Investigator Group Expedition 2006: Flexible Foraging Ecologyofa Temperate Herbivore, The Herring Cale, Olisthops Cyanomelas, in South Australia

Abstract

The odacine fish, herring cale (HC), Olisthops cyanomelas, is a facultative browser, feeding mainly on the secondary laminae of Ecklonia radiata, and the apical receptacles of the fucoids, Cystophora spp. and Sargassum spp. Diet, daily feeding rates and time budgets of HC were examined at two South Australian sites >1000 km apart and in different water movement conditions, with additional dietary data from an exposed site. The diet and feeding behaviour were habitat-dependent. At one partly-sheltered site with abundant Ecklonia, HC was most active immediately after dawn and toward dusk, whereas at the other more sheltered site, dominated by fucoid algae, it was inactive at dawn increasing to a moderate level of activity in mid-morning, and peaking toward sunset. Feeding bite rates were variable and mean rates ranged from 8 – 14.5 min−1 according to site. HC characteristically engaged in intermittent foraging bouts, interspersed with periods of inactivity, which averaged ~ 55% of daylight hours. Interactions with other species were few. Analysis showed no significant differences between small and large HC in bite rates, but significant between-site differences in bite rates, and in the proportion of time spent foraging and swimming. In this study HC did not destroy patches of the kelp, Ecklonia, as it does in eastern Australia, even when the kelp comprises the main diet, because it fed only on the distal parts of the kelp’s secondary laminae and meristem.