Wind-Forced Hydrodynamics and Their Interaction with Larval Fish and Plankton Abundance: A Time-Series Analysis of Physical–Biological Data

Abstract

We evaluated methods to measure simultaneously biological and physical properties essential for estimating short-term mortality of larval fish. We used the data to test Templeman's watermass exchange hypothesis and the associated safe-site hypothesis. Synoptic estimates of larval capelin (Mallotus villosus) and microzooplankton particle density were obtained simultaneously with a scale resolution of 200 m (horizontal), 2–4 m (vertical) and 6–8 h (temporal) in a 1-km2 coastal embayment in eastern Newfoundland. Statistically significant population estimates were derived from multiple regression models incorporating a limited number of samples. Spectral analysis of wind and current time-series and analysis of large-scale temperature oscillations were consistent with Templeman's hypothesis. Nearshore current responded to cross-shore wind forcing at periods of 2–6 d. Larval capelin abundance oscillations were coherent with wind and with current at periods of ~5 d, consistent with the watermass exchange and safe-site hypotheses. Although larvae and microzooplankton abundances showed similar spectral density and were in phase, their coherence was weak. Integrated measures of onshore wind and of the onshore–offshore wind spectrum were correlated, and either can be used as a composite measure of the considerable interannual variation evident in the frequency, magnitude, and duration of onshore winds, and hence of watermass exchange.