Bycatch Species Research Articles

Effect of ground gear modification on bycatch of rays in mediterranean bottom trawl fishery

Bycatch of rays and skates in towed fishing gears represents one of the major threats to these relatively slow-growing marine species. The objective of this study was to modify ground gear in a bottom trawl fishery to increase the escape of these species during towing without associated loss of target catch. Sea trials were carried out with a research vessel in Mersin Bay, North-eastern Mediterranean. Experimental ground gear was modified by cutting the rigging twine between the fishing line and the footrope in the central part of the ground gear. Capture of three unwanted bycatch species were estimated. The probability of capture of guitarfish (Rhinobatos sp.) and common stingray (Dasyatis pastinaca) was significantly reduced to 8% and 20% for guitarfish and stingray, respectively compared to standard ground gear. The results for spiny butterfly ray (Gymnura altavela) were inconclusive due to the wide confidence intervals. Further, the catch comparison results for five out of six target species investigated did not show significant reduction in catch efficiency when using experimental gear compared to the standard trawl. Only for common sole (Solea solea) the modified trawl had significantly lower catch efficiency than the standard trawl. We believe that this technical measure for reducing unwanted bycatch in bottom trawls has a potential to be adopted by the fishery due to being an efficient, low-cost measure which does not create additional challenges during handling of the gear.

Data‐limited approach to the management and conservation of the pelagic thresher shark in the Northwest Pacific

AbstractThe pelagic thresher shark is among the most heavily exploited shark species in the commercial fisheries of the tropical Indo‐Pacific oceans. Despite this severe exploitation, little is known about pelagic thresher population dynamics, particularly the species' life history traits, and overall stock status. The pelagic thresher exhibits slow growth and extremely low fecundity, indicating the need for reassessment of the population status of this globally threatened shark. Because information on catch and effort of this bycatch species is scarce, several data‐limited methods—quantitative demographic methods, per‐recruit analysis, and risk assessment—were employed in this study to provide an accurate measurement of the status of pelagic thresher shark stocks. For each sex, the composite risk assessments indicated that the probability of the current fishing mortality increasing beyond any level of yield‐per‐recruit (YPR) was approximately zero given the biological reference points (BRPs). Moreover, the current spawning potential ratio (SPR) was found to be significantly below the target reference point of SPR60%, but slightly above the limit reference point of SPR40%. However, because SPR‐based BRPs are much less sensitive to input parameter uncertainties than YPR‐based BRPs, results derived from the SPR model are more suitable for species management. Management strategy simulations based on demographic two‐sex models indicated that without mortality from fishing, female pelagic threshers have a higher population growth rate than males. However, the stock status of female pelagic thresher shark is poorer than that of males under current conditions. The findings suggest that sex‐specific management decisions must be made to achieve the sustainable utilization of this species. Overall, both the sex‐specific per‐recruit and demographic models determined that recruitment overfishing has occurred in the female pelagic thresher population of the Northwest Pacific Ocean, indicating that close monitoring of female sharks is urgent and necessary to ensure that stocks remain sustainable.

Stock Assessment of Four Dominant Shark Bycatch Species in Bottom Trawl Fisheries in the Northern South China Sea

Sharks occupy an important ecological niche in marine ecosystems. As top predators, they can restrict and control the behavior, numbers and composition of other species through downward effects, and play an essential role in ecosystem stability. Shark fishery data are limited, and for most Chondrichthyes species there is no formal fishery resource assessment at a global level. In this study, we applied the length-based Bayesian biomass (LBB) estimation method to assess the stock status of four common shark bycatch species of which more than 100 samples were collected in coastal waters of the northern South China Sea. Estimates of the length of 50% of individuals captured by gear/the length at first capture that maximized the catch and biomass (Lc/Lc_opt) of a species ranged from 0.49 to 1.4; the draughtsboard shark Cephaloscyllium sarawakensis had the highest value, and the shortnose dogfish Squalus brevirostris had the lowest. Estimates of the collected biomass/biomass of the maximum sustainable yield (B/BMSY) ranged from 0.86 to 1.9. Both C. sarawakensis and the spadenose shark Scoliodon laticaudus were fully exploited, while the spatulasnout catshark Apristurus platyrhynchus and S. brevirostris were in good condition. To verify the stability of the LBB, length frequency data for the most common species S. laticaudus were divided into different size-class intervals; simulations revealed estimated parameters based on these to be insensitive to differences in intervals, except for the smallest (10 mm), which did not affect evaluation results. These results can be used to provide a scientific basis on which shark fisheries in this region can be managed and prior parameters for related resource assessment methods can be determined.

