Uncontrolled fishing for food and sport has been identified as a major threat for the majority of freshwater fish species in Kerala, along their migratory route from rivers to inland canals and wetlands for spawning.

A variety of snakes, amphibians and birds are also slaughtered by hunters who go on a killing spree during the monsoon migratory season for fishes known as ootha in local parlance.

The mass mortality adds to the threat posed to biodiversity by reclamation of paddy fields, river sand mining and pesticide contamination, according to a study conducted by the Kerala State Biodiversity Board (KSBB).

The study warns that intensive fishing during migration would lead to depletion of fish stocks and threaten the survival of species. Fishing during the spawn disrupts the breeding cycle, resulting in a dramatic decline in stocks. The report says that spawning fish was regarded as easy target, attracting more people to the hunt. Non-resident Malayalis often timed their vacation with the ootha season to indulge in fishing for sport.

Very few fish could overcome the array of traditional and modern fishing equipment deployed on the migratory route from rivers through streams and canals to the breeding and spawning grounds in upland paddy fields. In some areas, fishermen used knives and choppers to kill the fish in large numbers.

A sizeable number of snakes, frogs, turtles and storks were also killed during the ootha season. Paddy fields were littered with mutilated bodies of snakes and eels after a fishing session.

KSBB chairman Oommen V. Oommen said the board would submit the report to the government with recommendations to impose a ban on fishing during the spawning season and take steps to protect the migratory routes and habitat of freshwater fishes.

The study which covered inland migration of freshwater fishes in Kottayam, Pathanamthitta, Thrissur, Wayanad and Kannur districts found that fishermen used electrocution, baskets, nets, rod and line and barriers to trap or kill fish. In the shallow paddy fields, the fishes were especially vulnerable and easy prey at night for the fishermen hunting by torchlight.

The survey listed 20 fish species that are commonly hunted in Thrissur district, 30 in Wayanad, 16 in Kannur, nine in Pathanamthitta and 15 in Kottayam during the ootha season. The inedible species were killed and thrown away. A few fish markets in Thrissur had stalls selling fish eggs.

The report said spawning fish commanded a higher price because the enhanced fat content was believed to make them tastier. Species like Wallago attu (vala), Channa marulius (cheran), Channa striata (varaal) and Harobagrus brachysoma (manhakoori) command the highest price, selling at Rs. 250 to 300 per kg.

KSBB member secretary K.P. Laladhas said the situation warranted an extensive awareness campaign to sensitize people to the biodiversity loss caused by unsustainable fishing during the spawning season. He also highlighted the need for more detailed studies on the issue.

Most fishermen interviewed during the survey reported declining catch. They attributed it to wetland reclamation and pesticide residue in paddy fields.

The report warned that destructive fishing practices like electrocution had made ootha fishing unsustainable, resulting in a stark decline in the population of several species.