Significant differences in the length-weight relationships of neighbouring stocks can result in biased biomass estimates: examples of haddock (Melanogrammus aeglefinus, L.) and whiting (Merlangius merlangus, L.).

摘要

Length-weight relationships of fish are often used to estimate the biomass of length distributions or to obtain indices of condition. Although large-scale spatial trends are known to exist, it is often assumed that length-weight relationships do not vary significantly within stocks or between neighbouring stocks. The present study examined length-weight relationships of 1334 haddock (Melanogrammus aeglefinus) and H 86 whiting (Merlangius merlangus) collected on a groundfish survey in the waters around Ireland in 2004. Additionally, condition indices were estimated for individual fish and for length-frequency samples in order to summarise the length-weight relationships. The length-weight regression showed a significant area effect but no significant differences existed between the sexes. The condition indices showed a moderate spatial structure for both species: around 25% of the variability could be explained by the location of the samples, the rest of the variability was due to other sources. Length-weight relationships did not appear to vary significantly within stocks, however differences between stocks were significant. In the present case, a bias of up to 10% could occur in biomass estimates as a result of applying length-weight relationships of one stock to length data of a neighbouring stock. [copyright] 2007 Elsevier B.V. All rights reserved.