DescriptionHumpback whales (Megaptera novaeangliae) are exposed to a high level of human activity in the Gulf of Maine relative to other primary North Atlantic feeding grounds. Observed levels of serious injury and mortality from entanglement and ship strikes have consistently exceeded management limits, but the population-level effects of these and other unwitnessed events has yet not been evaluated. We used a mark-recapture data set from 2000 through 2016 to estimate abundance, survival, population growth rate and the impacts of human activities. Data were obtained through dedicated photo-identification surveys across the Gulf of Maine and high-intensity data collection at smaller scales throughout the region. Population parameters were estimated annually using a hierarchical, Bayesian state-space model that included sex, age, and a random time effect on survival while allowing sex, annual and individual whale effects on capture probability. Based on the posterior distributions of parameter estimates, median abundances ranged from a low of 893 individuals in 2001 to a high of 1,393 in 2016. Average annual population growth was estimated to be 2.8%. The annual number of reported entanglements was not correlated with population size, and there was no evidence that the per capita entanglement report frequency declined after Federally-mandated changes to fishing practices in U.S. waters in 2009 and 2015. Model results also did not suggest overall improvements in population survival rates after 2009. An estimated increase in survival from 2015 to 2016 may have been related to a required reduction in fixed gear buoy lines, but requires further investigation. Observed serious injuries and mortalities from all human sources in US waters accounted for at least one-quarter of the estimated number of deaths. This long-term study of individual humpback whales suggests a slowly growing population with on-going impacts from anthropogenic activities.
|Period||9-Dec-2019 → 12-Dec-2019|
|Event title||World Marine Mammal Conference|
|Degree of Recognition||International|