the humboldt current system of northern and central chile - figema

THE HUMBOLDT CURRENT SYSTEM OF NORTHERN AND CENTRAL CHILEHCS (and in other EBCs) requires detailed understanding of the different components of therespective system (Moloney et al. 2005).Seabirds and marine mammalsIn marine environments seabirds and partially marine mammals are highly visible wide-ranging,upper trophic-level consumers. Upwelling systems are generally characterised by high productionand relatively short food chains/webs, enabling massive energy transfer to the higher trophic levels(Cushing 1971, Arntz & Fahrbach 1991). The upwelling system of the Humboldt Current isparticularly well suited for studying the effects of the marine environment on the biology andecology of seabirds and marine mammals.SeabirdsIn the HCS there is a rich diversity of seabirds, comprising at least 14 breeding species, 9 of whichare endemic (Table 2). According to available information, along the coast of Chile the mostimportant breeding colonies are found on islands of northern-central Chile, near upwelling areas.The grey gull (Larus modestus), which nests inland in the Atacama Desert, travels to the coast ona daily basis to forage in the upwelling zones off Antofagasta (~23°S). Although proximity to afeeding ground is relevant in endemic seabirds, it seems that inaccessibility to predators and humanintrusion strongly determines the distribution of breeding populations. Despite some protectivestatus, most islands in the HCS are subject to human disturbance. In the past, this was causedmainly by guano harvesting and egg collecting. At present, introduced mammals and unregulatedtourism (Ellenberg et al. 2006) are a major problem.The majority of the endemic seabirds breed once a year. However, in their northernmostbreeding areas (Peru), species such as the Humboldt penguin (Spheniscus humboldti) nest throughoutthe year. Apparently, the two-peak breeding strategy has evolved in response to more favourableoceanographic and climatic conditions off Peru, and this behaviour is preserved in northern-centralChile providing additional offspring to those produced during the spring event (Simeone et al.2002). Furthermore, differences in food availability along its breeding range (~4000 km) mightinduce lower breeding performance in southern colonies of this species (Hennicke & Culik 2005).These birds feed on the main pelagic fish species from the HCS, mainly anchovy and jack mackerel.The proportion of fish stocks taken by endemic seabirds is not well known, but most likely doesnot exceed 10%. Incidental mortality of endemic seabirds due to fisheries is mainly caused by gillnets (Simeone et al. 1999, see also Majluf et al. 2002).The HCS is visited regularly by a number of migrant species. Among the Procelariiformes, whitechinnedpetrels (Procellaria aequinoctialis), Buller’s albatrosses (Thalassarche bulleri), Antarcticprions (Pachyptila desolata) and Juan-Fernández petrels (Pterodroma externa) are the most abundantspecies during austral summer (Weichler et al. 2004). There is evidence that the HCS is also frequentedby other remarkable visitors such as the Chatham, wandering and royal albatrosses (Thalassarcheeremita, Diomedea exulans, and D. epomophora, respectively). Apparently the presence of thesespecies at such a distance from their colonies is related to the food abundance in the HCS, which insummer also attracts species like the black-browed albatross (Thalassarche melanophris) from southernislands (56°S) (Arata & Xavier 2003) and during winter species like the white-chinned petrelsfrom South Georgia (Phillips et al. 2006). The abundances of some of these visitors during australsummer may reach 2.5–5 birds km −2 , but at present it is not known which proportion of the entirepopulation of these visitors may at times use the HCS as a feeding ground. The large albatrossesmainly feed on cephalopods and pelagic fishes (resulting in deadly interactions with long-line fisheries),221