CO-OCCURRENCES OF SARDINE AND ANCHOVY LARVAE IN THE CALIFORNIA CURRENT REGION OFF CALIFORNIA AND BAJA CALIFORNIA

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1 COOCCURRENCES OF SARDNE AND ANCHOVY LARVAE N THE CALFORNA CURRENT REGON OFF CALFORNA AND BAJA CALFORNA ELBERT H. AHLSTROM Bureau of Commercial Fisheries FisheryOceanography Center La Jolla, California This is a report on the cooccurrences of sardine and anchovy eggs and larvae in the collections of the California Cooperative Oceanic Fisheries nvestigations (CalCOF) during. More important, it is also a study of the interaction between two species of fishboth filterfeeders on planktonic organismsoccupying the same trophic level. This study leads further into the problem of whether there is a limit to the biomass of sardines plus anchovies that can be accommodated in the environment and whether one species increases in abundance only at the expense of the other. During the period of the CalCOF surveys, which began in, the population of the Pacific sardine (flardinops caerulea) as determined from the distribution and abundance of eggs and larvae, decreased markedly, especially since. n contrast, the population of the northern anchovy (Engraulis mordax), as determined from the distribution and abundance of larvae, increased spectacularly. This relation brings up the question of whether the anchovy is moving into the ecological niche previously occupied by the sardine. CalCOF survey cruises have been made off California and Baja California for more than years. Coverage was fairly intensive in, when cruises were made at approximately monthly intervals. n, cruises were spaced at quarterly intervals. Temporal coverage, consequently, was much better during the decade, the years dealt with particularly in this report. One of the difficulties in working up the observations on sardine and anchovy eggs and larvae is the massiveness of the data. Even the data for the year period,, are based on more than, separate collections. Anchovy larvae occurred in,7 collections, or. percent of the total, and sardine larvae in,. or. percent. These data can be examined in many different ways. For example, the sardine and anchovy larvae from all collections are measured by millimeter intervals, for abundance and survival studies. Was survival of larvae better in samples where anchovy and sardine larvae cooccurred, or in samples where the larvae of one species occurred alone? What Tm the relation of cooccurrences to the temporal and areal distributions of the larvae of the two species or to their relative abundances per haul? What mas the influence of changing environmental conditions on the frequency with which sardines and anchovies eooccurred? The CalCOF survey cruises initially were planned to delimit and assay the distribution and abundance of the panktonic eggs and larvae of the Pacific sar,dine to determine indirectly the distribution and abundance of the adult population at time of spawning and to obtain information on the factors affecting the survival of year classes. Sardine spawning was found to have an extensive and variable areal distribution and to take place during much of the year. especially off Baja California. Consequently, we tried to cover systematically a rather large area of the ocean off California and Baja California. The CalCOF station pattern is illustrated in Figure. nasmuch as plan to discuss the distribution and abundance of eggs and larvae in different parts of the CalCOF region, have subdivided it into 7 areasthree off California and four off Baja California. The station lines included in each area are as follows : Area Station Line Northern California... 7 Central California... Southern California S Northern Baja California Upper central Baja California Lower central Baja California _ 7 Southern Baja California... 7 Not all areas were covered on each cruise. Four were consistently workedthose lying between station lines 87. The majority of cruises also included the central California area. Usually only or cruises per year were made off northern California and southern Baja California. With rare exceptions, only a single plankton haul was taken at each station occupied during a cruise. n the course of obtaining information about sardine eggs and larvae, we also obtained information about many other fishes with planktonic young. Even at the beginning of the surveys, sardine larvae were outnumbered by larvae of northern anchovy (Engraulis mordax), hake (Merluccius productus), rockfish (Xebastodes spp.), and usually jack mackerel (Trachurzu symmetricus). The occurrence of numerous species of larvae led to a decision to identify and enumerate all the kinds in the collections. This decision posed problems in identification, but these were solved with perseverance. t became evident that surveys of eggs and larvae constituted one of the indispensable methods of resource evaluation. Most pelagic fishes have planktonic stages that can be sampled more simply and quantitatively than the adults. Larvae of the Pacific sardine and northern anchovy occur mainly off southern California and off most of Baja California. The sardine also occurs throughout the Gulf of California. The northern anchovy, a somewhat more temperate species, does not occur in the Gulf, and its larvae seldom occur south of Magdalena Bay. t ranges farther north, however, than the sardine. n recent years there has been little spawning off central California (north of Pt. Conception) by either anchovies or sardines, although

