Coastal and Marine Ecosystem. Kerala has a coastline of about five hundred ninety kilometres which is about ten per cent of the total coastal length of India. The coastline comprises raised beaches, sand bars, mangroves, rocky shores, low lying marshes and cultivated fields, interspersed with 34 major estuaries and lagoons. Large loads of sediments deposited by the numerous rivers flowing to Arabian Sea has created splits and off shore bars in the near shore region. The body of water behind them formed the nuclei of the present day lagoons and estuaries.
The coastal and marine biodiversity of the state is not so well documented. Fisheries support the economy and nutritional security of the State. The formation of mud banks or 'Chakara' which results in increased fish landings, is a unique phenomenon in the Kerala coast. It is due to the highly productive coastal waters. The state has command over a fishing area of about twenty five thousand square kilometres. The major groups of marine organisms exploited include sharks, rays eels catfishes, sardines, ribbon fishes, carangids, seerfishes (Mackerel family), bill fishes, lizard fishes, thread fin breams, other perches, sciaenids, silver bellies, flat fishes, flat heads, anchovies and prawns.
The quantity and diversity of marine organisms discarded as by catch is huge. The discards are thrown back into the sea by the trawlers. It includes one hundred three species of fin fishes, two stomatopods, three echinoderms, five cephalopods, twelve crabs, eight shrimps, twelve bivalves, sixty five gastropods and four species of jelly fishes. About fifty percent of the commercially important marine fish species are under overexploitation, and in the case of another thirty eight per cent, the exploitation has exceeded sustainable levels. Commercially important species like parava, therandi, kadal aetta, two varieties of sharks, cat fishes, white fish and elasmobranches are fast declining due to overexploitation.