Anchovy boom and bust linked to trophic shifts in larval diet

Abstract

Although massive biomass fluctuations of coastal-pelagic fishes are an iconic example of the impacts of climate variability on marine ecosystems, the mechanisms governing these dynamics are often elusive. We construct a 45-year record of nitrogen stable isotopes measured in larvae of Northern Anchovy (Engraulis mordax) in the California Current Ecosystem to assess patterns in food chain length. Larval trophic efficiency associated with a shortened food chain increased larval survival and produced boom periods of high adult biomass. In contrast, when larval food chain length increased, and energy transfer efficiency decreased, the population crashed. We propose the Trophic Efficiency in Early Life (TEEL) hypothesis, which states that larval fishes must consume prey that confer sufficient energy for survival, to help explain natural boom-bust dynamics of coastal pelagic fishes. Our findings illustrate a potential for trophic indicators to generally inform larval survival and adult population dynamics of coastal-pelagic fishes.

Maternal Effects and Trophodynamics Drive Interannual Larval Growth Variability of Atlantic Bluefin Tuna (Thunnus thynnus) from the Gulf of Mexico

“…Our results are consistent with those summarized by Gerard et al [63] for the BLOOFINZ-GOM cruises, suggesting ABFT larvae are more likely to thrive by feeding at a lower trophic position regardless of the source of production (GOM18). These findings appear consistent with the newly proposed Trophic Efficiency in the Early Life hypothesis in which larval survival is linked to feeding on prey that are low in the food chain, thereby maximizing energy transfer [103] (Figure A2 and Table 3).…”

“…Similar observations have been reported for larval Shortbelly Rockfish where larvae with a lower TP were heavier and grew faster [101]. The TP reflects how the energy is transferred from the base of the food web up to the larva [99,102], and its estimation can be influenced by food chain efficiency [103,104], which causes a wide range of TP estimates in the GOM [64].…”

State of the California Current Ecosystem report in 2022: a tale of two La Niñas

“…It was previously thought that anchovy population size increased during cool periods when La Niña events were frequent (Chavez et al, 2003), but in recent years anchovy increased greatly in warm years (e.g., 2004-2005-2016(Thompson et al, 2019b)). The expectations for anchovy during La Niña events is thus currently unclear, and our understanding of drivers of the populations size of this important forage species (McClatchie et al, 2016a) is evolving (Swalethorp et al, 2023). Anchovy have been in a boom state in the CCE since 2015 (Thompson et al, 2019b), and in 2022 adult anchovy abundance remained high in central California but fell to average levels in southern California.…”