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Case Study: Using seabird foraging behavior to assess fish populations

Information about the marine environment is often difficult and expensive to obtain directly. Observing the behavior and physiology of seabirds may provide an easier, faster, and less expensive means of addressing certain questions regarding, for example, the abundance and distribution of fish populations, oceanographic features and pollution levels. In 1990, behavioral ecologist Pat Monaghan and colleagues teamed up with scientists at the Scottish Office Agricultural and Fisheries Department to examine the usefulness of seabird studies to assess fish populations in the Shetlandarea of the North Sea.

The principal prey of seabirds in Shetland is the lesser sandeel (Ammodytes marinus) and in 1974 an industrial fishery for sandeels was started in this area. Annual fishery catches peaked in 1982 and then declined rapidly, with the catch in 1989 equaling only 3% of that in 1982. During this same period, the breeding success of several seabird species dropped sharply (Harris & Wanless 1990, Monaghan 1992). The team conducted a four year study of the foraging and breeding success of four seabird species; Arctic tern (Sterna paradisea), black-legged kittiwake (Rissa tridactyla), shag (Phalacrocorax aristotelis) and common murre (Uria aalge), and of the distribution and abundance of sandeels. Also, in the third year of the study a major oil spill occurred in the study area after the Braer oil tanker sank on nearby rocks. These circumstances led to a unique opportunity to examine behavioral and demographic data on both the seabirds and the fish population before and after an environmental perturbation.

Monaghan's group examined several reproductive and behavioral parameters of the seabird species including; egg laying date, clutch size, average breeding success, body condition, foraging trip duration, foraging trip distance, and number of dives and dive duration (for shag and murre). Sandeel population parameters were measured using a combination of acoustic surveys and net hauls. Results clearly showed that the foraging behavioral data were much better indicators of the status of the sandeel population than were the reproductive data. Furthermore, comparison of changes in foraging behavior among the different species (diving vs. surface feeders) provided the best indication of fluctuations in sandeel distribution, abundance and age structure (Monaghan 1996). Although collection of some of the foraging data required the use of radio telemetry, which can be costly, the overall cost was considerably less than that for the direct fish surveys (Monaghan 1996).

In another study examining the link between behavior and environmental conditions, two researchers, Volker Summer and Domingo Mendoza-Granados, found that play behavior can be a sensitive indicator of habitat quality in langur monkeys (Presbytis entellus). They compared the frequency and duration of play behavior in two bands of Hanuman langurs in habitats that differed in availability of food and water. Langurs, particularly immature individuals, in the low quality habitat played less often and for shorter periods of time than those in the higher quality habitat. These studies demonstrate that behavioral studies not only contribute to the understanding of the focal species, they can also serve as an indirect assessment of the integrity of the environment in which these species live.

Furness, R. W. and Greenwood, J. J. D. (eds.) (1993). Birds as monitors of environmental change. Chapman and Hall, London.

Harris, M. P. & Wanless, S. (1990) Breeding success of British kittiwakes Rissa tridactyla in 1986-88: evidence for changing conditions in the northern North Sea. J. Appl. Ecol. 27: 172-187.

Monaghan, P. (1996) Relevance of the behaviour of seabirds to the conservation of marine environments. Oikos, 77: 227-237.

Monaghan, P. (1992). Seabirds and sandeels: the conflict between exploitation and conservation in the northern North Sea. Biodiver. Conserv. 1: 98-111.

Sommer, V. & Mendoza-Granados, D. (1995) Play as indicator of habitat quality: a field study of langur monkeys (Presbytis entellus). Ethology, 99: 177-192.

Wright, P. & Bailey, M. C. (1993) Biology of sandeels in the vicinity of seabird colonies at Shetland. Fisheries Research Report 15 93, SOAFD Marine Laboratory, Aberdeen.

Wright, P., Bailey, M. C., Heath, M. R., McIntosh, A. & Stagg, R. (1994) The impact of the Braer Oil spill on sandeel availability to seabirds around Shetland. ESGOSS Report, Scottish Office, Edinburgh.

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