Natural mortality of red bandfish, Cepola macrophthalma (L.), in the Aegean Sea (Greece): comparison of direct and indirect estimation methods

Abstract

The instantaneous natural mortality rate was estimated for unexploited populations of red bandfish, Cepola macrophthalma (L.), from experimental trawl samples collected in the Euboikos and Pagassitikos Gulfs (Aegean Sea) during 1986–1988. Two regions were identified within the study area (Region I to the north and Region II to the south of Euripos Strait). Natural mortality was estimated using four direct methods (from length and age frequencies) and four empirical regressions. The estimates from the direct methods ranged between 0.51 and 0.80 for Region I and between 0.80 and 1.23 for Region II. The estimates from the empirical regressions based on maximum observed age ( t max) were found to lie within the range of those derived using the direct methods. On the other hand, empirical regressions based on the Von Bertalanffy growth parameters ( K and L ∞) and water temperature produced the lowest estimates, outside the range of those derived using the direct methods (Region I: 0.38–0.41; Region II: 0.62–0.71). This difference was attributed to the atypical morphology and behaviour of red bandfish. The higher natural mortality of red bandfish in Region II is consistent with differences in other aspects of its life history, and all were attributed to phenotypic plasticity shaped by the different conditions of temperature and food prevailing in the two regions. The limitations of the methods used, the importance of using complementary methods for the estimation of M (rate of natural mortality), and the implications of the life history differences for the management of the oligotrophic Aegean Sea are also discussed.