Age, growth and reproductive status of the European conger eel, Conger conger (L.) in Irish coastal waters

摘要

A sample of 166 conger eel, Conger conger (Linnaeus, 1758) were captured between August 1998 and June 1999, from the inshore south coastal waters of Ireland using demersal trawl, longlines, lobster and shrimp pots. The range in length was 33-159 cm and weight was 0.05-12.0 kg. Age, determined from vertebrae and sagittal otoliths, ranged from 4 to 20 years. Vertebrae were found to be the most effective tool for ageing. A linear relationship was found between total length and otolith radius. A curvilinear model best described the relationship between total length and vertebral radius. Both otoliths and vertebrae were used in the back-calculation technique and the von Bertalanffy growth function was fitted. Population growth curves were constructed from both vertebral and otolith measurements. Growth parameters, L-infinity and k were estimated for individual fish showing large ranges in values. L-infinity from otoliths ranged from 170 to 320m, and k from 0.01 to 0.09. From vertebrae, L-infinity ranged from 130 to 390 m and k from 0.01 to 0.13. Population estimates from otoliths gave results of L-infinity = 271 cm, k = 0.037, t(0) = -1.396 and from vertebrae gave results of L-infinity = 214 cm, k = 0.059, t(0) = -1.960. Condition factor ranged from 0.03 to 1.73 and gonadosomatic, index from 0.53 to 7.05. The greatest increase in condition occurred between summer and autumn, while the greatest increase in gonadosomatic index occurred between autumn and winter. It was not possible to determine the sex of the eels from gross gonad appearance. Histological analysis of the gonads revealed that all conger eels were female. The absence of males and of ripe or spent females in the inshore south coastal inshore waters suggests that conger eels leave this region to spawn. This study has provided the first published data on age, growth and gonad development of a population of the species in the Northeast Atlantic