Simple application of using residuals from catch-curve regressions to assess year-class strength in fish

• Published in: Fisheries research 1997-11, Vol.32 (2), p.115-121
• Main Author: Maceina, M.J.
• Format: Article
• Language: English
• Subjects: Age; Catch-curve; Multiple regression; Residuals
• ISSN: 0165-7836; 1872-6763
• DOI: 10.1016/S0165-7836(97)00051-9

Residuals associated with catch-curve regressions can represent variable recruitment in fish populations. Catch curves are used to estimate steady-state mortality and assume relatively constant recruitment, but this assumption is rarely met. I documented the presence of abundant year classes of largemouth bass ( Micropterus salmoides), from earlier sampling and these dominant year classes persisted over time in two reservoirs. I expanded simple linear catch-curve regressions that used age (in years) as an independent regressor to multiple regression models each of which incorporated an additional independent environmental variable (ENVIR) that was measured when fish were age 0. The age term in the regression was proportionally weighted to the sample size at each age which deflated the influence of older and rarer fish in the analysis. This generalized regression equation: log e (NUMBER) = b 0 − b 1 (AGE) ± b 2 (ENVIR); explained variable abundance-at-age (NUMBER) and the environmental term was related to the formation of weak and strong year classes after accounting for the effects of age. Typically, age will explain the majority ( r 2 ≥ 0.5) of the variation in abundance-at-age. For two largemouth bass populations, environmental hydraulic variables were significant ( P < 0.10) terms in this equation and explained an additional 12 and 16% of the variation in number after accounting for the variation explained by age. For data collected in one population 2 yrs after the initial analysis, the same strong and weak year classes persisted, residuals from these catch curves were correlated ( r = 0.86, P < 0.05, N = 6), and the influence of hydrology on year class formation was duplicated. This approach can provide savings in labor and funds as abundance of young fish or recruitment indices do not have to be measured each year.