A comparison of the diets of silver (Seriolella punctata) and white (Seriolella caerulea) warehou

Abstract

The diets of the silver warehou (Seriolella punctata) and the white warehou (S. caerulea), were determined from examination of the stomach contents of 478 and 291 specimens, respectively, sampled by bottom trawl on Chatham Rise to the east of South Island, New Zealand. The diets of both species were dominated by pelagic tunicates, with the remainder comprising mostly small crustaceans. The importance of small crustaceans (amphipods, copepods, and euphausiids) to white warehou was much greater than for silver warehou. An unknown but small component of the crustacean prey was ingested unintentionally owing to a common commensal relationship between some crustaceans (primarily amphipods) and tunicates. The distributions of silver and white warehous on Chatham Rise overlapped geographically and by depth; the entire white warehou distribution overlapped that for silver warehou. While some between-species differences in dietary composition were apparent, these are unlikely to markedly reduce any competition between species for the tunicate resource. It is possible that the niches of silver and white warehou overlap considerably. There may be some behavioural or biological mechanisms not identified in this study that reduce the resource competition between these two species, but understanding the mechanisms that promote the coexistence of silver and white warehou requires further study.