Seasonality in marine ecosystems: Peruvian seabirds, anchovy, and oceanographic conditions

Abstract

In fluctuating environments, matching breeding timing to periods of high resource availability is crucial for the fitness of many vertebrate species, and may have major consequences on population health. Yet, our understanding of the proximate environmental cues driving seasonal breeding is limited. This is particularly the case in marine ecosystems, where key environmental factors and prey abundance and availability are seldom quantified. The Northern Humboldt Current System (NHCS) is a highly productive, low-latitude ecosystem of moderate seasonality. In this ecosystem, three tropical seabird species (the Guanay Cormorant Phalacrocorax bougainvillii, the Peruvian Booby Sula variegata, and the Peruvian Pelican Pelecanus thagus) live in sympatry and prey almost exclusively on anchovy, Engraulis ringens. From January 2003 to December 2012, we monitored 31 breeding sites along the Peruvian coast to investigate the breeding cycle of these species. We tested for relationships between breeding timing, oceanographic conditions, and prey availability using occupancy models. We found that all three seabird species exhibited seasonal breeding patterns, with marked interspecific differences. Whereas breeding mainly started during the austral winter/early spring and ended in summer/early fall, this pattern was stronger in boobies and pelicans than in cormorants. Breeding onset mainly occurred when upwelling was intense but ecosystem productivity was below its annual maxima, and when anchovy were less available and in poor physiological condition. Conversely, the abundance and availability of anchovy improved during chick rearing and peaked around the time of fledging. These results suggest that breeding timing is adjusted so that fledging may occur under optimal environmental conditions, rather than being constrained by nutritional requirements during egg laying. Adjusting breeding time so that fledglings meet optimal conditions at independence is unique compared with other upwelling ecosystems and could be explained by the relatively high abundances of anchovy occurring throughout the year in the NHCS.

Density dependence, prey accessibility and prey depletion by fisheries drive Peruvian seabird population dynamics

“…The other oceanographic factor that impacted the abundance of seabirds was SST, but this only concerned cormorants and the evidence was not strong. SST is closely related to the strength of the upwelling intensity and biological productivity in the NHCS and Passuni et al (2016) showed that breeding of cormorants mainly stopped when SST are warm. Passuni et al (2016) also suggested that seabirds in the NHCS possibly used SST as an environmental cue to initiate breeding.…”

“…SST is closely related to the strength of the upwelling intensity and biological productivity in the NHCS and Passuni et al (2016) showed that breeding of cormorants mainly stopped when SST are warm. Passuni et al (2016) also suggested that seabirds in the NHCS possibly used SST as an environmental cue to initiate breeding. Therefore, we can hypothesize that warm SST negatively impact the breeding propensity of cormorants.…”

“…Our choice for using annual values was motivated by several reasons. First, breeding is not strictly seasonal for the three seabird species as commonly observed for temperate of polar seabird species (Passuni et al 2016). Although Peruvian boobies and Peruvian pelican mainly breed during a given period of the year (from July to November), breeding may occur during the other months of the year.…”

Migratory routes and wintering locations of declining inland North American Common Terns

“…Additionally, during years of high water, competition with gulls often increases as a result of reduced availability of nesting habitat (Cuthbert et al 2003). Throughout the nonbreeding season, Common Terns follow the distribution and abundance of prey fish (Cabot and Nisbet 2013), and the northwest coast of South America is a hot spot for productivity (Jahncke et al 2004, Capone and Hutchins 2013, Passuni et al 2016. The Peruvian upwelling ecosystem, part of the Humboldt Current System, is one of the most biologically productive marine environments globally (Jahncke et al 2004, Capone andHutchins 2013).…”

“…In the late 1960s to early 1970s, the combination of heavy fishing pressure and 2 ENSO events (1965 and 1972) resulted in the collapse of the anchovy population, which led to major declines in seabird populations (Jahncke et al 2004). In addition to pressures from commercial fishing, changes in sea surface temperatures caused by ENSO events further reduced prey availability by altering the distribution and abundance of fish along the Peruvian coast (Jahncke et al 2004, Devney et al 2009, Passuni et al 2016. Declines in seabird and shorebird populations have been documented in years of extreme ENSO events such as 1982-1983, when populations of Red-necked Phalaropes (Phalaropus lobatus) assumed to be wintering in the region crashed (Nisbet and Veit 2015) and numbers of Common Terns wintering along the southern coast of Peru were substantially below normal (Hughes 1985).…”