Human influence on gull non-breeding distribution: Potential consequences of changes in fishing practices

Abstract

© Inter-Research 2015. Interpopulation mixing of migratory species at particular stopover and wintering hotspots increases their vulnerability to anthropogenic impacts. Animal associations with human activities at this time of the annual cycle should, therefore, inform management policies. The Gulf of Cadiz, Spain is a key non-breeding area for the Near-Threatened Audouin's gull Ichthyaetus audouinii and the over-abundant lesser black-backed gull Larus fuscus, both of which heavily depend on human fisheries. Here, we used long-term (1990-2013) data on coastal censuses, along with spatially-explicit information on fish landings (2000-2014) and on-board surveys of fishing vessels (2012-2013), to unravel the association of these gulls with human fisheries and evaluate its role in shaping their distribution at this important non-breeding hotspot. Fishing discards from trawlers were extensively used by lesser black-backed gulls, whereas Audouin's gulls apparently benefited from fish aggregations that occurred where purse seines were retrieved. Fishing influence was identified as an important driver of the non-breeding distribution of these gulls, particularly for the lesser black-backed gull, which congregated near main fishing ports. Within this scenario, we speculate that changes in fishing practices, such as those proposed by the upcoming EU Reform of the Common Fisheries Policy that includes a ban on fishing discards, will almost certainly impact the lesser black-backed gull. In contrast, the impact on the Audouin's gull remains unclear and will likely depend on how the proposed ban is implemented.