Demographics of a Heavily Exploited Deep Water Shark Echinorhinus Cf. Brucus (Bonnaterre, 1788) from the South-Eastern Arabian Sea (original) (raw)
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2018
This project endeavored to provide a formative, contemporaneously applicable, and fully quantitative baseline of a significant component of the shark harvest produced by the nation of India, namely, the longline bycatch mortality for sharks generated from the commercial-scale fishing activity in the extensive oceanic region of India's Exclusive Economic Zone (EEZ), the nature and scope of which is little understood. Worldwide, shark populations have experienced marked declines due to the advent of modern industrial fishing. Additionally, the life-history and reproductive characteristics of these species, which include longer lifespans, slower growth, fewer offspring, and generally reduced fecundity, constrain group level reproduction and replacement rate compared to that of many commercially targeted and managed teleosts. Although generally true at a global level, shark population depletion has varied in nature and/or rate around the world, with significant unknowns persisting in relation to the waters and seas surrounding developing and recently developed economies; in many cases these waters have not been subject to comparable levels of oversight, active management, and/or assessment as those found in other more established global fisheries. India, over the last decade and a half approximately, has been positioned as the second largest contributor to the global shark harvest in terms of overall tonnage which in turn raises the following question: Is this country mirroring similar global trends of shark population decline due to its fishing activity? Addressing this question in a formatively useful way defines the focal pursuit of this research venture.
2019
Stock assessment of Scoliodon laticaudus Muller and Henle, 1839 was made along with analysis of its few biological characteristics from its commercial landings during 2012-2016 from Gujarat waters of India to understand the population dynamics and stock status of the species. The average annual landing of the species was 5442 t, which constituted about 67% of the total shark landings at Gujarat coast. L∞, K and t0 were estimated as 75.53 cm and 0.54/yr, and -0.4 yr, respectively. Total mortality rate, fishing mortality rate and natural mortality rate were estimated as 1.95 yr-1, 1.04 yr-1 and 0.91 yr-1, respectively. The length at capture (Lc50) and length at maturity (Lm50) were 39.74 cm and 35.79 cm, respectively, which indicate that most of the sharks are exploited after attaining the sexual maturity. Length-weight relationship showed that the growth was isometric. The species was a continuous breeder and showed peak recruitment during September. The current exploitation ratio (E...
Indian Journal of Geo-Marine Sciences, 2017
Stock assessment of Rhizoprionodon acutus (Ruppell, 1837) was made along with a few biological characteristics in the commercial landings during 2012-2014 from Gujarat waters of India to understand the population dynamics and stock status of the species. L∞, K and t0 estimated were 93.8 cm, 0.32 yr-1 and -1.3 yr, respectively. Total mortality rate (Z), fishing mortality rate (F) and natural mortality rate (M) were estimated as 1.0 yr-1, 0.39 yr-1 and 0.61 yr-1, respectively. Length at capture (Lc50) and length at maturity (Lm50) were estimated as 50 cm and 61 cm respectively, which indicate that most of the sharks are exploited before attaining the sexual maturity. Length-weight relationship showed growth was isometric. The species was a continuous breeder and showed peak recruitment during May. The current exploitation ratio (Ecur) was found to be 0.39, which is lower than E0.1 estimated for the species using Beverton and Holt yield per recruit analysis. Thompson and Bell predictio...
Indian Journal of Fisheries, 2017
The life history and exploitation parameters of Rhizoprionodon oligolinx Springer, 1964 were assessed using commercial landing data of 2012-2015 from Mumbai waters of India to understand the population dynamics and stock status of the species. The average annual landing of the species was estimated to be 383 t, which formed about 9.1% of the total shark landings of Maharashtra. L ∞, K and t 0 estimated were 97.1 cm, 0.47 yr-1 and-0.79 yr respectively. Total mortality (Z), fishing mortality (F) and natural mortality (M) rates were estimated as 2.16 yr-1 , 1.48 yr-1 and 0.69 yr-1 respectively. The length at capture (L 50), length at female maturity (Lm 50) and male maturity (Lm 50) were estimated as 49.7, 62.3 and 59.5 cm respectively, which indicated that most of the sharks entered peak phase of exploitation before attaining sexual maturity. Length-weight relationship indicated allometric growth (b>3) for the species. The species was found to be a continuous breeder and showed peak recruitment during April. The current exploitation rate (E cur) was found to be 0.68, which is lower than E max estimated for the species using Beverton and Holt yield per recruit analysis. Thompson and Bell prediction model showed that at current exploitation level, the biomass (B) has reduced to 32% of virgin biomass (B0) where as, the spawning stock biomass (SSB) has reduced to 16% of the virgin spawning stock biomass (SSB0). Hence the exploitation level for the species should be reduced by 40% that will ensure the availability of SSB at a relatively safer 30% level to rebuild the stock for long term sustainability of the resource.
