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Population models in a conservation setting: A case study of the albatross and long-line fishing.
Arnold, Jennifer*,1, Brault, Solange2, Croxall, John3, 1 Auburn University, Auburn, AL, USA2 University of Massachusetts, Boston, MA, USA3 British Antarctic Survey, Cambridge, UK
ABSTRACT- Natural resource managers are regularly faced with making regulatory decisions for long-lived species that spend most of their life in remote places. Even if accurate information on vital rates is available, understanding the sensitivity of these populations to anthropogenic or environmental stresses is difficult. Population modeling, as a tool for management, addresses these issues; we present a stage-classified model designed to elucidate causes of fluctuations in a population of black-browed albatross over the past 3 decades. As with many albatross species, the black-browed albatross population at Bird Island, South Georgia, is currently declining. This may reflect fishing activities around their breeding and wintering habitats and the availability of krill, their primary food source. The model incorporates details of the life cycle, including variation in age at maturity and annual breeding, and behavioral differences between successful and unsuccessful breeders; it is tested with 23 years of demographic data. When using field-measured values for survival, reproductive success and breeding probabilities, our model trajectory closely follows the observed changes in breeding population size. The model projection gives a 98% chance pseudoextinction (N < 25 pairs) within 81 years given current conditions. Comparing pre-1988 and post-1988 demography reveals a 6.1% decrease in lambda, the population rate of increase. This decline is correlated with changes in fishing activities in the home range of this population. A life table response experiment (LTRE) shows that the decline in lambda is caused mostly by declines in return rates of breeders. These results provide clear evidence that management actions should focus on sources of adult mortality. We argue that the correlation between fishing activities and changes in adult survival in this albatross species supports increased regulatory effort for long-line fishing activities, including increased monitoring of illegal fishing.
Key words: fisheries, bycatch, albatross, modeling