Bycatch Species Research Articles

Distribution patterns and relative abundance of shortfin mako shark caught by the Taiwanese large-scale longline fishery in the Indian Ocean

The shortfin mako shark, Isurus oxyrinchus, is one of the most common bycatch species of the Taiwanese tuna longline fishery (Taiwan was second-largest shortfin mako shark-catching nation) in the Indian Ocean. The present study estimated the distribution and relative abundance indices of the shortfin mako in the Indian Ocean using observer records and logbook data from the period 2005–2018. To deal with the high number of zero catch records (∼90%), the catch per unit effort (CPUE) was standardized using a Zero inflated negative binomial model (ZINB). Cluster analysis was used to identify the fishing operations associated with different fishing strategies and then incorporated as a factor related to target species into the ZINB. Considerable variation was observed in the size distribution by region and season in the Indian ocean. Larger mako sharks (age>15 and age>7 yr for female and male, respectively) tend to occur in equatorial and tropical regions, while smaller specimens appear at higher latitudes in temperate waters. Cluster analysis produced five fishing clusters based on the catch compositions of the main species. The target factor (cluster) was important in explaining the variance in ZINB models. Overall, the standardized CPUEs and nominal CPUEs analysis for the shortfin mako caught by the Taiwanese longline fishery indicates a stable and increasing trend in recent years.

Comparison of beam trawl catch, by-catch and discard in fishing and non-fishing areas – a case study from the northern Adriatic Sea

Beam trawl fishery is highly important in the Croatian part of the northern Adriatic wherein 116 vessels have a licence for this type of fishing gear. A sharp decrease in the beam trawl catch observed since 2015 has raised concern about not only socio-economic issues but also ecological issues and the effect that beam trawl fisheries have had on exploited stocks. Besides the effect that beam trawl fisheries can have on targeted economically important species, intensive dredging can cause long-term changes in the benthic community. Therefore, this study aimed to detect the effect that this type of fishing gear has on target and by-catch species. Furthermore, survey data were compared with the official beam trawl fishery data gathered through Vessel Monitoring System data together with fishermen’s logbooks. Our research targeted two adjacent areas: an area where beam trawl fishing is allowed and an area where it is forbidden. The results demonstrate that the commercially important catch represented a minor share of the total beam trawl catch in both survey areas, while discard made up more than 93% of the total catch. The main beam trawl commercially important species in the Croatian part of the northern Adriatic Sea was Pecten jacobaeus, followed by Solea solea and Ostrea edulis. Our results suggest that beam trawl fisheries mostly affect target bivalve species and some non-commercial benthic species (e.g. sponges). The differences recorded between areas could suggest that beam trawl fisheries cause changes mostly in the P. jacobaeus population.

A Synthesis of Deepwater Horizon Impacts on Coastal and Nearshore Living Marine Resources

The 2010 Deepwater Horizon (DWH) oil blowout in the Gulf of Mexico began on April 20, originating in the deep sea 66 km off the Louisiana coast. By early June, DWH oil had spread to coastal Louisiana, Mississippi, Alabama and western Florida. An estimated 2,113 km of shoreline were oiled, making DWH the largest marine oil spill in global history by length of affected shoreline. Additionally, a series of oil spill response measures were deployed, including diversions of Mississippi River discharge to forestall oil coming ashore, and the establishment of large-scale fishery closures, with both affecting coastal resources to varying degrees. Here, we review published studies and describe additional analyses evaluating long-term impacts of DWH on coastal/nearshore biological resources. We assembled time-series data collected by state, federal and academic partners on population abundance and environmental conditions to evaluate species and community change. Our study focused on plankton, invertebrates, fishes and dolphins, and 13 “key species” were selected to conduct semi-quantitative vulnerability-resilience (V-R) analyses. At one extreme, early life stages of Gulf Menhaden (Brevoortia patronus) were not affected due to seasonal spawning and larval development preceding the spill. In contrast, demographically independent populations of the common Bottlenose Dolphin, (Tursiops truncatus) suffered a variety of severe and ongoing health effects owing to oil exposure. Virtually all of the heavily oiled salt marsh habitat was in Louisiana, with the majority occurring in Barataria Bay. Multispecies trawl survey abundances declined post-DWH throughout eastern coastal Louisiana but remained stable elsewhere. A regime shift in composition of Barataria Bay trawl survey catches occurred during and following the spill, the persistence of which was associated with long-term reductions in average salinity and increases in water clarity. In some cases, fishery closures were associated with measurable but ephemeral increases in abundance of some targeted and bycatch species. Freshwater flooding of marshes was ineffective in preventing coastal oiling and severely affected benthic euryhaline resources including Eastern Oyster (Crassostrea virginica) and Marsh Periwinkle (Littoraria irrorata). The flooding response measure experiment also indicates the directionality of impacts that further planned water diversions may have on ecological communities of lower Mississippi River basins.