2019
Marine fisheries are dynamic and always prone to change in tune with the changing demands, challenges, advancement of technologies etc, as is evident in modification of fishing crafts and fishing gear, extension of fishing ground, emergence of new resources, collapse and disappearance of certain resources and new forms of market demands. The overall results of such changes have both positive and negative impacts on the fishery and this necessitates continuous monitoring and interventions to ensure sustainability of the fishery as well as conservation of the resources. This policy guidance gives an overall picture of the present status of marine fisheries of Tamil Nadu, various changes in the crafts, gears, trends in landing of major resources over the years, their distributional range, status of stocks, social structure of the fishing community, economics of the fishing operations, main drivers for fishing and the need for improved management of the exploited stocks for overall sust...
2015
Div ersity and abundance of pelagic shark bycatch in the tuna longline operations in northern Indian Ocean were examined for the period 2004-2010. During the survey 1.2 million hooks were deployed in three regions of seas around India resulting in the catch of 1501 numbers of sharks. Significant variations in the diversity and abundance of pelagic sharks were observed among the three regions of Indian seas. Catches of sharks are prominent in Andaman & Nicobar region contributing 35.15% of the catch by number and 51.46% by weight. In the eastern Arabian Sea, sharks constituted 15.49% and 14.89% of the total catch by number and weight respectively. In western Bay of Bengal, this group contributed 7.74% (by number) and 9.33% (by weight) to the total catch. Alopias pelagicus, Carcharhinus limbatus, Alopias superciliosus and Carcharhinus falciformis were the dominant species of pelagic sharks observed in the Indian seas. Time series analysis of hooking rates revealed drastic decline in t...
Fishes
The silky shark (Carcharhinus falciformis) is the most common shark landed in Indonesian waters, including in the Indian Ocean. However, even though they are frequently caught, there is a lack of information on the population and abundance of silky sharks in the Indian Ocean. Cilacap and Tanjung Luar are two of Indonesia’s shark fishery hotspots, both located on the edge of the Indian Ocean, which is a part of the Indonesian Fisheries Management Area (FMA) 573. The fishers from both places usually have fishing grounds in that particular fisheries management area. This research aims to update the abundance, and to investigate the factors, which influence catches of silky shark in the FMA 573 based on monthly enumeration during 2015–2016. This study found that standardized catch-per-unit-effort (CPUE) or abundance indices of silky shark in the Indonesian FMA 573 increased from 2015 to 2016. We suggested that fish immigration and decreasing fishing pressure may affect the fish abundanc...
The objective of this project was to obtain scientific advice for the purpose of implementing the EUPOA on sharks as regards the facilitation of monitoring fisheries and shark stock assessment on a species-specific level in the high seas. The study was focused on major elasmobranch species caught by both artisanal and industrial large pelagic fisheries on the High Seas of the Atlantic, Indian and Pacific area, which are currently monitored and potentially managed by respective Tuna RFMOs. Estimated "potential" shark species catch in the Indian Ocean is around 160,000 t for 22,000 t. presently declared (7 times higher than declared). Considering all sharks that are not reported at species level, the total amount of shark declared was around 100,000 tons and, thus, the underreporting reduced to 1.6 times higher. 19 fisheries among the 195 fisheries found in IOTC database generate 86 % of potential investigated shark catches. In the Indian Ocean, Gillnet (GN) and a composition of Gillnet and Longline (GN-LL) are the most impacting one with 61 % of the total estimated studied shark species catches (97,000 t). It is followed by longline (LL and LL-swo) with 18 % and other métiers (OTH) with 12 %, which precise gear composition is unknown. The blue shark is estimated to be the major shark catch in the Indian Ocean followed by silky shark, threshers, Oceanic whitetip, shortfin mako and hammerheads sharks. The research framework to be proposed is organized in three steps: (i) estimation of shark catches by species using the method proposed here which allows identifying the most impacted shark species and the métier most affecting those species; (ii) a preliminary Ecological Risk Assessment (or other preliminary assessment based on fishery indicators) by fleets which allows to identify the most vulnerable species to focus the efforts in conjunction with point (i); and (iii) specific recommendations of how to apply possible management measures, to improve data collection and assessment of those fleets/species identified as priorities based on points (ii) and (iii). The implementation of the three steps is highly related.
Assessing stock status of grey sharpnose shark (Rhizoprionodon oligolinx Springer, 1964) in Java Sea
IOP Conference Series: Earth and Environmental Science, 2019
Increasing demand for shark products leads to over fishing of these species in many areas, damaging their population. Grey sharpnose shark (Rhizoprionodon oligolinx) is caught mostly by gillnet fleet in Java Sea. The objective of the study was to discuss the current stock condition of grey sharpnose shark in Java Sea. Research on shark resources has been conducted by placing enumerators at the main landing base in PPN Pekalongan. Biological parameters of R. oligolinx were estimated based on commercial landings data recorded by enumerators from 2014-2015. The growth parameters of grey sharpnose shark such as L∞, K, t0, values were 96.1 cm, 0.47 year-1 , and-0.78 year, respectively. Moreover, total mortality rate (Z) were estimated at 1.82 year-1 with fishing mortality and natural mortality rates (F and M) were 1.04 year-1 and 0.78 year-1 , respectively. Stock status of grey sharpnose shark in Java sea from view point of gill nets fisheries is still in the sustainable utilization status with biological reference point more than 30% SPR and level of exploitation rate (E) is 0.57.