José Manuel Arcos

OCEANOGRAPHIC HABITAT OF AN ENDANGERED MEDITERRANEAN PROCELLARIIFORM: IMPLICATIONS FOR MARINE PROTECTED AREAS

Marine protected areas (MPAs) require ecologically meaningful designs capable of taking into account the particularities of the species under consideration, the dynamic nature of the marine environment, and the multiplicity of anthropogenic impacts. MPAs have been most often designated to protect benthic habitats and their biota. Increasingly, there is a need to account for highly mobile pelagic taxa, such as marine birds, mammals and turtles, and their oceanic habitats. For breeding seabirds foraging from a central place, particular attention should be paid to distant foraging grounds and movement corridors, which can often extend to hundreds of kilometers from breeding colonies. We assessed the habitat use by the most threatened Mediterranean seabird, the Balearic Shearwater, Puffinus mauretanicus, using vessel-based surveys during the chick-rearing period (May-June). We used a hierarchical modeling approach to identify those environmental variables that most accurately reflected the oceanographic habitat of this species by (1) delineating its foraging range using presence/ absence data and (2) identifying important foraging grounds where it concentrates in dense aggregations. The foraging range comprised the frontal systems along the eastern Iberian continental shelf waters (depth <200 m) and areas close to the breeding colonies in the Balearic Islands. Shearwaters aggregated in productive shelf areas with elevated chlorophyll a concentrations. Following the model of a core-buffer MPA, we envisioned those areas of dense aggregation (i.e., the area of influence of the Ebro River discharge and Cape La Nao regions) as the core regions deserving elevated protection and more stringent management. More diffuse protective measures would be applied within the larger buffer region, delineated by the foraging range of the species. Marine zoning measures can greatly benefit the conservation of the Balearic Shearwater and other far-ranging seabirds by extending protective measures beyond their breeding colonies during both the breeding and non-breeding seasons.

Mass mortality of seabirds in the aftermath of the Prestige oil spill

In the winter of 2002–03 the Prestige tanker spilled 60,000 tons of oil over the northern half of the Iberian Coastal Large Marine Ecosystem (northern Portugal to France). Most (c. 85%) of the 22,981 oiled seabirds reported were alcids (i.e., auks): Common Murres (Uria aalge), Razorbills (Alca torda) and Atlantic Puffins (Fratercula arctica). Here we estimated the mortality of alcids in Galicia (northwestern Spain), the area that received most of the Prestige oil and where half of the oiled seabirds were collected. We performed three experiments that included: (1) a test of several drift block models in open sea, to select the one that best fitted the drift of alcid carcasses; (2) the release of 450 drift blocks at 9 offshore points to assess the recovery rate of oiled alcids and its spatial variation; (3) the assessment of beach survey effort and the detectability of drift blocks. Mean mortality estimates and their bootstrapped confidence intervals were obtained through an estimation model that established: (1) a temporal limit of 23 days to block drifting; (2) spatial differences in the recovery rates of blocks depending on how far away from the coast they were released; (3) a correction factor accounting for detectability, and (4) the distribution pattern of the three alcid species involved according to three distance classes, based on ship surveys. The Prestige oil spill, in terms of acute seabird mortality, was one of the worst oil spills ever reported worldwide. Compared to other major oil spills the estimated mortality for the Prestige oil spill was higher than expected from the number of carcasses retrieved. We recommend that drift block assessments of seabird mortality should be included in contingency response plans to oil pollution emergencies; therefore, a supply of drift-blocks designed to mimic the drifting behavior of the marine bird species of interests should be at hand.

Mediterranean Gulls Larus melanocephalus wintering along the Mediterranean Iberian coast: numbers and activity rhythms in the species' main winter quarters