A netting-based alternative to rigid sorting grids in the small-meshed Norway pout (Trisopterus esmarkii) trawl fishery.

A new bycatch reduction device, termed “Excluder”, is presented as an alternative to a traditional rigid sorting grid, mandatory in the small-meshed Norway Pout (Trisopterus esmarkii) trawl fishery in the North Sea. The fishery is a high-volume fishery with large vessels, large demersal trawls and catches up to 100 tons per haul of this small forage fish. The Excluder is a 30 m long netting-based sorting system, developed to reduce bycatch (70 mm square meshes) and improving on board gear-handling and safety. The Excluder was tested against a 5.8 m2 standard sorting grid (35 mm bar spacing) in a twin-trawl experiment from the commercial 70 m trawler “S364 Rockall”. Catch data were analysed by species and length using the catch comparison method. For all bycatch species analysed, the Excluder had significantly lower catches relative to the grid: herring (21%), whiting (6%), mackerel (5%), American plaice (70%), witch flounder (15%), and lesser silver smelt (71%). For Norway Pout there was a significant increase in the overall catch efficiency of 32%. These results are explained by a 10 cm smaller L50 (the length of fish with 50% probability of being rejected by the sorting system) of the Excluder and a 15 times larger sorting area, which reduces the risk of clogging and loss of function. With these documented effects of improved sorting and target species catch efficiency, implementation of the Excluder would improve sustainability and address two main barriers of the current Norway pout fishery that limit quota capitalization; a tendency for Norway pout to mix with herring and whiting and lowered catch rates from grid-clogging. Additionally, gear-handling and safety on board would be improved.

Demographics of Butterfly Fish, Heniochus acuminatus (Perciformes, Chaetodontidae) from the Gulf of Mannar, India

Butterfly fishes are widely distributed throughout the Indo-Pacific Ocean and are often caught in large quantity by shrimp trawlers as a by-catch species. These fish are ecologically and commercially important, as they are ecological indicators of coral health and a major component of ornamental and by-product fisheries. However, owing to their low value for direct human consumption as a food, there is dearth of research on their demographics and life–history traits. The present study was therefore conducted using Heniochus acuminatus, one of the common butterfly fish that is captured as a by-catch in the Gulf of Mannar (GoM) to generate basic data on its demographic estimates. Specimens (n = 833) were collected monthly from the four reef-fish landing stations for two consecutive years and the demographic parameters were estimated using a FAO–ICLARM Stock Assessment Tool (FiSAT). Fish in the length class of 10–11 cm dominated the landings. The length-weight relationship (LWR) was defined as the equation, BW = 0.0234TL3.156 suggesting positive allometric growth pattern of H. acuminatus in GoM. Estimated demographic parameters (asymptotic length, L∞ = 17.85 cm) showed low growth rate and growth performance index (K = 0.95 and ϕ = 2.481 respectively) in study species. The estimated potential longevity (tmax) and the observed length at first capture (Lc) were found to be 3.15 years and 7.9 cm respectively. The higher natural mortality rate (M = 2.00 yr−1) than the fishing mortality rate (F = 0.39 yr−1) with exploitation level (E = 0.16) below the optimum level indicates that the state of the stock of H. acuminatus in the GoM is sustainable. The current study provides the first population demographic report of the genus Heniochus and is likely to have a significant conservation and commercial impact.

