Feeding ecology of pelagic larvae of English sole Parophrys vetulus and butter sole Isopsetta isolepis off the Oregon coast

Abstract

The food habits of the 2 dominant larval pleuronectids off the Oregon coast-English sole Parophrys vetulus and butter sole Isopsetta isolepis-were analysed. Most specimens were collected during January-April 1971 and March-April 1973. As is typical of larval fishes, I. isolepis larvae ingested a variety of prey which changed with increasing fish size. Small larvae fed predominantly on tintinnids, invertebrate eggs, and nauplii, whereas large larvae consumed more copepodite and adult copepods. In contrast, the diet of P. vetuluslarvae is very specific; appendicularians (Oikopleura spp.) comprised 97 % of the total number of food items consumed in 1973. Both P. vetulus larvae and appendicularians are most abundant during fall and winter when total zooplankton concentrations off Oregon are low. I. isolepis larvae are most abundant during spring when upwelling stimulates productivity. In 1971, seasonal abundance peaks of P. vetulus larvae and appendicularians did not coincide. During this year, larvae fed less on appendicularians than in 1973 (66 % of the total number of food items), and more on other food sources such as tintinnids, invertebrate eggs, and nauplii. In 1971 more P. vetulus larvae had empty guts than in 1973; this observation suggests increased starvation. In addition, fewer large larvae were present in 1971, perhaps due to higher mortality rates. Hence, in contrast to I. isolepis larvae, P. vetulus larvae are dependent upon a specific prey; a mismatch of P. vetulus and appendicularian abundance peaks may result in significant food-related mortality.