Unbaited Light-Emitting Diode Traps Performance for Catching Orange Mud Crabs

Mud crabs (Scylla spp.) are a vital fishery resource and targeted for a valuable source of income for coastal communities throughout the Indo-Pacific region. Baited traps are a considerable expense in crustacean fishing. Hence, the present study was performed to investigate the catchability of Scylla olivacea in response to light-emitting diodes (LEDs) in captivity and field conditions. We used a new experimental setup in the captivity condition that revealed most S. olivacea were attracted to green, blue, and white LED lights and no attractive effect by red LED lights similar to the controls. Field studies have shown that the catch per unit of effort (CPUE) of S. olivacea and other organisms, including bycatch species, is significantly higher when conventional mackerel and chicken head baits are used. However, unbaited traps equipped with green LED lights produced low CPUE of S. olivacea. Moreover, baited trap with chicken head, mackerel and green LED caught 4.52 %, 7.28 % and 2.18% more CPUE of S. olivacea compare to empty trap, respectively. Besides, both the mackerel and chicken head treatments resulted in the higher average CPUE of S. olivacea than did the green LED treatments; 0.66, 0.38 and 0.13 per trap. No significant differences were detected in the average carapace width of S. olivacea across all treatments. Our findings demonstrated that mud crabs can be captured using artificial lights, like other aquatic species but further in-depth studies and specific modifications to improve the performance of LED lights are warranted.

Evaluation of collaboratively developed management measures to reduce coral and sponge bycatch in a fully monitored multispecies trawl fishery

To protect cold-water corals and sponges from fishing damage, management changes were made in 2012 to the groundfish bottom trawl fishery British Columbia, Canada. The Groundfish Trawl Habitat Agreement restricted the spatial footprint of the fishery and introduced a cold-water coral and sponge bycatch quota, which was among the world’s first. Using 12 years of catch records from the fishery, we found a 31% decrease in overall frequency of encounters of cold-water coral and sponge, a 76% decrease in mean catch weight, and an 89% decrease in total annual catch. We tracked changes in the relative utilization of fine-scale fishing grounds (“fishing opportunities”) and found evidence of active avoidance of areas with high cold-water coral and sponge density. The habitat agreement appears overall to have been successful at reducing impacts to cold-water coral and sponge, although we identified several areas of potential conservation concern where effort and catch have not decreased. Nonspatial management measures in a complex multispecies fishery can result in spatial changes in fishing behaviour, with positive conservation outcomes for bycatch species.

Adaptive Spatial Management to Deal with Postflood Inshore Bycatch in a Penaeid Trawl Fishery

AbstractAdaptive spatial management provides a way to balance the conservation of bycatch species and the potential economic effects of bycatch‐induced closures on a fishery, but implementation can be both data and resource intensive. We present a survey exploring a novel approach to adaptively manage an intermittent bycatch issue in an inshore trawl fishery where Sciaenidae bycatch species (including juvenile Mulloway Argyrosomus japonicus, a species of conservation concern) co‐occur with large aggregations of a valuable target species (eastern school prawn Metapenaeus macleayi), following flood‐induced egression from estuarine habitats. Diurnal sampling surveys followed three flood events and targeted permanent inshore closure zones (designed to protect the normally nocturnally harvested eastern king prawn Melicertus plebejus) and adjacent inshore nonclosure areas. Sciaenidae abundance was mostly <10 fish/ha trawled, but larger catches generally corresponded with larger catches of eastern school prawn, and these relationships appeared to be steeper within nonclosure zones. There were only minor differences in the size structure of eastern school prawn between zones, and patterns were event and location specific. Negligible eastern king prawn were encountered. The results show that temporarily allowing fishers access to permanent trawl closures following floods may support the exploitation of aggregated target species with reduced interaction with bycatch species of concern. The approach presented here is relevant to the consideration of adaptive spatial management in other trawl fisheries.

