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Seabird ecology in relation to fisheries

Meraz Hernando, Juan Francisco (2011) Seabird ecology in relation to fisheries. PhD thesis, University of Glasgow.

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Abstract

Previous research has hinted at changes in the migratory patterns of seabirds nesting in Scotland, including a decreasing number of Northern Gannets Morus bassanus wintering in the North Sea, and an increase in numbers of Northern Gannets and Great Skuas Stercorarius skua spending the winter off north-western Africa (NWA). Both species show increasing numbers of colonies in northern areas, including Norway and Russia. These seabird species move through the North Sea during autumn migration, and from there search for favourable wintering grounds mainly around Iberia, including the Atlantic coast of Portugal, the Bay of Biscay and the Gulf of Cadiz. By means of historic ring recovery data, provided by the British Trust for Ornithology, it was possible to establish that the number of records of adults of both species are increasing in recent years from NWA coasts, despite having to attend their nests in the colonies and, as a result, having limited time to migrate south. Differences were observed in ring recovery locations between years and months. The number of ring recoveries by month coincides with records from observation points along the coast of Western Europe. However, ring recovery data are limited and potentially biased. Using data loggers, it was possible to establish that both species are diurnal in habits during the entire winter period, showing noticeable differences in the times spent flying during the migration months (September-October) and during the wintering and breeding months (January and March respectively), and to confirm the increasing tendency to winter off NWA in recent years. Analyses of fishing landings, discard rates, and sea surface temperature data, show that food available to Northern Gannets and Great Skuas is increasing in NWA coasts where oceanographic conditions are stable; in contrast in the North Sea fisheries are decreasing and the sea surface is warming. Both species are apparently changing their migratory behaviour in order to face the constant changes in the abundance of food. Given the long life-span of Northern Gannets and Great Skuas, genetic changes can be ruled out of an explanation for the changes in migration behaviour, and the fact that the changes in winter distribution appear to be occurring within one generation of the birds. The winter distribution of Northern Gannets and Great Skuas may be due to an ideal free distribution over a wide range, in response to changes in the distribution of fish and the availability of discards.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Northern Gannet, Great Skua, Fisheries, Migration, Northwestern Africa, Bass Rock, Morus bassanus, Stercorarius skua
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QL Zoology
G Geography. Anthropology. Recreation > GC Oceanography
Colleges/Schools: College of Medical Veterinary and Life Sciences
Supervisor's Name: Furness, Prof. Robert W.
Date of Award: 2011
Depositing User: Dr JF Meraz
Unique ID: glathesis:2011-2684
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 09 Jun 2011
Last Modified: 10 Dec 2012 13:58
URI: http://theses.gla.ac.uk/id/eprint/2684

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