Reconstructing the population dynamics of eastern Pacific gray whales over the past 150 to 400 years

Abstract

Reconstructing the historic trajectory of the eastern North Pacific gray whale (Eschrichtius robustus) is important for the understanding of whale population dynamics and for management of the hunt on the population. Interestingly, the density-regulated BALEEN II model (Punt, 1999) will generally not reconstruct the trajectory because it does not reconcile catch history and abundance data unless additional ad hoc hypotheses are added to the model. Here, an alternative model of inertial dynamics is used to estimate the population trajectory over the past 150 to 400 years. This model is a traditional density-regulated model with superimposed density-dependent changes in the intrinsic life history. Nine different versions of the model are examined and Bayesian assessments performed for the complete catch histories from 1600 and 1846. This reconciles the data, can explain an independent abundance estimate from 1885 and it predicts an over-compensatory population that has increased steadily above the equilibrium abundance for the last three decades. The model predicts that gray whale abundance will begin to decline in a more or less drastic manner in the near future.