Growth and mortality rates of brown mussels Perna perna (Linnaeus) in Kwazulu-Natal: A comparison between sites and methods using non-parametric length-based analysis

Abstract

Three non-parametric, length-based methods were used to estimate growth and total mortality rates of Perna perna at five sites along the KwaZulu-Natal coastline. Monthly samples were split into quarterly intervals to estimate variances. Pauly’s growth performance index (Φ’)values obtained using the ELEFAN I method were significantly lower than those using SLCA or PROJMAT. A multiple comparison of group means divided site-specific growth rates into two groups; one group of sites had a mean Φ’ of 3.92 (95% confidence interval CI 3.83–4.02) and the other group had a mean Φ’ of 4, 11 (95% CI 4, 02–4, 19). Seasonality was marked at three sites and growth was slower during winter (annual monthly sea temperature range 4, 7°C). Total mortality estimates were positively correlated with growth rate estimates, which made between-site comparisons difficult; the mean was 1, 53·year− (95% CI 1, 07–1, 99). Variation within regions seems to override any latitudinal trend in growth rate of P. perna along the South African coast. © 1995 Taylor & Francis Group, LLC.