North American Journal of Fisheries Management 29:33–39, 2009 Ó Copyright by the American Fisheries Society 2009 DOI: 10.1577/M08-107.1
[Management Brief]
Implications of Recreational Fishing on Juvenile Masu Salmon Stocked in a Hokkaido River YASUYUKI MIYAKOSHI,* YOSHITAKA SASAKI,
AND
MAKOTO FUJIWARA
Hokkaido Fish Hatchery, 3-373 Kita-Kashiwagi-cho, Eniwa, Hokkaido 061-1433, Japan
KEIKO TANAKA
AND
NAOKAZU MATSUEDA
Fisheries Division, Industrial Promotion Department, Hokkaido Government Shiribeshi Subprefectural Office, Kita 1 Higashi 2, Kutchan, Abuta-Gun, Hokkaido 044-8588, Japan
JAMES R. IRVINE Canada Department of Fisheries and Oceans, Pacific Biological Station, 3190 Hammond Bay Road, Nanaimo, British Columbia V9T 6N7, Canada
SHUICHI KITADA Department of Marine Biosciences, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan
widely applied to fishery management (Guthrie et al. 1991; Kitada and Tezuka 2002). The masu salmon Oncorhynchus masou, a Pacific salmonid found only in the western portion of the North Pacific Ocean, is a valuable component of the coastal commercial fishery in northern Japan, especially in Hokkaido. To enhance commercially valuable but declining masu salmon populations, hatchery-reared juveniles are often stocked in rivers (Miyakoshi et al. 2004b). The masu salmon is also a popular target species for recreational fishing, both in freshwater (Ando et al. 2002; Ando and Miyakoshi 2003), and the nearshore marine environment (Miyakoshi et al. 2004a). Recreational fishing for age-0 masu salmon in streams, a traditional and popular pastime, can reduce the effectiveness of enhancement aimed at increasing commercial catches. Recent years have seen the introduction of freshwater fishing regulations in Hokkaido, including the following: (1) no fishing is allowed for adult masu salmon after they return to freshwater; (2) fishing for juvenile masu salmon is closed for 2 months in spring, when masu salmon smolts migrate to the ocean (April and May in southern Hokkaido; May and June in northern Hokkaido); (3) fishing is prohibited in 32 rivers in Hokkaido; and (4) river-specific regulations apply to several rivers. Where the freshwater fishing regulations do not apply, one can fish for masu salmon in rivers without any license and there is no bag limit. Hatchery-reared masu salmon are stocked into Hokkaido rivers at various life stages (e.g., age-0 fry reared for 1–2 months, age-0 juveniles reared for 6–7 months, and age-1 smolts reared for 12–13 months). Stocking of fry is typically cost effective because the
Abstract.—Freshwater recreational anglers in northern Japan sometimes catch significant numbers of juvenile masu salmon Oncorhynchus masou, thereby reducing the effectiveness of enhancement activities aimed at increasing marine catches of adult masu salmon. We stocked 66,500 juvenile masu salmon in the Shirai River, a major tributary of the Yoichi River in Hokkaido, northern Japan, during October 2005. Surveys conducted during the month after stocking revealed that approximately 65 fish/angler-day were caught, and catch varied between fishing gears (bait or fly) and locations (upper or lower reach). Estimated total number (mean 6 SE) of fish harvested was 5,647 6 2,394, equivalent to 8.5 6 3.6% of the fish stocked. The estimated number of fish remaining in the river at the end of the angler survey was 57,246 6 8,595, and survival rate during this month was 86.1 6 12.9%. While releasing hatchery-reared masu salmon in late fall can reduce fishing mortality in rivers compared with earlier releases, mortality could be further reduced by dispersing fish over large areas that contain locations with suitable overwintering habitat.
