Movement patterns of the European lobster Homarus gammarus : investigating the effects of habitat use and behaviour patterns on catchability

Abstract

Catch per unit effort (CPUE) is an index of abundance used in fisheries stock assessments. CPUE is typically calculated using fishery data and standardised using statistical methods. A major assumption of fisheries stock assessments is that all individuals are equally available to the fishery, neglecting the possibility that individual-level variability in physical traits, internal states, and expressed behaviour will likely change over time, affecting the probability of capture. However, many knowledge gaps exist regarding behaviour of free-ranging species. This study used fine-scale acoustic telemetry data to quantify free-ranging behaviour of the commercially important European lobster to improve uncertainty surrounding estimates of catch. Behaviour in the vicinity of traps was quantified using an experimental approach that highlighted the highly variable response rate at which lobsters approach traps, and the importance of field studies to capture the full range of movements when compared to mesocosm studies. The interaction between animals at traps is an important aspect of catch, but space-sharing and interaction between free-ranging lobsters has not previously been quantified. A hierarchical approach was used to assess space-sharing, contact rates, and fine-scale interaction between lobsters of the same, and opposite sex. Some lobsters interacted with multiple individuals, commonly on shelter providing substrate; space-sharing and interaction was likely driven by more mobile males. Trap exposure has previously been correlated with increased movement, but the fine-scale drivers of movement, and behavioural states relating to movement, have not been identified. Different aspects of lobster movement were investigated and drivers of movement varied by individual. Interpretation of results varied with the sampling period highlighting the importance of correctly matching the resolution of the behaviour to that of the data collection. Finally an individual-based model was used to demonstrate how movement and behaviour of lobsters can affect catch, to allow better informed sustainable management practices