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

128 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONSand 1954, when they were collected only twice asoften as sardine larvae, but increased yearly in1955-60; in the 1960 collections, anchovy larvae occurredseven times as often as sardine larvae. A correspondingincrease appeared in the co-occurrencesof anchovy larvae in the collections containing sardinelarvae, from 62 percent in 1954 to about 87percent in 1960.Obviously, as one species becomes more abundantand more widespread than another, it will occur alonemore frequently, and thus be free from possible competition.When anchovy larvae are collected in seventimes as many hauls as sardine larvae, as in 1960,the possible eo-occurrences with sardine larvae wouldbe only 14 percent. In fact, sardine larvae eo-occurredwith anchovy larvae in one haul out of eight (12.4percent), while anchovy larvae eo-occurred with sar-dine larvae in six hauls out of seven (86.5 percent).For the decade as a whole, anchovy larvae cooccurredin 1,489 (69.8 percent) of the 2,133 haulsthat contained sardine larvae, whereas sardine larvaeoccurred in only 1,489 (22.0 percent) of the 6,755hauls that contained anchovy larvae. Thus, anchovylarvae were present in two of every three hauls thatcontained sardine larvae, whereas sardine larvae occurredin little more than one of five hauls containinganchovy larvae. If interspecies competition is a factorin the survival of larvae, and eo-occurrence is a measureof competition, then the anchovy should have hada decided advantage over the sardine.Another factor must be considered : sardine larvaeare less likely to occur with anchovy larvae in someareas of the CalCOFI grid than in others (Tables 7and 8). Anchovy larvae have had decidedly less com-80(SARDINE LARVAE ALONECO-OCCURRENCES. SARDINE & ANCHOVY LARVAEANCHOVY LARVAE ALONE70(60(v)wVzwU5 50(00LL0U w40(83230(201IO((FIGURE 8.1951 1952 1953 1954-1955 1956 1957 1958 1959Graphic presentation, by year, of the number of CalCOFl plankton collections containing 1) sardine larvae alone, 2) bath sardine andanchovy larvae, and 3) anchovy larvae alone, 1951-60