Stock enhancement programs are conducted for many marine fish species to increase commercial catches. For many of the enhanced fish species, hatchery-reared fish are caught by recreational anglers, and therefore assessing the recreational catches is often an inevitable component in evaluating survival of stocked fish and stocking effectiveness. Angler survey methods have been scientifically studied and reviewed (Pollock et al. 1994; Kitada 2001) and have been * Corresponding author:
[email protected]. hokkaido.jp Received May 1, 2008; accepted July 30, 2008 Published online February 23, 2009
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MIYAKOSHI ET AL.
rearing period is shortest (Miyakoshi et al. 2001), but stocked fish are vulnerable to capture by freshwater recreational anglers and other sources of mortality. Ando et al. (2002) reported that 65% of age-0 fish stocked in spring were caught during summer in an urban stream in central Hokkaido. Of the three stocking strategies, stocking of smolts is biologically most effective because fish leave the river immediately after stocking, thus minimizing freshwater mortality (Ando and Miyakoshi 2003). However, recent studies on stock enhancement of masu salmon in Hokkaido indicated that cost effectiveness of smolt stocking is less than that of fry stocking because the rearing period is longest and production cost is highest (Miyakoshi et al. 2004b; Miyakoshi 2006). Stocking of age-0 masu salmon parr during the fall when the fishing season is almost finished is an intermediate strategy to reduce fishing mortality in freshwater and to reduce production costs in hatcheries. This strategy has been common since the 1980s, and stocking effectiveness was recently reported as almost twice that of fry stocking (Miyakoshi et al. 2006). Since fishing mortality of fall-stocked masu salmon had not been previously assessed, we conducted on-site surveys to estimate juvenile masu salmon catches in a recreational fall fishery in a Hokkaido river where hatchery-reared masu salmon had recently been stocked. Methods Study area and stocking of hatchery-reared masu salmon.—We assessed the recreational fishery in the Shirai River, a major tributary of the Yoichi River in Hokkaido, northern Japan. The 18.6-km Shirai River enters the Yoichi River 30 km from the ocean. There is a 5-km paved road along the lower Shirai River and a good footpath beyond. Since much of the river is accessible, it is visited by many recreational anglers and other outdoor enthusiasts. The Shirai River is one of the most famous fishing areas in central Hokkaido. An impassible waterfall located approximately 7 km upstream from the confluence marked the upper boundary of our study area. The wetted width of the river ranged between 10 and 20 m. On 18 and 19 October 2005, 66,500 age-0 masu salmon from the Chihase Salmon Hatchery in the Shimamaki Village were stocked at four sites along the Shirai River. Mean (6SD) fork length (FL) and weight of stocked fish were 9.9 6 1.0 cm and 11.1 6 3.3 g, respectively. Among stocked fish, 20,000 fish that were introduced at site 3 (Figure 1) had been previously marked by clipping an upper lobe of the caudal fin.
Estimation of fish caught by recreational anglers.— Total numbers of anglers were estimated by counting them at 2–7-d intervals, which were selected randomly. Since more anglers were expected on weekend days than on weekdays, survey days were chosen to include both weekdays and weekend days. On each survey day, we recorded numbers of anglers from 0700 hours (1 h after dawn) until late afternoon, when virtually all anglers had left the study area. On 11 and 12 November 2005, the area was covered with snow, making access to the river difficult. Few anglers visited the river on or after these 2 d, and we therefore finished our surveys. To estimate catch rate, we interviewed anglers to determine (1) fishing gear type (bait, fly, and others), (2) number of fish caught (captured and kept or released), and (3) fishing time. We also counted the number of juvenile masu salmon in the catch and recorded numbers of hatchery-reared fish and naturally spawned fish, which we were able to differentiate based on body shape and colors. Hatchery-reared fish typically had edges of fins that were rubbed and roundish, and their body colors were duller than those of wild fish. Marked fish from the upper site (site 3; Figure 1) were also recorded separately. We strived to interview anglers when they finished fishing; however, some anglers continued fishing after we interviewed them. In such cases, numbers caught were expanded by the duration of additional fishing time in the roving creel survey design (Pollock et al. 1994). Numbers of juvenile masu salmon captured were estimated (Cochran 1977; Kitada 2001) using formulae described below, where D ¼ total number of fishing days during the survey period, d ¼ number of fishing days surveyed, M ¼ total number of recreational anglers during the survey period, mi ¼ number of recreational anglers on the ith day, m ¼ mean number of recreational anglers, Y ¼ total number of fish caught by recreational anglers, yj ¼ number of fish caught by the jth angler, n ¼ number of anglers interviewed for catch, R ¼ catch rate (number of fish caught per angler-day), and Cov ¼ covariance. The unbiased estimator for number of anglers was calculated as ˆ ¼D M d
d X
mi ¼ Dm;
ð1Þ
i¼1
and the variance for the estimator was calculated as X ðmi mÞ2 ˆVðMÞ ˆ ¼ D2 D d : ð2Þ D 1 dðd 1Þ The estimator and variance for catch rate were determined by
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MANAGEMENT BRIEF
FIGURE 1.—Location of the Shirai River, a major tributary of the Yoichi River in Hokkaido, northern Japan. Solid arrows indicate sites that were stocked with juvenile masu salmon on 18–19 October 2005; hatched arrow indicates site 3, where finclipped masu salmon were stocked. Circles represent fishing sites for each angler on survey days (open circles ¼ bait anglers, black circles ¼ fly fishers).