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3 REPORTS VOLUME X, JULY TO JUNE anchovy spawning was common during 8 and. Some anchovies spawn as far north as British Columbia. A most important consideration of the data of is that we could define no such thing as an average distribution or abundance of either species. Each year differed from every other year. The distributions of both species changed from year to year ; the changes reflected their response to the varying oceanic environment. The changes in abundance of the two species, however, were more systematic, as is noted later. Examples of changing distributions are pointed out here. One of the most marked changes in the distribution of sardine eggs and larvae occurred in the and season. n, nearly all sardine spawning was off central Baja California; only about percent was to the north. n, spawning spread distinctly northward, and was widespread off both northern Baja California and southern California. The spawning in these northern areas increased to more than 8 percent of the season s total. Variations in the spawning may be temporal as well as areal. A marked temporal change in sardine spawning occurred off southern California in 8. During the preceding years which were characterized by belowaverage temperatures in winter and early spring off southern California, most spawning was in May and June. n 8, after temperatures had been above average in the eastern North Pacific since mid7, the peak of sardine spawning was in January 8, and spawning extended over a 7month period, from January to July. Changes in the distribution of anchovy eggs and larvae were less spectacular, but nonetheless real. n, one of the colder years in the California Current region during the s, anchovy larvae were much more numerous off southern Baja California (lines and south) than in previous years. n most years less than percent of the anchovy eggs and larvae collected were from this area, but in the area contributed nearly percent of the season s total. This change, in effect, indicated a southward extension of anchovy spawning of some to 8 miles. n contrast, anchovy spawning spread northward in 8 and. During the 7 years before 8, less than percent of anchovy larvae were from Cal COF stations off central California (north of Pt. Conception) ; the larvae were collected at only 8 of 8 stations occupied. The number of occurrences of anchovy larvae off central California rose to in 8 and in. n anchovy larvae occurred at more than half of the stations occupied off central California and constituted more than percent of the total larvae from all areas. With the return of normal temperatures in, the number of occurrences of anchovy larvae off central California dropped to 8. Two markedly contrasting years, and, illustrate changes in the areal distributions of the two species that also reflect changes in abundance. The areal distribution and relative abundance of sardine and anchovy larvae in are shown in Figure. During this year, sardine larvae were even more widely distributed than anchovy larvae. Note particularly that even in the offshore waters of southern California, sardine larvae were more abundant and more widely distributed than anchovy larvae. This distribution of sardine larvae (and eggs) was the most extensive ever encountered during CalCOF surveys. The distributions of anchovy and sardine larvae during are shown in Figure. Anchovies were widely distributed ; they were collected at nearly onehalf of the stations ( of the occupied). Sardine larvae occurred at 8 stations, or in only slightly more than percent of the stations occupied during the year. Most occurrences of sardine larvae (8 of the 8) were in the summer and fall cruises, mostly from off central Baja California. Anchovy larvae outnumbered sardine larvae in collections by more than to. The two species have somewhat different seasonal distributions. This difference is illustrated in Figure, which shows for each species the percentage of the yearly total that was taken in each month during. The peaks of abundance of the two species and the yearly patterns of abundance show little correspondence. Anchovy larvae tended to be markedly less abundant during the last half of each year, whereas sardine larvae usually had a second peak of abundance in AugustSeptember. This lateseason abundance was confined to Sebastian Viscaino Bay and adjacent waters off central Baja California, and represents the spawning of the southern subpopulation. Anchovy larvae outnumbered sardine larvae in the California Current region even at the time of high abundance of the sardine, as was the situation during spawning surveys off southern California in and. The ratio of larval anchovies to sardines was.8: in and.: in. These values are ratios of numbers of larvae, not the biomass of the two respective populations. An adult anchovy weighs only about onefifth as much as an adult sardine and has a shorter life span. John MacGregor (personal communication) has estimated that an anchovy produces about twice as many eggs per unit of weight as does a sardine. f survival is even roughly similar during the egg and larval stages of sardines and anchovies, then larvae can be converted to adult biomass by equating one sardine larva to two anchovy larvae. Stations are not equally spaced in the CalCOF survey pattern, but tended to be more closely spaced nearshore than offshore on all cruises and to be spaced closer throughout the survey area during the peak periods of spawning. t is necessary therefore to adjust for such unequal spacing when deriving estimates of abundance. This adjustment is accomplished by integrating collection data over area. Such a treatment of data on abundance yields what we term a ( census estimate. The estimates are derived for individual cruises, and each yearly estimate is simply the summation of monthly cruise estimates. Tables

4 CALFORNA COOPERATVE OCEANC FSHERES SVESTGATOKS " \ f / / ' SARDNE LARVAE (j P CAPE MENOOCNO ANCHOVY LARVA E YJ CAPE MENDOCNO '. O D CUMUL FGURE. / / / / ' Distribution and relative abundance of sardine and anchovy larvae in the CalCOFl survey area in.

