Survival rates of sea snakes caught by demersal trawlers in northern and eastern Australia

This paper examines the survival rates of sea snakes caught in research and commercial trawls in the main fishing grounds of northern and eastern Australia. Observers recorded whether the snake was alive or dead when it was landed on deck, and (if possible) its species, its length and weight, the duration of the trawl and the total weight of the catch. To estimate long-term survival, captured sea snakes were kept in sea water in drums on a large research vessel and monitored after 1, 6, 12, and 24 h then daily for up to 4 days. Up to 28% of all sea snakes landed on deck from commercial prawn trawling were found to be dead. Both duration of the trawl and catch weight had significant (P<0.001) positive effects on within-trawl (short-term) mortality of these sea snakes. About 30% of all sea snakes from 30 min duration trawls died during the 4-day survival experiment, with Hydrophis ornatus showing the highest mortality (< 50% alive after 96 h in a tank). Hydrophis elegans appeared to have the lowest mortality rate after capture (94% alive after 96 h). Overall, mortality from research and commercial prawn trawling was estimated as 48.5% of snakes caught. Visible damage to sea snakes by trawling was relatively low (5.4%). The introduction of Bycatch reduction devices, such as square mesh and fisheye windows, should improve the survival of sea snakes by reducing the catch weight and the number of sea snakes being caught.