1 Rˆ ¼ n
n X
ð3Þ
yj ;
j¼1
and n X ˆ 2 ðyj RÞ
ˆ RÞ ˆ ¼ Vð
j¼1
nðn 1Þ
:
ð4Þ
Total number of fish caught during the survey period was estimated by ˆ R: ˆ Yˆ ¼ M
ð5Þ
Variances for total numbers of fish caught were asymptotically estimated by the delta method (Seber 1982) as follows: ˆ RÞ ˆ þ Rˆ 2 Vð ˆ MÞ ˆ þ 2M ˆ Rˆ CovðM; ˆ RÞ: ˆ ˆ YÞ ˆ ffiM ˆ 2 Vð ð6Þ Vð Here, M and R are estimated in the same survey, and in such a case the covariance of M and R is often negative; in other words, catch rates often decreased when many anglers visited the fishing site. Since it is difficult to realistically estimate covariance, we ignored it, which resulted in high variance estimates and a conservative precision level. Fish remaining in the river after the angler survey was completed.—To estimate numbers of fish remaining in the river after the angler survey was completed,
we conducted a two-stage sampling survey (Hankin 1984) on 11 and 12 November 2005. For the first stage, we randomly selected five stream reaches of equal length (20 m). For the second stage, we used the double-pass removal method (Seber and Le Cren 1967) to estimate the numbers of fish in each of the stream reaches. Each pass consisted of initial samples taken using cast nets and subsequent samples collected using an electrofisher. To estimate total numbers of fish, we multiplied the mean number of fish in the survey reaches by the total number of 20-m sampling units accessible to masu salmon in the river. Variances for the total numbers of fish were generated. Each variance estimate had two components: (1) variation in numbers of fish among survey reaches and (2) variance of removal estimates within the survey reaches (Hankin 1984). When variance arising from variation among survey reaches was extremely large, the total study reach was stratified to reduce the variance. Estimates and variances were generated separately for each stratum, and total numbers were then obtained by summing the estimates and variances for each stratum. Results Number of Anglers During the 25 d poststocking, anglers were censused on 6 d, including three weekdays and three weekend days (Figure 2). The mean number of anglers on the
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MIYAKOSHI ET AL.
2.041, df ¼ 8, P ¼ 0.076). The catch rate for fly fishers in the lower reach (29.3 fish/angler-day) was lower than that for bait anglers in the same reach (48.0 fish/ angler-day), although the difference was not significant (t ¼ 0.589, df ¼ 10, P ¼ 0.569). Bait anglers kept all of the fish they captured, whereas fly fishers retained few of the fish they captured. Of the six fly fishers interviewed, four released all fish captured. When data from the six fly fishers were pooled, the mean number of masu salmon kept by fly fishers was 9.7 fish, which translates to onethird of the fish caught (Figure 3). FIGURE 2.—Number of recreational anglers observed on each day in the study reach of the Shirai River, Hokkaido, Japan, during fall 2005. Weekdays (open circles) and weekend days (black circles) are indicated.
