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Individuals in all life stages of the large oceanic diamondback squid Thysanoteuthis rhombus were observed in the southeastern Arabian Sea. A total of 82 individuals were collected from the Arabian Sea between February 2013 and December 2018. The length-weight relationship follows an allometric growth pattern. Age and growth were estimated by statolith increment analysis (n = 77) and demonstrated a rapid growth rate ranging from 1.42 to 4.80 mm dorsal mantle length (DML)/day. Based on back calculated hatch dates, T. rhombus spawned from May to December with a peak in July. Male and female squids matured at 6 months of age. The oldest individual was a mature female (655 mm DML) that was 220 days old with a growth rate of 2.97 mm DML/day. Differences in size-wise (DML) instantaneous growth rates were evident. Stomach content analysis revealed that fish and squid were the major prey of adults and sub-adults, while in juveniles, crustaceans were the dominant prey item. Ontogenetic differences in the diet were apparent.

The relative abundance and biological characteristics of the spadenose shark Scoliodon laticaudus, from the south eastern Arabian Sea along Karnataka, India was studied. The average annual catch of the species during the period 2012–2017 was estimated at 112 t which formed about 13% of the total shark landing in the region. The species is landed mostly by trawl nets. Monthly abundance estimates showed that highest landing of the spadenose shark was observed in January. A total of 852 specimens were studied for biological characteristics. The length range of 19–63 cm was observed and length group of 45–55 cm formed the mainstay of the fishery. The length weight relationship for male and female and sexes pooled were 0.06588 L2.2386; 0.01118 L2.7497 and 0.01396 L2.6840 respectively. Analysis of covariance showed significant differences between the male and female ( p 0 . 05 ). In the present analysis, the regression co-efficient ( b value) for the species differs significantly from the value 3 indicating allometric growth. Lm50 for female and male were estimated as 32 and 33 cm. Chi-square-test on monthly sex ratio for the period showed that there was significant difference in sex ratio only in the months of January, October and November. S. laticaudus was found to be predominantly piscivorous in diet. The fishery is declining and efforts have to be taken for sustainable exploitation of resources.

Environmental parameters influence the productivity and abundance of fish in marine ecosystems. In this study, we attempted to analyse the relationship between environmental parameters and abundance of fish in trawling grounds in south-eastern Arabian Sea along the coast of Karnataka. Among the 85 species of finfishes and shellfishes caught in the trawling grounds, 41 finfish species, 24 crustaceans, 18 molluscs and two echinoderms were recorded. Seasonal differences were seen in biomass with the highest biomass during the post-monsoon period (October-January). Water temperature and nutrients were the key contributing factors of seasonal differences in the biotic communities studied. Season specific diagnostic species were identified using SIMPER analysis. Squilla which formed the major prey item of most of the demersal fishes dominated (>40%) coastal grounds throughout all seasons. This could be considered as a fishery indicator of the region. The dominance and abundance of copepods was found to be influenced by sea surface temperature (SST) and nutrients. The results of the study have implications on the fishery, knowledge on environmental factors influencing the abundance and importance of non-commercial species in sustaining the fishery in the region.