5 REPORTS VOLUME X, JULY TO JUNE. *. / / / SARDNE LARVAE ANCHOVY L A R VA E PE MENDOCN mm] ijjjj, CUMULATVE TOTALS o., OVER, STATONS OCCUPED w / / / /

6 CALFORNA COOPERATVE OCEANlC FSHERES NVESTGATONS SARDNE k z w a w Q t L. FGURE. Percentages of the yearly total of sardine larvae (upper panel) and anchovy larvae (lower panel) taken in each monthly cruise,. ' ANC HOVY. Estimated number of larvae Northern California (7)..... Central California (77)... Southern California (8)_._....._. 8, Northern Baja California (77)_......,7 Upper central Baja California (),87,7,, Lower central Baja California (7)...._,7,,, Southern Baja California (7) _ Total...,77,, 7,7 Percentage of yearly totals taken in each area Northern California (7)..._..._.._.. Central California (77)..._.._.._... Southern California (8)......_....7 Northern Baja California (77) Upper central Baja California () Lower central Baja California (7).. _ Southern Baja California (7).._._ _ Total..._._._.... Spaces for each year on the abscissa depict a total of months. X indicates no cruise was made. TABLE CENSUS ESTlMATES OF ABUNDANCE OF SARDNE LARVAE, BY YEAR AND AREA, (Estimates in Billions) '"" Year Area and station lines 7 8 7,7 8 78, ,88 8 8, O , [,8,..; :;

7 ~~ REPORTS VOLUME S, JULY TO JUNE TABLE CENSUS ESTMATES OF ABUNDANCE OF ANCHOVY LARVAE, BY YEAR AND AREA, (Estimates in Billions) Area and station lies Estimated number of larvae Northern California (7)_ ~.... Central California (77).._..~ Southern Caliiornia (8)._ , Northern Baja California (77)_......_. 8 Upper central Baja California ()....., Lower central Baja California (7) ,7 Southern Baja California (7)_..._. ~ Total , Percentage of yearly totals taken in each area Northern California (7)..8. Central California (77) >. Southern California (8). _ Northern Baja California (77)._.._._._. 7.. Upper central Baja California ()._...8. Lower central Baja California (7) _ Southern Baja California (7)...,7,7,7,87 7,7.,,,7,,8.,, 7., 8, Year._ o 7, 8, 7,,88,7,, 8,88 7, 7,, 7,8 8,7 7,8 8,8, _.; _ ~ ,,8 7,,7,, _,7,,,7,, ANCHOVY SARDNE cn z U v W (L a O 7 8 FGURE. Annual census estimates for the total CalCOFl survey area of sardine and anchovy larvae,.

8 CALFORNA COOPERATVE OCEANC FSHERES NVESTGATONS and show census estimates for sardine and anchovy larvae, respectively, for, summarized by year and area. Census estimates for are not included, simply because they have not been worked up as yet. The estimates of sardine larvae ranged from a high of about 7. trillion in to a low of about. trillion in. Anchovy larvae increased from. trillion to more than 8 trillion between and, remained at this level through 7, and then increased further to about trillion in 8 and (Figure ). Anchovy abundance appears to have almost quadrupled during the s, while sardine abundance progressively decreased after. Whereas anchovy larvae outnumbered sardine larvae by less than :l in, the ratio had increased to more than : by. Abundance of anchovy larvae increased further from to. Although this change is not shown or expressed in AREA TOTAL LNE 77 8 NORTH N FRANCSCO & SOUTH FGURE. Sardine larvae: Annual census estimates by area,.

