Bycatch Species Research Articles

Reproductive biology of the southern pufferfish, Sphoeroides nephelus (Actinopterygii: Tetraodontiformes: Tetraodontidae), in the northern coast off the Yucatan Peninsula, Mexico

Background. Overexploitation of fishery resources has led to the capture of alternative species of a lower trophic level, considered previously unprofitable or unfit for human consumption. The southern pufferfish, Sphoeroides nephelus (Goode et Bean, 1882), is a bycatch species of the recreational fishery in the USA and Mexico. Unlike other species of the genus Sphoeroides, there is no background on their reproductive cycle. Therefore, this study aimed to describe several reproductive traits (sex ratio, gonadal development, annual reproductive cycle, and fecundity) of specimens from the northern coast of the Yucatan Peninsula, Mexico. This kind of information might serve as a point of reference for its potential use either in the pharmaceutical industry, aquarium trade, as well as in aquaculture. Materials and methods. The reproductive biology of the southern pufferfish was described based on 189 females and 223 males, caught off the northern coast off the Yucatan, Mexico, during an annual cycle. Several reproductive traits, such as the annual cycle of gonad development, sex ratio, and the batch fecundity were determined. Results. The sex ratio showed no significant difference from 1 ÷ 1 ratio. Male’s reproductive season lasted from August to May, although females were spawning from August to April. The size at 50% maturity was estimated at 14.93 cm TL for females. Batch fecundity ranged between 59 087 and 367 022 oocytes (mean 176 456) per spawning batch, and it was significantly fitted to both female size and weight based on power and linear regression models, respectively. The relative batch fecundity was estimated at 828 ± 182 oocytes per gram of eviscerated weight, and 11 989 ± 4774 oocytes per gram of gonad weight. Conclusion. It was determined that S. nephelus exhibited 1 ÷ 1 sex ratio, an asynchronous development of oocytes and indeterminate fecundity with batch spawning. The species has a protracted reproductive season that lasted almost all year round with peaks in February–March (before of the dry season) and a brief inactive period in June–July (before of the wet season). This latter information should be helpful to obtain a broodstock that would be the base to produce fingerlings to be raised, instead of collecting individuals from the wild.

Using individual-based movement information to identify spatial conservation priorities for mobile species.

The optimal design of reserve networks and fisheries closures depends on species occurrence information and knowledge of how anthropogenic impacts interact with the species concerned. However, challenges in surveying mobile and cryptic species over adequate spatial and temporal scales can mask the importance of particular habitats, leading to uncertainty about which areas to protect to optimize conservation efforts. We investigated how telemetry-derived locations can help guide the scale and timing of fisheries closures with the aim of reducing threatened species bycatch. Forty juvenile speartooth sharks (Glyphis glyphis) were monitored over 22 months with implanted acoustic transmitters and an array of hydrophone receivers. Using the decision-support tool Marxan, we formulated a permanent fisheries closure that prioritized areas used more frequently by tagged sharks and considered areas perceived as having high value to fisheries. To explore how the size of the permanent closure compared with an alternative set of time-area closures (i.e., where different areas were closed to fishing at different times of year), we used a cluster analysis to group months that had similar arrangements of selected planning units (informed by shark movements during that month) into 2 time-area closures. Sharks were consistent in their timing and direction of migratory movements, but the number of tagged sharks made a big difference in the placement of the permanent closure; 30 individuals were needed to capture behavioral heterogeneity. The dry-season (May-January) and wet-season (February-April) time-area closures opened 20% and 25% more planning units to fishing, respectively, compared with the permanent closure with boundaries fixed in space and time. Our results show that telemetry has the potential to inform and improve spatial management of mobile species and that the temporal component of tracking data can be incorporated into prioritizations to reduce possible impacts of spatial closures on established fisheries.

Preliminary report on bycatch fish species collected from the Tokyo Submarine Canyon, Japan.