survey days was 4.3. When weekdays and weekend days were averaged separately, means were 3.3 anglers/d for weekdays and 5.3 anglers/d for weekend days, but the difference was not significant (t ¼ 0.744, df ¼ 4, P ¼ 0.498). Most of the anglers started fishing in the morning, but a few started in the afternoon. Anglers who arrived in the morning typically started fishing at around 0600 hours (immediately after dawn), and those who arrived later started fishing at around 1300 hours. Fishing time varied among anglers, ranging from 1.5 to 7.0 h. On the six survey days, some anglers were repeatedly observed; 14 anglers were observed once, three anglers were observed twice, and two anglers were observed three times. Thus, of the 26 anglers observed during our on-site surveys, 12 (46%) were repeat visitors. Seven (27%) anglers were fly fishers, and 19 anglers (73%) fished with bait. One fly fisher used Tenkara, the traditional Japanese fly-fishing method, which requires a rod and an artificial fly but no reel. Many of the anglers in the survey reach were seen in the lower half, where access is easier and riparian cover is sparse. All observed fly fishers were in the lower part of the survey reach (Figure 1). Catch Rate Catch rate, including fish caught and released, was 64.9 fish/angler-day. Numbers of fish caught by anglers ranged from 6 to 223 fish/d, and an increase or decrease in catch was not observed during the 25-d poststocking period. Catch rate differed by fishing gear type and location within the survey reach (Figure 3). Catch rate of bait anglers was higher in the upper reach (143.5 fish/ angler-day) than in the lower reach (48.0 fish/anglerday); however, the difference was not significant (t ¼
Number of Masu Salmon Caught by Recreational Anglers The estimated number (mean 6 SE) of hatcheryreared masu salmon caught by recreational anglers was 6,167 6 2,604. When fish caught and released were excluded, the estimated number of hatchery-reared masu salmon retained was 5,647 6 2,394, equivalent to 8.5 6 3.6% of the number of fish stocked (Table 1). When data were stratified by fishing gear type and location, more anglers fished in the lower reach but the catch rate was higher in the upper reach, and as a result, numbers of fish kept were very similar between the two reaches (Table 1). Because the catch rate of fly fishers was lower and their release rate was higher, the estimated number of fish kept by fly fishers was less than 5% of the total number of fish kept in the survey reach (Table 1). Marked fish stocked in the upper reach (Figure 1, stocking site 3) were captured near the stocking site; based on the stratification by fishing gear type and location, the estimated number of marked fish kept was 1,339 6 1,161, equivalent to 6.7 6 5.8% of the number of fish stocked. Naturally spawned fish and hatchery-origin fish that had been stocked in spring, which could not be distinguished from each other, were also caught by recreational anglers; the estimated number caught was 582 6 338. Fish Remaining in the River after the Angler Survey was Completed When the survey ended at 25 d poststocking, estimated densities of hatchery-reared masu salmon ranged from 0.8 to 124.7 fish/100 m2. The extreme high densities of masu salmon were observed near the stocking site in the upper reach (108.8 and 124.7 fish/ 100 m2), whereas lower densities were found in the lower reach (0.8–26.5 fish/100 m2). Therefore, the study reach was stratified into the upper and lower reaches, and population estimates were then generated. The estimated number (mean 6 SE) remaining in the survey reach was 57,246 6 8,595 marked fish, of
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MANAGEMENT BRIEF
FIGURE 3.—Mean (6SE) number of masu salmon that were caught by recreational anglers (bait anglers or fly fishers) in upper and lower reaches of the Shirai River, Hokkaido, Japan, during fall 2005; the number of fish that were kept or released is indicated.
which 16,309 6 15,515 fish had been stocked in the upper reach (Table 1). From these results, we estimate that more than 80% of the stocked fish survived and remained in the river. Discussion This study represented an aspect of the recreational fishery for masu salmon in Japan. In the fishery, baitfishing is traditionally dominant and anglers target stream-resident masu salmon (including age-0 fish) using a fine tackle, although fishing with flies and lures has recently become more popular. This kind of bait fishery is uncommon in North America and other areas where fly or lure fishing is common. Catch and release is a usual practice for anglers using flies or lures, but bait anglers often retain most of the fish they catch. The on-site surveys reported here confirmed these features of Japanese recreational fisheries. During fall 2005 in the Shirai River, the mean number of anglers fishing for juvenile masu salmon
was 4.3 anglers/d. Catch rates were high, averaging 65 fish/angler-day. There was no obvious poststocking increase in anglers, although such increases have been observed elsewhere when information on fish stocking was known. However, repeat anglers were observed and some of them knew that hatchery-reared fish had recently been stocked. This contrasts with a summer recreational fishery for juvenile masu salmon assessed by Ando et al. (2002), although a direct comparison is not possible because their survey was conducted at a different site. In the study by Ando et al. (2002), catch rate was low (6.8 fish/angler-day), but many anglers (10 anglers on weekdays and 28 anglers on weekend days) visited the 8.5-km survey reach during a longer (134-d) fishing season and as a result 65% of stocked fish were caught. Recreational harvest of hatchery-reared masu salmon stocked in October was approximately 8.5% of the total number of fish stocked. Stocking of fish in fall rather than spring or summer effectively reduced recreational
TABLE 1.—Number of hatchery-reared juvenile masu salmon released; estimated number of anglers (using baitfishing or flyfishing gear), number of fish harvested, and fishing mortality during the first 25 d poststocking; and estimated number of fish remaining at the end of the study period during fall 2005 in upper and lower reaches of the Shirai River, Hokkaido, Japan. Fish that were marked with fin clips were only released into the upper reach; all other fish were unmarked.