Length–weight relationships of five selected demersal fishes from the Cabo Verde Islands (eastern‐central Atlantic)

The length–weight relationships (LWR) were estimated for five selected demersal marine fishes from the relatively undisturbed shelves and slopes of the Cabo Verde Islands. Most of them were of ecological and/or commercial interest. Occasional sampling was carried out during different fisheries research projects. LWRs were taken for the following bycatch species for which no such estimates exists in the science literature: Myroconger compressus, Synaphobranchus affinis, Physiculus cyanostrophus, Physiculus caboverdensis and Canthidermis maculata. Total length and fork length (to the nearest 0.1 cm) and total weight (to the nearest 0.1 g) were determined. The resulting length–weight equations are characterized by a high accompanying coefficient of correlation. The present data help improving the knowledge base needed for further fish biology studies and fisheries management.

Vulnerability level of target and by-catch species on tuna hand line (HL-TR) fishery in Indonesian Fisheries Management Area I-FMA 573 based at Sadeng Fishing Port

Tuna hand line-trolling line (HL-TR) fisheries have an essential role in Indonesia’s tuna fisheries, including Indonesia Fisheries Management Areas (I-FMAs) 572 and 573. The catch of tuna line in I-FMA 572 and 573 reached ~30.4% of the total catch 189,022 tonnes in 2019. Limited data and scientific advice for developing adequate management remain a challenge for tuna HL-TR fisheries in I-FMA 573 waters. Center for Fisheries Research (CFR) has conducted an assessment using the PSA method to obtain information of vulnerability level both of target and bycatch species on tuna HL-TR in 2020. Data used in the analysis were grouped into operational fishing, productivity, and susceptibility data. The operational fishing data were obtained from Sadeng Fishing Port in2019. The productivity and susceptibility data were obtained from literature review and expert consultation through a Focus Group Discussion (FGD) and expert consultative workshop. The result showed that both target and by-catch species included in the analysis have low to moderate vulnerability level scores. The results of this research are used to help managers at a national level to determine necessary management measures with high precautionary. While for by-catch species, in particular white tip sharks, its management measures must comply with agreed IOTC regulations.

Distributions of threatened skates and commercial fisheries inform conservation hotspots

Bycatch in commercial fisheries is a pressing conservation concern and has spurred global interest in adopting ecosystem-based management practices. To address such concerns, a thorough understanding of spatiotemporal relationships among bycatch species, their environment and fisheries is required. Here we used a generalized linear mixed model framework incorporating spatiotemporal random effects to model abundance patterns for 3 skate species caught as bycatch in commercial fisheries (thorny skate Amblyraja radiata, winter skate Leucoraja ocellata and smooth skate Malacoraja senta), as well as 10 target species on the Scotian Shelf, NW Atlantic. Spatiotemporal estimates of relative abundance for at-risk skates within the years 2005-2015 were modelled from research trawl survey data and overlaid with those for target species to identify hotspots of bycatch risk. In addition, abundance estimates for at-risk skates within the years 1975-1985, a period of higher stock abundance, were used to identify areas of previously important habitat. Historically, skate species densely occupied areas near Sable Island and Banquereau Banks, Georges Bank and the Bay of Fundy. Bycatch hotspots between at-risk skates and commercial targets were identified in regions across the Scotian Shelf. These hotspots were independently validated by predicting species presence from at-sea observer data that monitor skate bycatch directly. We discuss spatial relationships between target and bycatch species, highlighting limitations of at-sea observer programmes that this method helps to address. This framework can be applied more broadly to inform ecosystem management and priority areas for conservation or fisheries regulation.

When opportunistic predators interact with swordfish harpoon fishing activities: shark depredation over catches in the Strait of Messina (central Mediterranean Sea)

We describe the interaction between harpoon fishing activity and sharks, which opportunistically depredated harpoon catches in the Strait of Messina. Shark bite marks were observed on harpooned swordfish during the period 2014–2020, with different damages to the catches. Most of the depredation events have focused on large swordfish, generally weighing more than 60 kg. Data on direct observations were implemented by interviews and questionnaires to fishermen aimed to recover the information on their local fishing and ecological knowledge. Fishermen provided additional data on shark-harpoon fishing interactions also supplying information on by-catch species (i.e., bluefin tuna). Therefore, these results suggest that sharks migrating through the Strait of Messina are occasionally attracted by injured prey, due to their ability to detect chemical cues, fish distress stimuli and body fluids (i.e. blood) in the water. In addition, our investigations showed an increase in shark attacks on harpooned fish over time, likely due to an increase in harpoon swordfish catches. This may be related to the effects of the driftnets’ ban enforced by European Regulations in the last decades.

