Tracing the life history of red gurnard (Aspitrigla cuculus ) using validated otolith annual rings

Abstract

Back calculation, marginal increment analysis and modal progression analysis were used to trace growth processes of the red gurnard, Aspitrigla cuculus L., in the Mediterranean Sea. Three false rings appeared regularly on otoliths and were hypothesized to refer to the ontogeny on the basis of the study of the recruitment and reproduction processes of the species. The first two rings were laid down during the first pelagic period and the transformation to the bottom mode of life, respectively. The third ring corresponded to the first spawning at the end of the second year of life. The marginal increment analysis demonstrated that one opaque and one translucent zone is formed each year, the translucent ring corresponding to the period of slow growth in the winter. Temperature and salinity of Mediterranean waters below the thermocline where red gurnard live do not undergo seasonal variations. Therefore, traditional interpretation of the discontinuity patterns on otoliths related to the decrease of water temperature should be rejected for Mediterranean fish distributed on the deep shelf and slope. Discontinuities in otolith structure may be related to seasonal variation in feeding intensity as a consequence of decreases in the benthic mysids biomass and time available to find food due to reduced daylight. Future research should focus on the trophic ecology of the demersal fishes and the seasonal fluctuations of the prey resources during the year in order to assess the role of the food supply with regard to otolith growth patterns in the Mediterranean Sea.