An ichthyofaunal list of bycatch species was compiled, the fish captured by bottom gill-nets set at approximately 300 m depth in the Uraga Suido Channel central Japan. Fragmentary ichthyofaunal lists are available for this area; these lists have focused on chondrichthyans or commercial actinopterygians, but voucher specimens have not been prepared for museum storage. An initial list of the fish fauna was compiled with vouchers, and seven species not previously recorded from the channel are reported. Most of these species belong to the Class Actinopterygii; Apristurusplatyrhynchus (Tanaka, 1909), Beryxdecadactylus Cuvier, 1829, Hoplostethusjaponicus Hilgendorf, 1879, Sebastesiracundus (Jordan & Starks, 1904), Scalicusamiscus (Jordan & Starks, 1904), Atrobuccanibe (Jordan & Thompson, 1911), and an unidentified species of the eelpout family Zoarcidae. The taxonomic identity of the eelpout and the biogeography of the Uraga Suido Channel are considered. Further research is required to resolve outstanding faunistic issues, but live collections will likely end when the aging fishers who provide the specimens retire. At that point, existing museum collections will become increasingly important for future research. Examination of a collection that may have been previously deposited in the Chiba Prefectural Museum will be essential.

Recreational and small-scale fisheries may pose a threat to vulnerable species in coastal and offshore waters of the western Mediterranean

AbstractThis study evaluates the fishing pressure exerted by the most common recreational and professional, small-scale fishing practices on vulnerable target and bycatch species in coastal and offshore waters of the western Mediterranean. By combining multiple data sources, we assembled a unique dataset on catches at multiple sites in these areas by recreational (RF) and small-scale fisheries (SSF), covering the period from 1997 to 2015. Furthermore, a framework with which to identify the vulnerable species among all the species caught is provided; it is based on the IUCN Red List, international conventions for the protection of flora and fauna, the Habitats Directive and the intrinsic vulnerability index of marine fish. Overall, about a quarter of exploited species targeted by SSF and RF in coastal waters were vulnerable, making up nearly 50% of the total SSF catch and nearly 20% of the total recreational catch. In offshore waters, 100% of the RF and SSF catch was made up of vulnerable species. Among the species caught as bycatch in both areas by SSF and RF, there was a total of 27 vulnerable vertebrate species, which included birds, cetaceans, elasmobranchs and sea turtles. Our results highlight the need to differentiate between different fishing methods or gears when studying the fishing impacts on vulnerable species. The results also indicate that, although RF and SSF are often considered to have a relatively low ecological impact, a range of different fishing methods are affecting vulnerable species in coastal or offshore waters in the western Mediterranean Sea, be they targeted or taken unintentionally as bycatch.

Measuring the Welfare Impact of Soft-Catch Leg-Hold Trapping for Feral Cats on Non-Target By-Catch.

Simple SummaryFeral cats are linked to fauna extinctions and declines globally through predation, disease transmission, and hybridisation. Soft-catch leg-hold trapping, with or without olfactory lures, is used to capture feral cats; however, by-catch may occur, including species of conservation concern. Using data from 431 non-target animals trapped at six Western Australian sites over 18 years, we demonstrate that birds are at greatest risk of serious injury. Appropriate placement of traps, careful choice of lures depending on the non-target species known to be in the study area, adjustment of traps to minimize the chance of closing on small animals, and training of all personnel associated with trapping will minimize the risk to birds and other non-target fauna.To inform trapping protocols to reduce by-catch while trapping feral cats by-catch welfare costs should be quantified. During cat trapping programs at six Western Australian sites from 1997–2015, 431 non-target individuals, including 232 individuals from native species (132 mammals, 52 birds and 42 reptiles) were captured. Among the native fauna; birds were more likely to be severely injured (33%, compared to 12% in mammals and 21% in reptiles). Amongst other vertebrates, larger individuals were less likely to be injured. Olfactory lures used in these studies attracted reptiles, but repelled mammals. By-catch varied with climate and landscape. Trap injury to by-catch species poses ethical concerns, especially for threatened species that can least afford an additional threat. Future trapping should consider the timing of trapping, trap placement, trap settings (especially the treadle pressure needed to close the trap) and new innovations sending immediate capture alerts to minimise by-catch and potential injury associated with prolonged restraint. By-catch welfare data should be analysed to identify best practice and on-going improvement.

