The Prestige significantly reduced the reproductive success of the cormorant and this effect was maintained in the long term, to the point that the current population of this species in the Atlantic Islands National Park of Galicia is 60% smaller than it was at the beginning of the 2000s. This is demonstrated by the researcher from the Department of Ecology and Animal Biology Álvaro Barros in his doctoral thesis, a meticulous investigation into the conservation of peripheral populations in seabirds, focused on the case of the crested cormorant, in the northwest of the Iberian Peninsula.
Although, especially in the Ons Islands, the species has been showing signs of recovery in recent years, the researcher stresses that any new impact could cause the population to fall below what is considered the minimum viable population limit, and it could head towards extinction. These impacts could well be a particularly prolonged period of certain meteorological circumstances, a new oil spill, the arrival of more mink to the islands, or a particularly dramatic event of adult mortality, “motivated, for example, by gillnetting, which is clearly on the rise in the national park”, underlines the author of the thesis, who emphasizes that the conservation of the studied population requires the urgent application of multidisciplinary measures.
Urgent measures
And what should these measures be? The researcher stresses the need for the administration to provide the necessary funding to start a detailed study of the possible causes of mortality in the national park as soon as possible, with special attention to the interaction with fishing gear. “We need to analyze where people are fishing within the park, what they are fishing for and with what gear, and see if crows are dying in this type of fishing and in what quantities,” emphasizes Barros, while explaining that, once this detailed study has been carried out, specific measures can be proposed for managing fishing in this natural space. “We are aware that it is a controversial issue, but this is the key if we want crows to continue to exist on the islands, a species that, it is worth remembering, was one of the main values for which the Cíes Natural Park and then the current national park were first created,” points out the researcher.
Another crucial aspect in which we should not let our guard down is the monitoring of the island populations of predators: domestic cats and mink. In this sense, the author of the thesis recalls that American mink have been being eliminated for years and the cat population is also being controlled. “We must continue with this work, eliminate the cats and mink that still remain and, above all, control that new populations do not form, because if more specimens arrive, they would have to be eliminated as soon as possible”, emphasizes the scientist.
The effects of oil spills persist in the long term
Throughout his doctoral thesis, Barros addresses several of the problems that affect the conservation of the southernmost populations of the great crested cormorant, in particular and, in general, all seabirds, from predation by exotic vertebrates, to hydrocarbon spills, climate change and the effects of the loss of genetic diversity on biological effectiveness.
Regarding the long-term effects of a large oil spill such as the Prestige, the scientist shows that the accident caused a 45% decrease in the reproductive success of the cormorant in the affected area. “In other words, in central and southern Galicia, on average, pairs produced half as much after the spill as they did before,” emphasizes the researcher, who emphasizes that this effect was maintained in the long term, since ten years after the spill, the cormorants in the affected area have not yet recovered their pre-accident production values. “This result shows that the effects of hydrocarbons on marine organisms can be maintained in the long term, which is a very poorly documented aspect,” emphasizes Barros, who in 2014 published, together with his thesis directors, David Álvarez and Alberto Velando, a scientific article reporting on this aspect that was published in the journal Biology Letters and that was later referenced in Nature.
Source: Duvi