9 REPORTS VOLUME X, JULY TO JUNE terms of census estimates (only four cruises were made per year after, rather than to ), other methods of evaluating the increase indicate that abundance more than doubled between 8 and. The census estimates permit a better evaluation of abundance of sardine and anchovy larvae in the 7 areas of the CalCOF region during. As already noted, sardine eggs and larvae were obtained more consistently off central Baja California (lines 7) than off northern Baja California and southern California (Figure ). Sardine larvae were proportionately more abundant, however, off lower central Baja California (station lines 7) during than later. Off northern Baja California (lines 77) and southern California (lines 8) abundance was low in but proportionately higher during. Throughout the decade only negligible numbers of sardine larvae were taken off central California (lines 77) and none off northern California. The numbers taken off southern Baja California (lines 7) undoubtedly would have been higher if this area had N FRANCSCO NT CONCEPTON 8 SOUTH FGURE 7. Anchovy larvae: Annual census estimates by area,.

10 CALFORNB COOPERATVE OCEANC FSHERES NVESTGATONS TABLE SARDNE LARVAE *: SUMMARY OF TOTAL OCCURRENCES, COOCCURRENCES WTH ANCHOVY LARVAE, AND OCCURRENCES N HAULS WTHOUT ANCHOVY LARVAE N THE CaCOF SURVEY PATTERN, BY AREA AND YEAR, (Station lines given below each area, Total occurrences of sardine larvae Cooccurrences of sardine and anchovy larvae Occurrences of sardine larvae alone Jpper Lowei Jppei l ~ ~ e ~ Jppel Lower No. cent. cent. so. No. cent. cent. so. No. cent. cent. So. so. Baja Baja Baja Baja Cent. so. Baja Baja Baja Baja ent so. Baja Baja Baja Baja Calif. Zalif. Calif. Calif. alif Calif. alif Calif Calif. :alif, Calif. alif. Calif. Calif. Zalif Calif. Calif YW Total Total Total Monthly cruises _..._... _.._... _ _.._... 7 _..._._ _._..._ _ _ _.._._._ 8 Total....._, Quarterly cruises _._..._._...._ _..._._._ 8 8 No sardine larvae were obtained off northern California (station lines 7). ncludes additional closely spaced stations on inshore ends of station lines _ , TABLE ANCHOVY LARVAE: SUMMARY OF TOTAL OCCURRENCES, COOCCURRENCES WTH SARDNE LARVAE, AND OCCURRENCES N HAULS WTHOUT SARDNE LARVAE N THE CalCOFl SURVEY PATTERN, BY AREA AND YEAR, (Station lines given below each area) Year MontPly CNlsea L No. Calif. 7 Total occurrences of anchovy larvae ent alif, Total. 77 so. Calif !, No. Baja alif Jpper cent. Baja alif ,78 Lower cent. Baja Calif , rota _, so. Baja :alir ,7 Cwccurrences of sardine and anchovy larvae ~PP~,owe No. cent. cent. so. ent so. Baja Baja Baja Baja >alif. alif Calif. Zalif, alif. Calif rod 8 7 8,8 No. Calif 7 _ Occurrences of anchovy larvae alone ent. Mif so.?slit , NO. Baia Uppel cent. Baja,owe! cent. Baja so. Baja Calif. Calif. Zalif Calif Total , i. Q W ~ ~ Y cruises _

11 REPORTS VOLUME X, JULY TO JUNE 7 been sampled as consistently as the others off Baja California. The distribution of anchovy larvae was somewhat different than that of sardines (Figure 7). Anchovy larvae were important in the area off central California (lines 77) only during 8 and, and in the southernmost area (lines 7) only during ; they were taken in only a few hauls off northern California (lines 7). n the remaining areas, they were more consistently represented throughout the year period than sardine larvae. Anchovy larvae, like sardine larvae, were more abundant off California during the warm years, 7. n these years, the center of anchovy abundance shifted from central Baja California to southern California. wish now to deal more specifically with occurrences and eooccurrences of larvae and eggs of the two species. nformation concerning occurrences and eooccurrences of the two species in the seven areas are summarized in Tables and. For completeness, have included information on occurrences and cooccurrences of both species for, as well as for. The total number of stations occupied on CalCOF cruises during each year,, are summarized by area in Table. These summations are not limited to regular CalCOF stations, but include extra occupancies and special cruises (Table ). However, the analysis that follows is based on the data for. Throughout the CalCOF survey period, anchovy larvae always have occurred in more collections than sardine larvae (Figure 8). n the 's as a whole, anchovy larvae occurred in. times as many hauls as sardine larvae. The disparity was lowest in TABLE SUMMARY OF STATONS OCCUPED ON CalCOFl SURVEY CRUSES, BY YEAR AND AREA, (Station lines given below each area) Year Northern California 7 Central California 77 Southern California 8 Northern Baja Calif. 77 Upper central Baja Calif. Lower Baja central Calif. 7 Southern Baja Calif. 7 Total Monthly cruises in,,7,,7,,7,,8.8,8 Total.... 7,7,,,,8 78, , TABLE STATONS OCCUPED ON REGULAR CalCOFl CRUSES AND SPECAL CRUSES, NCLUDNG EXTRA OCCUPANCES, Late March cruise Extra occupancies of regular stations Special tows Additional inshore stations Multiple occupancies (not included) Total l o 8,,7,,7,,7,,8,8 :,8 Total._,78 8 (), ,, ncludes stations occupied on Norpac.