An innovative fishing gear to enhance the release of non-target species in coastal shark-control programs: The SMART (shark management alert in real-time) drumline

In response to a spate of shark attacks in Reunion Island in the southwest Indian Ocean since 2011, local authorities developed an experimental shark-control program based on those conducted for decades in Australia and South Africa. In order to greatly reduce, if not eliminate, the impact of such a shark fishing program on bycatch and undersized target shark species, the use of conventional “drumlines” was improved by the addition of an innovative “Catch-A-Live”® system, making the drumlines ‘SMART’ (Shark Management Alert in Real Time). This is a real-time strike alert system based on an adapted triggering mechanism, which links the fishing line to a GPS buoy connected to the Iridium satellite. This system alerts fishers on duty via a computer-based communication system within just a few minutes, enabling immediate intervention. Off Reunion Island, up to 20 SMART drumlines (SDLs) were deployed along the west and southwest coast in coastal waters to target bull (Carcharhinus leucas) and tiger sharks (Galeocerdo cuvier) in trials conducted between 2014 and 2017. During 58,770 h of fishing there were 269 catches of more than 14 species, of which 86.9% were retrieved alive. There were marked differences in survival among species. While the most fragile species were the giant trevally (Caranx ignobilis), scalloped hammerhead sharks (Sphyrna lewini) and small carcharhinid species, most of the other bycatch species (stingrays Dasyatis sp., giant guitarfish Rhyncobathus djiddensis, and tawny nurse sharks Nebrius ferrugineus) were generally found alive and in a condition suitable for tag and release. Of the target species, 94.8% of all individuals were found alive. These survival rates are far higher than those of other programs using conventional drumlines in KwaZulu-Natal (South Africa) and Queensland (Australia). There were strong diurnal and lunar catch patterns. This information is invaluable in planning fishing operations to maximise the catch of the target species, while reducing the chances of killing the bycatch. These results highlight the potential for use of SDLs in research programs aimed at tagging large sharks capable of tripping the trigger, especially in situations where catch rates are so low that it is impractical for the fishing vessel to remain at sea for the duration of each fishing operation.

Estimating blue marlin (Makaira nigricans) sustainable yield in the Indian Ocean using a data-poor approach

Blue marlin (Makaira nigricans) is a common bycatch species in the global tuna longline fishery. In this study, we applied a common data-poor approach, i.e., depletion-corrected average catch (DCAC) to assess stock status of the Indian Ocean blue marlin. Sustainable yield (Ysust), one reference point in this case, was estimated, and its uncertainty was integrated by using Monte Carlo simulation. The results revealed the estimate of Ysust by DCAC was lower than MSY of 11,926 t by BSP-SS and is also lower than the provisional reference point of 11,704 t by the management proposal. DCAC is reliable for blue marlin in driving precautionary management quantity based on the CPUE of Japan (1980–2015). This study also implies that DCAC could be applied to other billfish stocks and uncertainty be estimated for sustainable yield. However, data-poor methods could be adjusted with precautionary approaches.

