Effects of extensive seeding on abalone, Haliotis discus discus, abundance on the Pacific coast of Boso Peninsula, Japan.ABSTRACT Abalone abalone (ăbəlō`nē), popular name in the United States for a univalve gastropod mollusk of the genus Haliotis, members of which are also called ear shells, or sea ears, as their shape resembles the human ear. resources in Chiba Prefecture Chiba Prefecture (千葉県 Chiba-ken , the Pacific coast of central Japan, have been severely reduced in recent years. Our investigations have revealed that the density of the mature abalone in this area is 0.019 ind./[m.sup.2], which may be insufficient for successful reproduction. In this study, we investigate the effects of extensive seeding on stock enhancement of abalone, Haliotis discus discus /dis·cus/ (dis´kus) pl. dis´ci [L.] disk. dis·cus n. pl. dis·ci A flat circular surface; a disk. discus pl. disci [L.] 1. discus. We experimentally released 400,000 juveniles (3.0 cm in shell length, SL) to the research field of 8,000 [m.sup.2] in May 1998 and investigated the growth and stock conditions by SCUBA scuba: see diving, deep-sea. . The abalone seeds grew up to 10.2 cm SL on average in 3 y and 12.8 cm SL in 4 y, exceeding the legal catch size (12.0 cm) by the Chiba Prefectural pre·fec·ture n. 1. The district administered or governed by a prefect. 2. The office or authority of a prefect. 3. The residence or housing of a prefect. Regulation of Fisheries fisheries. From earliest times and in practically all countries, fisheries have been of industrial and commercial importance. In the large N Atlantic fishing grounds off Newfoundland and Labrador, for example, European and North American fishing fleets have long Adjustment, and subsequently commercial catches started in 2002. The catch per unit effort (CUPE CUPE Canadian Union of Public Employees ) was increased to a great extent from 3 kg/day-boat to 9 kg/day-boat. The inhabited area was considered to be expanded to 100,000 [m.sup.2] based on the catch logs by the local fishermen. As of May, 2002, a production of 57,000 abalones was estimated to be attained by the extensive seeding. KEY WORDS: seeding, stock enhancement, abalone INTRODUCTION Abalone catch used to be 800 t a year in Chiba Prefecture, the pacific coast of central Japan. The catch has been remarkably decreased to less than 100 t in recent years. Our investigation has revealed that the density of mature abalone is 0.019 ind./[m.sup.2], which may be insufficient for successful reproduction (Shepherd & Brown 1993, Shepherd & Partington 1995, Badcock & Keesing 1999). In this study, we investigate the effects of extensive seeding on stock enhancement of abalone, Haliotis discus discus. METHODS We experimentally released 400,000 artificial abalone juveniles (3 cm in shell length, SL; 4.3 g) to the research field of 8,000 [m.sup.2] in May 1998 and investigated the growth and density by SCUBA. The juveniles were produced from natural adults collected in the research filed and were 1.5 y old at the time of release. The research field is "reefy" seashore (3-5 m in depth) and is one of abalone fishery grounds in Boso Peninsula. The released abalone reached the legal catch size, and commercial catches started in May 2002. We analyzed the catch number and location data on the daily catch log recorded by all local fishermen (9 in total). The fishermen dived to catch the abalone with goggles goggles, n the protective eyewear worn by dental personnel and patients during dental procedures. goggles see periocular leukotrichia. and a bathing suit. It was prohibited for Ama fishermen to use a snorkel snorkel, tube through which a submarine or diver can draw air while underwater. When in use, the top of the snorkel tube extends above the water surface into the air. tube, fins, wetsuit wet·suit also wet suit n. A tight-fitting permeable suit worn in cold water, as by skin divers, to retain body heat. wetsuit wet n → combinaison f de plongée , and SCUBA