12 8 CALFORNA COOPERATVE OCEANC FSHERES NVESTGATONS and, when they were collected only twice as often as sardine larvae, but increased yearly in ; in the collections, anchovy larvae occurred seven times as often as sardine larvae. A corresponding increase appeared in the cooccurrences of anchovy larvae in the collections containing sardine larvae, from percent in to about 87 percent in. Obviously, as one species becomes more abundant and more widespread than another, it will occur alone more frequently, and thus be free from possible competition. When anchovy larvae are collected in seven times as many hauls as sardine larvae, as in, the possible eooccurrences with sardine larvae would be only percent. n fact, sardine larvae eooccurred with anchovy larvae in one haul out of eight (. percent), while anchovy larvae eooccurred with sar dine larvae in six hauls out of seven (8. percent). For the decade as a whole, anchovy larvae cooccurred in,8 (.8 percent) of the, hauls that contained sardine larvae, whereas sardine larvae occurred in only,8 (. percent) of the,7 hauls that contained anchovy larvae. Thus, anchovy larvae were present in two of every three hauls that contained sardine larvae, whereas sardine larvae occurred in little more than one of five hauls containing anchovy larvae. f interspecies competition is a factor in the survival of larvae, and eooccurrence is a measure of competition, then the anchovy should have had a decided advantage over the sardine. Another factor must be considered : sardine larvae are less likely to occur with anchovy larvae in some areas of the CalCOF grid than in others (Tables 7 and 8). Anchovy larvae have had decidedly less com 8( SARDNE LARVAE ALONE COOCCURRENCES. SARDNE & ANCHOVY LARVAE ANCHOVY LARVAE ALONE 7( ( v) w V z w U ( LL U w ( 8 ( O( ( FGURE Graphic presentation, by year, of the number of CalCOFl plankton collections containing ) sardine larvae alone, ) bath sardine and anchovy larvae, and ) anchovy larvae alone,

