Observed size distribution changes in American lobsters over a 12-year period in southwestern Nova Scotia, Canada.

Size distribution and size frequency information of American lobsters (Homarus americanus) are often used to help estimate the age distributions, and reproductive output for the species and to guide the determination of appropriate minimum legal sizes for the fishery. This study used truncated linear regression models to estimate the effects of sampling year, sampling month, lobster sex and water depth on the lobster size. A dataset of almost 130,000 trap-caught lobsters from the two most important lobster fishing areas of Atlantic Canada collected over a 12-year period (2004-2015) was analyzed. It was shown that truncated models can help to account for biases due to the trap sampling method from vessels and from wharf samplings. There were significant annual and seasonal changes in size distribution, and data collected outside the fishing season showed a significant increase in carapace length in 2014 and 2015, potentially reflecting a northward shift of the range of lobster populations due to more favourable settlement and recruitment habitats. Size also increased in late summer, likely due to moult. Our results demonstrated that landed lobsters, especially females, were smaller than the predicted size-at-maturity in the region (96.5 mm carapace length), which could have long-term repercussions for the stock's reproductive potential.

Fisheries dataset on moulting patterns and shell quality of American lobsters H. americanus in Atlantic Canada.

Monitoring the moulting phenology of American lobsters (Homarus americanus) is important for maintaining sustainable lobster stocks. Changes in lobster landings can affect reproduction and disease susceptibility. Data on lobster moult indicators and on life-history traits (sex, size) were collated from a twelve-year monitoring program (2004-2015) in six lobster fishing areas in Atlantic Canada. A total of 141,659 lobsters were sampled over 1,195 sampling events using a standardized protocol and commercial lobster fishing traps. The dataset contains pleopod stages, estimated hemolymph protein levels (°Brix values) and shell hardness as well as lobster sex and size. Evaluation of sex ratio dynamics is also possible but existing biases in sampling males and females needs to be noted. This dataset is valuable in terms of inferring spatio-temporal trends in the life history of lobsters, as well as in the analysis of their moult cycle, and hence more generally for fisheries science and marine ecology.