CalCOFI Reports, Vol. 11, 1967 - California Cooperative Oceanic ...

60 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONSFIGURE 2.7-IDistribution and fishing limits of the Argentine anchovy.A 1-A2-Geographical distribution.B 1-B 2-Area of the approximate fishing totality.Population ProblemsIn 1958, Fuster de Plaza and Boschi (1958) hadassumed the existence of different anchovy populationswith differentiable meristic characteristics. Furtherinvestigations by Fuster de Plaza (1964) led toconfirmation of this assumption and established theexistence of two different anchovy populations : onewhose reproduction takes place in the Spring andanother, whose reproduction takes place in the Autumn.This conclusion has been based on meristicdifferences (mean number of vertebrae), distributionof modal classes of the samples over a period oftime, biological differences in such variables as growthrate and the attainment of the first sexual maturity inindividuals of both populations, and also in observationsof the state of maturity of the gonads throughoutthe year. This conclusion is partially supported byresults obtained by the present author (1965). Theseresults are based on data obtained from eggs, larvaeand juveniles of the anchovy. They were gatheredby systematic sampling throughout the year, and wereelaborated with quantitative methods. They show thatthe reproduction of the anchovy takes place in itsmost intensive rhythm during October, as temperaturesof 11.5°-14" C, and reaches a slight peak inFebruary, at a water temperature of 20" C. The presentauthor has also shown by means of experimentsthat the optimum temperature for the embryonicdevelopment of the anchovies spawning in October isbetween 1O0-17" C, and that a temperature of 20'seems to be off the optimum point. This observationmay also lead to the same assumption of the existenceof two different populations of the anchovy with differentphysiological characteristics.This problem becomes somewhat complicated by thefact, discovered by the present author, that the Argentineanchovy reproduces throughout the entire year.The problems arising from the populations of Engraulisanchoita, such as is the case with other speciesare very complex and await further and more detailedresearch.FecundityThere are data published on the fecundity problemof the anchovy by Fuster de Plaza (1964), who determinedthe degree of fecundity of the Spring anchovyalone. There are no available data on theAutumn anchovy. This is due to difficulties in obtainingstudy material, since this population is not subjectto commercial exploitation at present. The results obtainedare based on counts of the number of ovocitesof greater length in the ovaries of mature females. Inthe ovaries of the females which are in process of maturation,four different egg groups of differing degreesof maturity can be distinguished. When spawning isnear, three of these groups can be more clearly observed.During t>he spawning the females lay the firstovocites from the group of greatest ovocites, and aftera certain period of time lay ovocites from the secondgroup. After this partial evacuation, the females leavethe spawning area, retaining in their ovaries ovocitesin different stages of development.There exists, in this species, as in several otherspecies of fish, a strong correlation between the numberof ovocites in the ovary and the total length ofthe individual. For instance, the number of ovocitesobserved in the group of greatest size for females ofdifferent total lengths are, according to Fuster dePlaza :Total length 115 140 160 175 190(mm)Number of 4,400 9,368 15,084 21,954 24,920ovocitesReproduction and Early Life HistoryThe first. sexual maturity of the anchovy is stronglyrelated to the minimum length and, according toFuster de Plaza (1964), anchovies of the Springpopulation reach their first maturity when they are120-130 mm long, while those from the Autumnpopulation reach theirs when their length is 115-120mm. This author states that from July to August,adult individuals of the Spring population gradually