Simulation of Temperature and Upwelling Effects on the English Sole (Parophrys vetulus) Spawning Season

Abstract

Spawning times for English sole (Parophrys vetulus) in Oregon waters were estimated for 13 yr using data on adult female gonadal condition, and surveys of pelagic larvae and benthic juveniles of known ages. The spawning season for this species is extremely protracted and variable. Some spawning may occur in all months, but most occurs between September and April, with a peak lasting 1–3 mo within this period. Variations in the English sole spawning season appear to be largely accountable by variations in a continental shelf temperature index (developed from a relationship with Neah Bay sea level). The following three hypotheses about temperature control of spawning were described by mathematical relationships which were incorporated into a simulation model that was driven by the time series of the bottom temperature index: (1) the rate of gonadal development is inversely related to summer bottom temperatures; (2) spawning is inhibited by temperatures below about 7.8 °C; and (3) spawning is delayed by rapid increases in bottom temperature. The model in its present form can be used to simulate spawning activity for years void of empirical spawning records and to design laboratory experiments capable of validating cause-and-effect relationships.Key words: Oregon, English sole, spawning time, upwelling, shelf temperature, hypotheses, simulation model