AGE COMPOSITION OF CALIFORNIA

Transcription

1 AGE COMPOSITION OF CALIFORNIA LANDINGS OF BLUEFIN TUNA, THUNNUS THYNNUS, 1963 THROUGH 1969 Donald 1. Schultze and Robson A. Collins 1 MARINE RESOURCES TECHNICAL REPORT NO

2 CALIFORNIA DEPARTblENT OF FISH AND GAME MARINE RESOURCES TECHNICAL REPORTS Marine Resources Technical Reports are research documents by Department personnel that are of sufficient importance to be preserved, but which for some reason are not appropriate for primary scientific publication. No restriction is placed on subject matter. These Reports may be cited in publicatinn, but care should be taken to indicate their manuscript status. The material in these Reports may eventually appear in the primary scientific literature. Inquiries concerning the Reports should be directed to The Editor, Robson A. Collins, 350 Golden Shore, Long Beach, California

3 AGE COMPOSITION OF CALIFORNIA LANDINGS OF BLUEFIN TUNA, THUNNUS THYNNUS, 1963 THROUGH 1969 DONALD L. SCHULTZE and ROBSON A. COLLINS Operations Research Branch MARINE RESOURCES TECHNICAL REPORT NO. 38 California Department of Fish and Game 1977

4 ABSTRACT California landings of bluefin tuna, Thunnus thynnus, were sampled for age and size composition from 1963 through Scales were used to determine the age. Landings primarily consisted of 1- and 2-year old fish. The maximum age found was 6 years old. Strong yearclasses of 1960 and 1961 combined to produce high catches in 1962 and Two year old fish appear to arrive in our fishery earlier than 1-year olds.

5 TABLE OF CONTENTS Page ABSTRACT ACKNOWLEDGMENT INTRODUCTION The Fi~her~ MATERIALS AND METHODS Collection of Samples Age Detemination Area and Date of Catch Calculation of Estimates RESULTS REFERENCES

6 ACKNOWLEDGMENT Many Department personnel have contributed substantially to the collection and analysis of this data. John Seapin conducted the sampling and collected the log data. James Phelan assisted in the reading of scales, while Robert Bell and Clark Blunt supervised the sampling. John Geibel participated in the summary and analysis of the data. Personnel of the Inter-American Tropical Tuna Commission, particularly Kenneth Fing of the commission's Terminal Island office were always helpful and cooperative throughout this work. Their cooperation and assistance is greatfully acknowledged. Seasonal employees Glenn Black, Ellen Gleason, Darlene Osborne, Ralph Sugg and Marjia Vojekovich assisted in the data summarization. Eugene Witeck contributed statistical advice and Harold B. Clemens critically reviewed the manuscript. This work was supported in part by Federal Aid to Fish Restoration Funds as part of Dingell-Johnson Project California F-32R, Southern California Marine Sportfish Research.

7 INTRODUCTION Increasing exploitation of bluefin tuna, Thumus thynnus, in the North Pacific has focused the attention of fisheries agencies in Japan and the United States on the status of these important sport and commercial fish. Information is needed from all segments of the fishery in order to assess the status and formulate management measures. Know- ledge concerning the age structure of the stock is of prime importance. This report presents data collected by the California Department of Fish and Game on the size and age composition of bluefin tuna landings in California from 1963 through The Fishery In the western Pacific, bluefin are fished from the East China Sea and Bonin Islands area north into Japanese waters and eastward to the Hawaiian Islands. In the eastern Pacific, a fishery is conducted in the coastal waters between Cape San Lucas, Baja California and Point Conception, California. There is some evidence to indicate that both fisheries exploit the same population, and that a portion of it undertakes trans-pacific migrations (Clemens and Flittner 1969). Bluefin tuna apparently arrive off southern Baja California in late May or June, travel northward during the summer months, and then depart in late October or November. The fishery follows the migrants up the coast as the season progresses. Fishing usually begins in the area off Cape San Lazaro and ends off southern California. A few fish have been found and caught near Guadalupe Island during the winter by San Pedro based purse seiners and long range sportfishing boats. These fish are larger and older than those found elsewhere in the eastern