Changes in logbook reporting by commercial fishers following the implementation of electronic monitoring in Australian Commonwealth fisheries

Technological advancement has allowed for consideration of electronic monitoring (EM) as a tool for improving the accuracy of logbook data and/or increasing the quantity of fishery-dependent data collected. In Australia, an integrated EM system was implemented in several managed fisheries, including the Eastern Tuna and Billfish Fishery (ETBF) and the Gillnet Hook and Trap (GHAT) sector of the Southern and Eastern Scalefish and Shark Fishery (SESSF) from 1 July 2015. We compare logbook data from the first two years of EM operation to the previous six years, to measure changes in reported nominal catch and discard per unit effort (CPUE and DPUE) and interactions with protected species per-unit-effort (IPUE). We observed no significant increase in CPUE between non-EM (2009–2014) and EM (2015 and 2016) years for any species group in both the ETBF and GHAT. In contrast, DPUE increased significantly during the EM years for target, byproduct and bycatch species in the ETBF and for target species in the GHAT sector. There was a significant increase in the IPUE for seabirds, marine mammals and turtles in the ETBF and for dolphins and pinnipeds in the GHAT sector. While not discounting possible environmentally-driven shifts in availability and abundance, as well as individual vessel effects, the weight of evidence suggests the use of an integrated EM system has led to significant changes in logbook reporting of discarded catch and protected species interactions, particularly in the ETBF. Assuming this supposition is valid, we identify fishery-specific factors that might have influenced reporting behaviour.

A data-limited method for assessing cumulative fishing risk on bycatch

Abstract To assess fishing effects on data-poor species, impact can be derived from spatial overlap between species distribution and fishing effort and gear catchability. Here, we enhance the existing sustainability assessment for fishing effect method by estimating gear efficiency and heterogeneous density from sporadic catch data. We apply the method to two chondrichthyan bycatch species, Bight Skate and Draughtboard Shark in Australia, to assess cumulative fishing mortality (Fcum) from multiple fisheries. Gear efficiency is estimated from a Bayesian mixture distribution model and fish density is predicted by a generalized additive model. These results, combined with actual fishing effort, allow estimation of fishing mortality in each sector and subsequently, the Fcum. Risk is quantified by comparing Fcum with reference points based on life history parameters. When only the point estimates were considered, our result indicates that for the period 2009 and 2010 Bight Skate caught in 14 fisheries was at high cumulative risk (Fcum ≥ Flim) while Draughtboard Shark caught by 19 fisheries was at low cumulative risk (Fcum ≤ Fmsy). Because of the high cost of conducting cumulative risk assessments, we recommend examining the distribution of fishing effort across fisheries before carrying out the assessments.

Short-term movement of a night shark (Carcharhinus signatus) in the western Caribbean with notes on the species’ distribution and threats in the region

Night sharks Carcharhinus signatus have suffered large declines in the western Atlantic Ocean, and while fishing mortality has slowed and populations stabilized in the northwestern Atlantic, they are still captured in high numbers as a targeted and bycatch species in the southern Atlantic Ocean. Considered one of the top five most vulnerable stocks in the Atlantic pelagic longline fishery, few records exist for this large-bodied species in the western Caribbean, and nothing is known about their movements or migration in the region. We found that mature night sharks occur in the western Caribbean from March through November and juveniles contribute to artisanal fisheries in the Guatemalan Caribbean. A seasonal aggregation of night sharks occurs at Glover’s Reef Atoll, Belize, in the summer months, possibly for mating purposes, making this a potentially important site for the species. We also document the first recapture of a tagged night shark in the western Caribbean, a subadult male that was tagged in northern Belize and recaptured after c. 60 days off Havana, Cuba. This recapture suggests that individuals undergo large scale movements, and coupled with known threats from fisheries, a regional approach for this species’ management is favored.

