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Understanding Seabirds at Sea: Why and How?

L. Ballance

Published 2007 in Marine Ornithology

ABSTRACT

SUMMARY BALLANCE, L.T. 2007. Understanding seabirds at sea: why and how? Marine Ornithology 35: 127–135.Studies of the at-sea component of seabirds’ lives are essential to a comprehensive understanding of seabirds, simply because so many species spend the vast majority of their time at sea. At-sea data can be collected using data recorders and remotely-transmitting devices, and from ships. The latter is usually accomplished using strip transect methods, which quantify the number and species identification of birds within a pre-determined distance from a ship as it moves. A number of methodologic variations exist, but all include two critical assumptions: that the strip width is accurately maintained, and that all birds entering the strip are detected. These at-sea data provide insights at a number of ecologic scales. At-sea data provide insights into the biology of individual species including distribution, the relationship between distribution and physical and biologic characteristics of the ocean (often termed species–habitat relationships), and abundance (particularly for species that are difficult to census on colonies). At-sea data provide insights into communities, including community composition (because seabird breeding communities almost always differ from seabird feeding communities) and interspecific interactions (particularly predation, competition and commensalism). And at-sea data provide insights into oceanic ecosystems, because seabirds have attributes (easy to detect and identify; wholly dependent upon marine systems for food; highly mobile, thereby integrating ecosystems on large spatial scales) that make them important as indicator species. A host of threats, both direct and indirect, exist for seabirds at sea. Reletive to direct threats, indirect threats tend to be poorly understood and are rarely acknowledged. In particular, the dependence of seabirds on fish of high commercial value or mammals subject to incidental mortality can be a significant indirect threat that is rarely acknowledged in management of those fish and mammal species. Because of the trans-habitat and trans-boundary nature of seabirds (they breed on land, yet feed in the sea and pay no attention to arbitrary political boundaries), the structure and function of many management schemes is a poor fit with seabird conservation needs. Integrating responsibility across agencies and countries is challenging. Seabirds provide a potential role model for successful management of oceanic resources that can provide a mechanism for conservation of other trans-habitat and trans-boundary species.Key words: Seabirds at sea, strip transect methods, abundance, distribution, species-habitat relationships, community ecology, foraging ecology, ecosystem indicators, seabird conservation, indirect effects

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