8 Pacific and appear to have taken up residence. Apparently these resi- dents are replenished periodically by migrants. A similar group resided near San Clemente and Santa Catalina Islands at the end of the nineteenth century. Early anglers, such as Charles F. Holder found the area around Santa Catalina Island an "angler's paradise", recording catches of bluefin or "leaping tuna" up to 114 kg (251 lbs) (Tuna Club of Avalon 1948). Holder extolled the fishing at Catalina remarking in 1910, "I have never seen a leaping tuna under seventy or eighty pounds" (Holder 1910). Entries of large fish gradually disappeared from Tuna Club records however, and the last one weighing over 150 lbs was recorded in Bluefin heavier than 80 lbs are now rarely caught by anglers. The commercial fishery essentially began in August 1917, when 69 Mg (76 tons) were netted off Point Dume, California. Commercial numbers of bluefin were difficult to catch with live bait or trolling gear so commercial fishermen have used round-haul nets since the beginning of the fishery. Today purse seining is conducted by a "local" fleet and a "high seas" fleet. The local fleet consists of small seiners of 27 to 181 Mg (30 to 200 tons) capacity which fish primarily for anchovies, EngrauZis mordax; Pacific mackerel, Scomber japonicus ; jack mackerel, Trachurms symmetricus; Pacific bonito, Sarda chiliensis and bluefin tuna. These vessels have been the backbone of the bluefin fishery. The high seas fleet, comprised of seiners ranging from 180 to 1,800 Mg (200 to 2,000 tons) capacity harvests primarily yellowfin and skipjack tuna, Thmnus azbacares and Euthynnus pelamis, off Central and South America and in the central Pacific. These fishermen scout for bluefin

9 while outbound from California and sometimes "top off" their loads while enroute home. The high seas fleet has accounted for an increasing portion of bluefin landed in California during the last decade, with the total exceeding 40% in 1968 and MATERIALS AND METHODS Collection of Samples Sampling the bluefin tuna catch for length and weight data was conducted by the Department from 1951 through In 1961 and 1962, methods were tested for determining the age of bluefin by examining their scales (Bell 1963). Routine collection of bluefin scales and lengths and weights began in 1963 and was continued through Primary objectives were to estimate the year-class contribution to the catch as well as the number of fish landed. Bluefin tuna are delivered to canneries at Terminal Island and San Diego for processing; we sampled only at Terminal Island. Two sampling methods were utilized; double sampling (two phase sampling) during 1963 through 1965 and stratified systematic sampling during In double sampling, vessels landing bluefin were sampled randomly each month. The fork length (FL) of 50 fish was measured on each occasion, and scales for age determination were taken near the dorsal finlets of every fifth fish. In addition, a select sample of small to large bluefin was measured each year until 1966, to determine the length-weight relat ionship. Beginning in 1966, 20 fish were sampled routinely for length, weight and age for every 200 tons landed from each 1-degree square area of latitude and longitude per month. Bluefin were caught from an average of 25 1-degree square which represent an area of about 280,000 km2 (81,600

10 miles). From 1963 through 1969 more than 1,000 fish were sampled each season. Age Determination We used the scale method of age determination (Bell 1963). Two studies validating this method for bluefin taken in the Pacific Ocean have been completed; one by Japanese investigators in the western Pacific (Yukinawa and Yabuta 1967) and the other by United States workers on bluefin taken in the eastern Pacific (Koski 1967). Both studies used scale reading, back calculation of fork length at age, analysis of length frequency modes, and length data from tagging experiments to conclude that (i) bluefin tuna scales show annuli formed about April, (ii) growth is most rapid (exceeding 8 cm per month) during the first summer of life, and (iii) the first annulus is formed at 1-year of age and at a fork length of 51 to 53 cm. Growth during the second summer is given as 3.25 cm per month by Koski and can be inferred as 3 to 3.5 cm per month from data by Yukinawa and Yabuta. Lengths derived for fish from 1 to 6 years old (by von Bertalanffy's equation) were similar for the two studies (Table 1, Figure 1). The growth indicated would result in a mean fork length for age 1 bluefin of 66 cm by August. The eastern Pacific fishery peaks during this month and if length frequencies are plotted the first mode is generally found between 63 cm and 68 cm, agreeing quite well with the calculated growth curve (Figure 2). In light of these studies on bluefin age and the agreement with our data, we accepted the scale method of age determination as valid and have used it in our work.

