Temporal patterns of fish and mesozooplankton near the Columbia River plume.

Abstract

The distribution of the dominant fish species in the California Current System is seasonal, with the timing and variability of these distributions having significant ecological consequences. The objective of this study was to observe the seasonal timing of fish school presence and to characterize the temporal patterns their abundance. Fish and mesozooplankton were observed near the Columbia River plume using 200-kHz bioacoustic moorings deployed throughout the transition period from winter conditions to summer upwelling conditions in 2008. Sea surface temperature, sea surface salinity, and ocean current data were used to characterize the oceanographic habitat. Acoustic mooring data revealed that the seasonal timing of schools of Pacific sardine and northern anchovy were linked with temperature and persisted after a rapid increase in temperature occurred near the end of May. The abundance of fish schools and mesozooplankton at two mooring stations was highly variable with dramatic fluctuations occurring over a period of hours to days that were linked with ocean conditions. The use of stationary acoustic moorings in this study provided an effective tool to monitor fish abundance at high temporal resolution and provides insight into the timing and variability of fish populations that will improve ecosystem-based management decisions.