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

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94 CALIFORNIA COOPERBTIVE OCEANIC FISHERIES INVESTIGATIONSThe low values since June 1963 is striking in all threeports Chimbote, Callao, and <strong>11</strong>0. It seems then thatthe reason for the poor fishing of 1963 was the lowabundance or low availability of the big adult fishduring this period.CAUSES OF REDUCED ABUNDANCE OF BIGADULT FISHNatural Fluctuations of RecruitmentThere is one phenomenon that is known to havecaused great fluctuations of stock size in a numberof marine fish populations, i.e., natural variations inrecruitment brought about by varying success of survivalof eggs and larvae from the different broods.The results of our length-measurements indicate thatsuch types of fluctuat,ions do occur also in the Peruviananchovy stock. Although direct age-determina-FIGURE 7. Abundance of recruit groups and the groups of adult fish.Chimbote and Callao together.tions are not available, it is possible from the sizecompositions to determine the age of the young fishand the size abundance curves offer a possibility toassess the abundance of the year-classes. In Figure 7,we have plotted the abundance of the recruit-groups1961 through 1964 as measured in two differentways, by their modal abundance and by the estimatedtotal number caught per unit of effort. Figure 7 alsoshows the abundance of the adult fish as the meanvalue of the months November through May eachyear. The recruitment apparently dropped off from1961 to 1962 and a further reduction took place in1963. In 1964, however, a very strong group wasrecruited to the fishery. As Figure 7 demonstrates,the reduction that occurred in the abundance of theadult fish is parallel to that of the recruits up till theseason November 1963 to May 1964. We expect thatthere will be a time lag of about one year between thestage at which we measure the abundance of therecruit-group (usually March to June) and the timewhen the group has reached the adult stage and thusmay influence the abundance of this group of 14-15ern fish. Figure 8 shows a comparison of recruitmentand abundance of adult fish when applying such atime-lag. A straight line from zero could be fittedreasonably well to these points, and confiding inthese results we could conclude that fluctuations inthe recruitment give cause to similar fluctuations inthe abundance of the total stock which again bringsabout considerable variations in the success of thefishing. Before drawing this conclusion, however, weshould await the results of the fishery during theperiod November 1964 through May 1965. The highrecruitment of 1964 should bring about a considerableincrease of the abundance of adult fish duringthis season. If this happens we think that the aboveconclusion can safely be drawn. It would then be amatter of great practical importance to be able toUJ600$00200200 400 600ABUNDANCE OF ADULT GROURNUMBER OF FISHES PER TRIP IN THOUSANDS2 4 6ABUNDANCE OF ADULT GROUPNUMBER OF FISHES PER TRIP IN MILLIONSFIGURE 8. Relation between abundance of recruit groups and groups of adult fish. The abundance of the recruit group is measured in two differ.ent ways.
REPORTS VOLURlE SI, 1 JULY 1963 TO 30 JUNE 1966 9.5measure recruitment-strength as accurately as possibleso as to get a better basis for forecasting yieldfluctuations.Effects of the Fisbery on the StockThere is little doubt that a fishery of about 6 milliontons per year must have some effects on the anchovypopulation. The total mortality rate must have increased.By how much we do not know, but from arough assessment of predation of birds and fish it isnot unreasonable to think that the mortality has atleast been doubled. We should expect that it wouldbe possible to demonstrate the effects of this increaseof mortality on the size composition of the fish. Suchdemonstrations are, however, complicated by the fluctuationsin recruitment. A longer series of data isnecessary to compensate for the natural fluctuationsin the size composition, and thus provide a normalaverage basis for a comparison.The comparisons of recruitment and adult fishabundance shown in Figure 8 have one feature whichmay indicate an increase of total mortality. The expectationof a straight-line relationship passing zerois only valid if the total mortality has been unalteredduring the period of observation. If mortality increasesone would expect the abundance of the adultgroup to fall off more than that of the recruits. Atendency of this nature can be seen in the dataplotted in Figure 8.We expect to be able to make more definite statementsconcerning the effects of the fishery on thestock after the season November 1964 to May 1965.If the abundance of the population of adult fish andthus the success of fishing do not rise to the expected“normal” level during this season as a result of thc.high recruitment in 1964, then it must be concludedthat the fishing mortality influences the stock to ilmarked degree.In practice the effects of increased mortality andthe resulting lower average size and age of the fishin the stock would be a corresponding decrease of themean size of the fish caught in the fishery. The totalstock abundance would also on the average be lowerwith a decrease of the catch per unit of effort. Theyield would be more variable from year to year becauseit would to a greater extent depend upon thefluctuating abundance of the recruit fishes. This ofcourse would make the operation of the industrymore difficult with higher costs of raw material andless continuity of operations. It is, however, notthought that any lasting or permanent harm will bemade to the stock by this form of over-exploitation.The recruitment in big oceanic fish stocks does notseem to be directly related to the size of the spawningstock : big-year-classes can result from the spawningof poor-ones. The direct economic effects on the industrywill be those arising from expensive and inperiods scarce raw material. These effects can, however,be serious enough as we have seen from thestate of the industry during 1963-64.REFERENCESSaetersdal, G., and J. E. Valdivia. 1964. A study of growth, sizeand recruitment of the anchovy ( Engradis ringens J.) basedon length frequency data. Inst. Invest. Recurs. Mar., Bol.,1 (4) ~121-136.Saetersdal, G., I. Tsukayama and B. Alegre. 1965. Fluctuationsin the apparent abundance of the anchovy stock in 1959-1962.Imt. Mar. Peru, BoZ. l(2) :87-104.
