SPAWNING FREQUENCY AND SEX RATIO IN THE PERUVIAN ANCHOVY, ENGRAULIS RINGENS'

Abstract

Spawning frequency was determined for the first time for the Peruvian anchovy, Engraulis ringens, using the incidence of postovulatory follicles. The agreement between two independent frequency estimates, one for females taken one day after spawning and another for females taken two days after spawning, demonstrated the reliability of this method. In August-September, the main period of annual spawning, 16.04% of the female population of the central and northern anchovy stock off Peru spawned per day: i.e., every 6.23 days the average female spawned a new batch of eggs. Hydration of ovaries began as early as 0700 hours in the morning. Spawning occurred at night between 1800 and 0200 hours, reaching a maximum at about 2200 hours. Sex ratio was 57.9% females by weight. The vulnerability of females to the purse seine changed with their reproductive state. Females with hydrated ovaries who were ready to spawn seemed to attract males and to form male-dominated ‘‘spawning schools” by segregating from “normal” schools at night. RESUMEN