Criteria for age estimation of anchovy otoliths in the Alborán Sea (Western Mediterranean Sea) based on the monitoring of the hyaline edge formation

Abstract This study determines the seasonality in the formation of rings in the anchovy otoliths by monitoring hyaline edge in the Alborán Sea. Monthly samples were collected between October 1989 and December 1992 from the catches of the purse seine fleet. Two hyaline zones in the otolith are deposited per year, one in winter (primary) and a minor one during the summer spawning season. The formation of hyaline rings is significantly correlated with the temperature of seawater. The highest percentage of hyaline edge formation, recorded over the four year study, periodically occurred in February, when the temperature is at its lowest. When the nutritional status of fish is better, the percentage of individuals forming hyaline edge is lower. Considering these facts, a number of criteria for interpreting the growth rings on the anchovy otolith were developed. The population is subjected to a high rate of exploitation, so with the absence of older individuals in the area, it means that growth can only be accurately described in the first year. With some variations, depending on the year, anchovy grows between 12 and 13cm in their first year of life