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

AN ATTEMPT TO ESTIMATE ANNUAL SPAWNING INTENSITY OF THE ANCHOVY(ENGRAULIS RINGENS JENYNS) BY MEANS OF REGIONAL EGG AND LARVALSURVEYS DURING 1961-1964H. EINARSSON and B. ROJAS DE MENDIOLAlnstituto del Mar del PerGlima, PerGINTRODUCTIONFrom the beginning of our investigations in August1961, until June 1964, we have covered three anchovyspawning cycles. During this period we have collectedquantitative samples with the Hensen net at1,422 localities in northern Peruvian maters. A descriptionof eggs and larvae of the Peruvian anchovywas published in 1963 (Einarsson and Rojas de Mendiola), and a preliminary description of the frequencyand distribution of eggs and larvae was presented atthe ‘‘Primer Seminario Latinoamericano sobre elOcEano Pacific0 Oriental’’ (Einarsson, Rojas de Mendiola.and Santander, in press). The present papercarries this analysis a step further and describes theyearly areal variations in spawning intensity, as wellas the variations within the whole northern regionfrom Callao to Punta Aguja, the main fishing areanow under exploitation.For the purpose of this analysis we use only samplestaken during the spawning season from August of oneyear to March of the next. The total number of stationsoccupied during the three spawning cycles was847. Of these, 185 were occupied during 1961-62, 317during 1962-63, and 34.5 during 1963-64.The number of eggs and larvae are calculated asnumber per square meter of surface in a column 50meters deep. As in our previous study the averagevalues are given in two ways; firstly, as average Valuesper station, which reflect the spawning intensitywithin the area as a whole, and secondly, as averagevalues per positive station which reflect the spawningintensity within the boundaries of the spawning area.The material is in many ways faulty, due to uneventiming of cruises and also because all areas have notbeen investigated on every cruise. In spite of thiswe find this analysis worthwhile, and the results seemto tally with other kinds of evidence, derived froman entirely different approach.ANNUAL AREAL VARIATIONS IN SPAWNINGINTENSITYWe have divided the Perurian coastal waters latitudinallyinto 2” areas from north to south as seenin Figure 1. In this evaluation only areas B-E comeunder consideration, since anchovy spawning does notoccur in area A and our material is insufficient asregards the more southern areas. The material isgraphically presented in Figure 2.The areas fall clearly into two groups, B and Cconstituting one, D and E the other (Figure 3). Inthe first group the spawning intensity has been on ahigh level during the three spawning cycles, the period1962-63 yielding the highest values, especiallyin the average per positive station. This means thatthe spawning was intensive but confined to restrictedzones. Only area B shows this maximum also in theaverage values per station, during the said period,while area C shows declining values from the firstto the third spawning cycle.Areas D and E show a rather marked decline inthe values during the two latter spawning cycles,especially in the numbers per station, and we mustconclude that during the latter two cycles the spawningwas both of lesser intensity and geographicallyless extensive.While the values were fairly similar in all areasduring the first spawning cycle, the last two cyclesshow values which sharply decrease from north tosouthH-- XI79” 76O 730 70°FIGURE 1.