ICHTHYOFAUNA BYCATCH OF THE ARTISANAL FISHERY OF PENAEID SHRIMPS IN PERNAMBUCO, NORTHEASTERN BRAZIL

The shrimp trawl fisheries are highly efficient in capturing target species but is an unselective gear that commonly catches untargeted organisms, which are usually discarded due to their small size or no commercial value. To understand and, eventually, mitigate the impacts of trawling on bycatch species, the whole capture should be addressed. The present study has the objective of determining the seasonal importance of the fish bycatch within shrimp trawling fishery in south Pernambuco, Sirinhaém. It also quantifies the importance of each fish caught within this fishery. Samples were collected monthly, between August 2011 and July 2012. Fish bycatch was described as % in number (%N) and weight (%W), while the seasonal abundance of the shrimp and fish bycatch was assessed based on the monthly catch rate given as the Capture Per Unit of Area (CPUA) in weight (CPUAb) and in number of individuals (CPUAn). Considering the fish bycatch, a total of 608 kg of organisms were sampled: 9,723 fish specimens from 17 families, 38 genera and 51 species. The largest CPUAb value of bycatch was observed in the months of June (488 kg.km-2), February (285 kg.km-2) and April (276 kg.km-2). The proportion target species: bycatch in weight was of 1:0.39. A clear annual cyclic pattern of the species composition of the bycatch based both CPUAn and CPUEb could be observed, following the rainfall patterns, possibly related to a higher productivity associated to river runoffs. Impacts on bycatch have been extensively reported in Brazil and around the world, with most of this bycatch being a relevant additional food source for the local community. However, basic information on bycatch from small-scale fisheries is still missing in many areas, making it difficult to identify and evaluate the management recommendations needed to sustain the resources and ecosystems.

Caught out! Scientists discover a cryptic stress response in a bycatch species.

Caught out! Scientists discover a cryptic stress response in a bycatch species.

North Atlantic Oscillation affects dolphinfish as target and bycatch species in fisheries from the western Mediterranean Sea

North Atlantic Oscillation affects dolphinfish as target and bycatch species in fisheries from the western Mediterranean Sea

Spatiotemporal bycatch analysis of the Atlantic halibut (Hippoglossus hippoglossus) longline fishery survey indicates hotspots for species of conservation concern

The Atlantic halibut (Hippoglossus hippoglossus) longline fishery is the second most valuable groundfish fishery in Atlantic Canada and received Marine Stewardship Council certification in 2013. The bottom longline fishery accounts for most halibut landings but incidentally catches nontargeted species (bycatch). Since 1998, Fisheries and Oceans Canada and the halibut fishing industry performed annual longline surveys across the Scotian Shelf and Southern Grand Banks stock management area to monitor halibut abundance, and at‐sea observers also recorded bycatch information. We examined the species composition and proportion of the survey bycatch and analyzed temporal and spatial trends in standardized weight of (a) halibut catch, (b) total bycatch, and (c) bycatch of species of conservation concern. From 1998 to 2016, 70% of the total catch by weight and 85% by number of individuals were bycatch. Over 100 identified species of finfish, sharks, skates, benthic invertebrates, marine mammals, and seabirds were caught as bycatch in the survey. This included four species listed under the Species at Risk Act (Northern wolffish, Anarhichas denticulatus; spotted wolffish, A. minor; Atlantic wolffish, A. lupus; Atlantic cod, Gadus morhua), and another 14 species awaiting a listing decision based on assessments by the Committee on the Status of Endangered Wildlife in Canada. Generally, the standardized weight of halibut and barndoor skate (Dipturus laevis) increased over time, while Atlantic cod, spiny dogfish (Squalus acanthias), white hake (Urophycis tenuis), and thorny skate (Amblyraja radiata) decreased. Spatial patterns indicated high bycatch levels on the southern Scotian Shelf and southern edge of the Southern Grand Banks, with hotspots for certain species of conservation concern. Our results identify temporal trends in threatened species and areas where they are susceptible to the Atlantic halibut longline fishery which can inform recovery strategies, bycatch levels and spatial zoning in fisheries management and marine conservation.