Effect of soaking time on targets and bycatch species catch rates in fish and crab trap fishery in the southern East China Sea

Management strategies for trap fisheries in the Taiwan Strait (TS) lack crucial information such as factors determining the catch rates and bycatch species as well as the effect of the soaking time (SKT) of traps. Therefore, we investigated logbook and voyage data recorder data from Taiwanese crab and fish trap vessels (2011–2016). The crab traps were distributed widely in the TS, whereas the fish traps were mostly used in the northeast and southwest of the TS. Hierarchical cluster analysis revealed that the TS could be divided into the Northern Taiwan Strait, where most fishers use crab traps to target Portunus sanguinolentus, P. pelagicus, and Charybdis feriatus; Kuroshio Current, with large catches of Dentex hypselosomus using fish traps; and Taiwan Bank, with large catches of Evynnis cardinalis and other species using both traps. The optimal target species catch rates were achieved for a SKT of 48 h, regardless of the trap type. The bycatch rates were found to be higher when the SKT was longer than 48 h for crab traps, whereas the bycatch rates for fish traps were unaffected by the SKT. These findings may aid the implementation of sustainable trap fishing through harvest strategy planning, spatiotemporal management, and bycatch reduction.

Vulnerability Assessment of Target Shrimps and Bycatch Species from Industrial Shrimp Trawl Fishery in the Bay of Bengal, Bangladesh

Productivity susceptibility analysis (PSA) is a semi-quantitative ecological risk assessment tool, widely used to determine the relative vulnerability of target and non-target species to fishing impacts. Considering the available information on species-specific life-history and fishery-specific attributes, we used PSA to assess the relative risk of the 60 species interacting with the shrimp trawl fishery in the Bay of Bengal, Bangladesh. Penaeus monodon, the most important target, and Metapenaeus monoceros, the highest catch contributor, along with other 15 species were in the moderate-risk category, while seven non-target bycatch species were in the high-risk category. PSA-derived vulnerability results were validated with IUCN extinction risk, exploitation rate and stocks’ catch trend. The majority of the identified species showed high productivity (37%) and high susceptibility (46%), and all the moderately and highly vulnerable species were subjected to overfishing conditions by shrimp trawl fishery, which coincided with the vulnerability scores (V ≥ 1.8). Species with V ≥ 1.8 mostly showed a decreasing catch trend, while the species with a stable or increasing catch trend had a V ≤ 1.72. Data quality analysis of productivity and susceptibility attributes indicated that the majority of species were considered data-limited, which emphasizes the acquisition of data on spatio-temporal abundance, catch and effort, and biological information specifically relating to species age, growth, and reproduction. However, our findings can assist fishery administrators in implementing an ecosystem approach to ensure the sustainability and conservation of marine biodiversity in the Bay of Bengal.

Transient perturbations reveal distinct strategies for reserve benefits in life history-dependent ecosystems

Marine reserves can improve fisheries yields of target species while maintaining the persistence of bycatch species. However, the prevalent equilibrium analyses prevent our understandings in transient behaviours to achieve fisheries adaptive management. By incorporating age structure, we develop high-dimensional theoretical frameworks including both target and bycatch species to compare the yields of target species under different fisheries management strategies. With practical applications to the West Coast groundfish fishery in the USA, our research suggests that strategies with reserves can perform more benefits than traditional strategies without reserves in both conservation and fisheries aspects if target species have old ages at maturity and low adult survivorships. In addition, if fisheries yields are measured by weight, fisheries management has multiple choices over short time scales, which is contrary to the conclusions when yields are measured by numbers. The generality of applying our theoretical frameworks to fisheries management is tested with hypothetical parameters. Our work can be used to choose suitable measurement metrics and design more precise optimal fisheries strategies for given natural systems with specific life histories.

New historical data for long-term swordfish ecological studies in the Mediterranean Sea

Abstract. Management of marine fisheries and ecosystems is constrained by knowledge based on datasets with limited temporal coverage. Many populations and ecosystems were perturbed long before scientific investigations began. This situation is particularly acute for the largest and commercially most valuable species. We hypothesized that historical trap fishery records for bluefin tuna (Thunnus thynnus Linnaeus, 1758) could contain catch data and information for other, bycatch species, such as swordfish (Xiphias gladius Linnaeus, 1758). This species has a long history of exploitation and is presently overexploited, yet indicators of its status (biomass) used in fishery management only start in 1950. Here we examine historical fishery records and logbooks from some of these traps and recovered ca. 110 years of bycatch data (1896–2010). These previously neglected, but now recovered, data include catch dates and amounts in numbers and/or weights (including individual weights) for the time period before and after major expansion of swordfish fisheries in the Mediterranean Sea. New historical datasets such as these could help understand how human activities and natural variability interact to affect the long-term dynamics of this species. The datasets are online and available with open access via three DOIs, as described in the “Data availability” section of the article.

Decline in Atlantic wolffish Anarhichas lupus in the North Sea: Impacts of fishing pressure and climate change.

