THE RELATIVE PROFITABILITY OF PARTICULATE-FEEDING AND FILTER-FEEDING IN THE HERRING, CLUPEA-HARENGUS L

Analysis of laboratory video‐recordings of herring feeding by biting and filtering on Calanus finmarchicus and three sizes of Artemia enabled the capture rates of the two methods to be estimated at different prey concentrations. At low concentrations the fish feed by selective capture of individual particles, but the capture rate achievable by this method is constrained by the maximum rate at which they can bite. Filter‐feeding is not subject to this constraint because capture rate is directly proportional to prey concentration and above a critical prey concentration its capture rate exceeds that of biting. The possession of two feeding methods allows the fish to maximize prey intake over a wide range of concentrations and the phenomenon of switching between feeding methods can be explained by their relative profitabilities at different concentrations. The observation that less than 50% of fish are filtering when capture rates by the two methods are equal suggests that filtering is energetically more costly than biting. Estimates of the energy cost of filtering indicated that it may be from 1.4 to 4.6 times higher than that of biting. Copyright © 1992, Wiley Blackwell. All rights reserved