Estimate type
Number of fish released on 18–19 Oct
Total stocked All gears and sites combined 66,500 Baitfishing in upper reach Fly-fishing in upper reach Baitfishing in lower reach Fly-fishing in lower reach Total Fin-clipped fish stocked in the upper reach only Baitfishing in upper reach 20,000
Total number of anglers
Total number of fish harvested
Fishing mortality (%)
Number of fish remaining in the river on 12 Nov
Estimate
SE
Estimate
SE
Estimate
SE
Estimate
SE
108 21 0 21 29 108
29 15 0 17 9 24
5,647 2,620 0 2,683 267 5,570
2,394 1,919 0 1,960 204 2,751
8.5 3.9 0.0 4.0 0.4 8.4
3.6 2.9 0.0 2.9 0.3 4.1
57,249
8,595
21
15
1,339
1,161
6.7
5.8
16,309
15,515
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MIYAKOSHI ET AL.
fishing mortality. However, fishing pressure and catchability differ among rivers and reaches; for example, in this study numbers of anglers and catch rates differed between the upper and lower reaches. In the upper reach during mid-November, many hatcheryreared fish were seen and captured in pools, and fish densities were extremely high (.100 fish/100 m2). A bait angler visiting such a site can catch a large number of fish. Fly fishers had a lower catch rate and a higher release rate than bait anglers; therefore, fly fishers caused lower fishing mortality of hatchery-reared masu salmon than did bait anglers. As river water temperature decreases in the fall– winter transition, juvenile masu salmon shift to habitats with slow current and abundant cover (Inoue and Ishigaki 1968; Suzuki et al. 2000; Miyakoshi et al. 2002). When hatchery-reared juvenile masu salmon were stocked in fall, most fish remained near the stocking site (Mayama 1992). If stocked masu salmon cannot find and occupy favorable overwintering habitats immediately after release, poststocking survival may be poor. To improve stocking effectiveness for marine fisheries, we recommend that stocked fish be dispersed over relatively large areas and that release sites within these areas be chosen based on the presence of good overwintering habitats. The fall stocking strategy is superior to fry stocking in terms of reducing recreational fishing mortality, but poststocking survival could be reduced unless appropriate numbers of fish are stocked at favorable sites. In Hokkaido, recreational anglers catch masu salmon at various life history stages; therefore, understanding the implications of recreational fisheries is important for proper management of masu salmon stocks. However, only a few scientific studies have evaluated recreational fishing effects on masu salmon (Ando et al. 2002; Ando and Miyakoshi 2003; Miyakoshi et al. 2004a). Most hatchery-reared masu salmon are stocked to increase catches in commercial marine fisheries, and freshwater recreational fisheries targeting juvenile masu salmon can reduce stocking effectiveness. Fishing is a popular outdoor recreational activity and an important social and economical activity that has biological effects on characteristics of the target species and the surrounding aquatic ecosystem (Lewin et al. 2006). The features of the recreational fishery for young masu salmon are different from those for salmon species in North America. To properly manage declining masu salmon stocks, additional scientific evaluation of recreational catches for this species is needed. Acknowledgments We thank the staff of the Shiribeshi Salmon Stock Enhancement Conference, the Shimamaki Village
Office, the Chihase Salmon Hatchery, and the Yoichi-gun Fisheries Cooperative Association for rearing and stocking hatchery-reared masu salmon. We are grateful to the staff of the Fisheries Division, Hokkaido Government Shiribeshi Subprefectural Office, for their assistance in the census of recreational anglers. We also acknowledge the anonymous reviewers, who provided helpful comments that improved the manuscript. References Ando, D., and Y. Miyakoshi. 2003. Estimates of catch numbers by recreational fishing for masu salmon smolts stocked in the lower area of a river. Scientific Reports of the Hokkaido Fish Hatchery 57:49–53. (In Japanese with English abstract.) Ando, D., Y. Miyakoshi, K. Takeuchi, M. Nagata, T. Sato, S. Yanai, and S. Kitada. 