NATURAL MORTALITY OF RED BANDFISH, CEPOLA-MACROPHTHALMA (L), IN THE AEGEAN SEA (GREECE) - COMPARISON OF DIRECT AND INDIRECT ESTIMATION METHODS

The instantaneous natural mortality rate was estimated for unexploited populations of red bandfish, Cepola macrophthalma (L.), from experime ntal trawl samples collected in the Euboikos and Pagassitikos Gulfs (A egean Sea) during 1986-1988. Two regions were identified within the st udy area (Region I to the north and Region II to the south of Euripos Strait). Natural mortality was estimated using four direct methods (fr om length and age frequencies) and four empirical regressions. The est imates 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 emp irical regressions based on maximum observed age (t(max)) were found t o lie within the range of those derived using the direct methods. On t he other hand, empirical regressions based on the Von Bertalanffy grow th parameters (K and L(infinity)) and water temperature produced the l owest estimates, outside the range of those derived using the direct m ethods (Region I: 0.38-0.41; Region II: 0.62-0.71). This difference wa s attributed to the atypical morphology and behaviour of red bandfish. The higher natural mortality of red bandfish in Region II is consiste nt with differences in other aspects of its life history, and all were attributed to phenotypic plasticity shaped by the different condition s of temperature and food prevailing in the two regions. The limitatio ns of the methods used, the importance of using complementary methods for the estimation of M (rate of natural mortality), and the implicati ons of the life history differences for the management of the oligotro phic Aegean Sea are also discussed.