Justification of Red List Category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (extent of occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The most recent assessment of the European population provided an estimate of 30,500-48,100 pairs, equating to 61,000-96,000 mature individuals (BirdLife International 2015). The largest colony on Zembra Island, Tunisia, is estimated at 113,720-176,750 pairs (Defos du Rau et al. 2012). The global population has been estimated at 142,478-222,886 pairs (Defos du Rau et al. 2012, Derhé 2012, Carboneras et al. 2013), assumed here to be equivalent to c.285,000-446,000 mature individuals.
The overall population trend is estimated to be declining. The species’s population is estimated and projected to be declining by c.2% over three generations (1980-2038), although this is based on data from only 6% of the population (Derhé 2012, Carboneras et al. 2013). The European population is estimated to be declining by less than 25% in three generations (BirdLife International 2015). Estimates of adult survival and breeding probabilities in Tunisia are required to fully estimate the global population trend (Carboneras et al. 2013).
This species breeds in Algeria, Croatia, France, Greece, Italy, Malta, Spain (excluding the Canary Islands), Tunisia and Turkey (Derhé 2012). The majority of the population spends the non-breeding season in the Atlantic, including areas off the west coast of Africa and east coast of Brazil (Péron et al. 2012). The global population is thought to be in slow decline overall, although more research is required (Derhé 2012, Carboneras et al. 2013).
Pelagic movements are easily divided into frequent foraging trips around the breeding areas, rapid long-distance migrations, and smaller-scale movements within a well defined wintering ground (González-Solís et al. 2009). Breeding starts in April on barren offshore islands, where breeding pairs occupy cliffs, caves and boulder fields (del Hoyo et al. 1992). Diet is mostly squid, which are obtained mainly by surface-seizing. It is regularly attracted to trawlers to feed on offal (del Hoyo et al. 1992).
The high rates of bycatch mortality in adults, principally within artisanal longline operations, are considered sufficient to be driving substantial and rapid population declines in the population (Belda and Sanchez 2001, Garcia-Barcelona et al. 2010, Laneri et al. 2010, Cortés and González-Solís 2018). It is one of the most frequent seabird species in Mediterranean bycatch (Valeiras and Caminas 2003, García-Barcelona et al. 2010, Laneri et al. 2010), with estimates of the number of individuals killed annually by Spanish fleets ranging from 200 (García-Barcelona et al. 2010) to 467-1,867, amounting to c. 4-6% of the local breeding population (Belda and Sanchez 2001). Together with Calonectris borealis, it is the most common seabird species caught as bycatch by the Spanish long-line fleet in the western Mediterranean (Báez et al. 2014). Results from a questionnaire suggest an annual bycatch of up to 1,220 individuals by Maltese fleets (8.5-10% of the breeding population), although this is could be an over-estimate, skewed by high bycatch in a small number of vessels (Dimech et al. unpubl. per Derhé 2012). The species may also suffer significant bycatch in its non-breeding range (e.g. Granadeiro et al. 2006).
House Rats Rattus rattus have negative impacts on a majority of the population, causing increased mortality and reduced reproductive success. These effects became clear as breeding success increased markedly following the implementation of rat control measures (Igual et al. 2006, Pascal et al. 2008).Light pollution, and consequent grounding of, predominantly immature, individuals is likely to reduce reproductive output, and is suspected to be contributing to declines in the population (Rodríguez et al. 2015).
Conservation Actions Underway
EU Birds Directive Annex I. Bern Convention Appendix II. The following information refers to the species's European range only: In most areas human exploitation has ceased or is only occasional and some breeding islands have been declared reserves. Feasibility of eradicating Rattus rattus from Italian islands with breeding seabirds has been evaluated, but would apparently be of much greater benefit to Puffinus yelkouan than the present species, while an intensive rat-control programme was successfully initiated at two subcolonies on Chafarinas Island (Spain) in 1999-2004 (Carboneras et al. 2014). In addition, censuses, monitoring, creation of protected areas and studies of the species's biology and ecology have all taken place. At colonies mammal control, provision of artificial nest sites and management to reduce disturbance have also been implemented (Anselme and Durand 2012).
Conservation Actions Proposed
The following information refers to the species's European range only: Rat control programmes appear to deliver only a small increase in the population growth rate, whereas change in adult survival has a much larger impact. Therefore, increasing adult survival is of greater importance and rat eradication programmes can only be used to 'buy' time (Igual et al. 2009). Further research and monitoring as well as the continuation of measures to reduce disturbance are required. Actions to reduce the impact of Larus michahellis where appropriate should be implemented. An international network with the aim to prioritize conservation actions and monitoring programmes should be developed. Mortality in longline fishing should be monitored and measures such as setting longlines only at certain times of the day to reduce the accidental catch should be followed (Belda and Sanchez 2001).
Text account compilers
Stuart, A., Symes, A., Taylor, J., Ekstrom, J., Butchart, S., Ashpole, J, Fjagesund, T., Hermes, C., Calvert, R., Martin, R., Newton, P.
BirdLife International (2020) Species factsheet: Calonectris diomedea. Downloaded from http://www.birdlife.org on 11/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 11/08/2020.