Knowledge of the winter distribution of the Mediterranean Gull Larus melanocephalus is poor. The limited and geographically patchy data on the species’ winter distribution is of concern because current estimates of the wintering population do not agree with those for the global breeding population. We assessed the winter distribution and abundance patterns of this gull in Mediterranean Iberia, a historically important wintering area for which recent data are lacking. Information for the whole study area was obtained from a systematic boat-based survey over the continental shelf in 2003. Then, particular attention was paid to St. Jordi Gulf, a known hotspot for the species, where we studied the temporal patterns in abundance throughout the winter months, and daily activity rhythms, between 2005–2006 and 2008–2009. To set our results in a global context, the available information of the winter range of the species was collated and synthesised. The results indicate that the Iberian Mediterranean coast is the main winter quarters of the species. An average population of ca. 41,000 individuals was present in the area, representing approximately half the 86,311 individuals (range 50,747–121,875) recorded across the whole of the species’ winter range. At the local scale, the St. Jordi Gulf represented the most important area for the species in winter, with an average of around 17,000 individuals and peaks of up to 45,000 in early and late winter. Thus, we argue that this is a globally important area for the species. Daily rhythms involve birds moving between offshore feeding areas during the day (where they largely consume fishing discards) to inland olive crops and bathing and drinking sites (Riudecanyes reservoir) in the afternoon, and finally to coastal roost sites at dusk (Cambrils). Given the global significance of the population wintering in this small area, measures to protect Riudecanyes reservoir and the marine and inland foraging areas should be implemented as a matter of priority. Further research is needed to assess the actual population size of the Mediterranean Gull global population and its conservation status, as well as the threats that the species faces.ZusammenfassungNur wenig ist von der Winter-Verbreitung der Schwarzkopfmöwen Larus melanocephalus bekannt; dabei sind gerade die begrenzten und geographisch nur sporadischen Verbreitungs-Daten dieser Art im Winter deshalb speziell interessant, weil die derzeitigen Schätzungen der Winterpopulation nicht zu denen der globalen Brutpopulation passen. Wir untersuchten das Vorkommen und Verteilungsmuster dieser Möwenart entlang der spanischen Mittelmeerküste, einem für sie schon seit langem wichtigen Überwinterungsgebiet. Die Daten wurden 2003 in einer systematischen Erhebung über dem Kontinentalschelf von einem Boot aus gesammelt. Daran anschließend wurde der Golf von St. Jordi, ein bekannter hotspot dieser Spezies, genauer untersucht: das zeitliche Verteilungsmuster der Möwen sowie ihr täglicher Aktivitätsrhythmus von Juni 2005 bis September 2008. Um unsere Ergebnisse in einen größeren Zusammenhang zu setzen, wurden alle anderen verfügbaren Informationen über die Winterverbreitung dieser Art gesammelt und vergleichbar gemacht. Die Ergebnisse legen nahe, dass die spanische Mittelmeerküste das Winterquartier dieser Möwenart ist. In dieser Gegend betrug die durchschnittliche Population ca. 41,000 Individuen, was etwa die Hälfte der 86.311 Individuen ausmacht (50.747 - 121.875), die über alle Winterquartiere dieser Art hinweg gezählt wurden. Im örtlichen Maßstab erwies sich der Golf von St. Jordi mit im Schnitt 17,000 beobachteten Individuen und Spitzen von bis zu 45,000 im frühen und späten Winter als wichtigstes Überwinterungsgebiet für diese Spezies. Deshalb postulieren wir, dass dies eine auch im globalen Maßstab wichtige Gegend für diese Art ist. Die Tagesrhythmen ergaben sich aus den Bewegungen der Vögel von den Futterplätzen auf dem Meer, wo sie sich tagsüber hauptsächlich von weggeworfenen Fischabfällen ernähren, zu den Olivenhainen und Bade- und Trink-Gelegenheiten (das Wasserreservoir von Riudecanyes) am Nachmittag und schließlich gegen Sonnenuntergang zu den Schlafplätzen an der Küste (Cambrils). In Anbetracht der globalen Bedeutung dieser in einem solch kleinen Areal überwinternden Population, sollten Maßnahmen zum Schutz des Riudecanyes-Reservoires und der Gebiete im Meer und auf dem Land, in denen die Vögel Nahrung aufnehmen, mit Priorität ergriffen werden. Weitere Untersuchungen sind notwendig, um die tatsächliche globale Populationsgröße der Schwarzkopfmöwen sowie die sie bedrohenden Faktoren und den aktuellen Stand ihres Schutzes festzustellen.

Frequency-dependent morph differences in kleptoparasitic chase rate in the polymorphic arctic skua Stercorarius parasiticus

The relationship between colouration and kleptoparasitic efficiency (success rate and chase rate) was studied in the polymorphic arctic skua, Stercorarius parasiticus, at a Mediterranean migration site. A shift in the ratio of morphs through the spring, presumably caused by differential migration between populations that differ in morph frequency (the higher the latitude, the more frequent is the pale morph), allowed the comparison of the relative performances of pale and dark birds under different scenarios of morph frequency. Chase rate showed a clear frequency-dependent effect in chases by solitary skuas, birds of the rare morph always conducting more chases than expected. This trend was explained by chases of yellow-legged gulls, Larus michahellis, a relatively large and aggressive species that was difficult to chase (i.e. chases resulted in low success rate) but provided potentially higher reward (i.e. more food) than any other host. These differences could result from the perceived cost-benefit balance of chases, as skuas from the rare morph could find an advantage in chasing this host species by being less rapidly recognised. This is in agreement with the apostatic selection hypothesis, which says that the rare morph in a predator or parasite population is favoured through its unfamiliarity to potential prey or hosts (the surprise effect). Differences in success rate could have provided further support to this interpretation, but sample size was not sufficient for a proper comparison at the host-species level.