Incidental mortality analysis of Harbour Porpoise (Phocoena phocoena) population: Random Leslie approaches

MANUEL O. CACERES & IRIS CACERES-SAEZ

Tampa, Florida

Conferencia; 19th Biennial Conferences on the Biology of Marine Mammals; 2011

Society of Marine Mammalogy

Demographic models are commonly used to study cetaceans population dynamics and are characterized by a representation of age classes. The primacy building blocks are age-specific survival or mortality and birth rates, which can be combined using a Leslie matrix to provide estimates of the maximum possible rates of increase for the population size. Specific mortality data are valuable for modeling the viability of threatened species. Depletion of prey, pollution, and other anthropogenic disturbances are believed to have contributed to population declines, but the evidence is less conclusive for these factors than it is for fishery bycatch. The harbour porpoise (Phocoena phocoena) in Canadian waters are subjected to considerable incidental mortality in commercial fisheries. In an attempt to estimate a population growth rate that incorporates uncertainties in vital parameters, we apply a random Leslie analysis to calculate an effective growth rate for the time-dependent mean-value population. An effective growth rate can be characterized by studying the time evolution of the mean-value population vector state (in an age-structured description). We show that the asymptotic behavior of the mean-value vector state, that characterizes the population growth rate when the model has random vital parameters, shows a value that is far below previous expected potential estimations. Thus we propose to reduce even more the indices of incidental mortality quotas to prevent mayor risk in the cetacean population.