13 ~. ~. ~ ~. ~. ~ ~. ~. ~ ~ ~. ~ ~~ ~~. ~. ~... ~ ~ REPORTS VOLUME X, JULY TO JUNE TABLE 7 SUMMARY OF TOTAL STATON OCCUPANCES, OCCURRENCES OF SARDNE LARVAE, AND COOCCURRENCES WTH ANCHOVY LARVAE, BY AREA, Area and station lines total occupancies Cooccurrences Occurrences Percentage with anchovy Percentage of of sardine larvae of positive hauls larvae eooccnrrencea Northern California (7).. Central California (77)._... ~ Southern California (8).. ~ ~ Northern Baja California (77) ~ Upper central Baja California () ~ ~..... ~. ~.. ~... ~ ~~... ~ ~.. ~.....~.. ~.~.....~ ~ ~.. ~. ~... Lower central Baja California (7). ~ Southern Baja California (7). ~. ~ 7,7,,,, o TABLE 8 SUMMARY OF TOTAL STATON OCCUPANCES, OCCURRENCES OF ANCHOVY LARVAE, AND COOCCURRENCES WTH SARDNE LARVAE, BY AREA, ~ Cooccurrences Area and station lines Northern Baja California (77) ~ Upper central Baja California (). ~ Lower central Baja CJiomia (7) ~. Southern Baja California (7). ~..... ~.... ~.. ~..... ~.... ~ _.... ~... ~....,,, ,.,78., ::.... Totals. _ ,8,7.,8. petition in the northern part of the CalCOF survey area. Off central California (station lines 77) sardine larvae occurred in less than percent of the collections, while anchovy larvae occurred in percent. n this area the percentage of eooccurrence of sardine with anchovy larvae was only. percent. Off southern California, anchovy larvae occurred in more than percent of all collections made during the 's, and sardine larvae in only 8. percent. Hence, even though the eooccurrence of anchovy larvae with sardine larvae was 7. percent, sardine larvae occurred in only. percent of the collections that contained anchovy larvae. Off southern California the anchovy must have had a decided advantage. The region in which the two species might have competed most intensely was off central Baja California. n this region sardine larvae occurred in one of every three hauls containing anchovy larvae ; anchovy larvae occurred in three of every four hauls containing sardine larvae. The occurrences of eggs in our plankton hauls were less frequent than occurrences of larvae. Probably a major reason for this lower frequency is that eggs of both the Pacific sardine and the northern anchovy hatch in only to days, depending on water temperature; consequently the eggs in any given haul represent a relatively short time span. A sample of larvae, on the other hand, can contain specimens accumulated during a span of perhaps days or more. Sardine eggs, on the average, occurred in only about 77 7 percent as many collections as sardine larvae. Anchovy eggs, which are not fully retained by the standard CalCOF net, occurred in little more than a third as many hauls as anchovy larvae. Hence, the frequency of occurrence and, as it happens, cooccurrence of eggs is less than for larvae. n only 8 and did sardine eggs cooccur in more hauls with anchovy eggs than they occurred alone. For the decade as a whole, anchovies spawned in the same waters with sardines only about percent of TABLE COMPARSON OF AVERAGE NUMBER OF LARVAE PER HAUL OF "COOCCURRENCES," WTH SAMPLES CONTANNG SARDNE OR ANCHOVY LARVAE ALONE. _._ Ll All hauls Alone _. 7.O _ 7_.._ _._ Average..l..7 Sardine larvae coccurring cooccurring Alone ll hauls _ Anchovy larvae

14 ~~ ~ CALFORNA COOPERATVE OCEANC FSHERES NVESTGATONS = a W n r SARDNE LARVAE ALONE COOCCURRNG WTH ANCHOVY LARVAE ALL SARDNE HAULS FGURE. Comparison of the annual average,number of sardine larvae obtained per haul, ) in hauls containing sardine larvae alone, ) in hauls in which sardine larvae cosccurred with anchovy larvae, and ) in all hauls containing sardine larvae,. ANCHOVY LARVAE ALONE COOCCURRNG WTH SARDNE LARVAE ALL ANCHOVY HAULS f 8 FGURE. Comparison of the annual average number of anchovy larvae obtained per haul, ) in hauls containing anchovy larvae alone, ) in hauls in which anchovy larvae cooccurred with sardine larvae, and ) in all hauls containing anchovy larvae,.

15 ~~ the time. n contrast, the larvae of anchovies eooccurred with sardine larvae about 7 percent of the time. The numbers of larvae in ~~cooccurring haus7f REPORTS VOLUME X, JULY TO JUNE G than in hauls where they occurred alone. The consistently larger numbers of anchovies taken in hauls containing sardine larvae over numbers in hauls containing anchovies alone, usually by about to, was especially striking. Numbers of sardine larvae in with containing Only One Or the Other samples that contained anchovy larvae usually were species alone are summarized in Table and illus also considerably larger than in hauls where they trated in Figures and. More larvae were obtained occurred alone+nly two exceptions in the loyear per sample in hauls where the two species eooccurred series. TABLE SARDNE LARVAEALL OCCURRENCES: AVERAGE NUMBER PER POSTVE HAUL SUMMARZED BY SZE AND YEAR, Year Size class (mm) 7 8 average,8, ,8.,, ,78, ,, ,, _.., ,87, ,, _., _ wsied,7, ,8., ,7.8,.,887.,.,., SARDNE LARVAECOOCCURRNG TABLE WTH ANCHOVY LARVAE: AVERAGE NUMBER PER POSTVE HAUL (X lo), SUMMARZED BY SZE AND YEAR, Year wzld Size class (mm) 7 8,,8, _., _.,78, ,77, ,,, ,8, , O.8,78, , Total ,.,.8 7,. 8,.7,.,8.,7.,., average,7, 7 8.,., _,7. 7,.

