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未成熟で市場価値の低い水ガニのズワイガニ漁期中の入網数とリリース直後の生残率を推定した。底曳網で漁獲された水ガニを篭に入れ，海底に約 6 時間浸漬した後に再び回収し生死を判断した。京都府沖合での水ガニ平均入網数は，2006～08 年の標本船日誌から 168,400 個体と推定され，成熟で市場価値の高い雄ガニの約 1.7 倍であった。生残率は甲幅 90～109 mm では 14.8～95.9%, 110～129 mm では 5.0～89.8%, 130 mm 以上では 0～62.5% と推定された。水ガニ漁期（1～3 月）に水ガニをリリースした場合，平均生残率は 83.6% と高く，雄ガニの増加に寄与すると考えられた。

東北地方太平洋岸沖（東北海域）におけるズワイガニの成長を，甲幅組成解析等により調べた。2001～2005 年の雄の甲幅組成は平均甲幅 27～93 mm の 6 齢期群に，雌では 30～77 mm の 5 齢期群にそれぞれ変換され，成長速度は雌雄でほぼ同様であった。最終脱皮割合は，雄で甲幅 110 mm，雌では甲幅 76 mm でほぼ 100% に達していた。雄の齢期別甲幅は日本海における知見とほぼ同様であったが，最終脱皮割合は全ての甲幅で東北海域のほうが高かった。東北海域に大型の雄ガニが少ないことが知られているが，その要因の一つとして日本海との最終脱皮サイズの違いが考えられた。

ズワイガニの硬ガニと水ガニの品質を評価する手法を検討した。生きた状態で硬ガニと水ガニの特性を比較する場合，肥満度と歩脚長節腹面の b*値を測定する方法が有効であることが示唆された。解剖する場合には，歩脚長節の水分，背甲の強熱減量および肝膵臓の色調と，その成分（とくに粗脂肪）により判別可能であることが分かった。背甲の強熱減量の違いは甲殻の厚み（おもにクチクラ層）に，また，肝膵臓の色調（L*値および b*値）は脂肪蓄積量に関連のあることが推測された。

ズワイガニ幼生の適正飼育水温を明らかにする目的で，ふ化幼生を 1L ビーカーに収容し，水温 10, 12, 14, 16℃ で飼育した。第 2 齢ゾエアまでの生残率は各水温区とも 90% 程度の値を示したが，16℃ 区ではそれ以降に大量減耗がみられた。第 1 齢稚ガニまでの生残率は 14℃ で最も高い値を示した。各齢期までの発育日数は水温の上昇にともない指数関数的に減少し，発育日数の変動係数は 14℃ 区で小さい傾向があった。以上のことから，ズワイガニ幼生の適正飼育水温を 14℃ 程度と結論付けた。

調査用トロール網の漁獲からズワイガニ類 (ベニズワイガニとズワイガニ) の現存量を正しく推定するために, 袖先間隔を基準とした調査用トロール網の採集効率を推定した。調査は, 太平洋東北沖において2000年6月に, 曳航式深海用ビデオカメラを用いてズワイガニ類の生息密度を観測後, トロール網の操業を行った。トロール網の採集効率は, 生息密度に対するトロール網の掃過面積と漁獲個体数から求めた密度との関係から回帰分析によって求めた。調査用トロール網の採集効率を0.30, その95%信頼区間を0.23～0.37と推定した。

1997～2000年の夏季にオホーツク海南西部でトロールによりズワイガニ採集調査を行い, 分布と成熟サイズを検討した。水深100～300 mで主に採集され, 分布の中心は150～200 mで, 300 m以深ではほとんど採集されなかった。ズワイガニが採集された調査点の底層水温は−0.96～6.00℃で, 500個体/km2以上採集された調査点では−0.96～5.77℃の範囲に限定されていた。水深別甲幅組成から, 雌雄とも深所ほど大型の個体が多かった。50%成熟率甲幅は, 雄106.0 mm, 雌63.4 mmであった。

1990年, 1995a1997年に成体雌の標識放流を行い, 再捕データをもとに最尤法により死亡係数を推定した。1990年放流群の全減耗係数(Zi)は1.699 (year)-1, 1995a1997年放流群のZiは0.975a1.181 (year)-1と推定された。一方, 操業が周年禁止されている保護区内に放流された群のZiは0.561 (year)-1と低い値であった。1990年と1995a1997年放流群とのZiの差を混獲投棄による資源減耗を軽減するための底曳網の操業禁止区域の設定と絡めて考察した。

