Seasonal trends in European lobster (Homarus gammarus), spider crab (Maja brachydactyla), and brown crab (Cancer pagurus) populations in the Bailiwick of Jersey (Channel Islands) and the relevance to environmental and biological parameters

The thesis examined the variation in Landings Per Unit Effort (LPUE) as an indicator of activity for three commercially significant species in Jersey, those being, European lobster (Homarus gammarus), spider crab (Maja brachydactyla), and brown crab (Cancer pagurus). Isolated trends were identified for each species, highlighting the seasonal variation in LPUE between 2007 and 2022. Notably, the overall seasonal trends varied among the species, indicating distinct responses to environmental conditions. This thesis investigates potential drivers of these trends, focusing on temperature, biology, and life cycles. Individual annual LPUE data was compared to the decomposed LPUE (a component isolated in the decomposition analysis process which is the suggested pattern for seasonal variation) for each species to first confirm that the extracted patterns are genuine recurring trends and secondly, identify which years deviate most significantly from these seasonal trends. The majority of the years demonstrated a strong correlation between the decomposed and annual LPUE
data (r > 0.6). However, six years of the dataset, the correlation was weaker, prompting further investigation into potential drivers for these deviations. This thesis provides valuable insights into the seasonal fluctuations in LPUE, the causes of these fluctuations, and possible contributing factors.