Aligning Fishing Gear Selectivity With Harvest Slot Limits for Ballan Wrasse Labrus bergylta

Abstract

Selectivity is an important parameter used to identify the portion of a stock caught by a fishing gear. In principle, fisheries management aligns the length at which 50% of individuals are selected for ($L_{50}$) with minimum landing sizes. Harvest slot limits (the implementation of minimum landing sizes alongside maximum landing sizes) are in place for ballan wrasse, a sequential hermaphrodite commercially exploited in northern Europe. The selectivity of fishing gears used has yet to be investigated for this fishery. Two fishing gears were dismantled into their selective apertures, and fall-through experiments were used to determine the selectivity of each aperture, alternative escape panels and alternative entrances. Binomial logistic models were fit to estimate the relationships between selectivity, fish length and condition factor for each aperture. Linear models were used to investigate the relationships between $L_{50}$, escape panel width and entrance diameter. Both commercial fishing gears retained fish both smaller and larger than the size-based harvest slot limits. Empirical relationships were developed to estimate escape panel widths and entrance diameters to align the $L_{50}$ with harvest slot limits. Fisheries managers may use these relationships to propose modifications to fishing gear that align their selectivity with harvest slot limits. However, it should be considered that these relationships were based on morphology and do not account for behaviour within the estimation of selectivity.