Disaggregating species unit costs in mixed fisheries: the case of the Irish whitefish fleet

Many fishing fleets operate in mixed fisheries where several target species are caught together along with other bycatch species unintentionally caught. In some cases, fleets operate in multiple mixed fisheries depending on various factors such as time of year or current market conditions, among other factors. Data collection in the European Union (EU) involves various levels of detailed data. Economic data is generally collected on an annual time-step whereas other sources provide information at much higher resolution such as the fishing trip (landings declarations), fish day (logbook) or even in real-time (electronic logbook). In this paper a methodology is described to disaggregate the annual cost of a fleet segment into a cost per fishery and per species within the fishery. This information is of interest as it permits incorporation of the economic implications of fishery dynamics into fisheries management. Assessment of these unit costs on a fishery basis also allows accurate input into value chain analysis which is carried out on a species basis.

Weight/carapace length relationship and condition factor of the roughneck shrimp, Rimapenaeus constrictus (Stimpson, 1874), on the southeastern Brazilian coast.

Rimapenaeus constrictus is a penaeid shrimp widely distributed in the Western Atlantic, frequently captured as bycatch in trawling activities. Here we describe the weight vs. carapace length relationship and the condition factor of the species. Shrimps were sampled in the Ubatuba region, northern littoral of São Paulo State, monthly. We analyzed 4,952 individuals (1,371 males and 3,581 females). We measured the individuals' weight and carapace length, and the condition factor (CF) was calculated for both sexes. Females had a heavier body when compared to males, probably due to their greater maximum body size achieved. Both sexes presented a negative allometric growth in weight, probably due to their reproductive pattern and activities. We found similar mean CF values for males and females. From temporal analysis, the highest CF values for females were observed during the seasons with lower water temperatures. Such a situation may happen because females' CF tend to be influenced by a greater food availability in the environment, induced by the intrusion of the South Atlantic Central Water during the spring and early summer in the Ubatuba. The information presented here could be used as subside in protection actions and management of bycatch species.

Right on target: using data from targeted stocks to reconstruct removals of bycatch species, a case study of longnose skate from Northeast Pacific Ocean

Fisheries stock assessments rely heavily on historical catch information to understand how a stock responds to exploitation and make meaningful forecasts under alternative management and environmental scenarios. However, for many bycatch species historical removals are virtually unknown, as a large portion of the catch was discarded at sea. For example, historical discard of elasmobranch species such as skates and sharks have been reported as 95 percent of the total catch based on available data. The longnose skate is one the most abundant groundfishes on the continental slope of the U.S. Pacific Coast by biomass, and the most abundant skate species in the Northeast Pacific Ocean. We developed a method to estimate catch of longnose skate on the U.S. West Coast based on the catch of Dover sole, a co-occurring targeted species with which longnose skate is caught. This method allowed us to reconstruct historical longnose skate catches back to the beginning of the bottom trawl fisheries and improve stock assessment for this species. We also examined the impact of using our method versus other common methods of catch reconstruction to inform stock assessment models, and found that the target-based predictive method produced results that more accurately reflected the life history and typical stock dynamics of elasmobranch taxa. Our method is not limited to the specific case of longnose skate and could be easily adapted for other species and areas.

Effects of monofilament nylon versus braided multifilament nylon gangions on catch rates of Greenland shark (Somniosus microcephalus) in bottom set longlines.

