© 2005 International Council for the Exploration of the Sea
First report of sablefish in spawning condition off the coast of Kamchatka and the Kuril Islands
a Russian Federal Research Institute of Fisheries and Oceanography (VNIRO) Moscow 107140, Russian Federation
b Sakhalin Research Institute of Fisheries and Oceanography (SakhNIRO) Yuzhno-Sakhalinsk 693016, Russian Federation
*Correspondence to A. M. Orlov: tel: +7 (095) 264 9143; fax: +7 (095) 264 9187. e-mail: orlov{at}vniro.ru.
The population status of sablefish Anoplopoma fimbria (Anoplopomatidae) inhabiting the Asian coast of the western North Pacific is still uncertain, with no direct observations of sablefish spawning. This paper describes the first capture of pre-spawning and spawning individuals in Pacific waters off the Kuril Islands and Kamchatka, suggesting that sablefish spawning may occur on the southwestern edge of their range. Traditionally these areas have not been considered as suitable sablefish habitat. The spatial distribution of sablefish during pre-spawning periods suggests the use of quasistationary eddies. Further study of juvenile sablefish presence and survival will require ichthyoplankton surveys, and elucidation of population status of sablefish inhabiting the study area will require genetic investigation.
Keywords: Kamchatka, Kuril Islands, North Pacific, sablefish, spawning
Received 30 June 2004; accepted 4 March 2005.
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Introduction |
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The sablefish Anoplopoma fimbria (Pallas 1814) is an endemic species of the North Pacific and is a common component of the ichthyofauna in the inshore waters of the Northeast Pacific (Novikov, 1961, 1969; Allen and Smith, 1988; Kodolov et al., 1991). The species has an uninterrupted range along the North American west coast, and from Honshu Island to the Okhotsk Sea and Bering Sea on the Asian side (Novikov, 1969, 1994; Hart, 1973; Sasaki, 1985; Kim, 2000). Sablefish are abundant in the eastern North Pacific and undergo notable long-term fluctuations in biomass (Sasaki, 1984).
There is a debate regarding the status of sablefish population inhabiting Asian waters. Kodolov (1986) believed that the species reaches the Bering Sea and eastern Kamchatka and the Kuril Islands on the Pacific side, from the Northeast Pacific; Asian waters are not considered suitable habitat for the species. Dudnik et al. (1998) suggest that sablefish stocks off east Kamchatka and Kuril Islands recruit from adult fish migrating from the Bering Sea along the continental slope and from young-of-the-year exported from Northeast Pacific waters. Another theory (Novikov, 1994) is that Asian waters, including the Okhotsk Sea, are permanently inhabited by sablefish and constitute an integral part of its North Pacific range.
Dudnik et al. (1998) recognized the possibility of sablefish spawning in this area but suggested that low water temperatures may obstruct normal development of larvae and juveniles. Conversely, Novikov (1994) asserts that observed juvenile survival in Asian waters demonstrate the ability of juvenile sablefish to adapt to low temperatures.
To date no direct observations of spawning sablefish have been made in Pacific waters off northern Kuril and southeastern Kamchatka. Dudnik et al. (1998) reported mature and post-spawned fish and males with remains of milt from this area. However, it is known that sablefish can make extensive horizontal migrations including those between western and eastern parts of the North Pacific (Sasaki, 1985; McFarlane and Saunders, 1997; Kimura et al., 1998; Tuponogov and Kodolov, 2001), so the reports made by Dudnik et al. (1998) may have resulted from the migration of mature fish from the Northeast Pacific. Tokranov (2002) describes milting sablefish males in catches from Kamchatkan waters without specifying the time and place of capture or other biological characteristics. As sablefish spawning in this area has yet to be conclusively demonstrated, any information is of interest. This paper presents recent data suggesting that sablefish spawning may occur in this area.
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Material and methods |
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TopIntroductionMaterial and methodsResults and discussionConclusionsReferences |
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Data presented in this paper are based on the capture of adult sablefish by bottom trawls in Pacific waters off the northern Kuril Islands and southeastern Kamchatka Islands during November–December 1997–2002 aboard chartered Japanese trawlers "Tomimaru No. 82" and "Tomimaru No. 53". Catch distribution was determined from the results of 74 bottom-trawl hauls, containing sablefish, conducted during this time period. Lengths and weights were measured for each specimen, and maturity was recorded. Gonad maturity is reported as follows: II – immature, III – developing, IV – ripe, and V – running.
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Results and discussion |
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TopIntroductionMaterial and methodsResults and discussionConclusionsReferences |
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From 1997 to 2002, 55 sablefish with maturity stages III–V were captured within the study area during the months of November and December (Table 1).
