Ghost fishing capacity of lost experimental gillnets: a preliminary study from Indian waters.

Abandoned, lost, or otherwise discarded fishing gear contributes considerably to global marine debris. These lost gears, mostly made of non-biodegradable synthetic materials, persist in the marine environment for longer periods of time and pose a great threat to marine life by entangling and killing target fishes and other non-target species such as turtles, birds, and mammals, a phenomenon known as ghost fishing. Other environmental impacts include physical impacts on aquatic habitats, transfer of microplastics into food web, and interference with fishing. Information regarding the catching efficiency and catch rates of lost nets in Indian waters is lacking. Ghost fishing capacity of simulated lost gillnets is being reported for the first time in India. This study investigates the ghost fishing capacity of lost gillnets through an experimental approach at Aroor, Vembanad lake, Kerala, India. Simulation studies using purposefully abandoned shrimp gillnets (32 mm mesh size) were conducted to understand the fishing capacity of lost gillnets during two seasons (monsoon and post-monsoon) as separate experiments. The gillnets maintained their catching efficiency until the 15th day during the first experiment and up to the 50th day in the second experiment. Catches showed an exponential reduction over time in both experiments. A total of 251 specimens comprising of 27 species were caught from both sets of experimental nets, and the state of catch in the nets showed different decaying stages from the second day itself along with fresh stages. As the days progressed, particulate matter and detritus began to accumulate on the experimental nets, increasing net visibility and reducing their catching efficiency. The results of the study on ghost fishing capability will contribute to the development of strategies for reducing the effects of lost nets on the aquatic ecosystem and for suggesting improved management strategies.

Food selectivity and reproductive biology of small indigenous fish Indian river shad, Gudusia chapra (Hamilton, 1822) in a large tropical reservoir.

Assessment of life history strategies of economically important small indigenous fishes (SIF) which are rich in nutritive values is essential and imperative to artisanal and subsistence small-scale inland fisheries of Indian tropical reservoirs. The present investigation aims to estimate the food selectivity in juveniles and adults, reproductive traits such as sexual maturity, gonadosomatic index, ova diameter, and fecundity of Gudusia chapra from a large impounded ecosystem of India. A total of 668 (Juvenile 129, adult 539) specimens, 37 to 142 mm standard length and 0.89-25.68 g body weight were collected during October 2014-September 2015. The qualitative estimation of the stomach contents revealed herbi-omnivorous feeding behavior of fish. The mean relative gut length (mRGL) of the species was 1.557 ± 0.024 in juveniles and 1.154 ± 0.012 in adults. The sex ratio was 1:1.30 with dominance of females in the population though insignificant. The total length at which 50% individual attain maturity (TL50) was estimated as 80.50 mm based on the logistic curve. The absolute fecundity of the individuals ranged from 749 to15044, and ova diameter ranged from 0.10-2.00 mm. The gonadal indices (GSI, MGSI, and DI) indicated that spawning extended throughout the year with peak reproductive activity in October, March-April, and July (mean absolute fecundity ranged from 4000 to 6000). The present study characterized biological and reproductive traits of G. chapra from a large reservoir ecosystem and demonstrated a new trend of reproductive pattern which will serve as benchmark data for future assessment and management planning of this species in impounded waters. The study also suggested some specific management measures for sustainable exploitation and conservation of small indigenous species.

Studies on the growth and mortality of Indian River shad, Gudusia chapra (Hamilton, 1822) from Panchet reservoir, India.

The Indian river shad, Gudusia chapra (Hamilton, 1822), is a commercially important freshwater clupeid that contribute to the livelihood of subsistence and marginal fisheries in inland open waters of India and its adjacent countries. The present study was carried out on the growth and mortality of Indian River shad, Gudusia chapra (Hamilton, 1822) based on the commercial length-frequency data collected monthly during October 2014 to September 2015 of a large reservoir located in the border of Jharkhand and West Bengal. The ELEFAN-I (Electronic Length Frequency Analysis) module in FiSAT (FAO-ICLARM Stock Assessment Tools) was used for estimation of growth parameters (L∞, K). The total mortality was estimated following Pauly (ICLARM Fishbyte 2(1):9-13, Pauly 1983) whereas exploitation ratio and maximum sustainable yield were calculated following Gulland (1979). The asymptotic length (L∞) and growth coefficient (K) were estimated as 194 mm and 1.23 year-1, respectively. The species grows to 141.56 and 182.91 mm at the end of the 1st and 2nd years of life. The total natural and fishing mortalities were 6.63, 2.45 and 4.18 year-1 respectively. The value of growth performance index was 2.69. The exploitation ratio (E) was estimated as 0.63. As the exploitation ratio (E) is slightly beyond the optimum, there is likelihood of some threat of overexploitation. Though recruitment was continuous, major pulse was observed during April-May. The present investigation is a first report from Indian reservoir. The maximum sustainable yield of this species was estimated as 485.6 t against the present annual yield of 612.3 t. Avoiding overfishing and wise use of available resources are of prime importance for sustainable fishery management of the reservoir.