Circle Hook Size and Spacing Effects on the Catch of Pacific Halibut

Joint fishing for halibut (Hippoglossus stenolepis Schmidt, 1904) and sablefish (Anoplopoma fimbria Pallas, 1811) in Alaska in recent years has created questions about the use of fishing effort data in the halibut stock assessment. The optimum gear for halibut uses larger hooks and longer spacing than sablefish gear. We conducted a randomized block fishing experiment to estimate the relative fishing power of different hook sizes and spacings. The blocks consisted of 12 randomized treatments, each a combination of one of four hook sizes and four hook spacings. All possible treatments were not tested because some are not used in the fishery. Each treatment consisted of a single 100-hook skate of gear. Primary response variables were the weight of legal-sized halibut for commercial retention and the count of sub-legal sized fish. The experiment was conducted in a high fish density region in 2005 and in a lower fish density region in 2007. There was no evidence of an interaction effect between hook size and hook spacing in either year, for either legal-sized weight or sub-legal count. Hook size had an effect on sub-legal fish counts in both areas, with highest catches on smaller hooks, but there was evidence of a hook size effect on legal weight in the high density area. Hook spacing had an effect on weights and counts with higher catch seen on the longer spacings.