Reproductive biology of thin sharpbelly, Toxabramis swinhonis Günther, 1873 in a shallow lake (Biandantang Lake) along the middle reach of the Yangtze River basin (China): implications for fisheries management

The reproductive biology of Toxabramis swinhonis, one of the most abundant bycatch species in freshwater fishery in China, was first reported based on 783 specimens collected in Biandantang Lake, central China from October 2016 to September 2017. The overall sex ratio (female/male) was 1.03:1, not significantly different from the expected value 1:1. Nevertheless, sex ratio varied with seasons: 1.32:1 in the early stage of the spawning season (March–April), while 0.46:1 in the later stage (July–August). The monthly succession of the average gonadosomatic index (GSI) and percentages of mature individuals co-indicated that T. swinhonis was a spring-summer (March–August) spawner. Further, the bimodal distribution of the size of eggs from one gravid ovary and histological analysis of mature gonads suggested that T. swinhonis was a multiple spawner with indeterminate fecundity and high degree of spawning asynchronicity. The sizes and ages at first maturity for females and males were 84.47 and 81.86 mm, and 1.62 and 1.56 yr, respectively. The batch fecundity (FB) of this species varied in a wide range from 2006 to 73592 eggs per fish with a mean value of 26487.15 ± 2675.61 (S.E.) eggs and increased with the increasing of the gonad weight (WG), eviscerated weight (WE), total length (LT) and age (A). Overall, T. swinhonis in Biandantang (BDT) Lake is characterized by high fecundity and prolonged spawning season, resulting in easy population explosion. Thus, to remove T. swinhonis moderately or release predator fish discreetly to control its population is proposed considering its reproductive characteristics.

Spatial and temporal distribution of mobulid ray species in the eastern Pacific Ocean ascertained from observer data from the tropical tuna purse-seine fishery

This research focuses on the description of the spatial and temporal distributions of mobulid ray species (Mobula birostris, Mobula mobular, Mobula thurstoni, Mobula tarapacana and Mobula munkiana) using data from the observer program (1993–2014) of the Inter-American Tropical Tuna Commission (IATTC). The tuna purse seine operations in the region extend from 70 to 150°W to 20°S-30°N. Significant differences on the captures per sets between fishing modes and species were found. Results showed that the most common species taken are M. thurstoni, M. mobular and M. birostris in School sets (sets on unassociated tuna schools). The temporal distributions showed high variability of the catches by species and years. The spatial distribution showed several areas of importance depending of the type of fishing, such as the coast of Peru, Galagapos or the Costa Rica Dome, and possible relationships with some oceanographic processes of the eastern Pacific Ocean (i.e. coastal and seasonal upwelling systems). The frequency of the captures per set showed that, although the greatest numbers caught in a set were very low (around 53.7% of sets with one capture), in some areas and periods there were captures of aggregates of hundreds of individuals of some of these species, such as Galapagos Islands during December, Costa Rica Dome during August, or Baja California during June. These events are of biological interest, and may offer good opportunities for conservation. This project has been developed with the aim of identifying the most important areas for these bycatch species and thus, improving the knowledge on them to reduce their mortality.

Modelling the effects of more selective trawl nets on the productivity of European hake (Merluccius merluccius) and deep-water rose shrimp (Parapenaeus longirostris) stocks in the Strait of Sicily

Single-species Gadget models were used to assess the effects of using a sorting grid mounted on the traditional trawl net used by Sicilian trawlers to exploit the deep-water rose shrimp in the Strait of Sicily. The main commercial by-catch species of this fleet is the European hake (Merluccius merluccius), often caught at sizes well below the minimum conservation reference size. Selectivity curves based on the results of an experimental survey carried out in the area using a commercial trawler equipped with an ad hoc-designed sorting grid were incorporated into single-species Gadget models to forecast the effects of changing fishery selectivity on the performance of the two stocks in terms of catch and biomass. The models included catch data from the Italian, Tunisian and Maltese fleets as well as MEDITS trawl survey data for the period 2002-2016. Several scenarios were defined to simulate the effect of the Italian trawlers’ adopting the sorting grid under different stock-recruitment assumptions. The results obtained, when compared with status quo simulations of fishing without a sorting grid mounted on the trawl net, indicated a beneficial effect for both stocks in terms of an increase in biomass and for the fleets in terms of the amount and size composition of annual landings.

