Differences in diet between the two largest breeding colonies of Audouin's gulls: the effects of fishery activities

Authors

  • Vittorio Pedrocchi Dept. Biologia Animal, Facultat de Biologia, Universitat de Barcelona
  • Daniel Oro Dept. Biologia Animal, Facultat de Biologia, Universitat de Barcelona - Institut Mediterrani d’Estudis Avançats IMEDEA (CSIC-UIB)
  • Jacob González-Solís Dept. Biologia Animal, Facultat de Biologia, Universitat de Barcelona
  • Xavier Ruiz Dept. Biologia Animal, Facultat de Biologia, Universitat de Barcelona
  • Lluís Jover Dept. de Salut Pública i L.S (Bioestadística). Facultat de Medicina, Universitat de Barcelona

DOI:

https://doi.org/10.3989/scimar.2002.66n3313

Keywords:

Larus audouinii, fishery discards, abundance, diet composition

Abstract


We analysed and compared the diet of Audouin´s gulls Larus audouinii between their two largest breeding sites in the world: the Ebro Delta and the Chafarinas Islands (western Mediterranean). These two localities showed marked differences in the features of the commercial fishing fleet: in the Ebro Delta area a large fishing fleet produced large amounts of discards, while in the Chafarinas the fleet discarded smaller amounts of fish and marine invertebrates, due to the smaller number of vessels. It is also likely that the percentage of discards from total catches is also lower around the Chafarinas than at the Ebro Delta. We distinguished two types of fishing to compare diet compositions: diurnal (only trawling activity) and diurnal and nocturnal (trawling and purse-seine activity, respectively). We also differentiated regurgitates from young nestlings (up to 20 days old) and from older nestlings or adult birds. At the two localities, fish was the main food of Audouin´s gulls, with epipelagic prey (mainly clupeoids) being more important when both diurnal and nocturnal fisheries were operating. This confirms that epipelagic prey either caught actively by the gulls or linked to fisheries was particularly important in the feeding habits of Audouin´s gulls. Nevertheless, differences between the two colonies appear mainly when only trawlers operated: while at the Ebro Delta gulls showed higher consumption of benthic-mesopelagic prey (probably linked to a higher trawler discard availability), gulls from the Chafarinas Islands consumed higher biomass of epipelagic prey probably caught actively at night. When both fleets operated around the two colonies, the average biomass of prey in a regurgitate of younger chicks was significantly higher at the Ebro Delta than at Chafarinas, and the opposite trend was recorded for older nestlings and adults. Niche width was broader in Chafarinas than in the Ebro Delta for both age classes and for any fishing fleet schedule, suggesting again that the exploitation of discards was higher at the Ebro Delta than at the Chafarinas, where gulls showed a more varied diet. Despite the fact that availability of discards was probably higher at the Ebro Delta than at Chafarinas, the per capita availability was not so different at both localities due to the increasing seabird community population at the Ebro Delta, which ca. doubled that at Chafarinas in the last decade.

Downloads

Download data is not yet available.

Downloads

Published

2002-09-30

How to Cite

1.
Pedrocchi V, Oro D, González-Solís J, Ruiz X, Jover L. Differences in diet between the two largest breeding colonies of Audouin’s gulls: the effects of fishery activities. scimar [Internet]. 2002Sep.30 [cited 2021Mar.7];66(3):313-20. Available from: http://scientiamarina.revistas.csic.es/index.php/scientiamarina/article/view/590

Issue

Section

Articles

Similar Articles

You may also start an advanced similarity search for this article.

Most read articles by the same author(s)