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In November and December 1997, 11 pre-spawning sablefish were collected from three hauls targeting deepwater fish. Two pre-spawning males were collected from the southernmost region of a plateau opposite the Shiashkotan–Harimkotan Islands on 7 December. On 28 December, one female was captured along with six males off the coast of southeastern Kamchatka. Three days later one female and one male were captured on the same plateau described for the 7 December catch. In general, males were smaller than females: average length and weight for males was 66.37 cm and 3.53 kg, respectively, compared with 79.75 cm and 6.8 kg for females.
On 31 December 1998, one pre-spawning female was captured.
On 30 December 2001, four male sablefish were collected. Three of the males contained fluid milt (running) and one male was pre-spawning with stage IV gonad maturity.
The biggest number of pre-spawning sablefish was caught in 2002. In all, 35 individuals were sampled from 238 captured during a haul targeting deepwater fish on 29 November. Twenty-one males were sampled; one-third contained fluid milt (running) and two-thirds were classified as maturity stage IV (Figure 1). The remaining 14 sampled were females; over half (57%) of these were at maturity stage III–IV. In general, females were larger than males. One pre-spawning male was captured on 19 December (Table 1), and two pre-spawning females were captured on 24 December. Gonadosomatic indices (GSI) for females captured on 24 December were 13.63 and 17.11, respectively, with the ovaries in the larger female occupying a larger proportion of the abdominal cavity (Figure 2). One pre-spawning female with GSI 16.34 was captured on 25 December.
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Results of the survey indicate that sablefish aggregations occur in three limited ranges (Figure 3): southeastern Kamchatka; south and central coast of Paramushir Island; and the eastern slope of a plateau southeast of Onekotan Island, in the southern extreme of the study area. The largest concentrations of sablefish (>100 fish per trawl) were found in the southeastern Kamchatka and plateau ranges. This observation is consistent with the suggestion that mature fish may be distributed evenly throughout the area during the feeding period (Orlov, 1997; Tokranov, 1997), then congregate within quasistationary eddies during the pre-spawning period (Orlov, 2000). This behaviour is typical of some species in the area which lay pelagic eggs and produce early juveniles (Orlov, 2003). In comparison with adjacent areas, eddies may improve reproductive success by protecting eggs and larvae from drifting and ensuring higher temperatures and higher concentrations of plankton (Orlov and Mandych, 2001).
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Near-bottom temperatures at capture sites ranged from 2.0°C to 4.2°C, with an average of 2.8°C. Most fish were captured in water temperatures of 2.6–3.0°C (44%) or 3.1–3.5°C (40.3%). Hatching of sablefish larvae off British Columbia occurs at temperatures around 6°C (McFarlane et al., 1997). Jensen et al. (1992) showed that sablefish eggs can be stored at 3–4°C for several days without significant loss in viability. Sogard and Olla (1998a, b) showed that juvenile sablefish are capable of surviving sharp temperature changes from 12°C to 2°C.
Sablefish larvae inhabit waters with different surface temperatures. Off the west coast of America they occur at 9.0–16.7°C, while in the southeast Bering Sea larvae can be found in 5.6–8.7°C water (Kodolov, 1968). Taking account of the fact that eddies can provide warmer conditions (several degrees higher) than surrounding waters (Orlov and Mandych, 2001) and the above mentioned adaptations to low temperatures, it is possible that successful sablefish spawning occurs in the Pacific waters off southeastern Kamchatka and northern Kuril Islands.
The state of the gonads in the sampled fish indicates that sablefish in the area start spawning in late December, ending in April–May. Fragmented coverage and shallow sets on the Pacific side of the Kuril and Kamchatka Islands between January and April 1992–2002 resulted in no collection of sablefish. A low occurrence of spawning individuals in trial catches may be explained by the observation that sablefish spawn at great depth, seawards of the continental slope (Kodolov, 1968).
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Conclusions |
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TopIntroductionMaterial and methodsResults and discussionConclusionsReferences |
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The capture of pre-spawning and spawning (free-flowing milt) sablefish off the Kuril and Kamchatka Islands and known sablefish adaptation to low temperatures suggest the possibility that sablefish spawn in this area. However, the presence and survival of larval and juvenile sablefish need to be confirmed by conducting target ichthyoplankton surveys. In addition, investigation of the population structure of sablefish in the area would benefit from appropriate genetic research. Despite the uncertainty, variations in sablefish abundance near the Asian coast (Sasaki, 1984) suggest that this is a population capable of reproducing only during periods of high abundance in the major breeding regions of the Northeast Pacific.
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References |
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