11 TABLE 1. Comparisons of Bluefin Length at Age Determined from von Bertalanffy's Equation. AUTHOR KOSKI (1967) YUKINAWA & YABUTA (1967)

12 A- Yukinawa and Yabuta 1967 m-.. Koski I lr m E P AOE FIGURE I. Growth Curves Derived (by von Bertalanffy's equation) for Bluefin tuna in the Pacific Ocean.

13 FORK LENGTH (em) FIGURE 2. Length Frequency of I-Year Old Bluefin Tuna,

14 Following the work of Bell and Koski we selected scales from an area located above the lateral line and below the dorsal finlets, These scales were placed in numbered tissue capsules, cleaned with potassium hydroxide, and stained with eosin as described by Bell (1963). Finally they were examined wet under a binocular microscope at 7 to 15X magnification using both direct and transmitted light. The scales from every fifth fish, and all scales unusually difficult to read were checked by a different reader. If the age could not be determined from the scales, we assigned an age based on that of other fish of the same length in the same sample. We preferred this approach because bluefin tend to school by size and age, grow rapidly during the summer months, and because of the normal overlap in length of fish 1 year apart in age. The percent of scales that could not be read varied from 1.2% in 1967 to a high of 13.8% in 1964 (Table 2). Generally, scales from bluefin tuna 1 or 2 years old are considered easier to read than those from older fish. However a Kolomogorov-Smirnov one sample test (Siege1 1956) was used to compare the length frequencies of bluefin having readable scales with those having unreadable scales during the period 1963 through A significant difference at the 99% level of confidence was found with the greatest difference in the cm size range corresponding to 1-year-old fish. Scale from bluefin of all ages are often "blistered" and oil saturated making them difficult to read. Frequently, scales are missing from the desired area on a fish because of handling at sea and while being unloaded. In such cases, scales are taken from an adjacent area and they are of poorer quality. Small fish 1 and 2-years old receive the rougher handling,provided the greater number of unread- able scales, and comprised the bulk of the catch.

15 TABLE 2. Scales Examined During Years Number of Unreadable scales Number of unreadable Total as a percent Year readable scales scales scales of total

16 Area and Date of Catch In 1917 the Department began collecting information about species, pounds landed, area caught, and port and date of landing for each load of fish delivered in California (Greenhood 1963). With an increase in tuna research during the early 19501s, it became necessary to obtain additional details concerning the activities of the fishing fleet and the Department in cooperation with the Inter-American Tropical Tuna Cormnission (IATTC) began to collect information about the activities of all boats landing bluefin in California. We used this information to identify the catch date and location for each sample we took. Calculation of Estimates Estimates were made of the proportion of numbers and weights of bluefin tuna at each age, by month and one degree square. These were then combined for annual estimates. j = age class i = month 0 h = 1 square block number W = weight of bluefin tuna reported landed A W = estimated weight of bluefin tuna landed w = weight sampled n = number of bluefin tuna samples A N = estimate of number of bluefin tuna landed W Q = W Kilograms of blugfin tuna of age j landed during a hij hiw month i from a 1 square area of latitude and hi longitude h.. A A W = c c W Kilograms of bluefin tuna of age j landed during a year. j h i hij N = w nhij Number 06 bluefin tuna of age j landed during a month i hij hij whij from a 1 square area of latitude and longitude h.