The Greenland shark (Somniosus microcephalus) is the main bycatch species in established and exploratory inshore longline fisheries for Greenland halibut (Reinhardtius hippoglossoides) on the east coast of Baffin Island, Canada. Bycatch and entanglement in longline gear has at times been substantial and post-release survival is questionable when Greenland sharks are released with trailing fishing gear. This study investigated the effect of the type of fishing line used in the gangion and gangion breaking strength on catch rates of Greenland shark and Greenland halibut in bottom set longlines. Circle (size 14/0, 0° offset) hooks were used throughout the study. Behavior of captured sharks, mode of capture (i.e., jaw hook and/or entanglement), level of entanglement in longline gear, time required to disentangle sharks and biological information (sex, body length and health status) were recorded. Catch rates of Greenland shark were independent of monofilament nylon gangion breaking strength and monofilament gangions captured significantly fewer Greenland sharks than the traditional braided multifilament nylon gangion. Catch rates and body size of Greenland halibut did not differ significantly between gangion treatments. Although most (84%) of the Greenland sharks were hooked by the jaw, a high percentage (76%) were entangled in the mainline. The mean length of mainline entangled around the body and/or caudal peduncle and caudal fin was 28.7 m. Greenland sharks exhibited cannibalistic behavior with 15% of captured sharks cannibalized. All remaining sharks were alive and survived the disentanglement process which can be attributed to their lethargic behavior and lack of resistance when hauled to the surface. Thus, as a conservation measure fishers should be encouraged to remove trailing fishing gear prior to release. Our results are used to demonstrate benefits to the fishing industry with regard to an overall reduction in the period of time to disentangle sharks and damage to fishing gear by switching from braided multifilament to monofilament gangions in Greenland halibut longline fisheries.

Parasitic flatworms infecting thorny skate, Amblyraja radiata: Infection by the monogeneans Acanthocotyle verrilli and Rajonchocotyle emarginata in Svalbard.

Parasite diversity above the Arctic circle remains understudied even for commercially valuable host taxa. Thorny skate, Amblyraja radiata, is a common bycatch species with a growing commercial value. Its natural range covers both sides of the North Atlantic including the Arctic zone. Svalbard is a Norwegian archipelago located on the northwest corner of the Barents Shelf which sustains a spectacular species diversity. So far, several monogenean species have been reported infecting thorny skate across the Atlantic Ocean. In the present study, we intend to fill in the knowledge gap on monogenean parasites infecting thorny skate in the northern part of its range and thus indirectly assess the connectivity between the thorny skate populations off the Svalbard coast and from previously studied locations. 46 monogenean individuals were recovered from 11 specimens of thorny skate. Following morphological and molecular assessment, two species of monogeneans, Acanthocotyle verrilli and Rajonchocotyle emarginata, were identified. The results serve as the northernmost record for both parasite genera and the first record of monogenean species off Svalbard. Detailed morphometric evaluation revealed a relatively high level of morphological variation in A. verrilli compared to its congeners. Phylogenetic reconstruction placed A. verrilli in a well-supported clade with A. imo. Our study also suggests high diagnostic significance of sclerotised structures in the identification of Rajonchocotyle. Even though the occurrence of two directly transmitted parasite species supports the previously suggested long-distance migration of A. radiata, future studies employing highly variable genetic markers are needed to assess the ongoing and historical migration patterns.

The effect of light attractor color in pelagic longline fisheries

Improving the selectivity of the fishing gear is one of the most promising methods to mitigate deleterious impacts of longline fisheries upon bycatch species. Light lures have recently become widespread in epipelagic longline fisheries since they increase the catch rates of valuable target species such as swordfish and tunas. Yet, little is known about their effect upon the incidence of bycatch. Here, we compared the catchability of target and bycatch species in a pelagic longline fishery targeting swordfish and tunas equipped with light attractors with three different colors to ascertain if any of the light attractor colors would enhance the selectivity of the fishing gear. A total of 3488 individuals were caught across 57 fishing sets. The proportion of target species to bycatch species was high (58–65 %) in each color treatment. Overall, green attractors (peak wavelength at 525 nm) exhibited the highest catch rates of target species, but they were also responsible for the highest incidence of bycatch, rendering 73 % and 82 % of the blue shark and sea turtle catch, respectively. Blue (peak wavelength at 465 nm) and white attractors caught significantly less individuals of both target and bycatch species. Further, significant interactions between light attractor color and the intensity of lunar illumination were observed for most species analyzed. Differences in the catchability of bycatch such as blue sharks and white marlins across attractor color treatments were more conspicuous at high lunar illumination levels (i.e. full moon periods), when white attractors rendered the lowest catch of these taxa. In contrast, the catchability of target species such as swordfish, yellowfin tuna and albacore showed greater differences between treatments at low illumination levels (i.e. new moon periods). The observed differences in the performance of the three light attractor colors across the lunar cycle might provide an opportunity to mitigate bycatch incidence in longline fisheries. Yet, further research is required to fully understand the combined effects of light lures and lunar illumination on the behavioral responses of pelagic species.

