Incidental capture of sea-snakes (Hydrophiidae) by prawn trawlers in the Gulf of Carpentaria, Australia

Abstract

Sea-snakes were collected from research trawlers and commercial prawn trawlers in the Gulf of Carpentaria during the period from April 1976 to December 1991. The data were analysed on the basis of CPUE (catch per unit effort) for depth, latitude and season. The research trawlers, operating in the eastern Gulf of Carpentaria, and the commercial prawn trawlers, operating in the south-western Gulf of Carpentaria, caught sea-snakes at a rate of 0.028 and 0.026 sea-snakes per metre of headrope length per hour, respectively. Lapemis hardwickii was the sea-snake most commonly caught by the research trawlers-53% of all snakes-and Hydrophis elegans was the sea-snake most commonly caught by commercial trawlers-25% of all snakes. Depth was the most significant factor affecting CPUE, with more than 70% of all sea-snakes being caught in waters less than 15 m deep. When catches of all species were combined, a significant interaction (P<0.05) existed between depth and season. L. hardwickii specimens were caught more frequently in shallow coastal waters (< 15 m deep) in spring but in deeper water further offshore in autumn. A significant interaction between latitude and depth was found for Astrotia stokesii; specimens were caught more frequently in deeper water at 14% Enhydrina schistosa is generally coastal, with 8800 of specimens being caught in water less than 10 m deep. Seasonal movement of sea-snakes between inshore and offshore waters may be linked to their breeding cycles. The estimated number of sea-snakes captured in the Gulf of Carpentaria for the 1991 prawning season ranged from 73 583 to 165 559, with a mean of 119 571. The survival rate of sea-snakes from commercial prawn trawls was about 60% and hence between 29 801 and 67 051 sea-snakes are estimated to have died.