The relative condition factor (Kn) based on length-weight relationship and food and feeding habits of Jones’ pony fish Eubleekeria jonesi (James, 1971) off Mandapam waters was studied during December 2016 - April 2018. The Kn values showed variations on a monthly basis with maximum value during September (1.23) for male and March (1.53) for female. Analysis of fullness of stomach of 961 samples within the size range of 51-130 mm revealed 40.87% fishes as actively fed, 36.19% as moderately fed and remaining 22.94% as poorly fed. The monthly mean fullness index (FI) was highest during September for both sexes. Highest gonadosomatic index (GSI), vacuity index (VI) and Kn value were observed during March-April in females, probably indicating a spawning peak and hence meagre feeding, which resulted in lowest fullness index (FI). Fishes of smallest length group (51-70 mm) had highest FI and minimum VI and vice versa. The values of index of relative importance (IRI) indicated that the species was planktivorous as well as detritivorous, with top priority towards crustaceans (27.6%) followed by bivalves (23.6%), foraminifera (15.4%), phytoplankton (12.5%), gastropods (9.1%) and nematodes (8.3%) in the gut contents. Diet did not show significant variation either sex-wise or size-wise.
1. Hammerhead sharks are represented by four species in India's marine fishery -Sphyrna lewini, Sphyrna mokarran, Sphyrna zygaena and Eusphyra blochii. This paper describes the hammerhead shark fishery in India during 2007-2018 and summarizes observations on the biology of S. lewini exploited along the Indian coast.2. Hammerhead sharks are caught by trawl nets, gillnets, seines and line gear, mostly as bycatch. Annual average landing of hammerhead sharks during 2007-18 was 639 t, with a low of 290 t in 2018, of which S, lewini was the dominant species, comprising 95% of landings. Hammerhead sharks formed nearly 1.31% of the total elasmobranch landings. About 54% of hammerhead sharks were landed by trawlers.3. Length range of S. lewini in regular landings was 36-300 cm total length (TL). The dominant size class was 30-100 cm TL; 79.5% of males and 83.2% of females measured between 40 and 100 cm TL. Length-weight relationship was derived as W = 0.0218*(L) 2.634 and W = 0.0131*(L) 2.769 for males and females, respectively. 4. Overall sex ratio (F: M) was 1.3:1; below 100 cm TL, the sex ratio was skewed in favour of females. The length at first maturity of males was estimated as 168 cm.The length at first maturity of females was estimated at 239.6 cm. Fecundity ranged from 12-40, size at birth was 36-45 cm TL. Bony fishes were the preferred prey, followed by cephalopods.5. The S. lewini landings in India are dominated by juveniles and threatens sustainability of the stock. Capture of juvenile sharks can be excluded to a considerable extent through strict implementation of minimum legal size of capture, and a conservative minimum legal size of 220 cm is suggested for this species in Indian waters. Identification of recurring juvenile aggregation grounds, their spatio-temporal closures, gear restrictions and greater stakeholder awareness could lead to conservation of the resource and a sustainable fishery.
Three incidences of bloom (Noctiluca scintillans) has been recorded in Gulf of Mannar (GOM) during 2019(September) 2020(September& October) and 2021 (October). On 10th September 2019, a deep green bloom started along the coast of Gulf of Mannar stretching from Kunthukkal(9.2579° N, 79.2213° E) to Vedalai (9.2723° N, 79.1040° E) (about 10 kms) and algal crashing started on 11th and 12th September, 2019, resulting in mass mortality of about twenty wild fish groups mostly associated with coral reefs. The ichthyo-diversity affected during the bloom period have been identified and quantified. Noctiluca cell density was high ranging from 1.33 x 103cells/L to 1.24 x106cells /L with slight year to year variations. High chlorophyll concentrations (> 7.5 mg /m3) were measured during the bloom event at the cage site. Remote sensing images acquired from MODIS –Aqua 4 km data during the bloom period indicates very high concentration of chlorophyll in most of the northern areas of GOM indicating the presence of algal bloom. Low concentration of dissolved oxygen (less than 3.5 mg/L) was measured during the bloom in all the three years. Concentration of ammonia in surface and sea bottom waters was quite high 7.54 & 18.86µg-at/L. Wild fishes in the coral reefs and fishes cultured in cages (Cobia and Silver Pompano), were found dead due to acute hypoxia and anoxia. Decay of the bloom led to enormous ammonia production, sudden reduction of dissolved oxygen in the water and, eventually stress, shock and mortality of all fishes.
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