Note on observations of daily rings on otoliths of deepwater snappers

Abstract

To encourage the development of deep-sea fishing in Vanuatu, the Office de la Recherche Scien-tifique et Technique d'Outre Mer (ORSTOM) is studying growth in some of the major species: Erelis carbunculus, E. coruscans, Pristipomoides multidens and P. flavipinnis. Traditional techniques for estimating age from rings on hard structures (otoliths, scales and dorsal spines) cannot be used, because seasonal rings, if they exist, are not easily discernible and because the environment (temperature, salinity, oxygen level and concentration of other salts) varies little at depths between 200 and 300 m in the tropics. We were unable to differentiate age groups of these fish by modal progressions in size distribu tion. Therefore, we decided to study rings on thin sections of otoliths. This technique, first suggested by Pannella (1971), is being used successfully in the tropics, notably in Hawaii (Uchida et al. 1982; Uchiyama, pers. comm.; Ralston 1976). The major difficulty lies in establishing the frequency at which the rings are laid. Results shown here depend on the validity of the hypothesis that the rings observed are produced daily.