Assessment of cetacean\u2013fishery interactions in the marine food web of the Gulf of Taranto (Northern Ionian Sea, Central Mediterranean Sea)

The exploitation of fishery resources acts as a driving force on cetaceans both directly, by determining their fishing mortality or injury as by-catch species, and indirectly, through the lowering the availability of their prey. This competitive overlap between fishing and cetaceans often results in inadequate solutions so that in some cases there have been cases of intentional cetacean culling to maximize fishing production. A modelling approach applied to investigate the ecological roles of cetaceans in the food web could prove more effective to integrate ecological and fishing aspects and to provide suggestions for management. The comparative analysis carried out in the Gulf of Taranto (Northern Ionian Sea, Central Mediterranean Sea) showed that fishing exploitation provides impacts on the investigated food web greater than those due to cetacean predation. Trawling was estimated to be the most negatively impacting fishing gear considering the mortality rates and consumption flows. On the other hand, the striped dolphin was the main impact on the food web due to its highest consumption flows. Analysis showed a negative and non-selective impact on the exploited species due to the fishing gears, while the odontocetes proved to select their prey species and provide a positive impact in the assemblage. In particular, while the fishing gears are primarily size selective, targeting mostly large and economically valuable fish, the odontocetes seem to follow a co-evolution process with their prey, developing a specialization in their resources, providing control of the meso-consumers and ensuring a trophic stability in the ecosystem.

Assessing the vulnerability of bycatch species from Hilsa gillnet fishing using productivity susceptibility analysis: Insights from Bangladesh

Productivity susceptibility analysis (PSA) is being widely used as a semi-quantitative risk assessment tool in data and capacity limited situations. This tool rapidly and cost-effectively assists in identifying the potential risk of a fishing type regarding its bycatch stocks. The Hilsa (Tenualosa ilisha) is an iconic flagship species and geographical indication product of Bangladesh. We performed a PSA to evaluate the relative risk to bycatch stocks in gillnet fishing (gillnet shares > 95 % of Hilsa catch) along with target stock, Hilsa. Of the 130 identified species, Hilsa and 74 bycatch stocks were subjected to a PSA depending on data availability and the magnitude of capture. We validated our vulnerability results by comparing them with two other empirically derived assessment outcomes, the IUCN Red List and the exploitation rate. We also compared PSA scores with the catch trend of stocks from fisher's subjective recognition. Hilsa was found to be moderately vulnerable to gillnet fishing. The majority of the bycatch were found to be highly susceptible to fishing, with 17 bycatch species found to be in the high-risk category. Five species classified as high-risk group were known to be threatened species listed in the national IUCN Red List. Our finding revealed 82 % accordance level between the exploitation rate and PSA-derived vulnerability scores. It implies that the exploitation rate associated with overfishing corresponds to the vulnerability scores. Moreover, with few exceptions, we found that species with vulnerability score over 1.8 was at depleted stock state. Our result also revealed that around 55 % of inland bycatch and 42 % of marine bycatch is associated with overfishing (vulnerability score > 1.8). Data quality analysis indicated that the majority of bycatch species received the low data quality scores. It emphasizes the need for improved data collection on species-specific life-history traits. However, the baseline information of our current study could assist the fishery managers to formulate a better management plan for the sustainability of Hilsa and the bycatch stocks.

Using a Bayesian modelling approach (INLA-SPDE) to predict the occurrence of the Spinetail Devil Ray (Mobular mobular)

To protect the most vulnerable marine species it is essential to have an understanding of their spatiotemporal distributions. In recent decades, Bayesian statistics have been successfully used to quantify uncertainty surrounding identified areas of interest for bycatch species. However, conventional simulation-based approaches are often computationally intensive. To address this issue, in this study, an alternative Bayesian approach (Integrated Nested Laplace Approximation with Stochastic Partial Differential Equation, INLA-SPDE) is used to predict the occurrence of Mobula mobular species in the eastern Pacific Ocean (EPO). Specifically, a Generalized Additive Model is implemented to analyze data from the Inter-American Tropical Tuna Commission’s (IATTC) tropical tuna purse-seine fishery observer bycatch database (2005–2015). The INLA-SPDE approach had the potential to predict both the areas of importance in the EPO, that are already known for this species, and the more marginal hotspots, such as the Gulf of California and the Equatorial area which are not identified using other habitat models. Some drawbacks were identified with the INLA-SPDE database, including the difficulties of dealing with categorical variables and triangulating effectively to analyze spatial data. Despite these challenges, we conclude that INLA approach method is an useful complementary and/or alternative approach to traditional ones when modeling bycatch data to inform accurately management decisions.