Anarhichas lupus is a boreo-Arctic species with biological characteristics often associated with vulnerability to overexploitation. Although not commercially targeted in the North Sea, A. lupus is a bycatch species in mixed demersal fisheries. Here we provide an overview of the status of A. lupus in the North Sea, as observed from commercial landings and fishery-independent trawl survey data. A. lupus was once common across much of the central and northern North Sea but, since the 1980s, have declined in abundance, demographic characteristics (reduced size) and geographical range, with the shallower and more southerly parts of its range most impacted. A. lupus is still relatively frequent in the northern North Sea, where fishing intensity, though decreasing, is high. Bycatch through fishing remains a potential threat and, considering the likely impacts of predicted climate change on cold-water species, risks of further regional depletion and/or range contraction remain. Whether or not A. lupus is able to re-establish viable populations in former habitat in UK coastal waters is unknown. Given the lack of data, the precautionary principle would suggest that manageable pressures be minimized where the species and its habitat are at risk of further impacts, and more regular assessments of population status be undertaken.

Area‐based management of blue water fisheries: Current knowledge and research needs

AbstractThe pelagic fisheries beyond the continental shelves are currently managed with a range of tools largely based on regulating effort or target catch. These tools comprise both static and dynamic area‐based approaches to include gear limitations, closed areas and bycatch limits. There are increasing calls for additional area‐based interventions, particularly expansion of marine protected areas, with many now advocating closing 30% of the oceans to fishing. In this paper, we review the objectives, methods and successes of area‐based management of blue water fisheries across objectives related to food production and environmental, social and economic impacts. We also consider the methods used to evaluate the performance of area‐based regulations and provide a summary of the relative quality of evidence from alternative evaluation approaches. We found that few area‐based approaches have been rigorously evaluated, and that it is often difficult to obtain requisite observational data to define a counterfactual to infer any causal effect for such evaluation. Management agencies have been relatively successful at maintaining important commercial species at or near their target abundance, but success at meeting ecological or social goals is less clear. The high mobility of both target and bycatch species generally reduces the effectiveness of area‐based management, and shifting distributions due to climate change suggest that adaptive rather than static approaches will be preferred. We prioritize research and management actions that would make area‐based management more effective.

Catch rates and distribution pattern of the silky shark, Carcharhinus falciformis, caught by the Taiwanese large-scale longline fishery in the Indian Ocean

The silky shark, Carcharhinus falciformis, is widely distributed in tropical and temperate waters, and it is a common bycatch species for tuna longline fisheries. This study examined the distribution of and presents relative abundance indices of the silky shark in the Indian Ocean by using logbook and observer data from the Taiwanese large-scale tuna longline fishery between 2005 and 2019. Due to the high zero catch rate, a zero-inflated negative binomial (ZINB) model was used to standardize catch per unit effort. Due to a lack of detailed targeting information, the fishery strategy was identified by using cluster analysis based on catch composition and then incorporated as an explanatory variable related to the target species in the ZINB model. Size segregation was observed for males and females in the Indian Ocean. Juveniles were mostly concentrated between 10° S and 10° N. Cluster analysis results revealed five fishing clusters based on catch composition that explained the variance in the ZINB models. Our integrated approach improves the understanding of spatiotemporal silky shark dynamics in the Indian Ocean and can be used to derive relative abundance indices for stock assessment and management.

Quantifying bycatch risk factors for the Chinese distant water fishery

AbstractMitigating bycatch of non-target fish species is a common objective in fisheries management that may be supported by the gathering of data from fishery observer programs and quantitative analysis of bycatch risk factors. We build three GLM models based on Chinese tuna longline fishery observer data in terms of analysis of total bycatch rate (TB rate), total bycatch ratio (TB ratio), and species-specific bycatch rate, respectively. The positive log-linear models assumed a Gaussian observation error model and a linear combination of categorical independent variables, including area, year, month, depth, and bycatch species. Results show that distributions of TB rate and TB ratio followed different trends and a latitudinal decrease was observed from both the northern and southern hemisphere of the equator. Comprehensively, the Pacific is a better place to fish compared to the Indian and Atlantic Oceans in terms of relatively lower TB rate and TB ratio. Fishing in open oceans can somehow avoid a high TB ratio than fishing in coastal waters. As a result, we recommend area 2SW, 2SE, 2 NW, 14SW, 14SE, and 14 NW as appropriate fishing ground for Albacore (Thunnus alalunga) while area 11N, 11S, 18SW, and 18SE to be appropriate fishing ground for fishing bigeye tuna (Thunnus obesus). Setting fishing gears deeper than 500 m would also help to get a low TB rate and TB ratio.

