation in this and similar longline fisheries. Future efforts should focus on improving operational integration and reducing implementation costs to encourage voluntary uptake and thus avoid non-compliance and the need for costly monitoring. The use of this technology could bring about marked improvements to the conservation situation for affected odontocete populations and to the economic situation for affected longline fisheries.