Climatic and anthropogenic factors changing spawning pattern and production zone of Hilsa fishery in the Bay of Bengal

Hilsa (Tenualosa ilisha Hamilton) as a single species accounts 12% for more than half of the total marine catches. About 2% of the entire population of the country is directly or indirectly engaged with Hilsa fishing. Hilsa has a wide geographical distribution in Asia from the Persian Gulf to the South China Sea. Particularly large stocks are found in Upper Bay of Bengal (BOB) region sustained by the large river systems. The global Hilsa catch is reported 75% from Bangladesh water, 15% from Myanmar, 5% from India and 5% from other countries such as Thailand and lran. Hilsa is a highly migratory and anadromous fish with the same migratory and same breeding behavior as that of Atlantic Salmon fish (SaIrrio sp.). Due to various anthropogenic activities, climate change effect, increased siltation and rising of the river basins, the migratory routes as well as spawning grounds of Hilsa are disturbed, displaced or even destroyed. During last two decades hilsa production from inland water declined about 20%, whereas marine water yield increased about 3 times. Major Hilsa to catch has been gradually shifted from inland to marine water. Hilsa fish ascend for spawning migration from sea into estuaries, It has been found that the major spawning areas have been shifted to the lower estuarine regions of Hatia, Sandwip and Bhola. At the spawning ground of Hilsa, the fishing level E=1.36 yr(-1), where in the river Meghna the F-msy=0.6 yr(-1) and exploitation rate E=0.70 is (E-msy>0.5). Oceanographic changes viz, high turbidity increased noodling, more tidal action and changes of salinity etc. have accelerated the change of migration patterns of spawning, growth and its production. Hilsa fecundity ranges from 1.5 to 2.0 million eggs for fish ranging in length from 35 to 50 cm. Hilsa fecundity is declining in different areas due to climate change and the declining fecundity impacting greatly on Hilsa production. Due to shifting of the spawning ground at the lower zone, the survival rate of juvenile Hilsa is seriously affected. (C) 2015 Published by Elsevier B.V.