Original Paper
Title Morphometric discrimination between Japanese charr and brook trout
Authers Kei'ichiro IGUCHI*1, Satoshi KITANO*2, and Naoto MATSUBARA*1
Keywords morphometry, principle component analysis, discriminant analysis, invasive alien species, Salvelinus
Citation Bull. Fish. Res. Agen. No.1, 1-5, 2001
Native Japanese charr (Salvelinus leucomaenis) and introduced brook trout (S. fontinalis) are sympatric in the Azusa River, Kamikochi, where the former has decreased in the number presumably due to the hybridization with the latter. We validated the morphometric method in discriminating them and their hybryds using photographed body shapes. Principal component analysis factored out that these two species differed in morphometoric characteristics around the head and tail. Discriminant analysis successfully separated the two species by the morphometric characteristics, but failed for hybrid individuals. Providing the species-specific proportion, applying the morphometric method to photographed data was judged to be useful in discriminating the two species.

Accepted on August 20, 2001
Contribution No.A 1 from Fisheries Research Agency
*1 National Research Institute of Fisheries Science, Komaki 1088, Ueda, Nagano 386-0031, Japan
*2 Nagano Nature Conservation Research Institute, Kitasato 2054-120, Nagano, Nagano 380-0075, Japan

Title Nonlinear energy transfer among wind waves in coastal region
Authers Kosei KOMATSU*1 and Akira MASUDA*2
Keywords wind-wave spectrum, nonlinear resonance interaction, finite depth water
Citation Bull. Fish. Res. Agen. No.1, 7-21, 2001
It is necessary for accurate wind-wave forecasts in coastal region to develop an efficient scheme for calculating nonlinear energy transfer among resonance wind-waves in finite-depth water. In previous works, however, it was reported that the straightforward extension of a representative efficient scheme for deep water (the RIAM method) to finite-depth water tends to yield a ragged distribution of nonlinear energy transfer for depths a few times smaller than the wavelength of dominant waves. In addition, xtraordinary fine resolution is required to obtain a smooth and stable nonlinear transfer function. In this paper a new scheme was developed by improving and generalizing the deep-water RIAM method, by virtue of which quite smooth nonlinear energy transfer functions were obtained even with coarse resolution.

Accepted on August 20, 2001
Contribution No.A 2 from Fisheries Research Agency
*1 National Research Institute of Fisheries Science, Fukuura, Kanazawa, Yokohama 236-8648, Japan
*2 Research Institute for Applied Mechanics, Kyushu University, Kasuga-koen, Kasuga 816-8580, Japan

Title Distribution and growth of 0-age-group tonguefish (Cynoglossus lighti) in northeast Ariake Sound
Authers Yuichi KOSHIISHI*1, Yukio OHSAKA*1, Munenori HAYASHI*2, Motohiko SANO*3, and Takeshi MURAI*4
Keywords Cynoglossus lighti, tonguefish, distiribution, growth, Ariake Sound
Citation Bull. Fish. Res. Agen. No.1, 23-34, 2001
Distribution and growth of 0-age-group tonguefish, Cynoglossus lighti, in shallow water (less than 20m) of northeast Ariake Sound, were studied from 1990 to 1995. C.lighti occurred all year round in the sampling area and 0-group fish were collected mainly in the area shallower than 10m isobath. The newly settled juveniles were found from July to November, though some annual fluctuation in the settling period was evident. They first settled in the nearshore area and their distribution expanded offshore with growth. One year and/or older fish distributed somewhat deeper area than 0-group, and seemed to show seasonal inshore and offshore migration on a small scale. The growth of 0-group fish estimated from the change in body length frequency was fast from April to November when the ambient temperature exceed 15℃. The maximum growth was estimated to be 0.93mm/day. Their growth was virtually stagnant during winter. The verage body length of one year old was estimated to be about 140mm.

Accepted on August 20, 2001
Contribution No.A 3 from Fisheries Research Agency
*1 Seikai National Fisheries Reseatch Institute, Fisheries Research Agency, 3-30 Kokubu, Nagasaki, 850-0951, Japan
*2 Fukuoka Fisheries and Marine Technology Research Center, 1141-1 Imazu, Nishi, Fukuoka, 819-0165, Japan
*3 Ishigaki Tropical Station,Seikai National Fisheries Research Institute, Fisheries Research Agency, 148-446 Fukai Ohta, Ishigaki, 907-0451, Japan
*4 National Fisheries University, 2-7-1 Nagata-honmachi, Shimonoseki, 759-6595, Japan

Short Paper
Title Histological studies on the gonadal development in Java medaka (Oryzias javanicus
Authers Akira KAKUNO*1, Kazunori FUJII*1, and Jiro KOYAMA*2
Keywords Java medaka,sexual differentiation,maturation,secondary sexual characters
Citation Bull. Fish. Res. Agen. No.1, 35-37, 2001
Sexual differentiation and maturation in Java medaka(Oryzias javanicus) were examined histologically. At 14 days after hatching, the oocyte at the perinucleolus stage was observed in fry. In the male gonad, the primary spermatocyte was observed in testis at 18 days after hatching. The urino-genital papillae in female and the longer dorsal fin in male, which are constituted secondary sexual characters,were observed at 60 days after atching. At 100 days after hatching, spawning was observed. These results suggest that the sexes in fry of Java medaka were identified histologically at 14 days after hatching,and externally at 60 days after hatching.

