Seabird diets provide early warning of sardine fishery declines in the Gulf of California

Abstract

Small pelagic fisheries show wide fluctuations, generally attributed to oceanographic anomalies. Most data on these fisheries come from landings, often reporting sustained catches-per-unit-effort (CPUEs) until a decline occurs. Fishery-independent data are important as management tools. In this study we show that the proportions of Pacific Sardine and Northern Anchovy in the diet of three seabird species (California Brown Pelicans, Heermann's Gulls, and Elegant Terns) nesting in spring in the Gulf of California show significant relationships with CPUEs during the following season in gulls and terns, or during the same season in pelicans. As sardine availability for seabirds declines, CPUEs remain high until the fishery falls, one or two seasons later. A declining proportion of sardines in the seabirds' diet, combined with the status of the Pacific warm-phase anomaly (El Niño), give a reliable forecast of diminishing CPUEs and signals the need to reduce fishing efforts in the ensuing season.

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

“…The fact that studies on 5 additional species, aside from Heermann's Gull, show evidence of expansions during the late Pleistocene (100,000-30,000 yr BP) indicates that regional oceanographic change during that period affected multiple marine species in a similar manner. The results of Díaz-Viloria et al (2012) on the northern anchovy are most relevant to our results, given that long-term studies on the diet of Heermann's Gull have shown that northern anchovy is an important prey species (Velarde et al 1994(Velarde et al , 2013(Velarde et al , 2015a. The population expansion of northern anchovy (Díaz-Viloria et al 2012) could have been a key factor in the increased breeding success of Heermann's Gull and its own demographic expansion.…”

“…The population-expansion interpretation is also supported by the highly significant negative value of Fu's F S , a more sensitive indicator than Tajima's D. Evidence from MDA and BSP indicates that Heermann's Gull experienced a demographic expansion between 100,000 and 45,000 yr BP, a period that roughly coincided with the end of the Pleistocene glacial maxima to the last glacial retreat. The signature of major population expansion during the late Pleistocene for Heermann's Gulls is likely related to large-scale ecological shifts in the North Pacific and Gulf of California due to historical climate change and the subsequent demographic expansions of associated marine species, including species that are presently important components in the diet of Heermann's Gulls, such as the northern anchovy (Engraulis mordax; Velarde et al 1994Velarde et al , 2013Velarde et al , 2015a.…”

“…Recently the species has been reported to nest in 14 sites, with Isla Rasa harboring~130,000 pairs; Isla Cardonosa (4 nautical miles north of Isla Rasa), with 4,000 pairs, is the second-largest colony (Velarde 1999, Mellink 2001, Velarde et al 2005. The species feeds on small pelagic fishes and is an important part of the regional trophic web (Velarde et al 2004(Velarde et al , 2013(Velarde et al , 2015a.…”

“…Several studies have examined the biology and ecological relationships of Heermann's Gull, including adaptation to the hot, arid environment in which it nests (Bartholomew and Dawson 1979, Bennett and Dawson 1979, Rahn and Dawson 1979; interactions with predators and breeding biology (Velarde 1992(Velarde , 1993(Velarde , 1999; effects of parental age and food availability on breeding success (Vieyra et al 2009); and how its diet composition can be used to predict forage fish abundances (Velarde et al 2004(Velarde et al , 2013(Velarde et al , 2015a. However, the effects of past climate change on this species' population size through time, and whether changes in its population size are at all related to population changes in other marine species in the region, have been unknown.…”

Spatio‐temporal dynamics of ocean conditions and forage taxa reveal regional structuring of seabird–prey relationships

“…Because life history attributes and behaviors vary (e.g., morphology, foraging habitat preference, diving ability), seabird species have differential sensitivities to variation in prey availability (Ainley et al 1995, Furness and Tasker 2000, Velarde et al 2013. Therefore, our overall goal is to understand spatially explicit oceanprey and seabird-prey relationships from the perspective of variation in life histories.…”