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Trawling remains a controversial method of fishing due to the perceived lack of selectivity of the trawl net and the resultant capture of a huge quantity and diversity of non-target species, including endangered species such as sea turtles, coupled with its effect on the marine ecosystem. The impacts of trawling on the physical, chemical and biolog...
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... large trawlers performing 'stay-in fishing', the target species are stored in refrigerated fish holds, and non-target species are thrown back into the sea. Some of these trawlers bring back the last day's by-catch to the landing centre to be used as food, manure and animal feed (Figure 1). Larger, economically valuable fish and shell fish in the by-catch are marketed fresh. ...
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Cryptic, not readily detectable, components of fishing mortality are not routinely accounted for in fisheries management because of a lack of adequate data, and for some components, a lack of accurate estimation methods. Cryptic fishing mortalities can cause adverse ecological effects, are a source of wastage, reduce the sustainability of fishery r...
Citations
... For example, turtles that spend more time at the surface may be at higher risk of vessel strikes (Shimada et al., 2017;Fuentes et al., 2021), of inhaling airborne pollutants (Jernelv, 2010) or encountering floating debris (Gregory, 2009;Duncan et al., 2017;Abreo et al., 2023). In contrast, when turtles are at the bottom of the ocean, they may be more susceptible as bycatch to trawling fishing vessels (Brewer et al., 2006;Kumar and Deepthi, 2006) and various bottom-set fishing gear (Wallace et al., 2010b), as well as pollution that accumulates on the seafloor (Putman et al., 2015). Although the spatial distribution of threats in the Rio Grande do Norte region are poorly known, artisanal fisheries and marine traffic are likely to pose the greatest in-water threats (Santos et al., 2021a), so identifying behaviors that increase the vulnerability to such threats (e.g., long surface times) is of importance. ...
Introduction
An understanding of animal behavior is critical to determine their ecological role and to inform conservation efforts. However, observing hidden behaviors can be challenging, especially for animals that spend most of their time underwater. Animal-borne devices are valuable tools to estimate hidden behavioral states.
Methods
We investigated the fine-scale behavior of internesting hawksbill turtles using the mixed-membership method for movement (M4) which integrated dive variables with spatial components and estimated latent behavioral states.
Results
Five latent behavioral states were identified: 1) pre-nesting, 2) transit, 3) quiescence, and 4) area restricted search within and 5) near the residence of turtles. The last three states associated with a residency period, showed lower activity levels. Notably, when compared to other behaviors the pre-nesting exhibited shallower and remarkably long dives of up to 292 minutes. We noted high fidelity to residence core areas and nesting beaches, within and between nesting seasons, with residence areas decreasing within a season.
Discussion
The latent behaviors identified provide the most detailed breakdown of turtle movement behaviors during the internesting period to date, providing valuable insights into their ecology and behavior. This information can inform marine turtle conservation and management efforts since utilization distributions of individual behavioral states can be used to determine spatially-explicit susceptibility of turtles to various threats based on their behavior. The analyses of utilization distribution revealed a minimal overlap with existing marine protected areas (0.4%), and we show how a new proposal would expand protection to 30%. In short, this study provides valuable guidance for conservation and management of internesting marine turtles at a fine spatiotemporal resolution and can be used to enhance national action plans for endangered species, including the expansion of existing Marine Protected Areas. By flexibly incorporating biologically informative parameters, this approach can be used to study behavior outside of the hawksbill breeding season or even beyond this species.
... The trawling operation has high flexibility, adaptability, and production efficiency, but can unselectively damage fishery resources, especially for endangered species or a spawning population 57 . Trawling remains a controversial method of fishing due to the perceived lack of selectivity of the trawl net and the resultant capture of a huge quantity and diversity of non-target species, including endangered species such as sea turtles, coupled with its effect on the marine ecosystem 7 . Bottom trawling, one among the most damaging fishing methods still remains unmanaged in many countries including India even though many studies have proved its impact on fisheries, benthic biodiversity and sea floor structure 54 . ...
