Multi-scale quantification of the effects of temperature on size at maturity in the American lobster (Homarus americanus)

•Mean size at maturity in the American lobster has decreased over the last 20 years.•The size range across which lobsters become mature has broadened in the last 20 years.•Lobsters living in warmer waters mature at smaller size.•Temperature and likely fishing have contributed to the decrease in size at maturity.

Like most ectothermic species, American lobster growing in warmer environments mature at smaller sizes. A formal quantification of this pattern at multiple spatiotemporal scales has not been developed, impeding the development of tools to predict the impacts of climate change on American lobster life-history and fishery. In this study, data from sea sampling programs from southern New England to the Bay of Fundy are used to estimate female lobster size at maturity, and to quantify the effects of water temperature on maturity at three spatial scales: i) regional (∼1000 km), ii) stock (100 s km), and iii) Statistical Area (10 s km).Resultsshow that female lobsters living in warmer waters mature at smaller sizes and that other factors, likely fishing, also contributed to the observed decrease in length at 50% maturity. This study suggests that adaptive management plans need to consider temperature-induced trends in size at maturity to ensure sustainability of the valuable American lobster fisheries. Additionally, this study provides a maturity function for use in models that aim to project effects of climate change on American lobster populations and fisheries dynamics.