現在の漁業の下では本種の性比(経産卵雌に対する形態的成熟雄の割合)は0.35と計算されており, 未開発時の0.49よりも低い。形態的成熟雄の"たてガニ"に対する漁獲強度は現状のままとし, 形態的未成熟雄の"水ガニ"の現状の漁獲開始サイズと漁期とを調整することにより, 低下した性比をもとに戻す方法を検討した。"水ガニ"の単価は解禁直後や小型個体ほど低いことから, 性比の引上げおよび経済的な有効利用という点では, 漁獲開始サイズは現状よりも大きく, 解禁日は遅くすることが効果的と考えられた。本種の資源管理では雌に対する現状の漁獲強度を軽減することが指摘されている。雌の漁獲係数を半減したときには, 未開発時性比は"水ガニ"の漁獲制限だけでは得られず, "たてガニ"を含めた漁獲制限を検討する必要がある。

The present paper investigates the carapace width compositions of soft-shell males Chionoecetes opilio caught by Danish seiners and the effectiveness of prohibition of catching soft-shell males in order to keep the optimum sex ratio at 0.47 (ratio of the number of terminal molt males with hard-shell to the number of multiparous females). The sex ratio was estimated to be 0.37 in the present fishing intensity for multiparous females, hard-shell and soft-shell males in the Sea of Japan.Soft-shell males were mainly less than 100mm carapace width and non-terminal molt regardless of carapace size, and terminal or non-terminal molt cannot mate with multiparous females. It seems that the abundance of recruitment to functional maturity males with hard-shell decreases due to the catch of soft-shell males.It was ascertained that the optium sex ratio would be maintained at the present fishing condition for hard-shell males with fishing coefficient 0.5 year-1 decreased effort for multiparous females and prohibition of soft-shell males catch.

Eight experimental fishings with crab traps were made to study the spatial distribution pattern of snow crab Chionoecetes opilio on the bottom of a bank known as the Yamato-tai located in the center of the Japan Sea. The size of the terminal molt crab was comparatively examined for three regions, i. e. Yamato-tai in the Japan Sea, coastal waters of the Japan Sea off Kyoto Prefecture, and coastal waters of the Pacific Ocean off Fukushima Prefecture.Adult females were mainly distributed in an area shallower than around 320m in depth in conditions of a gradual down ward slope with a muddy bottom. On the other hand, males were distributed in all survey areas from 290m to 349m in depth.Terminal molt males were divided into five groups with average carapace sizes of 64.9mm, 80.5mm, 96.4mm, 110.5mm, and 125.0mm. Adult female sizes of terminal molt females was 69.8mm. These sizes were 10-20mm smaller than the terminal molt size of crabs obtained from the coastal areas off Kyoto and Fukushima Prefectures.

In spite of the shortening of the fishing season and restrictions on the use of fishing grounds, the resources of snow crabs Chionoecetes opilio have been declining in the western region of the Sea of Japan. If such a low level of crab stock persists, more effective improvements will be needed in the snow crab fishery. The present paper deals with analyses of catch data of the crabs by Danish seines, and gives some suggestions for the improvement of the crab fishery. The results obtained are as follows: male crabs can be caught as fishing targets from the 12th molting stage (93.4mm in carapace width; legal size is 90mm or larger) in the crab fisheries resources off Wakasa Bay. On the other hand, female crabs embracing fertilized eggs can be caught as fishing targets from the adult stage, a year and a half after the 11th molting stage. Therefore, both male and female crabs are caught at the same age. More than half of the male crabs caught are those in the 12th molting stage and soft crabs. Similarly, on the basis of identical patterns found in the fluctuation in annual catches of male and female crabs, more than half of these newly adult female crabs are assumed to be fished.Judging from an analysis of the catch data and biological information, it is necessary to use soft crabs effectively and to conserve the adult female crabs newly caught as fishing targets by the Danish seine fishery.

The present paper deals with survival rates per year after terminal molting and between two successive molting stages of the male snow crab Chionoecetes opilio, using 3, 247 individuals collected by crab trap and Danish seine at the sea bottom with a depth range of 220 to 350 min the Japan Sea off Kyoto Prefecture from March 1989 to November 1990. Snow crabs with a carapace width of more than 60mm were divided into four molting stages, having a mean carapace width of 67.4, 91.2, 111.1 and 130.2mm. The molting stage with the largest mean width (130.2mm) was constituted only by terminal molting crabs. The three molting stages with smaller mean widths of 67.4, 91.2 and 111.1mm, however, had two different groups comprising terminal molting crabs and non-terminal molting crabs. According to the percentage occurrences of the terminal molting crab in four molting stages at periods of soft and hard shell crabs, it was estimated that the survival rates of male crabs within a year after terminal molting and more than one year after the molt were less than 0.35-0.43 (year-1) and 0.58-0.71 (year-1), respectively.

