Warm oceanographic anomalies and fishing pressure drive seabird nesting north

Abstract

Since 2000, Elegant Terns have begun migrating northward in the face of warm oceanographic anomalies.

Brown Pelicans, Pelecanus occidentalis californicus (Aves: Pelecanidae): Five decades with ENSO, dynamic nesting, and contemporary breeding status in the Gulf of California

“…The 2014-2016 period represented an unprecedented, continuous breeding failure or under-performance of pelicans and other seabirds (in nearly half a century of study by DWA and since studies in the Gulf began in 1969, Keith et al 1971), largely range-wide (see also news article perspective by Kintish 2015 andVelarde et al 2015b). Typical views comparing this contrast between optimal (baseline) and suboptimal (warm-period) conditions are clearly illustrated in Figure 8.…”

“…Still, another species of Gulf seabird, the Elegant Tern (Thalasseus elegans), has made a partial range-shift during this same time period (~10% of expected Rasa Island Elegant Tern populations shifted to the SCB) ( Fig. 1a) (Velarde et al 2015b). Several questions need further clarification: (1) Can Brown Pelican populations adapt to long-term warming effect?…”

The demographic decline of a sea lion population followed multi-decadal sea surface warming

“…Because the shape of the curve of that model was unimodal, the population size would also be lower under extreme cold anomalies, at the multi-decadal scale. The optimum sea surface temperatures revealed by this model could hypothetically benefit the aggregation of high quality prey in the Gulf of California, such as sardine, whose fishery also increased during the 1970’s and early 1980’s (Lluch-Belda et al, 1986; Nevárez-Martínez et al, 2001; Velarde et al, 2015). Though it could be argued that this California sea lion population increased during that period as a result of its recovery from documented legal hunting prior to the 1970’s (Cass, 1985; Masper et al, 2019; Zavala-González and Mellink, 2000), there is no evidence that the level of hunting was high enough to produce an appreciable decline of the population from which it would have recovered, at least not enough for a bottleneck effect on the population (Gonzalez-Suarez, 2010).…”

“…The catches plummeted from almost 300,000 tons to 7,000 tons in less than three years. Since then, several rises and falls have occurred, including the most extreme in 2008, when catches fell from over 500,000 tons to 3,000 tons in five years (Velarde et al, 2015). Nevertheless, as sardine fisheries plummeted and their trend became more unpredictable, other small pelagic fishes such as the thread herring ( Opisthonema libertate ), the Pacific mackerel ( Scomber japonicus ), the northern anchovy, and the bigmouth sardine ( Cetengraulis mysticetus ), gained relative importance in the catches (Lanz et al, 2009).…”

Demographic history of Heermann's Gull (Larus heermanni) from late Quaternary to present: Effects of past climate change in the Gulf of California

“…Furthermore, recent local and regional weather and oceanographic anomalies have been shown to affect both the marine productivity and the breeding distribution and success of several seabird species (Humphries et al 2015, Velarde et al 2015b. Studies of the demographic responses of seabirds to similar events in the past can help us have an early understanding of possible effects of such anomalies on species that may be particularly vulnerable.…”