Trawl-net is an important fishing gear in Andaman and Nicobar Islands (ANIs) India since three decades with minimum number(n=10) of boats meeting the daily fish consumption of Islanders with minimum costs. A study was carried out between 2014 to 2018 to investigate the major fish landings of Trawl-net in the ANIs coast. The trawl-net landing is occurring only from Junglighat fish landing centre(FLC) which is having loading and unloading facilities in ANIs. The total number of FLC visits, fishing-trips, operations and fish-landing of trawl-net recorded during this period were 692(n), 533(n), 7561(n) and 691(tonnes) respectively. The maximum fishing-trips(149) and fishing-operations(2086) occurred during the year 2018 and minimum of same (87 and 1218) occurred during 2015. Similarly, the maximum(170.51tonnes) and minimum (109.33tonnes) of fish landings were observed during the year 2014 and 2015 respectively with an average of 138.21±10.54tonnes/year. The contribution of trawl-net landing amongst other gears was 17.8% including fin-fishes(598.7tonnes) and shell-fishes(115.34tonnes) during the study period. The trawl-net operation was occurring at very few fishing grounds(n=14) in ANIs and the maximum fish catch occurred in the Coast of Havelock Island (26.7%). Totally 52 genera of fishes were recorded in trawl-net landings under 37 families in which Leiognathidae was found more dominant(21.38%). Altogether 21 Trawl-net validations were conducted at each PFZ and Non-PFZ during the period. The fishes captured at PFZ 3288kg with an average of 156.6±13.5kg/operation and at Non-PFZ 1237kg with an average of 58.9±5.3kg/operation. The minimum range of fish cost in the market was maintaining in this Island due to the trawl-net landings, in-spite of there was controversy of non-selective fish catch and by-catch in trawl-net fishing. Figures : 03 References : 58 Tables : 04
... to the lack of target catch selectivity (Kumar and Deepthi, 2006). According to Amoroso et al. (2018), bottom trawlers catch around 19.0 million tonnes of fish and invertebrates per year or about one-quarter of all marine landings. ...
... This issue is more severe in tropical waters, where the trawlers randomly target diverse faunal assemblages and ultimately destroy dynamic benthic habitats. Several authors studied the trawl catch, bycatch, discard, and faunal diversity in India (Rao, 1998;Sujatha, 2005;Kumar and Deepthi, 2006;Gibinkumar et al., 2012;Velip and Rivonker, 2015;Bhendekar et al., 2016Bhendekar et al., , 2019Behera et al., 2017;Singh et al., 2017;Samanta et al., 2018;Kodeeswaran et al., 2020). ...
... From the studied trawlers, bycatch and discard contributions to the total catch were around 40.42 ± 3.07% (SE, n = 9) and 8.97 ± 0.86 (SE, n = 9), respectively. Trawl bycatch comprises 56%-93% of the total catch landed in the different maritime states of India, with the lowest from Maharashtra (George et al., 1981;Kumar and Deepthi, 2006). Alverson et al. (1994) reported a total of 28.7 million tonnes of bycatch and 27.0 million tonnes of discards generates from the global marine fisheries sector. ...
Trawl fishing is well-known for its high catch rate, but due to its non-selective nature, it is now widely acknowledged to have an impact on biodiversity and habitat. The geographical and temporal aspects of trawl catch, bycatch, discard, and ichthyofaunal trawl diversity along the south Konkan coast of Maharashtra, India, are contemplated in the current study. The data of 177 georeferenced trawl hauls, towed between 15°53’38”N to 17°34’52”N latitude and 72°54’29”E to 73°25’48”E longitude, revealed that maximum bycatch (70–110 kg/haul) and discard (60–110 kg/haul) regions were found towards the southern direction, near ecologically sensitive estuarine areas off the south Konkan coast, Maharashtra. The post and pre-monsoon seasons were found to be much more productive in terms of catches, while the post-monsoon and winter seasons had the highest species diversity 38.15% and 33.86%, respectively, with the winter season having higher discard rates. In the present study, bycatch contributed nearly 49% of the total catch, with the maximum catch per hour recorded in October (62.20 kg) and the discard per hour in January (14.59 kg). There were 134 different species of fish and shellfish recorded, and the family Carangidae (8.21%) was prominent in terms of species richness, followed by Penaeidae (6.72%), Clupeidae (5.22%), Engraulidae (5.22%), and Sciaenidae (4.48%). The results of various biodiversity indices confirmed that the studied region is blessed with rich and evenly distributed biodiversity. The mapped predictive values of trawl fishing showed a high fishing pressure zone towards the south off the Maharashtra coast, and it highlighted the need for suitable strategies for the conservation and management of fisheries resources to achieve long-term sustainability in that region.
