A simple method for comparing age- length keys reveals significant regional differences within a single stock of haddock (Melanogrammus aeglefinus)

摘要

A multinomial logistic model is presented as a tool for comparing two or more age-length keys. The model provides an objective way to fill in missing values and can be used for estimating uncertainty and visualizing age-length keys (ALKs). An example of haddock (Melanogrammus aeglefinus) in ICES Division Via (West of Scotland) is used to illustrate significant regional differences in the proportions of age-at-length. These differences are caused by regional variation in both length-at-age and relative abundance at age. As the length-at-age data are normally not weighted by the local catch rate (abundance), the ALK of the combined age data can result in strongly biased estimates of numbers-at-age. In the present case, the use of unweighted age data would have resulted in an overestimate of recruitment of nearly 200%, and an underestimate of spawning-stock biomass of 15%. Comparing ALKs using this method has several practical applications.