Low-value bycatch diversity in coastal fisheries of Purba Medinipur, West Bengal, India

Introduction

Fisheries is a major sector in the economics of many countries. Fisheries have played an important role in food and nutritional security of people, especially in rural India. The affordability of the fish, which has been shown to be the most nutritious health food, has contributed to a better nutritional status of the people (Ghufoorunissa, 2001) [17] . Fisheries and aquaculture production has grown significantly over the last 50 years -particularly in the last 20 years -resulting in an increase in the world's capacity to eat diverse and nutritious food. Fish is a rich source of nutrients such as calcium, iron zinc and vitamin A, and protects against some diseases. For example, a serving of 150 gm of fish contains around 50-60% of the protein needed by an adult, making fish and fisheries products an excellent source of animal protein (FAO, 2014) [14] . The continuous production of fish in aquaculture is important to increasing global fisheries production (Harris, 2004) [19] . More than 60% of the world's 128.8 million tonnes of fish production are destined for human consumption and more than 40% remain unused. 'Bycatch' is the name given to species captured along with the target fish species. Lizardfish, pufferfish, silverbelly and more are examples of bycatch. There are 20 million tons of wastage bycatch and 30 million tons of small pelagic fish are converted to fishmeal (Chandrapal 2005 and Chavan et al., 2008). Bycatch of non-useful species is a threat to the world's oceans (Kelleher, 2005). The ecological consequences of long-lived marine mega fauna bycatch include direct and indirect effects of reduced mega fauna populations (Heppell et al., 2000) and indirect effects on the structures of oceans (Estes et al., 2011;McCauley et al., 2015) [8, 9, 13, 21, 29, 31] . Many of these species are threatened because of declines due to increased incidental mortality from fisheries (JaramilloLegorreta et al., 2007). This is a multifaceted environmental issue with sociocultural, scientific and socioeconomic implications in understanding the issues and finding more effective ways to reduce bycatch. In recent years, bycatch studies have grown considerably, giving us more knowledge of which species are affected, the quantities are involved, and the spatial extent of bycatch. Progress has also been made in the development of mitigation strategies. This kind of research identifies the vulnerability of bycatch, mitigates bycatch directly through changes in fishing operations or gear, and mitigates bycatch indirectly through a better understanding of the distribution of bycatch in both time and space (Soykanet al., 2008). Bycatch plays a role in the overfishing of some target species because they are discarded or used as bait before they reach their first maturity. According to (Funge-Smith et al., 2005) and (Nunoo et al., 2009) [16] , one of the reasons for an increase in the landing of previously discarded www.extensionjournal.com bycatch is that it is used as livestock and aquaculture feed, as farm manure and as human product. Efforts have been made to develop products from fish waste that are valuable (Nilsang et al., 2005) and (Bhaskar et al., 2008). Fish wastes are a valuable source of high biological value proteins, lipids and minerals (Toppe et al., 2007) and (Kacem et al., 2011) [4, 23, 27, 34, 35, 40, 43] . Trawling is one of the most effective technological innovations in history of fisheries. It has been widely adopted around the globe and is responsible for enhancing marine fish production. But, primarily because of nonselective practices, bottom trawling has resulted in damage to the sea's bottom and biota (Jennings and kaiser, 1998). In India, the trawl fleet accounted for 51% of the marine fish landings in 2008-2012 (CMFRI, 2012). Through intensive dragging of the sea bottom and use of very fine mesh size (15-20 mm knot-to-knot) in cod-end, huge marine damage to marine life including fish was observed a decade and half ago in the Indian coast (Devaraj and Vivekanandan, 1999) Bhanja et al., 2024). In this study, the variety of LVBs from marine fishing of the coastal areas of Purba Medinipur, West Bengal was chosen [1, 2, 5, 10, 11, 12, 25, 32, 46] .

Materials and methods

Study areaand duration:

The present study area is locatedin the coastal area of Purba Medinipur, West Bengal. The selected sampling sites are -Digha (21°38′18″N 87°30′35″E); Sankarpur (21.6491° N, 87.5699° E); Tajpur (21.652882°N, 87.629272°E); Mandarmoni (21.6681° N, 87.7025° E); Junput Sea Beach (21.7129° N, 87.8208° E) and Patuaghat (21.79472°N, 87.88333°E). Field surveys were carries out over a six-month period from August, 2025 to January, 2026. Data collection occurred at weekly intervals during peak fishing hours (06:00-10:00 and 15:00-17:00) to ensure representative sampling of the local landings.

Sample Collection and Identification

All specimens were photographed (Realme RMX3392) and identified based on morphological features such as shell colour, claw shape, body colour and size. Taxonomic identification was performed using standard keys and literature (Talwar and Jhingran, 1991;Jayaram, 1999;Jeyabaskaran and Wafar, 2002;Viswanath, 2002;Motoh and Kuronuma, 2015;Harshith et al., 2016) and cross referenced with global databases including [Fishbase] and [WoRMS] [15, 20, 24, 26, 33, 42, 45] .

Biodiversity indices

Species diversity and community structure were evaluated using the following ecological indices:

Simpson index (λ):

To calculate the probability of interspecific encounter:

Shannon-Wiener index (H'):

To determine species diversity and relative abundance: Here, niis the number of individuals of species i, N is the total number of individuals, and S is the total species richness.

Statistical analysis:

The statistical analysis was done through Ms-Excel and Past Software.