16 CALFRhTTA COOPERATVE OCEANC FSHERES NVESTGATONS The problem then is to account for the higher number of each species in hauls in which they cooccurredto determine whether they mere obtained in centers of heavier spawning for both species or whether survival was better in areas of cooccurrence. f the latter were true, it would be difficult to justify any hypothesis that postulates that competition between the two species would adversely affect their survival. The average numbers of larvae per positive haul are summarized by size and year in Tables to. For each species these data are summarized in three ways : () for all occurrences, () for hauls in which the larvae of one species eooccurred with those of the other, and () for hauls in which the larvae of a species occurred alone. A semilog plot (Figures and ) gives a simple method of illustrating changes in abundance with SARDNE LARVAEOCCURRNG Size class (mm) TABLE ALONE (NO ANCHOVY LARVAE): AVERAGE NUMBER PER POSTVE HAUL (X lo'), SUMMARZED BY SZE AND YEAR,. Year 7 8 8,,,7,7.7,8 7,,7,,,,, , _ 8,.7..7,7.... _, ,7., ,7. 8..,7. ;li,.7 i!. Unweighted average ~ ~ _,8,, _ _.7 ::. ::.7.. _. TABLE ANCHOVY LARVAEALL OCCURRENCES: AVERAGE NUMBER PER POSTVE HAUL (x lo), SUMMARZED BY SZE AND YEAR, Size class (mm) Year 7 8 Unweighted average,,78,8,,7,,7,.8,,,,,,7,8,7,78,,,,,88,7,,7.7.,,,8,7,,7,87,7,,88,,7 7,.,,,8,8.,77.,7.,7.,.,7 8 7, ,,8 8 7,.7, 7 88,88,,87,7 7,,, 888 8,,8, 7.8,, 7 7,, 8 78,8., ,7.,.,8.,7.8,7.,78.,.,.,.,87.

17 ~~ ~~ REPORTS VOLUME X, JULY TO JUNE increase in size. Two curves are plotted for each species, one illustrating abundance of eooccurring larvae, the other of the species taken alone. The two curves for anchovy larvae tend to converge with increase in size. This convergence would be expected if survival were better in hauls in which the larvae of a species occurred alone, free from competition. t is well to remember that the upper curve represents the average of,8 hauls and the lower the average of, haulslarge amounts of data. Data on changes in relative abundance with increase in size are less consistent for sardines. The upper curve, sardine larvae in eooccurrences with anchovy larvae, necessarily is based on the same number of hauls as is its counterpart graph for anchovies (,8), but the lower curve is based on considerably ANCHOVY LARVAECOOCCURRNG TABLE WTH SARDNE LARVAE: AVERAGE NUMBER PER POSTVE HAUL (x % SUMMARZED By SZE AND YEAR, Year 7 8 Unweighted average,8,,,7,8,8,78,,8,,77,,7,,,7,877,8,87,7,7,7,88,78,,,,,7,,8,, 8, 7,8,8,8,,,,8 8,78 7,78,,7,8.,.,.7,.,8.,7,,, 7,78,, 8 8,,8,,,,7,7,,7,7,7,87,8,.. ;,7,,8.8. 7,78,, 78 7,.7,.8,87., _ _ ,8. 8,.,.7,.,.8,8.,. 7,7.,8.,8.8 TABLE ANCHOVY LARVAEOCCURRNG ALONE (NO SARDNE LARVAE): AVERAGE NUMBER PER POSTVE HAUL (X ld), SUMMARZED BY SZE AND YEAR, Size class (mm),,,,8.. ;77,8 ;,8,,8 88 Year _ Un 7 8,,7 8, ,7,,,78,7, ,,7,,87,,7, ,78,,87, ,,,,78,7,7,7, ,,7,8,888,,8, ,7,,77,7,,, ,8.7,. 7,.7,.,.,8.,8.7 8,7. weighted average,7,77,7,8,,7, ,.,.,8.,.8,.,.,