... An area of 32,440 km 2 ranging from the shore and going down 40 meters (m) of water depth is accessible for 67,669 unauthorized boats, where about fifty percent of country boats are in the BoB (Shamsuzzaman et al., 2020). Trawl nets are operated from mechanical vessels known as trawlers and are made to catch economically beneficial target species (Biju Kumar and Deepthi, 2006). The shrimp trawl and fish trawl are two variations of the bottom otter trawl, which is the primary equipment. ...
The study was conducted on the commercially and economically important fish species in the Bay of Bengal (BoB) that were collected from an otter trawling vessel in March 2020. Within the study period, a total of 52 species were identified, including 17 orders, and 43 families. Perciformes were found to be the most dominant order over all others, contributing about 46.15% of the fish species (24 species under 23 families). A record of catching immature species has been found, which can reduce the sustainability of fisheries. We have found one critically endangered (CR), two near threatened (NT), twenty-five least concerned (LC), four data deficient (DD), and twenty not evaluated (NE) species among the fifty-two species in the BoB during the study period. Many commercially important fish species within the bay need to be exploited properly to get maximum economic benefits. J. Asiat. Soc. Bangladesh, Sci. 49(1): 13-25, June 2023
... (Akhilesh and Kizhakudan et al.2014), with decreasing catch data in recent decades (CMFRI 2000(CMFRI -2018 [11] . In general, ray fish were captured by trawl nets (Akilesh KV et al., 2018), due to its lack of selectivity of the gears used for trawling (Kumar et al., 2006) [13] . Ray fishes are economically significant as food fish and for their ornamental value (Brisset et al., 2006) [14] . ...
... (Akhilesh and Kizhakudan et al.2014), with decreasing catch data in recent decades (CMFRI 2000(CMFRI -2018 [11] . In general, ray fish were captured by trawl nets (Akilesh KV et al., 2018), due to its lack of selectivity of the gears used for trawling (Kumar et al., 2006) [13] . Ray fishes are economically significant as food fish and for their ornamental value (Brisset et al., 2006) [14] . ...
The sustainability of marine ecosystems depends on the ancient and varied class of animals known as chondrichthyes. An increase in fishing pressure brought on by an excessive demand for chondrichthyes has threatened the extinction of around 30% of species in recent years. India, which is India's major contributor to its exports of sharks, is the second-largest shark landing country in the world. The present study was carried out for period of six months from October 2021-September 2022 in Mudasalodai landing centre of East coast region. Totally 13 rays were recorded, belongs to six families. Due lack of data on diversity of rays and taxonomical identification carried out in this research.
... One of the most urgent threats to the world's remaining marine stocks is commercial fishing, especially the indiscriminate capture of non target organisms, typically referred to as 'bycatch' [1,2]. Whilst bycatch may be sold, it may also be unusable or unwanted for a variety of regulatory and economic reasons and subsequently thrown back to sea, often dead or dying [3]. ...
Net entanglement in derelict fishing nets is a major threat to the conservation of endangered species of cetaceans, birds and reptiles. Nets made of nylon and plastics are non degradable and are a major source of risk to many species whether aquatic or terrestrial which often get trapped and killed which continue to be present in the environment even when not in use. Lack of awareness and careless handling of these fishing gears by fishermen poses serious damaging impact on the biodiversity and ecological health of the habitat.
... Trawling or dredging. Trawling accounts for approximately 25% of the global capture of fishing [39], and it is increasingly being considered as an unsustainable fishing technique [40][41][42]. It has two impacts on benthic ecosystems. ...
