International species action plan for the Balearic shearwater, Puffinus mauretanicus.

EXECUTIVE SUMMARY The Balearic shearwater has been long considered as a subspecies of either the Manx shearwater Puffinus puffinus or the Yelkouan shearwater Puffinus yelkouan, but was recognised as a distinctive species about ten years ago. As such, this shearwater has been catalogued globally as Critically Endangered following IUCN criteria, on the basis of both its extremely rapid population decline (-7.4% per year) and its small population size, which taken together could lead to the extinction of the species in less than 3 generations (average extinction risk of 40 years). Moreover, the global breeding population is restricted to the Balearic Islands, with an effective breeding range of less than 100 km2 . This alarming situation has led to its inclusion in several international lists and conventions. This action plan updates and revises the previous Species Action Plan (Aguilar 1999), and covers the whole distribution range of the species. The species breeds exclusively in the Balearic Islands and primarily forages, during the breeding season (March-July), off eastern Iberia and (most likely) also off Algeria. After the breeding period the bulk of the population abandons the Mediterranean and congregates in the Atlantic waters of W Europe up to S UK. The return passage takes place mostly between September and December, and the species mainly congregates off the NE and E Iberian coasts during the winter, where often forms large congregations of up to several thousands of birds associated to concentrations of small pelagic fish. The breeding population has been estimated at around 2,000 breeding pairs across the last decade, although a recent reassessment (due to both the discovery of new sites and the change of methodological census assumptions for some colonies) provide a new figure of 3,193 pairs. Alternative estimates at sea suggest either an even larger figure or an unusually large non-breeding population. Nevertheless the species is severely declining according to the existing demographic data, primarily as a result of an unusually low survival rate for adults (0.78 vs. expected values over 0.90 in Procellariiforms). This parameter was estimated using data from colonies free of terrestrial predators (at least the most harmful ones, carnivores), and therefore must be taken as conservative. Still, using these data (but also the former estimate of about 2,000 breeding pairs), a Population Viability Analysis (PVA) carried out in 2004 predicted a high probability of extinction risk, of over 50% in 40 years. An updated PVA is necessary to re-evaluate the status of the species, taking into account the new population estimates and improved demographic data. The main threats identified are the predation of adults at colonies by introduced carnivores (feral cats, genets and pine martens) and most probably the bycatch in fishing gear at sea, both factors affecting adult survival. Acute pollution events, such as oil spills, also pose a very serious threat for the species, as its highly congregatory behaviour could result in a large number of casualties in case that a spill occurred in a congregation area. Other threats include the reduction of prey due to fishing overexploitation and/or anthropogenic environmental change, habitat degradation and 6 disturbance in the breeding grounds, background pollution, human harvesting (nowadays a relict activity), and the development of marine windfarms. The aim of the plan is to stop the negative population trend of the Balearic shearwater, and revert it if possible, while ensuring the conservation of its habitat. Objective 1 of the plan is to get a population growth rate (lambda, λ), such that λ≥1 within 10 years (i.e. no population decline), out of current value of λ=0.952. To evaluate this, it is very important to set an annual monitoring scheme in a sufficient number of representative colonies that will allow assessing with confidence the population trend of the species. And to accomplish this target, action must be focused on those threats causing significant adult mortality, i.e. predation by introduced carnivores and fishing bycatch. Objective 2 is directed at keeping or improving the good environmental status of the current breeding colonies and main marine hotspots through effective site protection and adequate management plans implemented, including habitat restoration if appropriate.




Arcos, J.M. (compiler) 2011. International species action plan for the Balearicshearwater, Puffinus mauretanicus. SEO/BirdLife & BirdLife International.