18 CALFORNA COOPERATVE OCEANC FSHERES NVESTGATONS fewer hauls (). Some of the irregularities in this curve, compared with the other three, may be due to fewer data. At first glance at the two curves for sardine larvae, one gets the impression that survival may have been somewhat better in the eooccurring hauls. On closer inspection however, it is seen that larvae larger than.7 mm followed no consistent trend, except as noted below. The greatest difference in relative abundance was between the smaller larvae (..7 mm long) and all larger larvae. This difference could be interpreted as poorer initial survival of sardine larvae in situations where they occur alone. An equally logical explanation for the difference, however, is based on the increasing frequency of cooccurrences of sardine and anchovy larvae with increase in size. t was noted earlier that the frequency of eooccurrence of sardine and anchovy eggs was markedly lower than for larvae. A natural corollary is that newly hatched larvae of the two species would cooccur less frequently than the larger larvae. The effect on abundance curves would be to increase the numbers of larger larvae in hauls in which the species eooccurred than in hauls in which they occurred alone. Furthermore, the two curves for sardine larvae do converge if all largersized larvae (7.. mm) are taken into account. As many larger larvae were taken in hauls in which sardines occurred alone as in hauls in which both species occurred.7 larvae per haul on the average. Thus, the basic question has been answered j better survival was not indicated by the hauls in which both species were caught even though average numbers of larvae per haul were larger. Although the analysis has been confined largely to the ~~ the report can be brought up to date. Tables and include the number of occurrences and cooccurrences of sardine and anchovy larvae during the first years of quarterly cruises,. Anchovy larvae occurred in percent of the hauls in, percent in, and percent in. Sardine larvae occurred in percent of the hauls in, percent in, and. percent in. (Data for are not closely comparable to those for other years because a number of closely spaced inshore stations were added.) Anchovy larvae occurred in nearly percent of the hauls containing sardine larvae. n contrast, sardine larvae occurred in only percent of the hauls containing anchovy larvae. Cooccurrences of anchovy larvae with sardine larvae were even higher than in the late ~~ and even a higher percentage of the collections of anchovy larvae contained no sardine larvae. Anchovy larvae now seem to be completely dominant..,,. W c ul g K W a a W m. w W. ANCHOVY WTH SARDNE LARVAE ANCHOVY LARVAE ALONE l f l J l J a y O t v) K W a K w m W Cll a K w z Z! LENGTH N MM. FGURE. Comparisons of average number of sardine larvae per positive haul as related to length (mm) for ) hauls containing both sardine and anchovy larvae and ) hauls with sardine larvae alone. Data for combined.

19 REPORTS VOLUME X, JULY TO JUNE REFERENCES Ahlstrom, Elbert H. 8. A record of the pilchard eggs and larvae collected during surveys made in to. U.S. Fish and Wild. Serv., Spec. Sci. Rept., ():7.. Pilchard eggs and larvae and other fish larvae, Pacific coast. U.S. Fish and Wild. Serv., Spec. Sci. Rept.: Pish. () :.. Pacific sardine (pilchard) eggs and larvae and other fish larvae, Pacific coast. U.S. Fish and Wild. Serv., Spec. Sci. Rept.: Fish. () :7. 8. Sardine eggs and larvae and other fish larvae, Pacific coast,. U.S. Fish and Wild. Serv., Spec. Sci. Rept.: Fish. () :8.. Sardine eggs and larvae and other fish larvae, Pacific coast, 7. U.B. Fish and Wild. Serv., Spec. Sci. Rept.: Fish. (8) :. a. Distribution and abundance of sardine and anchovy larvae in the California Current Region off California and Baja California, : A summary. U.S. Fish and Wild. Serv., Spec. Sci. Rept.: Fish. () :7.. Size composition of larvae of the Pacific sardine and northern anchovy obtained on CalCOF survey cruises, 8 and. A Preliminary Data Eept., 7 p. U.S. Bur. Comm. Fish., La JoZZa (available on request). 7. Size composition of larvae of the Pacific sardine and northern anchovy obtained on CalCOF survey cruises,. A Preliminary Data Rept., 8 p. U.S. Bur. Comm. Fish., La JoZla (available on request). Ahlstrom, Elbert H., and D. Kramer.. Pacific sardine (pilchard) eggs and larvae and other fish larvae, Pacific coast,. U.S. Fish and Wild. Serv., Spec. Sci. Rept.: Fish. ():7.. Sardine eggs and larvae and other fish larvae, Pacific coast,. U.S. Fish a d Wild. Serv., Spec. Sci. Rept.: Fish. (8) :7. 7. Sardine eggs and larvae and other fish larvae, Pacific coast,. U.S. Fish and Wild. Serv., Spec. Sci. Rep?.: Fish. () :. Marr, John C., and E. H. Ahlstrom.. Observations on the horizontal distribution and the numbers of eggs and larvae of the northern anchovy (Engraulis mordax) off California in and. U.S. Fish and Wild. Serv., Spec. Sci. Rept. () :7.