Abstract
The influence of the well-known 1976–1977 regime shift on the Northern anchovy (Engraulis mordax) and the Pacific sardine (Sardinops caeruleus) populations in the California Current System (CCS) is investigated using a climate-to-fishery model. This model consists of four coupled submodels (regional ocean circulation model; Eulerian nutrient-phytoplankton-zooplankton-detritus model; individual-based full life cycle anchovy and sardine model; agent-based fishery model). Analysis of a historical simulation (1958–1990) showed that survival fraction of age-0 anchovy was lower just after 1977, while survival fraction of age-0 sardine was relatively unaffected by the regime shift. The age-0 survival of both species was influenced by the growth in the larval stage. Simulated zooplankton densities in the historical simulation shifted from high to low in 1976–1977 in the CCS, with the shift being most drastic in winter in the coastal area. The model also shows that anchovy larvae feed extensively from winter to early spring in the coastal area, while sardine larvae were mainly distributed in the offshore area. The differential seasonal and spatial responses of zooplankton in the simulation caused anchovy survival to be more sensitive than sardine to the 1976–1977 regime shift. The model-generated zooplankton shift was a result of reduced phytoplankton production due to lowered nutrient concentrations after 1977 due to the weakening of both the coastal upwelling and mixed layer shoaling, which reduced the vertical nutrient flux from the bottom layer to the surface layer.
Highlights
Anchovy (Engraulis sp.) and sardine (Sardinops sp.) are important harvested species in four regions of the world: California Current system (CCS), Humboldt Current System, Benguela Current System, and the KuroshioOyashio Current System
Observations show that the El Niño in 1983 had a strongly negative influence on anchovy populations (Fielder 1984), which may be underestimated in the model simulation
The purpose of this study is to investigate the influence of the 1976–1977 regime shift on Northern anchovy and Pacific sardine in the California Current System (CCS) by using a climate-to-fishery model
Summary
Background Anchovy (Engraulis sp.) and sardine (Sardinops sp.) are important harvested species in four regions of the world: California Current system (CCS), Humboldt Current System, Benguela Current System, and the KuroshioOyashio Current System. Those stocks exhibit a low frequency (decadal) variability and, except for the Humboldt system, out-of-phase-like synchrony (to various degrees) of stock variation between anchovy and sardine (Lluch-Belda et al 1989; Lluch-Belda et al 1992; Schwartzlose et al 1999). Our approach here is to use a coupled modeling system and apply the model to sardine and anchovy in the CCS to elucidate the various processes that connect climate forcing to sardine and anchovy stock variation.
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