Circular 170. Monofilament Gill Net Fishing for Skipjack Tuna in Hawaiian
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Created in 18,19, the Departll1pnt of the I nterior-~\m e ri l':\', Department of Katnral Re ource--is concprner] with the ll1an~ agell1ent, conspn-ation, and derelopll1ent of the :\";I(lOn\ watpr. fish. "'ildlife, mineral, forest, and park and rccreational n' ~OlllTes. It also has major re>'ponsibilities for I IH ]iall :\1,,] TelTitoria I afl'a irs. ~\s the Kation's principal consenation agpnl'y. thc Depart ment ",ork~ to a~snre that llol11'pne\rahle reSOllrl'es are (]p\"clojlPd and n~prl ,,"isely, th:1t park am] recreational resonrces arp COIl spnerl fur thp flltllre. and that renewable rpsomCl'" m:lkc their full contnlllltlOn to the progrp ~. prosperity. and seclll'lty of thp rnited ~tates-no\\' and in the fnture. Cover Photo: Setting gill nets from a Hawaiian skipjack boat. TINITED STATES DEPARTMENT OF THE INTERIOR, STEWART L. UDALL, SECRETARY FISH AND WILDLIFE SERVICE, CLARENCE F. PAUTZKE , COMMISSIONER BUREAU OF COMMERCIAL FISHERIES , DONALD L.McKERNAN, DIRECTOR ~@~@~~[&~m~IT @~[[ ~~IT ~~~oo~~@ ~@~ ~[{~~B&~[{ ITlW~& ~~ OO&~&~~&~ ~&IT~~~ ~®®~ 0 ®~ BY RICHARD S. SHOMURA FISHERY RESEARCH BIOLOGIST BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY HONOLULU , HAWAII Circular 170 October 1963 ABSTRACT The Hawaiian skipjack fishery is showing signs of economic trouble. This is especially evident in the size of the fleet, which has decreased 40 percent since 1948. Theproblem is one of a static level of fishing efficiency with the pole-and- line method, and in creasing operational costs. The solution requires increasing th e catch without a proportionate increase in cost. On the basis of recent developments in monofilament fibers and the success of monofilament gill nets in other fisheries, netting techniques for catching skipjack tuna were investigated in 1961 and 1962,withthejointsupportof the State of Hawaii and the Bureau of Commercial Fisheries. The study was carried out by Bureau per sonnelon a chartered skipjack boat from July 23 to September 29, 1961, and May 9 to August 25, 1962. The results indicated that the monofilament gill net method of fishing will not supplant nor effectively supp1ement the present pole-and-line method of catching skipjack tuna. The principal method of fishing used in the tests was to locate a skipjack school, c hum the school to the stern of the boat using live baitfish, set the net while continuing the chumming, and haul in the net with a powerblock. Although skipjack can be captured by this method, the catch was found to be too small to be of commer cial significance. The largest catch from a single. set was 127 skipjack. The passive method of gill net fishing was tried on 14 occasions. In this method the nets were set at sunset and allowed to drift passively throughout the hours of dark. The gear and the catch were then picked up the following morning. The catch of only one skip jack from the 14 sets indicated that the method is not applicabl e for commercial skipjack fishing in Hawaiian waters. ii CONTENTS Experimental gill net fishing f or skipjack _____________ 1 Funds _____________________________ 2 Plans_______________________________ 2 M on ofil am en t net s ____________________________________________ 2 Vessel ______________________________________________________ 3 Res ult s of pre lim in ar y tr i al s ______________________________ 3 Re s ults of field tr i a l s ____________________________________ 4 Opera tional d ata _________________________________________ 4 Baiting _______________________________________________ 7 Gill net fi shing _____________________________________ 7 Cannery acceptability of gill net skipjack ____________________ 10 Summary and conclusions 11 Literature c ite d 12 Appe ndix 1 - Description of the M /V Broadbill 13 Appe ndix 2 - Stability test ___ 15 Appendix 3 - Station list, M /V Broadbill, July 23, 1961 to Sep te m ber 29, 1961 _________________________ 17 Appendix 4 - Station list, M/V Broadbill, May 10, 1962 to August 25, 1962 _____________________________ 19 iii oC (I) focuS forusFOCU S' PoG'S EXPERIMENTAL GILL NET FISHING FOR SKIPJACK strength of the U .• w t co few years ago was m t b} mcr At present, despite the generally vigorous efflcl nc), of th purse growth of Hawaii's economy, the Hawaiian skip synthetIc fIber and Po\\ jack fishery gives indications of slow deteriora {Mc,'eely, 1961), tion. From a modest start in the early 1900 's this fishery increased in importance until in re cent years the skipjack landings h ave represent ed from 50 to 70 percent of the total fish land ings in the State of Hawa ii (Yamashita, 1958). Since 1948 the annual skipjack landmgs have varied between 6.1 a nd 14.0 milllon pounds (fig. 1). Total landings do not, however, show the serious condition facing the f ishery; trends in the size and age of the fishing fleet more accu rately depict the existing situation. The history Figure 2.