17 A Nj = h f Nhij Number of bluefin tuna of age j landed during a year. The calculations require that an age and weight be assigned to every fish in an age sample. Length-weight equations developed for years , from select sampling of the catch, were used to assign a weight to each fish sampled for age during these years (See Appendix 1). RESULTS The migration of bluefin tuna into the California fishery consisted of predominantly 1-and 2-year-old fish (Tables 3-9). Estimates for indicate that they contributed 91 to 99% by numbers and 80 to 97% by weight to the total California landings (Table lo). Relatively few 3-year-old bluefin were caught. However, their contribution in total weight landed has been close to 18% in some years. Only small numbers of fish older than 3 years and none over 6 years have been sampled. Judging by the contribution made to the catch, the 1960 and 1961 year classes were strong ones. The 1960 year class contributed nearly 2,400 Mg in 1963, while the 1961 year class accounted for more than 7,000 Mg. These two year classes combined to help produce near record catches of 14,165 and 13,451 Mg in 1962 and 1963 respectively (Table 10). A comparison of total numbers and weight for successive year classes can be made for the year classes 1962 through 1966, which provided large amounts of age 1 through 3 fish (Tables 11, 12). In total contribution to the catch, three year classes (1963, 1964 and 1965) appear to have been strong ones. In 1966 they helped pro'duce a record of more than 15,000 Mg. The 1963 year class accounted for 90% of the total catch by number when it was 1 year old and for 48% when 2 years old. The 1964 and 1965 year classes accounted for 45% of the catch by number when

18 TABLE Length and Age of Bluefin Tuna Sampled During LENGTH cm AGE GROUP 0 I I1 I11 IV v TOTAL

19 TABLE 3.' Continued. LENGTH cm 0 AGE GROUP I11 IV TOTAL TOTAL 3 537

20 TABLE 4- Length and Age of Bluef in Tuna Sampled During LENGTH AGE GROUP cm 0 I I1 I11 IV VI MTAL

21 TABLE 4. Continued. LENGTH cm 0 I AGE GROUP I11 IV v TOTAL

22 TABLE 5. Length and Age of Bluefin Tuna Sampled During LENGTH AGE GROUP cm 0 I I I I11 IV v TOTAL

23 TABLE 5. Continued LENGTH cm I I I I I I TOTAL 0 AGE GROUP I11 IV v TOTAL 1

24 TABLE 6. Length and Age of Bluefin Tuna Sampled During LENGTH AGE GROUP cm 0 I I I I11 IV v VI TOTAL

25 TABLE 6. Continued. LENGTH cm 0 I AGE GROUP I11 IV TOTAL , I TOTAL 1 687

26 -24- TABLE 7. Length and Age of Bluefin Tuna Sampled During 1967, LENGTH AGE GROUP cm 0 I I1 I11 IV TOTAL

27 TABLE 7. ' Continued. LENGTH AGE GROUP cm 0 I11 IV TOTAL TOTAL

28 -26- TABLE 8- Length and Age of Bluefin Tuna Sampled During LENGTH AGE GROUP cm 0 I I1 I11 IV v VI TOTAL

29 TABLEI. Continued. LENGTH cm 0 AGE GROUP I I1 111 IV TOTAL

30 -28- TABLE 9. Length and Age of Bluefin Tuna Sampled During 1969, AGE GROUP 0 I I I I11 IV v TOTAL

31 r * TABLE 9. Continued. LENGTH cm 0 AGE GROUP I11 IV TOTAL I TOTAL

32 TABLE 10. Numbers, Megagrams and Percent of Bluefin Tuna at Each Age Landed in California During Years 1963 Through Age 0 I I I I11 IV V VI Total 1963 Year-class Numbers of fish 3, , ,500 97,200 5, ,206,000 Percent Megagrams , , , ,451.2 Percent Year-class Numbers of fish -- 1,147,800 79,500 24,400 4, ,255,800 Percent Megagrams -- 6, Percent , Year-class Numbers of fish Percent Megagrams Percent 1966 Year-class Numbers of fish Percent Megagrams Percent 1967 Year-class Numbers of fish -- 97, ,900 33, ,160 Percent trace Megagrams , ,992.9 Percent

33 Age 1968 Y ear-class Numbers of fish Percent Megagrams Percent VI Total , , Year-class Numbers of fish Percent Megagrams Percent

34 TABLE 11. Number of Bluefin Landed by Age Group and Year Class from Age group Year class I11 IV Total , , , ,850 1,474,170 1,031, , , , , Totals

35 TABLE 12. Megagrams of Bluefin Landed by Age ~ r o u and ~ Year Class from Age group Year class 0 I I I I11 IV V VI Total , , Totals , , , ,157.6

