Assessment of demographic risk factors and management priorities: impacts on juveniles substantially affect population viability of a long-lived seabird

Authors


Correspondence
Myra E. Finkelstein, Department of Microbiology and Environmental Toxicology, University of California, 1156 High St Santa Cruz, CA 95064, USA. Tel: +1 831 459 4571; Fax: +1 831 459 3524
Email: myraf@ucsc.edu

Abstract

Predicting population-level effects from changes in demographic rates of different life stages is critical to prioritize conservation efforts. Demographic modeling and sensitivity analysis in particular, has become a standard tool to evaluate how management actions influence species' survival. Demographic analyses have resulted in the robust generalization that, for long-lived species with delayed reproduction, population growth rates will be most sensitive to changes in survivorship of older-aged individuals. Although useful in guiding management, this simple maxim may limit options for conservation by causing managers to overlook actions that, although possibly not the most effective in terms of increasing a population's growth rate in an ideal world, can nonetheless more feasibly and rapidly slow a population's decline. We examine the population-level benefits of increasing chick survival in a long-lived seabird, the Laysan albatross Phoebastria immutabilis. Specifically, we use a simple deterministic modeling approach to evaluate the impact of chick mortality (from ingestion of lead-based paint) on the population growth rate (λ) for Laysan albatross that breed on Sand Island, Midway Atoll (part of the Hawaiian Archipelago). We estimate that up to 7% of chicks on Sand Island fail to fledge as a result of lead poisoning, which will create a 16% reduction in the Laysan albatross population size (∼190 000 less birds) at 50 years into the future. We demonstrate how straightforward management actions that increase juvenile survivorship (e.g. removal of lead-based paint) can help slow population declines while efforts are underway to reduce politically and logistically challenging threats to adult survivorship (e.g. mortality from international fisheries bycatch). Our work exemplifies a situation where overgeneralizations about demography can stifle useful conservation actions and highlights the need to consider the population-level benefits from multiple management strategies.

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