Eliminating interactions between killer whales and longline fisheries
Increased sablefish or black cod (Anoplopoma fimbria) catches in the 1980s in Prince William Sound and the Bering Sea lead to more reports of killer whales interfering with fishing vessels by removing the hooked sablefish from the longlines as they were being hauled to the surface. In addition to taking the fish, the orcas were damaging gear by straightening hooks, breaking gangions, and breaking or tangling groundlines.
Our objective was to develop new technologies, or adapt existing ones, to reduce or eliminate the interaction between killer whales and the longline fishing fleet. We recorded various underwater sounds of the longline fishing vessels. Given prior experiments on killer whale hearing, we were able to determine which sounds would be most audible to killer whales: 1) the tonal “whine” of the hydraulic system as it powers the line winch, 2) the “clatter” sound produced by the power wheel rotating to retrieve the long line, 3) the sounds produced by turning the propellers on and off while backhauling, and/or 4) the sound of the groundline anchor as it comes off the sea floor. It’s been proposed that the sound of the fish struggling on the line coule be attracting the whales, but this seemed unlikely given the smallness of the fish and the great distances involved.
We returned to Prince William Sound to play these sounds back under water in an attempt to attract killer whales to determine what noises the orcas were using to locate vessels. We found that relatively inexpensive modifications to decouple the boats’ hulls from the vibration of their boats’ machinery reduce the sound radiated from the vessel by 20 dB. The distance a whale could hear the vessel would be reduced from over 18 km to 2 km with these quieted vessels, which would would reduce killer whale depredation to an insignificant level.
Francine, J.K. and F.T. Awbrey. 1993. Avoiding prohibited species: proposal to resolve the conflict between the sablefish longline fishery and killer whale conservation in Alaska. Final report, grant number NA89AB-H-SK001. Hubbs-SeaWorld Research Institute, San Diego, CA, USA: 52 pp