Status of seabird nesting populations on Arrecife Alacranes, Gulf of Mexico

Abstract

Arrecife Alacranes is the largest coral atoll of the Campeche Bank, situated in the southern end of the Gulf of Mexico and encompassing 60 ha. It has five coral islands: Isla Chica, Isla Blanca (or Isla Pájaros), Isla Pérez, Isla Desertora (or Isla Muertos), and Isla Desterrada, some with significant seabird nesting colonies. Trans-Gulf migrating birds use Arrecife Alacranes for resting. Fisheries, tourism, and oil-drilling activities have been a threat to the reef’s biodiversity. However, the protection recently granted by the Mexican Government, on 6 June 1994, designating the area a National Park, has reduced human disturbance. Before this survey, the impact of this designation on seabird colonies was unknown. The last seabird survey, in 1986, had determined that the archipelago is home to the largest colony of Masked Boobies Sula dactylatra in the Atlantic region and the only known nesting site of Red-footed Boobies Sula sula in the Gulf of Mexico. Herein, we report on totals of abundance, which ranged from 140 000 to 13 nests, and on the nesting phenology of nine seabird species: Sooty Tern Onychoprion fuscatus, Brown Noddy Anous stolidus, Masked Booby, Laughing Gull Leucophaeus atricilla, Cabot’s Tern Thalasseus acuflavidus, Magnificent Frigatebird Fregata magnificens, Royal Tern Thalasseus maximus, Brown Booby Sula leucogaster, and Red-footed Booby. We observed a significant increase in nesting populations of most species, except Magnificent Frigatebirds and Masked Boobies. However, some aspects of the breeding biology of these seabirds may have been influenced by introduced species. Among the population of Red-footed Boobies, which had only 13 nests, we observed three color morphs, thus leading to uncertainty about their geographic affinities. Despite the increased protection, which includes the presence of park rangers, human activity and related factors, such as increased fisheries pressure, damages to the atoll, risk posed by rising sea levels, and oil drilling, continue to threaten this important seabird nesting area.