1500 years of anchovy and sardine population response to coastal upwelling off Southern California

Abstract

Young pelagic, planktivorous fish species feed on phytoplankton and zooplankton larvae, which respond to nutrient delivery by upwelling. Off the coast of Southern California, wind-driven coastal upwelling is affected by the position and strength of the North Pacific High Pressure system (NPH). When NPH strength increases, coastal upwelling intensifies and dry climate conditions prevail. Here we determine the abundance of four pelagic fish species; Northern anchovy (Engraulis mordax), Pacific sardine (Sardinops sagax), hake (Merluccius productus), and surfperch (Embiotocidae spp.), in Santa Barbara Basin (SBB) over the last 1500 years and relate population fluctuations to regional upwelling and the strength of the NPH. Proxies for marine productivity, drought and surface water masses based on sediment geochemistry are used to reconstruct NPH strength and surface ocean circulation. Sediment core SPR0901-02KC was collected from the SBB (34 16.8′ N, 120 02.3′ W) and sampled continuously at 0.5 cm resolution (~5-year resolution) for fish scale counts from which scale deposition rates (SDR) and relative abundance (%) were estimated. Anchovy scales generally comprise >50% of total scales. Anchovy SDRs were >30 scales cm-2 year-1 1000 between 510-675, 860-1075, 1425, 1500, 1560-1700 and 1750-1825, and 1870-1900 CE when the NPH was strong producing both intense coastal upwelling and drought in Southern California. Sardine SDRs (<20% of scales) were generally in phase with anchovy, with lower and more variable abundance. Sardine comprise >10% of scales between 680-875, 1050-1300, 1340-1380, 1480-1510 and 1690-1740 CE. Hake scales comprise ~30-50% of total scales and are most abundant between 760-1030 and 1275- 1470 CE when Eastern Tropical North Pacific water entered the basin, with a maximum SDR of ~35 scales cm-2 year-1 1000. Surfperch scales generally comprise <10% of total scales. Anchovy abundance increases during intervals supporting a strengthening of the NPH, while hake respond to variations in poleward currents. Sardine and surfperch have no notable correlations with these environmental factors.