Spatial overlap, proximity, and interaction between lobsters revealed using acoustic telemetry

Abstract

The cryptic nature of Homarus lobsters has restricted past behavioural studies to aquaria, mesocosms, or shallow coves. As such, spatial overlap and interactions between free-ranging Homarus lobsters have received little attention. However, it is clear that dominance behaviours directly affect their probability of capture, negatively affecting catch and complicating population monitoring. This study describes lobster behaviour at a scale that could not be achieved in aquaria or mesocosms. Home-range overlap and contact rates among free-ranging, acoustically tagged H. gammarus (n = 44) were assessed at multiple spatial scales. Data were analysed as unique pairings of lobsters (dyads), which could be single- or mixed-sex pairings. If home-range overlap between tagged lobsters occurred, interactions between lobsters were classified as attraction or avoidance. The number of times a lobster overlapped with the home range of another lobster was related to the mean substrate hardness within the home range of the focal lobster. Fewer interactions occurred between female lobsters, compared to males and mixed-sex pairings. Interactions between lobsters that occurred at 10 m, and interactions between mixed-sex pairs at 5 m, were identified as attractions. Interactions between male lobsters at 5 m were largely identified as avoidance and may indicate small-scale spatial exclusion. Understanding the drivers of movement and behaviour in wild free-ranging lobster populations is relevant to stock assessments, disease management, protected areas designation, and the development of sustainable evidence-based fisheries.