gears. The fishing season was from May to August. The stock size was estimated by the DeLury method, which is based on the regression between CPUE CPUE Catch Per Unit Effort (fishing industry) and cumulative catch number. The occurrence rate of released abalone out of the total catch was multiplied to the estimated stock size to obtain the stock size of the released abalone. Released abalone can be easily recognized by greenish color of the shell; however, because the recognition results differed between fishermen and us, we used our results. The horizontal distribution of the released abalone was estimated with the estimated stock size and the CPUE values calculated for each 50-m transects. The survival rate of released abalone seeds is supposed to be low within the first 1 mo after releasing and become higher and stable afterwards (Tanaka & Sakamoto 2001). We set the stable natural mortality coefficient to be 0.223/year (Simizu 2000), and the early survival rate was set to be 0.33, which was calculated with estimated stock size and the number of released shells, The expected catch of released shells in weight and price within 15 y after releasing were evaluated by growth-survival model (Beverton & Holt 1956), and the price values were compared with the expenditure, which is required for seeding. The average fishing mortality values (0.184) was used for the evaluation. RESULTS AND DISCUSSION Growth and Maturation The abalone seeds grew up to 10.2 cm SL on average in 3 y and 12.8 cm SL in 4 y, exceeding the legal catch size (12.0 cm) by the Chiba Prefectural Regulation of Fisheries Adjustment (Fig. 1). Because the size at the time of release (1.5-y-old) was small compared with natural abalone (Simizu 2000, 2001), subsequent growth was also slower. Testes testes or testicles Male reproductive organs (see reproductive system). Humans have two oval-shaped testes 1.5–2 in. (4–5 cm) long that produce sperm and androgens (mainly testosterone), contained in a sac (scrotum) behind the penis. of 4 males (mean SL = 7.3 cm) were in mature stage (Tomita 1968), and ovaries Ovaries The female sex organs that make eggs and female hormones. Mentioned in: Choriocarcinoma ovaries (ō´v of 4 females (mean SL = 7.5 cm) were in premature stage or mature stage (Tomita 1967) in October 1999 (Fig. 2). We observed that some abalones recaptured in May 2002 and kept in a tank spawned eggs in following November. [FIGURES 1-2 OMITTED] Habitation HABITATION, civil law. It was the right of a person to live in the house of another without prejudice to the property. 2. It differed from a usufruct in this, that the usufructuary might have applied the house to any purpose, as, a store or manufactory; whereas Our SCUBA investigations revealed that the abalone densities, which were 50 ind./[m.sup.2] at the time of release, were 0.17 to 0.20 ind./[m.sup.2] 1.5-3 y after the release, and 0.45 ind./[m.sup.2] 4 y after the release. According to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. the analyses based on the catch logs by the local fishermen, the densities were 0.56 ind./[m.sup.2] on average, and the maximum was 1.8 ind./[m.sup.2] 4 y after the release. Higher density values in 4 y rather than in 1.5 y after the release was probably because of the difficulty in finding smaller individuals hiding between rocks. The habitation range expanded to 10,000 [m.sup.2] in May 2002 (i.e., 4 y after the release) shoreward toward shallow areas with many stones (Fig. 3). This may be because seabed with many stones is more suitable than reefy bottom as a habitat. [FIGURE 3 OMITTED] The Catch and Production of Abalone Resources by Seeding Because the seedlings had not been done in the survey fishery ground, occurrence of released abalone was low. However, it increased rapidly to 68% in 2002 (Fig. 4). Increased number of released abalone increased CPUE to a great extent from 3 kg/day-boat to 9 kg/day-boat (Fig. 5). [FIGURES 4-5 OMITTED] The number of abalone