The terminal molt of the male snow crab Chionoecetes opilio was studied using 1, 638 male crabs with a carapace width larger than 60mm caught by Danish seine, trap and beam trawl in the Japan Sea from August 1989 to October 1990. For estimation of the molting stages of male crabs, the second maxilla was taken, and the carapace width and chela height of each individual was measured. In examination of the relationship between carapace width and chela height, male crabs were divided into two groups, those with a relatively large chela height (large-clawed crabs), and those with a relatively small chela height (small-clawed crabs). In the small-clawed crabs, intermolt, premolt and postmolt stages were mainly observed from February to May, from June to September, and from September to October, respectively. On the other hand, almost all the large-clawed crabs were at the intermolt stage throughout the year, and the postmolt stage was observed from September to October. These results indicate that small-clawed crabs continue to molt once a year, whereas large-clawed crabs have already undergone the terminal molt.

Horizontal distribution pattern and carapace size composition were derived for snow crab Chionoecetes opilio from data collected by long-line trap and Danish seine surveys conducted at 242-244m depth in the Japan Sea off Kyoto Prefecture in May 1990. Distinct difference in horizental distribution was noted between male and female crabs, while samplings were made at the same contour in depth. Estimates of dispersion of unit patchness for mature males ranged from 100 to 200m within a large schooling dispersion (600-1, 500m). Mature female crabs might dis-perse rather densely ranging from 100 to 300m within a large school dispersing over 1, 500m and immature females ranging from 100 to 300m within a large dispersion (400-900m). It is surg-gested that growth and/or maturation of snow crab may influence horizental distribution pattern, as well as seasonal aggregation. It was clearly showed that the carapace size compositions of crab were different between two catches by the trap and the Danish seine, which was mainly due to the differences in the frequency distribution of sub-legal male crab and mature female crab. The results showed that the trap has higher selectivity towards the large sub-legal crabs more than 80-90mm carapace width. Es-timated mean carapace width from two gears were 51.0, 67.6, 86.6, 106.9mm for males and 51.8, 68.7, 79.0mm for females.

For developing the vocabulary that can describe the taste characteristic of natural and synthetic extracts of boiled snow crad Chionoecetes opilio, 5 trained panelists first tasted the extracts and selected a total of 18 terms (items), which consist of 9 primary qualities for taste, 8 secondary qualities for taste, and overall taste. Using this descriptive vocabulary, a 30 member panel evaluated the differences in taste between the two extracts. Mean scores of each of the primary qualities showed that the synthetic extract had almost the same intensity of sweetness and sourness as the natural one, but had weaker saltiness, stronger pungency, and somewhat stronger astringency, metallic taste, and alkaline taste. Of the secondary qualities, mean scores for the synthetic extract were lower than those for the natural one in all of the 8 items. Pattern and subtracted pattern similarities calculated for the primary and secondary qualities suggested that preferential increases in saltiness, pungency, bitterness, astringency, naturalness, and viscosity should be effective in reproducing the taste of the natural crab extract. Correlations among the 18 items computed in accordance with the theory of quantification IV showed that umami, sweetness, saltiness, complexity, fullness, naturalness, continuance, viscosity, and extension should be considered first in the preparation of a synthetic extract as a flavoring material.

Reproductive ecology of female tanner crab Chionoecetes opilio was studied by the use of six samples caught by traps and trawl net in the southwestern Okhotsk Sea from 1970 to 1971. Frequency distribution of the carapace width of the mature female in range 46-95mm were distinguished into several length groups composed of normal distribution with distinct modes, presumably corresponding with the plural molting instars in mature female. Main spawning season was restricted from May to June. Gonad index (IGI) showed custo-marily bimodal distribution for most of the year to suggest a reproductive cycle with two year period. Individual variations of five measurements in the reproductive characteristics were analyzed by means of principal component analysis, consequently, variations of total egg numbers and clutch weight in the pleopods are both chiefly controlled by body size. On the contrary, the size of an egg shown as egg numbers per gram clutch weight, has a tendency to be independent withthe body size.

At present, management agencies enforce size limit restrictions in the Japan Sea which prevent the landing of male C. opilio less than 9cm carapace width. Since Danish seiners cannot avoid capturing illegal sized crabs, a large number of the crabs are discarded at sea in the hope that they will eventually recruit into the legal size. However, catches of this crab have declined accom-panied by a reduction in average crab size. We demonstrate that crab yield can be increased by switching the gear to long line traps with 15cm streched mesh. Thus, by changing the size selec-tivity of the gear, crabs smaller than 9cm carapace width can be protected from the fishery.

