Assessment of the Effect of Hook Shape on Fishing Mortality of Multi-Taxa Fish Species Using Experimental Longline Operation Data

To evaluate the effect of circle hooks (C-hooks) on fishing mortality of fish species (blue shark, shortfin mako, striped marlin and swordfish) other than sea turtles in experimental longline operations, Bayesian estimation using statistical models was used to examine whether there were differences in haulback mortality rate, CPUE, mortality per unit effort (MPUE), and hooking position between 3.8 sun tuna hooks and size-different C-hooks. The results showed that the haulback mortality rate, CPUE, and MPUE did not improve with either size of C-hook, but rather tended to worsen. In addition, the use of the C-hook did not reduce the hook swallowing which can lead to post-release mortality. In addition, the mortality rate may be greatly influenced by environmental factors such as soak time and water temperature. These results suggest that it is necessary to consider the trade-off between the effects on sea turtles and on multi-taxa fish species when discussing the use of C-hooks.