--Year of c natruction ( r. p. " boau active- in 19 1 i!l 13 8.. 12 The pole-and-line fishery h S 11 and chummed do not re pond to th andOtsu, 1955; Yuen, 1959). Ob on commercial boats also sho\\ per school Is ~ ry sm 11, su g 19411 19 19 1950 1951 1952 1953 195~ 1955 1956 195, 1958 1959 1960 1961 successfu11 Figure 1. --Annual landings of Hawaiian skipjack The patch from 20 of th fishery, 1948-61. of the fishery in the post- World War II period shows a n initial flurry of activity, born of opti mism , which included the construction of nine ne w v essels between 1946 and 1950 (ftg. 2). This was followed by a stable period in the early 1950 's when only one new vessel was added to time each set ')01 I the fleet. In recent years, with the withdrawal schoo:~ ex min d, 0 of a num bel' of the older boats from the acti\ e for a period 01 1C'ss th fle e t a nd th absence of ne\\ construction, th fleet has been reduced from a total of 32 boats In e senc ,th solu Ion in 194 (June, 1951) to the present total of 20 restoring thE' Ha\\ al an s Ip boats. Even with the withdrawal of some of the family of growmg Industr older boats the present fleet may still be consid ered old; of the 20 boats fishing today, 7 were built between 1926 and 1931. While the factors responsible for this state of decay in the fis hery are complex, they are basl cally r elated to the wide fluctuations in the catch from year to year and to method of hshmg, with pole- a nd-line and li\'e bait, \\hich has re mained virtually unchanged sll1ce the begll1nm of the fishery. This unchanging le\'el of fl hm", efficiency, again t a background of constantly ri ing operational costs. hn had S rlOU'" effect on th indu try, particularly during poor -" ~on A similar situation which affect d th omp tltl 25 al aspects of fishing monofilament gill nets, to be carried out on the Bureau's research vessel 20 Charles !i. Gilbert; and (2) a consideration of possible methods of fishing the gear. The methods 15 contemplated fell either into an active fishing I category, in which a skipjack school would be 10 pursued and the net set in the midst of the school or into apassive fishery category, where the net would be set at a predetermined location and 5 I allowed to drift over a period of time, usually II I I . 1 1- during the hours of darkness. II .. 50 60 70 80 90 '0 20 30 40 FISHING DURATION (MINUTES ) Figure 3b.--Frequency distribution of fishing duration. (Data from Yuen, 1959). MONOFILAMENT NETS level of fishing efficiency, either by (1) improv Before detailing the types and specifications ing the existing pole-and-line method or (2) in of the monofilament gill nets purchased and used troducing an entirely different mode of fishing. in the experiments, some information on the n a The present study is primarily concerned with ture of monofilament is necessary to point out the latter approach. its advantages over other netting materials. In recent years the use of monofilament fiber FUNDS for gill nets has increased considerably through out the world. Monofilament is one of several Aware of the recent success of net fishing synthetic fibers commonly known under the gen methods in the west coast tuna industry, the Bu eral term "nylon. " These fibers belong to the reau of Commercial Fisheries and the State of polyamide group, which along with other synthe Hawaii decided to undertake a study to determine tic fibers have revolutionized the textile and fi sh the commercial feasibility of netting skipjack in ing industries. Among the advantages nylon pos Hawaiian waters. The objective of the study was sesses over natural fibers are: (1) it i s virtually to be the development of a method of netting skip unaffected by age, (2) it loses strength only on jack which could be adopted by the existing fleet. prolonged exposure to sunlight, (3) it is resis In April 1961 the Fish and Wildlife Service made tant to many chemicals, and (4) it is immun e to available $25,000 in Salton stall-Kennedy funds to bacteria action, which permits leaving the gear the Bureau of Commercial Fisheries Biological in water for prolonged periods of time. The im Laboratory in Honolulu for the purchase of equip portant attribute of monofilament nylon fiber is ment and gear. The State of Hawaii Legistature, its very high transparency in water, which gives in its 1961 session, passed Senate Bill 387, ap it a higher fishing efficiency than natural or propriating $45,000 for the program.