Catch and release patterns for target and bycatch species in the Northeast Atlantic deep-water shrimp fishery: Effect of using a sieve panel and a Nordmøre grid.

The Nordmøre grid and the sieve panel are two of the main devices used to reduce fish bycatch in trawl fisheries targeting shrimp species. However, even when using such devices, some small-sized fish enter the codend of the trawl together with the targeted shrimp. Therefore, bycatch reduction remains a problem in some shrimp fisheries. One such fishery is the Northeast Atlantic deep-water shrimp (Pandalus borealis) fishery where it is mandatory to use a Nordmøre grid. In this study, the bycatch reduction efficiencies and patterns for several fish species using the standard Nordmøre grid and an experimental sieve panel were investigated and compared. The effect of combining these devices was also explored. The bycatch reduction patterns differed significantly between the two devices and a more efficient bycatch reduction was obtained by combining them. However, while the loss of commercial-sized shrimp was only between 0 and 2% for the Nordmøre grid, it was between 37 and 56% for the tested sieve panel, making this completely unacceptable for commercial fishing. Therefore, before a sieve panel can be considered as an option for the fishery, other sieve panel designs that have a significantly lower loss of shrimp catches need to be identified.

By-catch species susceptibilities and potential for survival in Algarve (southern Portugal) deep-water crustacean trawl fishery

Bottom trawling for crustaceans in Portuguese coastal waters is an important fishery in terms of revenue, despite its negative impacts on deep-sea ecosystems. This fishery catches large amounts of unwanted species that were discarded for various reasons before the introduction of the Landing Obligation, which banned the discarding of regulated species. However, where it can be demonstrated that a species has an acceptably high likelihood of survival, exemptions to this ban may be granted. In this study, time-to-mortality was used to estimate immediate mortality rates and identify important biological characteristics determining the susceptibility of 14 by-catch species, most with commercial interest (Conger conger, Galeus melastomus, Helicolenus dactylopterus, Lepidorhombus boscii, Lophius budegassa, Lophius piscatorius, Merluccius merluccius, Micromesistius poutassou, Mullus surmuletus, Phycis blennoides, Scyliorhinus canicula, Trigla lyra, Trachurus trachurus and Trachurus picturatus). Species with potential to survive after the discarding process were identified and a short-term survival assessment of conger eel (Conger conger) was performed. The results suggest that species with scales, gas bladder and high metabolic rates have higher post-discard mortality. Size was a critical factor determining survival in some species, with smaller individuals dying faster. The short-term survival rate of conger eel was determined to be 84% (95% CI: 75.5 to 93.3%). The methodology and results from this study can help identify species that may survive the discarding process and factors influencing their survival.

Bycatch and discard survival rate in a small-scale bivalve dredge fishery along the Algarve coast (southern Portugal)

Although the bivalve dredge used on the Algarve coast (southern Portugal) is highly selective for the target species, in some periods of the year the bycatch can exceed the catch of the commercial species. The present study aimed to quantify the bycatch and discards, estimate damage and mortality, and propose management measures to minimize discards and mortality. A total of 15 fishing surveys (60 tows) were performed using two types of dredges (“DDredge” targeting Donax trunculus and “SDredge” targeting Spisula solida and Chamelea gallina). Of the 85257 individuals (392.4 kg) of 52 taxa that were caught, 73.4% belonged to the target species, 22.1% to commercially undersized target species and 4.5% to bycatch species. Bycatch rates were lower for SDredge (13.5% in number and 6.3% in weight) than for DDredge (46.0% in number and 32.9% in weight). Damage and mortality rates were also lower using SDredge (1.3% and 1.0% of the total catches, respectively) than using DDredge (4.0% and 2.8% of the total catches). Survival experiments revealed the diverse vulnerability of the taxa and confirmed the influence of the damage score on the mortality rate. The results gathered in the present study encourage the adoption of a bycatch reduction device to reduce both direct and indirect mortality.