Cheriyan P. Letha^1,, Oommen Manu²

Interruption in the connectivity provided by the free-flowing river is the most critical issue threatening the life of migratory fishes. Unlike other rivers of Southern Western Ghats, the Meenachil River does not have any hydroelectric dams. Instead, it has several check dams without fish passages along its course, fragmenting the river into discrete lentic zones hampering fish migration. The present study conducted in the Meenachil River of Southern Western Ghats from 2015 to 2019 documented the different migratory fishes of the river and their abundance during different seasons in correlation to the precipitation pattern of the region. Thirteen fish species under catadromous, anadromous, and oceanodromous migrants belong to seven orders, ten families, and twelve genera were recorded in the study. Monsoon is the only season when the river overflows the check dams, restoring the river’s continuity and lateral connectivity. A significant positive correlation was observed (p=0.59 .p< 0.05) between the rainfall pattern and the abundance of migratory fishes during the study period. The nearly threatened migrants of the river, Anguilla bengalensis recorded the lowest relative abundance of 0.23 and Wallago attu 1.14, respectively. Indiscriminate monsoon catching of the gravid species Labeo dussumeiri and Wallago attu during their spawning migrations upstream using specially designed aerial traps was reported. Other monsoon traps Cheru and Perumkoodu set along the flooded river’s lateral connections targeted the floodplain migrants of the river Heteropneustes fossilis, Channa striata and Channa marulius. Gill net traps were set along the migratory pathways to catch Horabagrus brachysoma, a vulnerable species. The salinity barrier Thanneermukhom Bund in Vembanadu Lake, the confluence zone of the river, prevents the migration of the Anguilla bengalensis, Megalops cyprinoides and Mystus gulio between Meenachil River and the Arabian Sea.

Migration, riverine fishes, check dams, spawning migrants, salinity barrier