Halibut Hooking Success By Hook and Fish Size Determined By Direct Observation

The International Pacific Halibut Commission has studied Pacific halibut catch on hooks since the 1920s. Observing cohorts from ages 6 or 7 through at least 12 years of catches has allowed the theoretical determination of catchability as the fish grow in size and recruit to the hook gear.  Cameras and underwater sonars have allowed the direct determination of hooking success. Our first looks with a low light camera suggested a strong relationship between fish length and the probability that the hook attack would result in the fish being hooked, or captured.  A later study with scanning sonar reinforced our earlier observations, and allowed construction of a hooking success curve as a function of length for two sizes of circle hooks.  Most recently, a study with a drop camera is expected to confirm the value for hooking success of larger halibut, which were not observed during the sonar study. All of these studies have led to the belief that for Pacific halibut, the result of a hook attack is determined almost entirely by the size of the fish (the thickness of the jaw) and by the size of the hook.  Findings of these studies and our conclusions will be presented.