In order to apply the bioluminescence of luminous bacteria to finshing industry, studies on the attracting effect of a luminous material containing immobilized luminous cells and a luminous raw bait attached with luminous cells on various kinds of fish were carried out. Water tank experiments showed that the luminous material had an attracting effect on freshwater shrimp Palaemon paucidens, but on the contrary, apparent evading effect on parrot fish Oplegnathus fasciatus. Fishing ground experiments revealed that the luminous material had an attracting effect on king crab Paralithodes camtschaticus caught with a trap, squid as well as prawn Penaeus orientalis caught by trawl fishing, neither and attracting nor an evading effect on crab Chionoecetes opilio caught with a trap, and a distinct evading effect on shrimp Pandalus borealis caught with a trap. Fishing guound experiments also showed that the luminous raw bait attached with luminous cells had a tremendous effect on bottom fishing by which grunt, gopher, dorado, scorpionfish, mullet, flatfish and shark were caught, and the number of caught fish was 4.8 times larger than that of the control. In addition, the luminous raw bait seemed to have some attracting effect on tuna caught with tuna long lines and the number of caught tuna was 1.2 times larger than of the control.

The number of ovarian eggs and eggs held in the pleopods of the tanner crab, Chionoecetes opilio, were examined from specimens captured off Wakasa Bay of the Japan Sea. The number of eggs may be expressed as a function of the carapace width (X, mm).(a) For mature eggs in the ovary just before spawning, N1=3, 151X-145, 676 (correlation coefficient: r=0.9895);(b) For fertilized eggs, held in the abdominal pouch two to four months after spawning, N2=2, 295X-106, 597 (r=0.9902);(c) For fertilized eggs, one to three months before hatching, N3=1, 014X-25, 366 (r=0.9870).As diagnosed from the parameters of these equations, the number of eggs increase with progressive enlargement of the carapace width, although the rate of increase differs with the different developmental stages of the eggs. The ratio of the number of fertilized eggs shortly before hatching to mature ovarian eggs is quite inversely proportional to the increase in carapace width.The number of fertilized eggs shortly before hatching carried by a crab in an average carapace width of 77.4mm corresponds to about 54% of the number of mature ovarian eggs in a crab of comparable size. It is believed that about 50% of the deposited eggs may be lost during the course of embryonic development.

In recent years, several investigations on Chionoecetes opilio elongatus RATHBUN, one of the most important crabs in the deep waters of the Japan Sea, were carried out with a view to keep its resources, but comparatively little is known of its feeding habits. This paper is a record of observations made on the stomach contents of Chionoecetes collected by trawl-net during the period from September, 1964 to June, 1965 in Wakasa Bay of the southern Japan Sea (Fig. 1). About 1, 500 specimens were examined under microscope, frequently comparing with the residues (skeletons, spicules, shell fragments, etc.) obtained by boiling 10-20% KOH or NaOH solution, various known benthonic animals that were collected from the same fishing grounds. The results are summarized as follows: 1) More than 30 species of benthonic animals belonging to 6 phyla, and 3 species of phytoplankters belonging to 1 phylum were found in the digestive organ of the crab (Table 1). 2) The bulk of the stomach contents was composed of Echinodermata (especially, Ophiuroidea), Crustacea (Decapoda and Amphipoda) and Bivalvia, while fish scales and skeletons, Cephalopoda, Gastropoda, Scaphopoda and Polychaeta were found less frequently. 3) Small planktonic Copepoda, Cirriped larvae, Foraminifera, Diatomacea were also found, but these were considered as having been ingested incidentally. 4) From the facts mentioned above, it seems that Chionoecetes is a feeder upon benthonic animals of quite various kinds, occasionally it may even be necrophagous.

The influence of starvation on the survival and growth of larvae of the zuwai crab, Chionoecetes opilio, were investigated in the laboratory. Out of 150 newly hatched individuals of zoea reared without food, about 80 per cent of them survived for 7 days, but none of them lived longer than 18 days. Fifty zoeas of the second stage administered sufficient food during the first stage were also reared without food. More than 80 per cent of the zoeas to which no food was given survived for 12 days, but none of them lived longer than 18 days. The initial delay of feeding brought about the prolongation of the intermolt period. The period of the prolongation was almost equal to the duration of delay of feeding, if its duration was within a week. On the other hand, in the case of delay beyond 7 days a longer prolongation than the period of the initial delay resulted. If the larvae were starved for 14 days, all the animals died within 20 days without molt.

The haemocyanins of Erimacrus isenbeckii, Paralithodes camtschaticus and Chionoecetes opilio were examined for starch gel electrophoretic patterns in order to contribute to their classification. There were detected 4, 3, and 5 components for E. isenbeckii, p. camtschaticus and C. opilio, respectively. There was no difference between both sexes of E, isenbeckii.