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

134 CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONSfewer hauls (644). Some of the irregularities in thiscurve, compared with the other three, may be due tofewer data.At first glance at the two curves for sardine larvae,one gets the impression that survival may have beensomewhat better in the eo-occurring hauls. On closerinspection however, it is seen that larvae larger than6.75 mm followed no consistent trend, except as notedbelow. The greatest difference in relative abundancewas between the smaller larvae (3.0-5.75 mm long)and all larger larvae. This difference could be interpretedas poorer initial survival of sardine larvae insituations where they occur alone. An equally logicalexplanation for the difference, however, is based onthe increasing frequency of co-occurrences of sardineand anchovy larvae with increase in size. It wasnoted earlier that the frequency of eo-occurrence ofsardine and anchovy eggs was markedly lower thanfor larvae. A natural corollary is that newly hatchedlarvae of the two species would co-occur less frequentlythan the larger larvae. The effect on abundancecurves would be to increase the numbers oflarger larvae in hauls in which the species eo-occurredthan in hauls in which they occurred alone. Furthermore,the two curves for sardine larvae do convergeif all larger-sized larvae (17.25-25.25 mm) are takeninto account. As many larger larvae were taken inhauls in which sardines occurred alone as in haulsin which both species occurred-0.73 larvae per haulon the average.Thus, the basic question has been answered j bettersurvival was not indicated by the hauls in which bothspecies were caught even though average numbers oflarvae per haul were larger.Although the analysis has been confined largely tothe 1950’~~ the report can be brought up to date.Tables 3 and 4 include the number of occurrencesand co-occurrences of sardine and anchovy larvaeduring the first 3 years of quarterly cruises, 1961-63.Anchovy larvae occurred in 43 percent of the haulsin 1961, 49 percent in 1962, and 54 percent in 1963.Sardine larvae occurred in 5 percent of the haulsin 1961, 6 percent in 1962, and 9.5 percent in 1963.(Data for 1963 are not closely comparable to those forother years because a number of closely spaced inshorestations were added.) Anchovy larvae occurredin nearly 90 percent of the hauls containing sardinelarvae. In contrast, sardine larvae occurred in only13 percent of the hauls containing anchovy larvae.Co-occurrences of anchovy larvae with sardine larvaewere even higher than in the late 1950’~~ and even ahigher percentage of the collections of anchovy larvaecontained no sardine larvae. Anchovy larvae now seemto be completely dominant.100.0-,, I I I I I I I I I I I I I100I I I I I I I I I I I I I I2 10.0-IW2culgKWaaWmI ‘2 1.0-w2W20.1I1 1-ANCHOVY WITH SARDINE LARVAEANCHOVY LARVAE ALONEl f 1 1 1 1 1 1 l J 1 l IJ3aIy IO-tv)2KWaKwm52WCllaKwzI 1 1 1 1 1 1 1 1 1 1 1 1 I3.00 4.75 675 8.75 1075 12.75 14.75 IZ2!LENGTH IN MM.FIGURE 12. Comparisons of average number of sardine larvae perpositive haul as related to length (mm) for 1) hauls containing bothsardine and anchovy larvae and 2) hauls with sardine larvae alone.Data for 1951-60 combined.