Factors affecting the fluctuations of the European lobster populations in Scottish coasts
The European lobster (Homarus gammarus L.) fishery in all coasts of Scotland records total annual landings of nearly 900 metric tonnes and total value of about £7 millions. Two Scottish lobster populations were investigated, the Hebrides and Southeast with data from early 1960’s to late 1990’s. Diverse sources of information were used and when possible comparisons between the populations were carried out at varied spatial and temporal scales emphasising on two components, the sub-legal and legal lobsters. The lack of accessibility to the Hebrides fishery limited the comparisons between the populations. More studies on the southeast lobster population were possible. Varied methods and traditional and innovative techniques applied to the data showed dissimilarities between the populations. Differences in the size-structures, estimates of fecundity, size at the onset of sexual maturity (SOM), sex ratio, fishery duration, influence of environmental variables on the catch of undersized and legal size lobsters, and respective exploitation rates were found. The Southeast lobster population showed high historical exploitation levels but recruitment levels indicated strong resilience of this population to environmental or fisher-related processes. Increasing landings with time might be related to an increase in temperature at large and small spatial scales. Habitat type and shelter availability affect the size-structure of this population. Exploitation rate estimates indicated a relatively healthy state of this fishery but risks of growth over-fishing might be considered. Fluctuations of the Hebrides fishery were strongly related to density-independent processes. The historical patterns of exploitation and the little evidence of good recruitment levels questioned the resilience of the population. Assumptions of over-fishing risks and recruitment failure were weak. The results contribute to the knowledge of the European lobster fishery in Scottish waters and for other commercially important lobster fisheries.