Results and Discussions Taxonomic Composition of Low value bycatch

The recorded total 27 finfish species (Table-1) belongs to 12 orders, 17 families and 8 shellfish species (Table -2) belonging to 1 order, 4 families during the study period. Out of finfishes, the species under Clupeiformes were dominant (22%), followed by Carangiformes (15%), Acanthuriformes (15%) and Anguilliformes (7%), Centrarchiformes (7%), Mugiliformes (7%); while orders like Aulopiformes, Beloniformes, Carcharhiniformes, Gobiiformes, and Myliobatiformes recorded at 4% availability (Figure -2). On other side, shellfish species under, Portunidae (45%) constitutes the largest share followed by Matutidae and Orengoniidae each account for 22%, while Grapsidae contributes the least, comprising only 11% of the recorded shellfish species (Figure -3). Similarly, (Rajkumar et al. 2025) found that in the Palk Bay, fishing is done throughout the year, with the peak seasons being June-July and January-February. During our study period we also recorded that peak commercial landings were observed in January with a huge amount of LVB with it [38] . www.extensionjournal.com

Conservation status and Human Interaction

In terms of IUCN conservation status, most species are classified as Least Concern (LC), including relatively stable populations. However, several species fall under Data Deficient (DD) and Not Evaluated (NE) categories, suggesting a lack of sufficient information of proper assessment. Notably a few species such as Carcharhinus dussumieriand, Pateobatis bleekeriare categorized as Endangered (EN), while Dasyatis zugei is listed as Vulnerable (VU), highlighting potential conservation within bycatch. The table also provides insight into human interaction, showing that the majority of species are harmless with very few exceptions such as Pateobatis bleekeri, which is noted as venomous. On the other hand, the conservation status of all listed shellfish species is marked as Not Evaluated (NE), indicating that they have not yet been assessed under standard conservation frameworks such as the IUCN Red List and all recorded shellfish are harmless and do not pose any direct threat. Species under IUCN-DD are frequently overlooked in conservation programs (Bland et al., 2015). In Digha and Kakdwip, there is an analysis by (Kar et al., 2017) on the marine fish standards, 4.46% of species has certain information, population in the northern Bay of Bengal, found that 18.47% species were under LC category, 6.37% NT, 66.56% species were unknown according to IUCN 2.23% VU, 0.95% EN and 0.95% CR [6, 28] .

Ecological and Environmental Implications

The findings confirm that the bycatch in the region remains a high-stakes ecological issue, with bottom trawling contributing significantly to the capture of non-targeted juveniles threatened species. (Gibinkumar et al., 2012) also found that amongst the fishing gears, trawling is responsible for a higher bycatch rate, because of low selectivity of gear. The high abundance of LVB at Junput (S5) and Petuaghat (S6), followed by Digha (S1) suggests these are highintensity fishing zones where the loss of trophic balance and diversity is most acute. The presence of endangered species in the Low-Value Bycatch (LVB) necessitates the immediate implications of Bycatch Reduction Devices (BRDs) and sticker monitoring of trawl selectivity to ensure long-term fishery sustainability and the protection of Bengal's marine biodiversity. (Stobutzki et al. 2001) also suggested that technological interventions such as, Turtle Excluder Devices (TEDs) and Bycatch Reduction Devices (BRDs) help to reduce mortality and prevent the removal of juveniles [18, 41] .

Conclusion

The present study showed a comprehensive overview of finfish and shellfish species occurring as low-value bycatch (LVB) along the coastal waters of Purba Medinipur, revealing a high level of taxonomic diversity across multiple orders and families. This diversity reflects the wide ecological range of species unintentionally captured in marine fisheries. Although the majority of species are classified as Least Concern, the presence of Data Deficient and Not Evaluated species indicates significant gaps in scientific knowledge, while the occurrence of Endangered and Vulnerable species highlights potential conservation risks associated with bycatch. Most species pose little threat to humans, with only a few exceptions. Overall, the findings emphasize the ecological importance of bycatch species and the urgent need for improved monitoring, assessment, and management practices to ensure sustainable fisheries and the protection of threatened marine biodiversity. LVB consists of a wide variety of species occupying different trophic levels -ranging from small forage fish to juveniles of larger predators. These species are integral to marine food webs, acting as prey for commercially important fish, seabirds, and marine mammals. Removing them in large quantities can disrupt ecosystem balance, alter species composition, and affect overall marine productivity. Changes in the composition and quantity of bycatch can reflect shifts in biodiversity, habitat conditions, and fishing pressure. A high proportion of juveniles or sensitive species in LVB may indicate overfishing or habitat degradation, www.extensionjournal.com making bycatch data a useful tool for monitoring ecosystem health. Even though labelled 'low-vale' these species are frequently used for fishmeal, animal feed, dried fish products, and local consumption, especially in coastal communities. Thus, they contribute indirectly to food security and rural livelihoods. Understanding LVB consumption helps in designing sustainable fishing practices, such as gear modifications, seasonal restrictions, and bycatch reduction technologies. It also supports ecosystem-based fisheries management approaches. Lowvalue bycatch is not 'low importance'. It is critical component of marine ecosystems and fisheries systems, and its proper monitoring and management are essential for maintaining biodiversity, ecosystem stability, and sustainable fisheries. Present investigation can be serves as a useful baseline dataset for understanding the diversity and consumption of low-value bycatch in the region. It also contributes to ecological knowledge, fisheries management, and future biodiversity and conservation studies in the coastal waters of Purba Medinipur.

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