Bioactivity of the Protein Hydrolysates Obtained from the Most Abundant Crustacean Bycatch.

The animals from bycatch of the shrimp fisheries can be a source of natural products and bioactive compounds. Thus, the present study aimed to evaluate the bioactivity of protein hydrolysates prepared from the two most abundant crabs from the bycatch of shrimp fisheries in Brazil (Callinectes ornatus and Hepatus pudibundus). Samples of C. ornatus and H. pudibundus were collected in the region of Ubatuba, State of São Paulo, Brazil. Muscles with small pieces of exoskeleton of both species were hydrolyzed using two enzymes, Alcalase 2.4 L® or Protamex®. The in vitro antioxidant capacity was analyzed used three methods: DPPH, sulfhydryl groups, and peroxyl radicals. Additionally, the cytotoxicity of the hydrolysates was investigated using pre-osteoblasts cells. The results showed that the degree of hydrolysis (DH) of H. pudibundus was superior to DH of C. ornatus using both enzymes and was higher when using the enzyme Alcalase 2.4 L® (32.0% ± 1.9). The analysis suggested that the hydrolysates have antioxidant activity. Besides that, no cytotoxic effect was observed on cell viability. Thus, protein hydrolysates of C. ornatus and H. pudibundus have bioactivity, which add value to these bycatch species and suggests their potential use as nutraceutical ingredient in the food industry.

Reproductive biology of the shorthead drum Larimus breviceps (Acanthuriformes: Sciaenidae) in northeastern Brazil

The shorthead drum Larimus breviceps is one of the main bycatch species of the shrimp fisheries in Brazil. However, studies addressing the biology and fisheries impacts on this species are still scarce. Here we describe the main aspects of the reproductive biology and the female gonadal development of L. breviceps on Paraíba, northeast Brazil. The reproductive tract was described by macroscopic and microscopic analysis. The ovaries were composed by oogonia, pre-vitellogenic, vitellogenic, mature, and atretic oocytes. A total of 970 individuals (549 females and 421 males) were caught between December 2016 and November 2017 through beach seining. The total length (TL) varied from 4.2 to 23.0 cm. Females dominated over males (1 female: 0.77 male). The length–weight relationship did not differ between the sexes, presenting a positive allometric growth. The following stages were thus defined for females: immature, initial development, advanced development, mature, and regressing. The period of highest reproductive activity occurs between November and March and immature individuals occur throughout the year. Mean length at first maturity (L50) was estimated as 11.1 cm TL. The information provided here contributes to the overall knowledge of this species and may be helpful for further development of management practices that ensure the sustainability of marine species exploitation.

Bycatch Estimates From a Pacific Tuna Longline Fishery Provide a Baseline for Understanding the Long-Term Benefits of a Large, Blue Water Marine Sanctuary

Bycatch on pelagic tuna longlines has contributed to population declines in several far-ranging, oceanic species and presents a conservation challenge that area-based management tools are increasingly promoted to address. In January 2020 the Republic of Palau, concerned about the impacts of longline fishing in its waters, closed 80% of its exclusive economic zone to all extractive activities, reserving the remaining 20% for a domestic fishing zone (DFZ). One of a growing number of very large marine protected areas, the Palau National Marine Sanctuary (PNMS) spans ∼500,000 km2 and was established inter alia to allow for the recovery of fish stocks adversely impacted by tuna longline fleets. Given that the main tuna stocks targeted in the western Pacific are not overexploited, the benefits of protection potentially afforded by the sanctuary are likely greater for vulnerable bycatch species. Evaluations of the sanctuary’s performance require, in part, a baseline of historical catch rates and effort distribution in the distant-water fleet (DWF) and locally based fleet (LBF) operating in Palau prior to sanctuary implementation. We describe the fishing effort, catch rates, catch estimates and fishing mortality in Palau’s longline fishery based on logbook, observer and electronic monitoring data. We defined bycatch as any species, retained or discarded, other than targeted tunas. Between 2010 and 2020, 104.8 million hooks were deployed, catching over 2 million individuals from 117 taxa at an overall target:bycatch ratio of 1:1, with a retention rate of ∼62%. Pronounced differences in fishing strategies and spatial distribution of effort between fleets were associated with large variations in catch rates and composition. The LBF had a larger effect on populations of at-risk species relative to the DWF, with higher catch rates and magnitudes for several vulnerable species and higher observable fishing mortality rates (64% vs 50% in the DWF). The sanctuary reshaped Palau’s longline fishery, contracting the fishery’s area and capacity. The relocation of the DFZ eliminated the LBF and constrained the DWF to an area where the fleet’s total catch rates and those of a number of vulnerable species were historically lower relative to former fishing grounds now closed by the sanctuary. Our results highlight the importance of consistent bycatch monitoring and emphasize the need for regional area-based approaches for managing longline fisheries.

