Sea snake by-catch of fish trawlers on the northern Australian continental shelf

During 1986-90, 206 sea snakes were collected from Taiwanese pair-trawlers (North West Shelf, 1986-87), Thai stern-trawlers (Arafura Sea, 1986-87), RV Soela (North West Shelf, 1986) and RV Clipper Bird (Timer and Arafura Seas, 1990). Taiwanese (58 specimens; 294.8 h trawled) and Thai (71 specimens; 1244 h trawled) vessels trawled in 50-75 m and caught 10 and 7 species respectively. The Soela (41 specimens; 72.5 h trawled) and Clipper Bird (36 specimens; 103 h trawled) operated in depths of 19-198 m and each caught 12 species. Hydrophines (10 species plus one specimen from an undescribed taxon) represented 68.4% of the specimens. Aipysurines (6 species) were more common in samples from the North West Shelf (46.2% of taxa, 56.6% of specimens) than from the Timer and Arafura Seas (28.6% of taxa, 11.2% of specimens). Taiwanese boats on the North West Shelf (1980-90) and Thai boats in the Arafura Sea (1985-90) were estimated to have caught 49 000 (+/- 5600) and 10 000 (+/- 1250) sea snakes respectively. Trawl surveys (e.g. Soela and Clipper Bird) may be unsuitable for monitoring sea snakes, because approximately 25 surveys would be needed to detect a 20% exponential decline in absolute abundance.