36 they were 1 year old. At 2 years of age the 1964 year class accounted for 52% while the 1965 class accounted for 70% of the catch as two year olds. The 1967 year class contributed 72% by number in 1968, but it totaled only 3,695 Mg. This large percentage is due more to a weak 1966 year class (2-year old fish) than to a strong one in The 1968 year class was not particularly strong. The 1962 and 1966 year classes were relatively weak contributors to the catch. The 1962 year class made a weak appearance as 1 and 2-year old fish but appeared strong when 3-years old. Two or three strong year classes in succession have produced large catches. A series of weak year classes could result in small catches for a year or more. The fishery primarily exploits only three age groups thus increasing the chance of several weak year classes resulting in a small harvest. Each season the fishery moves northward with the first migrants and as newly arrived schools enter coastal waters in more northerly latitudes (Table 13). By July, bluef in are being caught from latitude 23'~ to 33'~, and by August almost all are caught north of latitude 27'~. During the early months and in the southern latitudes, 2-year-old bluefin comprise a larger portion of the catch by numbers then those 1 year old. Later, in more northerly latitudes, 2-year-old bluefin generally make up less than 50%. The percent of 2-year-old bluefin caught in each lo square for the years 1963 through 1969 was plotted against latitude, and a line fitted to the 106 points by the method of least squares. he correlation coefficient of -.52 was significantly different from 0 at the 99.9% level. Apparently 2-year-old bluefin arrive early off

37 TABLE Latitudes in Which Bluefin Tuna Were Caught Each Month and Each Year Month 1 Year

38 California compared to 1-year-old fish and were available in relatively greater numbers during the first few months of the fishery (Figures 3-9). REFERENCES Bell, Robert Preliminary age determination of bluefin tuna, Thunnus thynnus. Calif. Fish Game, 49(4):307. Clemens, Harold B., and Glenn A. Flittner Bluefin tuna migrate across the Pacific Ocean. Calif. Fish Game, 55(2): Greenhood, E. C California's tuna record gathering system. FA0 Fish. Rept. (6), Vol. 3: Holder, Charles Frederick The Channel Islands of California. A. C. McClurg & Co. Chicago. 397 p. Koski, Robert Age and growth determinations of bluefin tuna in the North Pacific Ocean. Long Beach California State College. 51 p. Siegal, Sidney Nonparametric Statistics. McGraw-Hill Book Co., Inc., New York. 312 p. Tuna Club of Avalon The History of the Tuna Club. Tuna Club, Avalon, Calif. 197 p. Yukinawa, Mori, and Yoichi Yabuta Age and growth of the bluefin tuna, Thwmus thynnus (Linnaeus), in the North Pacific Ocean. Report of Nankai Regional Fisheries Research Lab. (25):

39 FIGURE 3. Age Composition and Sampling Areas of Bluefin Samples Dark Line Encloses Bluef in Fishing Grounds. Sampled lo Squares Contain Roman Numerals (Age) Followed by the Percent Contribution of That Age Within the lo Square.

40 FIGURE 4. Age Composition and Sampling Areas of Bluefin Samples Dark Line Encloses Bluefin Fishing Grounds. Sampled lo Squares Contain Roman Numergls (Age) Followed by the Percent Contribution of That Age li'ithin the 1 Square.

41 FIGURE 5. Age Composition and Sampling Areas of Bluefin Samples Dark Line Encloses Bluefin Fishing Grounds. Sampled lo Squares Contain Roman Numerals (Age) Followed by the Percent Contribution of That Age Within the lo Square.

42 FIGURE 6. Age Composition and Sampling Areas of Bluefin Samples Dark Line Encloses Bluefin Fishing Grounds. Sampled lo Squares Contain Roman Numerals (Age) Followed by the Percent Contribution of That Age Within the lo 8quare.

43

44 FIGURE 8. Age Composition and Sampling Areas of Bluefig Samples Dark Line Encloses Bluefin Fishing Grounds. Sampled 1 Squares Contain Roman Numerals (Age) Followed by the Percent Contribution of That Age Within the lo Square.

45

46 APPENDIX 1. Length-Weight Relationship Used in Calculation of Numbers and Weight of Bluefin Tuna Landed, Range Year N Weight (kg) Length (cm) Equation