California Sea Grant College Program

The extent to which exploitation may alter marine life population structure anddynamics is incompletely understood because past research overwhelmingly relies on time series that date back less than 30 years and begin long after the onset ofexploitation. This study seeks to partially fill this gap with respect to the Californiaspiny lobster, Panulirus interruptus, by fitting a recently developed Bayesian sizestructuredmodel to a newly assembled 120-year historical time series of catch and effort to quantify the effects of fishing on the population’s size-structure and dynamics. In a little over a century, as fishing effort increased, the abundance andproportion of large-sized lobster (> 100mm carapace length) progressively declined.Severely reducing the lobster's average lifespan and size has increased thepopulation's short-term variability, potentially diminishing the resilience of thespecies and the kelp forest ecosystem by compounding the effects of ‘fishing downthe food web.’  This work also demonstrates how integrating nontraditional independent historical sources into ecological studies can help meet challenges typically posed by longer time series, including validating potentially questionable historical data points, corroborating model predictions, verifying the temporal scale of baselines, and identifying alternative anthropogenic causes for the observed or predicted ecological variability. In the lobster case study, historical sources verified an annual catch estimate previously considered an outlier, strongly corroborated the model predictions of fishery-induced lobster population size truncation, and clarified that 1888 was a reasonable pre-exploitation baseline. Further, placing the model reconstruction within the broader historical context of marine conservation over the last 300 years illuminates how lobster conservation tactics based on outdated ecological ideas have facilitated and accelerated the size truncation of the lobster population, and may be undercutting contemporary ecosystem-based conservation measures such as reserves. This approach, which melds contemporary ecological and historical techniques, could be applied to any species to achieve a deeper and more comprehensive understanding of the history of the environment.