Blue sharks (Prionace glauca) by-catch in the Indonesian industrial tuna longline fishery in the eastern Indian Ocean

The Indonesian tuna longline fisheries in Indonesia have been targetting four main tuna, including yellowfin tuna, bigeye tuna, albacore, and southern bluefin tuna. In reality, there are many by-catch species, including blue sharks. This study aims to provide integrated information on blue shark species as by-catch species in Indonesian industrial tuna longline fisheries, including nominal and standardized CPUE and biomass of blue shark exploited by Indonesian longliners in the eastern Indian Ocean. This research is expected to become a reference point in shark management in the Indian Ocean. The scientific observer collected 2951 set-by-set longline fishing data based on Research Institute For Tuna Fisheries (RITF) from January 2006 to December 2018, on which the present analysis was made. The result indicated that there were eighteen shark species caught by Indonesian longliner were dominated by a blue shark (Prionace glauca) (60%) followed by crocodile shark (Pseudcarcharias kamoharai) (23.84%), bigeye thresher shark (Alopias superciliosus) (3%) and other species (<3%). Nominal CPUE was fluctuating and needed to be standardized in GLM analysis. The results of CPUE standardization can then be used as a reference in calculating the biomass blue sharks exploited by Indonesian Longliners. By considering several aspects, including the average of hook/set/fleet, an average of size (length and weight), the total number of set/year, reported the number of vessels, it is obtained that the estimated catch of blue sharks ranges from 366.3-2,616 tons per year with an average of about 1,282 tons.

Bycatch from seagrass fisheries: implication for conservation

Fishing activities conducted on seagrass bed to capture fishes and other seagrass associated fauna are very massive especially in the Pacific regions and undeveloped countries. This is due to the high abundance of economically important species associated to seagrasses, and additionally, seagrass area is the most accessible fishing ground throughout the year and with low capital. Seagrass meadows are importance habitat to support an abundance and diverse fish assemblages that form the basis for artisanal fisheries, which are vital in maintaining food security of coastal community in the regions. The seagrass fishery is considered a small-scale, multi-species and multi-gear fisheries. One of the fishing gear used in this fishery is traditional permanent fish trap called “sero”. Bycatch from some small-scale fisheries have been reported such as from trawls, traps, gill nets, and longline fisheries. This study aimed to identify bycatch species from “sero”, a type of seagrass fisheries which is in the form of fish fences with nets positioned on intertidal area of seagrass bed to the subtidal for approximately 200m. The result shown the bycatch from this fisheries was dominated by either low value fishes or invaluable and even toxic fishes for consumption, such as the puffers (Tetraodontidae and Diodontidae), juveniles of Apogonidae and Chaetodontidae. Additionally, sharks, turtles, and rays were also found in the bycatch. This result should be put into consideration as the bycatch would have an ecological consequences on the population, predator-prey relationship, and ecosystem resilience to stressor in general. Information from this study will be important for sustainable small-scale fisheries management and seagrass conservation, and therefore, further research into bycatch reduction in this fishery would be desirable.

First record of Pteroplatytrygon violacea (Bonaparte, 1832) with annotation of cartilaginous fishes by-catch by gill nets (Egyptian Mediterranean)

Five cartilaginous fish species were recognized and identified as by-catch species during studying the catch of gill nets operated in the coastal area of Alexandria City from the Egyptian Mediterranean Waters during the study periods from Feb. 2018 to June 2018 and from Dec. 2019 to Nov. 2020. The by-catch included the first record of Pteroplatytrygon violacea, the closely related species Dasyatis pastinaca and Dasyatis tortonesei, the rarely found species Rhinoptera marginata, and the blackchin guitarfish Glaucostegus cemiculus. Among these five species, four species are listed in the IUCN Red List; as least concern for P. violacea, data deficient for D. pastinaca in the Mediterranean Sea, near threatened for R. marginata, and critically endangered for G. cemiculus. Morphological characters and morphometric measurements were studied to provide identification of these species. The species have been dissected for more biological information.