Estimation of the effect of gear design changes on catch efficiency: Methodology and a case study for a Spanish longline fishery targeting hake (Merluccius merluccius)

• A method to estimate the relative catch efficiency of different fishing gear.
• Assess effect of gear changes on catch efficiency for a Spanish longline fishery.
• Results demonstrated that a thicker snood line reduced catch efficiency on hake.
• Hook type and snood line length used had no effect on the efficiency of the fishery.

This paper describes a method to estimate the relative catch efficiency of different fishing gear designs based on comparison of catch data. This method does not require an equal number of deployments or alternation between gears, but it accounts for multiple competing models describing the data by using multi-model inference. By applying a double bootstrapping procedure, this method also accounts for the uncertainty in the estimation resulting from between-deployment variation in catch efficiency and availability of fish as well as uncertainty about the size structure of the catch for the individual deployments. Finally, by incorporating the multi-model inference into each bootstrap iteration, the method also accounts for the uncertainty due to uncertainty in model selection. Using the described method, we investigated the effect of gear design changes on catch efficiency for a Spanish longline fishery targeting hake (Merluccius merluccius). We tested and compared four different designs against the traditional design used in the fishery. The first was a design compatible with automation that differed from the traditional one in hook size, snood line length, and snood line diameter (new automatized design). In the other three designs, only one of the parameters was changed. The results demonstrated that the new automatized design resulted in a significant decrease in catch efficiency due to its thicker snood line. The hook type and snood line length used had no effect on the efficiency of the fishery.