2002. Estimates of numbers of juvenile masu salmon Oncorhynchus masou caught by recreational anglers in an urban stream. Nippon Suisan Gakkaishi 68:52–60. (In Japanese with English abstract.) Cochran, W. G. 1977. Sampling techniques, 3rd edition. Wiley, New York. Guthrie, D., J. M. Hoenig, M. Holliday, C. M. Jones, M. J. Mills, S. A. Moberly, K. H. Pollock, and D. R. Talhelm. 1991. Creel and angler surveys in fisheries management. American Fisheries Society, Symposium 12, Bethesda, Maryland. Hankin, D. G. 1984. Multistage sampling designs in fisheries research: applications in small streams. Canadian Journal of Fisheries and Aquatic Sciences 41:1575–1591. Inoue, S., and K. Ishigaki. 1968. Notes on the biology of juvenile masu salmon (Oncorhynchus masou) during winter in the Chihase River, Hokkaido. Japanese Journal of Limnology 29:27–36. (In Japanese with English abstract.) Kitada, S. 2001. Fish stock enhancement assessment with Japan examples. Kyoritsu-Shuppan, Tokyo. (In Japanese.) Kitada, S., and K. Tezuka. 2002. Longitudinal logbook survey designs for estimating recreational fishery catch, with application to ayu (Plecoglossus altivelis). U.S. National Marine Fisheries Service Fishery Bulletin 100:228–243. Lewin, W.-C., R. Arlinghaus, and T. Mehner. 2006. Documented and potential biological impacts of recreational fishing: insights for management and conservation. Reviews in Fisheries Science 14:305–367. Mayama, H. 1992. Studies on the freshwater life and propagation technology of masu salmon, Oncorhynchus masou (Brevoort). Scientific Reports of the Hokkaido Salmon Hatchery 46:1–156. (In Japanese with English summary.) Miyakoshi, Y. 2006. Evaluation of stock enhancement programs and stock assessment for masu salmon in Hokkaido, northern Japan. Scientific Reports of the Hokkaido Fish Hatchery 60:1–64. (In Japanese with English summary.) Miyakoshi, Y., H. Hayano, H. Omori, M. Nagata, and J. R. Irvine. 2002. Importance of instream cover for young
MANAGEMENT BRIEF
masu salmon, Oncorhynchus masou, in autumn and winter. Fisheries Management and Ecology 9:217–223. Miyakoshi, Y., T. Koyama, T. Aoyama, S. Sakakibara, and S. Kitada. 2004a. Estimates of numbers of masu salmon caught by recreational fishermen in the coastal area off Iburi, Hokkaido, Japan. Fisheries Science 70:87–93. Miyakoshi, Y., M. Nagata, K. Sugiwaka, and S. Kitada. 2004b. Evaluation of stock enhancement programs for masu salmon in Hokkaido, northern Japan, by two-stage sampling surveys of commercial landings. Pages 187– 198 in K. M. Leber, S. Kitada, H. L. Blankenship, and T. Sva˚sand, editors. Stock enhancement and sea ranching, developments, pitfalls and opportunities, 2nd edition. Blackwell Scientific Publications, Oxford, UK. Miyakoshi, Y., M. Nagata, K. Takeuchi, K. Sugiwaka, and S. Kitada. 2001. Effectiveness of stocking masu salmon Oncorhynchus masou fry as a means of increasing commercial catches. Fisheries Science 67:1184–1186.
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Miyakoshi, Y., K. Takeuchi, D. Ando, T. Kitamura, and M. Nagata. 2006. Stocking effectiveness of hatchery-reared masu salmon stocked in fall. Aquaculture Science 54:407–408. (In Japanese with English abstract.) Pollock, K. H., C. M. Jones, and T. L. Brown. 1994. Angler survey methods and their applications in fisheries management. American Fisheries Society, Special Publication 25, Bethesda, Maryland. Seber, G. A. F. 1982. Estimation of animal abundance and related parameters, 2nd edition. Griffin, London. Seber, G. A. F., and E. D. Le Cren. 1967. Estimating population parameters from catches large relative to the population. Journal of Animal Ecology 36:631–643. Suzuki, K. T., M. Nagata, M. Nakajima, and H. Omori. 2000. Microhabitat and physical environment of wintering juvenile masu salmon in northern Hokkaido stream. Scientific Reports of the Hokkaido Fish Hatchery 54:7– 14. (In Japanese with English abstract.)