was greatly reduced from 400,000 to 132,000 in 1 mo after the release in May, 1998, and it became 57,000 in May 2002 (Fig. 6). A part of the abalone with fast growth was caught in 2001 (1,600 individuals), and all individuals recruited to fishing in May 2002. During the fishing season in 2002, 4,500 individuals were caught. [FIGURE 6 OMITTED] Trial Calculation of Seeding Effects The overall recapture landing was provisionally calculated to be 31,000 individuals or 10.4 t. Recapture rate was calculated to be 7.8%. Seeding used to be conducted in the survey area from 1968 to 1981, and the recapture rate during this period was estimated to be 8.8% (Sakamoto et al. 1986). The average unit price of the abalone is assumed to be 6,200 yen/kg, thus the effect of seeding is calculated to be 65 million yen. The expenditure of seedlings was 19 million yen; therefore, substantial benefit is considerable LITERATURE CITED Badcock, R. & J. Keesing. 1999. Fertilization fertilization, in biology, process in the reproduction of both plants and animals, involving the union of two unlike sex cells (gametes), the sperm and the ovum, followed by the joining of their nuclei. biology of abalone Haliotis laevigata: laboratory and field studies. Can. J. Fish. Aquat. Sci. 56: 1668-1678. Beverton, R. J. H. & S. J. Holt. 1956. On the dynamics of exploit fish populations. Fish. Invest. Series 2. 19. 533 pp. Sakamoto, J., O. Ishida & T. Matsuoka. 1986. Liberation effect of juvenile Japanese black Japanese black breed of cattle developed by crossing one of the indigenous breeds of Japanese cattle with European cattle. Black, horned (some polled), small, fine-boned; used principally for meat, some draft, occasionally milk. Similar breeds are Japanese brown, Japanese polled. abalone in preserved area at Kawaguchi, Chiba Prefecture. The Aquaculture aquaculture, the raising and harvesting of fresh- and saltwater plants and animals. The most economically important form of aquaculture is fish farming, an industry that accounts for an ever increasing share of world fisheries production. . 34(1):25-30. Shepherd, S. A. & L. D. Brown. 1993. What is an abalone stock: implications for the role of refugia In the most basic biological sense refugia (singular: refugium) are locations of isolated or relict populations of once widespread animal or plant species. This isolation (allopatry) can be due to climatic changes or human activities such as deforestation and over-hunting. in conservation. Can. J. Fish. Aquat. Sci. 50:2001-2009. Shepherd, S. A. & D. Partington. 1995. Studies on the Australian abalone (genus Haliotis). XVI. Recruitment, habitat and stock relations. Mar. Freshwater Res. 46:669-689. Simizu, T. 2000. The resource management of the abalone by the size regulation. Bull. Chiba Pref Fish. Exp. Sta. 56:15-20. Simizu, T. & T. Tanaka. 2001. The maximum size of the abalone in Chiba prefecture. Bull. Chiba Pref Fish. Exp. Sta. 57:273-274. Tanaka, T. & J. Sakamoto. 2001. A comparison between recovery rate and discharge size, technique of abalone seed. Bull. Chiba Pref. Fish. Exp. Sta. 57:237-239. Tomita, K. 1967. The maturation of the ovaries the abalone, Haliotis discus hannai Ino, in Rebun Island Rebun Island (礼文島, rebuntō) lies in the Sea of Japan off the northwestern tip of Hokkaidō, Japan. Rebun stretches 29 kilometers in the North-South direction and 8 kilometers East-West, covering about 80 square kilometers. , Hokkaido, Japan. Sci. Rep. Hokkaiso Fis. Exp. St. 7:1-7. Tomita, K. 1968. The Testis testis (tĕs`tĭs) or testicle (tĕs`tĭkəl), one of a pair of glands that produce the male reproductive cells, or sperm. maturation of the abalone, Huliotis discus hannai Ino, in Rebun Island, Hokkaido, Japan. Sci. Rep. Hokkaiso Fis. Exp. St. 9:56-61. TOSIATU SIMIZU * AND KANAKO UCHINO Chiba Prefectural Government, Fisheries Research Center, Japan * Corresponding author. E-mail: t.shmz7@mb.pref.chiba.jp |
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