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STATE OF CALIFORNIAMARINE RESEARCH
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STATE OF CALIFORNIADEPARTMENT OF FI
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RONALD REAGAXGovcriwr of the Slate
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PART 1REVIEW OF ACTIVITIESJuly 1,19
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REPORTS YOLUAIE SI, 1 JULY 1963 TO
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REPORTS VOLUNE XI, 1 JULY 1963 TO 3
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REPORTS YOLUME SI, 1 JULY 1963 TO 3
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REPORTS VOLUME XI, 1 JULY 1963 TO 3
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REPORTS vor,uiwIi; SI, 1 JULY 1063
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REPORTS TOT2T71\IF: SI, 1 JUJIT 196
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IiEPOHTS TOLUME XI, 1 JULY 1963 TO
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REVIEW OF THE PELAGIC WET FISHERIES
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KEI'OiiTH TOLUJIE SI, 1 JULY 1963 T
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PART IISYMPOSIUM ON ANCHOVIES, GENU
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OCEANIC ENVIRONMENTS OF THE GENUS E
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KEI'OKTS VOLIXI.: SI, 1 JULY 1963 T
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~~~REPORTS VOLUME XI, 1 JULY 1963 T
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Page 47 and 48: 130'E 132' 134' 136' 138' 140' 142-
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Page 57 and 58: KI3I’ORTH VOLUJIE XI, 1 JULY 1963
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Page 67 and 68: REPORTS T’OLUME XI, 1 JULY 1963 T
Page 69 and 70: INFLUENCE OF SOME ENVIRONMENTAL FAC
Page 71 and 72: REPORTS Y‘OLUJIE XI, 1 JULY 1963
Page 75 and 76: ~table shows the values calculated
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Page 79 and 80: REPORTS POLGNE SI, 1 JU LY 1963 TO
Page 81 and 82: REPORTS VOLUXE XI, 1 JULY 1963 TO 3
Page 85 and 86: _________--_____REPORTS VOLUJIE SI,
Page 87 and 88: REPORTS TOLTIJIE SI, 1 JULY 1963 TO
Page 89 and 90: -20/5-0 10-f 5-w 25-0 20-= 15-: 10-
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Page 107 and 108: THE PREDATION OF GUANO BIRDS ON THE
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Page 115 and 116: FISH E RYThe California anchovy fis
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Page 119: CO-OCCURRENCES OF SARDINE AND ANCHO
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Page 124 and 125: CALIFORNIA COOPERATIVE OCEANlC FISH
Page 128 and 129: 126CALIFORNIB COOPERATIVE OCEANIC F
Page 132 and 133: ~~ ~130 CALIFORNIA COOPERATIVE OCEA
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Page 138 and 139: THE ACCUMULATION OF FISH DEBRIS IN
Page 143 and 144: PART IllSCIENTIFIC CONTRIBUTIONS
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REPORTS VOLUME SI, 1 JULY 1963 TO 3
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REPORTS VOLU&IE XI, 1 JULY 1963 TO
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SUMMARY OF THERMAL CONDITIONS AND P
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SEASONAL VARIATION OF TEMPERATURE A
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including the semiannual harmonic?
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REPORTS VOiLUME XI, 1 JULY 1983 TO
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170 CALIFORNIA COOPERATIVE OCWIC FI
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172 CALIFORNIA COOPERATIVE OCBANIC
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174 CALIFORNIA COOPERATIVE OCEANIC
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184CALIFORNIA COOPERATIVE OCEANIC F
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CONTENTSI. Review of Activities Pag
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