Accepted on August 20, 2001
Contribution No.A 4 from Fisheries Research Agency
*1 National Research Institute of Fisheries and Environment of Inland Sea,Maruishi 2-17-5,Ohno, Hiroshima, 739-0452, Japan
*2 Faculty of Fisheries, Kagoshima University, 4-50-20, Simoarata,Kagoshima-shi, Kagoshima, 890-0056, Japan)

Technical Report
Title Researching and evaluation methods of working environment at the fishing ports
Authers Nobuo TAKAKI* and Kimiyasu SAEKI*
Keywords fishing port, fisherman,working environment, field survey, evaluation technique
Citation Bull. Fish. Res. Agen. No.1, 39-57, 2001
It is required to investigate fisheries’ working environment and develop evaluation methods of that. The fishing ports in Japan have been constructed as public enterprises. Although many quays and sites have been constructed for the past fifty years, systematic inspections of the situation of the working environment have not performed yet.
 The working environment includes thermal environment, distribution of working hours, evasion from danger and various elements. As for factory environment,there are sufficient evaluation methods to measure those elements.
 In this paper, the outline of the evaluation methods of the working environment at the fishing ports is explained. That technique will be a basis of the evaluation, and then it should be taken account of the characteristic matters of fishing ports as working sites, such as overlap with a life space, difficulty of renovation of facilities and so on. If those methods are systematized,they will contribute to improve comfortableness and safety of fisheries’ working environment, and to solve the problems of an aging society.

Accepted on August 20, 2001
Contribution No.A 5 from Fisheries Research Agency
* National Research Institute of Fisheries Engineering, Ebidai, Hasaki, Kashima, Ibaraki 314-0421,Japan)

Doctoral thesis
Title Effect of Waves on Grazing by Sea Urchins and Abalone on the Coast of Northern Japan
Authers Shigeru KAWAMATA*
Keywords Abalone, Algal recruitment, Barrens, Grazing, Kelp bed, Sea urchin, Waves, Water velocity
Citation Bull. Fish. Res. Agen. No.1, 59-107, 2001
Laboratory and field studies were conducted to explore the effect of wave-induced water motion on grazing by commercially important sea urchins Strongylocentrotus nudus, S.intermedius and abalone Haliotis discus hannai as an important mechanism regulating their distribution and the abundance of food algae on the coast of northern Japan. Oscillating-flow-tank experiments conducted at moderate temperatures (10-15℃) indicated that grazing on a leaf-like kelp by sea urchins was nearly impossible when water velocity amplitude, Umax, was only about 0.4m/s. This velocity limit for grazing was considerably lower than that for movement (approximating 0.7m/s) because of their unstable grazing posture. In contrast, H. discus hannai could graze on adult kelp of Undaria pinnatifida at much higher velocities (Umax>0.9m/s). Flow-tank experiments simulating natural subtidal areas with a depth gradient of water velocity showed that S. nudus could graze freely on small juvenile algae where Umax<0.3m/s but could scarcely crawl into areas with Umax>0.45m/s at temperatures of 4-13℃. This result and observations in Oshoro Bay on the Japan Sea coast of Hokkaido, which was haracterized by shallow algal and deep S. nudus-dominated barren zones, suggested that wave-induced limitation of sea urchin grazing would lead to colonization by algae of barren areas even adjacent to large aggregation of sea urchins if the frequency of Umax<0.4m/s remains at <0.5 from the settlement of spores to establishment of kelp beds. S. nudus are susceptible to the whiplash effect of kelp blades swaying under waves so that they never move into dense kelp stands and graze only on the peripheral plants during periods of calm seas. A laboratory flow-tank experiment with kelp beds showed that S. nudus were completely dispersed from dense Laminaria stands when Umax>0.2m/s. Although S. intermedius had higher tolerance to water motion independent of temperature, they rarely graze even on small juvenile algae for Umax>0.4m/s. In contrast, S.intermedius appeared less susceptible to the whiplash effect of blades than S. nudus:they moved into dense Laminaria beds and remained there for Umax<0.25-0.30m/s. H. discus hannai have highest tenacity to water motion but lowest resistance to low temperature. The abalone remains at areas with least water motion fat low temperature up to 10℃ if food algae are there.
 For higher temperalture with established kelp beds, the tank-flow experiment showed that foraging by H. discus hannai dramatically become active regardless of water motion of <0.6m/s. This result is consistent with the observation that the abalone occurred only inside a dense Laminaria bed in Oshoro Bay.
 Monthly averaged probabilities of Umax<0.4m/s and <0.2m/s were estimated from 19-20 year long offshore wave data along the Japan Sea coast of southwestern Hokkaido and along the Sanriku, (northeastern Pacific) coast of Honshu, where food algae have been often limited by overgrazing by Strongylocentrotus nudus. The estimates partially explain the marked differences in physical disturbances and food availability to abalone and sea urchins between the two coasts. The paper describes the importance of wave-induced physical disturbance in abalone and sea urchin aquaculture and in artificial development of kelp beds in sea urchin-dominated barren areas.

Accepted on August 20, 2001
Contribution No.A 6 from Fisheries Research Agency
* National Research Institute of Fisheries Engineering, Ebidai, Hasaki, Kashima, Ibaraki314-0421, Japan