Abundance and distribution of larval and juvenile fish in Coos Bay, Oregon: time-series analysis based on light-trap collections

Abstract

Recent interest in the role of estuaries as 'essential fish habitat' has led to more precise definitions and quantitative assessments of estuaries as nursery habitat. Although the larvae and juveniles of >20 fish species are found in Pacific Northwest estuaries, information on their presence in and use of Oregon's estuaries is scarce. The objectives of this study were to use a long-term time series (3.75 yr) of high-frequency (every 1-2 d) light-trap collections from Coos Bay, Oregon to doc- ument species diversity, compare intra- and interannual patterns of species abundance and size, and identify potential wind- and/or tidally-driven transport mechanisms. Thirty-five taxa (28 species) of larval and juvenile fish were identified. Five species consistently comprised >70% of the catch. On average, the majority (94 ± 6% SD) of the catch at the most ocean-dominated site occurred during the downwelling season (1 October to 31 May) with 15 to 62% of that catch collected during the spring transition (1 April to 31 May) when conditions shift from predominantly downwelling to upwelling conditions. Conversely, <1 km farther up estuary an average of 64 ± 12.7% SD of the catch occurred during downwelling conditions with only 8% during the spring transition. Relative abundance patterns indicate seasonal and spatial variation in estuarine use and potentially extended residence periods for some species. Time-series analyses indicate the presence of the larval and juvenile fish collected in the estuary may have been primarily regulated by a combination of tidally-driven trans- port and reproductive timing with less evidence for wind-driven transport.