Using global fishery outputs from 62 countries during the period 2001–2020, this study applies the threshold panel data model of Hansen (2000) to empirically explore the nonlinear relations between the number of fishing vessels, fishers, and fishery production, with distinct overfishing stocks (overfishing) and fish caught by trawling or dredging techniques (trawling) as the threshold variables. Our findings show that the levels of fishery outputs could be increased by different combinations of primary factors, such as the number of fishing vessels and fishers. More specifically, when the number of fishing vessels and fishermen operating in countries with a high ratio of overfishing (overfishing > 4.4456) increased, their fishery outputs significantly increased as compared with countries with a low percentage of overfishing. As overfishing activities increase, they can result in significant shortages and imbalances of fishery resources, directly influencing fish biomass, biodiversity, and sustainability of fisheries, as well as making destructive fishing practices worse for marine ecosystems. Countries with a relatively high proportion of trawler net usage (trawling > 4.5516) would have significantly lower fishery outputs, as more fishing vessels are invested in them, compared with countries with a low proportion of trawling net use. This implies that trawler net usage is a non-sustainable fishing technique and harms fishery resources. The policy implications of this study indicate that taxing overfished species and implementing trawling regulations could significantly improve species richness and site-based abundance, thus helping to sustain fishery outputs.
... However, increasing the mesh size of shore seine nets may lead to the loss of small pelagic fish that form valuable catch. Mesh size regulations are not always complied with in Indian fisheries (Kumar and Deepthi, 2006). Hence, a post-capture release may be a more effective measure for threatened bycatch species. ...
Shore seines are traditional fishing gear that supports the livelihoods and subsistence of thousands of fishers in India. However, their impact on elasmobranchs that inhabit the coastal waters is relatively less known. This study assessed elasmobranch capture, biology, and their value from inshore seines of Malvan, Maharashtra. Six elasmobranch species were found in the shore seine nets, dominated by the scaly whip ray (Brevitrygon walga, n=107) and including two Critically Endangered guitarfish species (Glaucostegus obtusus and G. granulatus). Most captured elasmobranchs were juveniles, suggesting that the inshore Malvan waters may serve as nursery grounds for these species. Among the sampled B. walga 64.1% were dead upon capture, with small-sized rays showing significantly higher mortality, indicating a higher vulnerability of juveniles. 49.5% of the captured elasmobranchs were discarded, 19.6% were used as take-home catch for consumption and only 30.9% were commercially sold, albeit for a low value. These findings indicate that while the shore seine fishery may affect coastal elasmobranchs, these species are important for local subsistence. Conservation efforts can be directed towards the live release of elasmobranchs that would otherwise be discarded and die, particularly for endangered species.
... The non-target species may have key roles in the marine food-webs that fortify ecosystem processes and functioning, which in turn determines the productivity of marine capture fisheries (Auster and Langton, 1999). The environmental damage caused by repeated high bottom trawling can be substantial and irreversible, threatening the biological diversity and economic sustainability (Kumar and Deepthi, 2006). ...
... Interactions between marine megafauna and commercial fisheries have occurred throughout recent history and continue to increase as a result of human population growth and industrialization of the fisheries industry (DeMaster et al., 2001;Gray and Kennelly, 2018;Lewison et al., 2004). Bycatch is a principal negative interaction between fisheries and marine animals, and typically refers to non-target animals that become hooked, trapped or entangled in fishing gear (Davies et al., 2009), resulting in mortality or injury (Biju Kumar and Deepthi, 2006). The gillnet fisheries industry has been identified as having the highest bycatch intensity score for air-breathing animals, including seabirds (Lewison et al., 2014). ...
As diving foragers, sea ducks are vulnerable to underwater anthropogenic activity, including ships, underwater construction, seismic surveys and gillnet fisheries. Bycatch in gillnets is a contributing source of mortality for sea ducks, killing hundreds of thousands of individuals annually. We researched underwater hearing in sea duck species to increase knowledge of underwater avian acoustic sensitivity and to assist with possible development of gillnet bycatch mitigation strategies that include auditory deterrent devices. We used both psychoacoustic and electrophysiological techniques to investigate underwater duck hearing in several species including the long-tailed duck (Clangula hyemalis), surf scoter (Melanitta perspicillata) and common eider (Somateria mollissima). Psychoacoustic results demonstrated that all species tested share a common range of maximum auditory sensitivity of 1.0-3.0 kHz, with the long-tailed ducks and common eiders at the high end of that range (2.96 kHz), and surf scoters at the low end (1.0 kHz). In addition, our electrophysiological results from 4 surf scoters and 2 long-tailed ducks, while only tested at 0.5, 1 and 2 kHz, generally agree with the audiogram shape from our psychoacoustic testing. The results from this study are applicable to the development of effective acoustic deterrent devices or pingers in the 2-3 kHz range to deter sea ducks from anthropogenic threats.
