Match of the day: optimized experimental design in alternate-haul gear trials

Abstract

Abstract European Union (EU) fishers need a range of gear options to comply with requirements under the landing obligation. Alternative fishing gears may be implemented provided equivalent selectivity can be demonstrated. Catch comparison is a valid method of testing the size selectivity of two or more fishing gears and simultaneous gear deployment helps minimize between-haul spatiotemporal variability in abundance. Non-simultaneous or alternate-haul deployments are generally required for single-rig trawls or seines nets. In those gears, matching consecutive test and control hauls helps minimize such variability. Random-haul matching strategies have also been employed where consecutive deployments are not logistically possible. Here, we investigated the effects of different matching methodologies by simulating a range of stylized scenarios of between-haul variation in abundance. We resampled data from a multi-rig catch comparison trial and emulated consecutive or randomly matched hauls. We examined how haul matching methodology influences catch curve estimates and uncertainty. Aiming for a balance in abundance across consecutively matched hauls is optimal, while random-haul matching may be the best strategy if neither balanced abundance nor consecutive hauls can be achieved. Based on these outputs, we provide practical guidance for experimental design during planning and at-sea operations to optimize trial outputs.