Search

Ten-year satellite derived data (January 2007 to December 2016) were used to investigate the variability of Chlorophyll-a (Chl-a), sea surface temperature (SST), net primary production (NPP) in the eastern Arabian Sea (AS). This study is aimed to show the coupling of physical and biological processes to understand how temporal, annual and inter-annual variations occur and the forcing mechanisms behind these variations in the ocean environments. This work is linked to Indian Ocean Dipole and the El Nino/Southern Oscillation, which frequently co-occur and drives inter-annual changes within the AS. Vertically Generalized Production Model was used to estimate NPP using chl-a, Photosynthetically Available Radiation, euphotic depth, and maximum photosynthetic rate from SST. The relationship between NPP and SST showed change in the pattern over the study period. The NPP in the AS is characterized by an unusual decline during El Nino events. AS is more productive during summer monsoon (June–September) due to coastal upwelling, wind driven mixing and lateral advection processes. There was decline in NPP after 2014 and this trend continued in the following years. The present investigation revealed that the strong El Nino condition was observed in 2015 and productivity of AS declined by ~ 19%, while SST increased by ~ 2% from an overall average of 2007–2016. Increased SST and low productivity could result in low fish catch in AS. Increasing trend in SST could be attributed to the extreme events like cyclones occurring along the west coast of India.

Investigations were carried out to determine the nutritional profile of Indian Ocean swimming crab Charybdis smithii, which is emerging as an unconventional resource in trawl discards of India. The average protein content was 9.38 g/100 g, fat 0.86 g/100 g, ash 0.34 g/100 g, fiber 0.13 g/100 g, and carbohydrate 1.8 g/100 g. One-way analysis of variance showed no significant variations of constituents except in dry matter and carbohydrate between sexes. Macronutrients, Na (317.1, 327.6/100 g), K (148, 177.40 mg/100 g), Ca (187.90, 285.80 mg/100 g), and Mg (34.31, 41.49 mg/100 g), showed significant variation between sexes. The composition of micronutrients in male and female were Cu (0.28, 0.15 mg/100 g), Fe (0.57, 0.71 mg/100 g), and Zn (1.71, 2.75 mg/100 g). Mineral content showed significant difference between sexes. Amino acid analysis showed that 12.04 and 11.47 g/100 g essential amino acid glycine was present in male and female, respectively, and lysine concentration was 13.96 and 12.65 g/100 g, respectively. The nutritional profile of the species was determined the first time and shows that it is comparable with any other edible crabs and could be exploited as a commercial resource to supplement nutritional demand.

The effectiveness of GIS-based resource mapping to strengthen the database for Ecosystem-Based Fisheries Management (EBFM), was tested in an attempt at resolving the existing gap in the data on non-commercial resources. In this paper we describe the result of that try by giving an example of one of the most important influential species in the benthic ecosystem of the Southeast Arabian Sea (SEAS). An estimated 2803 t of Charybdis hoplites, a relatively little known species from the coast, are yearly caught and discarded by trawlers operating from the Mangalore fisheries harbour. A GIS-aided study on distribution and abundance estimated, that the average biomass of the species is 322.7 t, at any time in the area covered. This study brings out the fact that a number of non-commercial biota are serving as non-detectable factors in sustaining productivity. The identification of their role and the quantification of their biomass thus constitute important data for an effective implementation of EBFM.

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.

The feeding regime of organisms depend on the plankton community structure which is being studied worldwide to assess the changes in marine ecosystem structure due to climate change or anthropogenic activities. An attempt is made here to study the seasonal and long term variation in feed composition of Indian mackerel over a period of 40 years and its relationship with sea surface temperature to elucidate structural changes in food composition if any over period of time and its relationship to the primary and secondary productivity in eastern Arabian Sea marine ecosystem. The diet study during 2011-2014 reported the domination of phytoplankton consisting of Coscinodiscus sp. consistently and the presence of macroplankton and fish larvae whereas the diet during 1960-1961 showed the dominance of zooplankton and copepods. It could be assumed that increase in sea surface temperature which resulted in dominance of phytoplankton community as reported elsewhere in the world is also observed in eastern Arabian Sea which is reflected in the diet regime of Indian mackerel. The results also indicate its facultative feeding behaviour by compensating the low value phytoplankton with high value macroplankton and hence can be considered as a resilient species with regard to climate change.