Reviewing hook degradation to promote ejection after ingestion by marine fish

Abstract

A widely recommended strategy for releasing fish that have ingested hooks is to simply cut the line. The utility of this approach is based on the premise that the individual will eventually eject the hook following sufficient oxidation. However, few quantitative data are available describing the mechanisms affecting hook decay. We addressed this issue by testing the independence of various technical factors on the degradation of 828 hooks comprising 23 designs (absolute sizes 227-611 mm²) after protracted submersion in seawater. Twelve replicates of each hook were destructively assessed for compression and tensile strengths (using a force gauge) and 24 replicates were weighed, photographed and submersed in seawater. After submersion for 8 and 28 days, 12 replicate hooks were removed, re-photographed, re-weighed and tested for compression and tensile strengths to provide indices of decay. Hook degradation was mainly affected by the wire material and diameter and could be significantly promoted by choosing carbon steel designs, either with a wire diameter of ≤0.9 mm for the examined sizes or, alternatively, bait-holder barbs (or similar modifications) along the shaft. By rapidly oxidising and weakening after ingestion, such designs could ultimately help to reduce negative impacts of hooks on released fish.