Assessing the ichthyofaunal diversity and trophic level from trawl bycatch of Chennai Fishing Harbour, Southeast Coast of India

The present study aimed to document the temporal diversity and trophic level of ichthyofauna from the Chennai Fishing Harbour, Southeast coast of India. The trawl bycatch consists of 45,527 ichthyofauna individuals collected fortnightly during the period June 2018 to April 2019. The recorded ichthyofaunal diversity includes 156 species belonging to 2 classes, 14 orders, 66 families, and 119 genera. The order Perciformes dominantes with 74 species (47%) followed by Scorpaeniformes (12%; 19 species) and Tetraodontiformes (11%; 18 species). Temporal diversity analysis revealed that the maximum species diversity was observed during the North-east monsoon (123 species) while the minimum was observed during the post-monsoon (107 species) period. Numerically dominant bycatch species were found to be Leiognathus equulus (6%), Equulites lineolatus (5%), Gazza achlamys (5%), Karalla dussumieri, (4%) Otolithes ruber (3%) and Nibea maculata (2%). Biodiversity analysis revealed that the Shannon–Wiener​ species diversity index ranged from 5.37 (South-west monsoon) to 5.53 (North-east monsoon) whereas the species evenness was observed from 0.77 (South-west monsoon) to 0.81 (Post-monsoon). The habitat-wise diversity analysis revealed that demersal species group was dominant (72 species; 46%) followed by reef-associated (70 species; 45%), benthopelagic (8 species; 5%), pelagic (5 species; 3%) and bathy-demersal (1 species; 1%). The results of the trophic level shows that the bycatch fish species was dominated by top-level carnivores (49%) followed by mid-level carnivores (26%), apex predator (19%), primary carnivores (5%) and herbivores or planktivores (1%). The IUCN categories of bycatch species are mostly classified as Not Evaluated, Least Concern, Data Deficient and Vulnerable viz., 58%, 36%, 5% and 1% respectively. The present study also gives information on juvenile fish that are encountered in trawl bycatch along the Chennai coast. The outcome of the study gives baseline information on the bycatch diversity which paves the way for the sustainable exploitation and also the management of exploited fisheries resources in this region.

Bycatch and discards from two types of bivalve dredges targeting Donax trunculus and Chamelea gallina used in the southern coast of the Marmara Sea, Turkey

Intensive commercial harvesting of the wedge clam Donax trunculus and the striped venus Chamelea gallina was conducted along the southern coast of the Marmara Sea using a mechanical dredge (MD) and a hand dredge (HD). The purpose of this study was to characterize and quantify the bycatch and discards of both types of dredge. The dredge tows were performed along sandy bottoms at depths ranging from 0 to 2 m between August 2011 and July 2012. A total of 29 species belonging to 20 families were collected from 137 tows during 67 fishing trips. The total catch in terms of biomass was 107,752.69 g for the MD and 94,257.40 g for the HD, of which 10.78% and 5.08%, respectively, comprised commercial bycatch species, discards, individuals of the target species smaller than the minimum legal size (< MLS), and mortality. Besides the target species (D. trunculus and C. gallina), 27 other species were caught as bycatch and partially discarded. The predominant commercially valuable species in the bycatch were Ruditapes philippinarum (0.94%) and Mytilus galloprovincialis (0.48%) for the HD, and Acanthocardia tuberculata (0.34%) and Rapana venosa (0.34%) for the MD. The rate in weight of discards including < MLS and mortality were 9.22% for the MD and 2.82% for the HD. The gastropods Cerithium vulgatum (58.28%) and Tritia neritea (13.80%) and the crustacean Liocarcinus depurator (5.57%) comprised 77.65% of the discards in weight. Overall, a lower commercial bycatch species + discards + < MLS + mortality rate in terms of weight (5.08%) was observed for the HD compared to the MD (10.78%). The findings of this study are important for the development of policies for the conservation and sustainable fishing of bivalves.