Can PVA models using computer packages offer useful conservation advice? Sooty shearwaters Puffinus griseus in New Zealand as a case study

Abstract

Population viability analysis (PVA) can guide conservation management and research by identifying the cheapest and most effective actions required to conserve populations and by prioritising research. The usefulness of a very preliminary PVA model is illustrated here for managing New Zealand mainland colonies of sooty shearwaters Puffinus griseus, a long-lived seabird that is preyed on by small carnivores and harvested by Maori for food. The model suggests that chicks can be safely cropped for transfer to depleted colonies, or for human consumption from the two large Otago colonies with populations exceeding the most conservative MVP of 520 individuals. The model also helps direct managers to where and when predator control will be most efficient. It predicts that predation of adults is more likely to have a greater effect on growth rates and MVPs than chick predation. Therefore, funding should be directed towards predator control at the beginning of the season when adults are most vulnerable. However, the model cannot determine population trends, nor rightly assure conservation managers that predator control is essential or even sufficient to prevent extinction. Preliminary models can assist by formalising how uncertain our current understanding is, but should not be expected to work a miracle of divining certainty from a lack of field information that still may take decades to collect. Less reliance should be placed on the predictions of population trends or extinction probabilities than on the model's guidance to the relative efficacy of different management actions.