Comparison of Bottom Faunas as Sources of Available Fish Food
- 1 January 1942
- journal article
- Published by Oxford University Press (OUP) in Transactions of the American Fisheries Society
- Vol. 71 (1) , 275-283
- https://doi.org/10.1577/1548-8659(1941)71[275:cobfas]2.0.co;2
Abstract
To obtain a true estimate of the actual quantity of fish food which any fauna represents, allowance must be made for the differences in the availability to the fish of the various component species. The ratio between the percentage occurrence in a sample of stomach contents and in samples of the corresponding bottom fauna has been suggested as a measure of the availability. The theoretical basis of this ratio—the “forage ratio” or “availability factor”—is discussed, and it is shown to be essential, when using this factor in comparing faunas as sources of available food, to use the ratios as determined and without change, and to apply the same series of values to all the faunas being compared. The availability of a food animal varies in respect not only to the species but also to the size of the fish concerned. Comparisons of faunas should therefore be based on two or more determinations of the “apparent available density” of each, these being made in respect to different size groups of fish present. The same arbitrary standards for the classification of fauna can be applied to the apparent available densities as to the actual densities of the fauna. Availability factors and apparent available densities can be determined on a numerical or gravimetric or volumetric basis. The numerical determination of availability factor is the most simple, and results obtained in this way can probably be applied satisfactorily to volumetric or gravimetric determinations of density. Sufficient bottom samples should be taken to minimize the sampling error in determining the mean faunistic density, and all types of environment should be proportionately represented. Seasonal variation both in the density of the fauna, and in availability factors, should be allowed for by sampling at several times of the year. Samples should not be taken soon after floods. Further work is required on methods of eliminating inaccuracies due to selection by the fish and to different rates at which animals are digested.This publication has 0 references indexed in Scilit: