Seasonal Growth Patterns of Wild Masu Salmon Parr in a Subarctic River

Transcription

1 National Taiwan Museum Special Publication No. 14: 87-93, 2010 Seasonal Growth Patterns of Wild Masu Salmon Parr in a Subarctic River Kentaro Morita 1*, Shoko H. Morita 1, and Toru Nagasawa 2 ABSTRACT Seasonal changes in the length and weight of wild masu salmon parr were examined in a subarctic river in northern Japan. Somatic growth of masu salmon parr greatly varied among seasons. Masu salmon parr increased in length and weight during the summer and did not grow or decreased in length and weight during the winter. Seasonal changes in specific growth rates generally corresponded to changes in temperature, but the peak specific growth rates occurred slightly earlier than temperature maxima. Seasonal changes in parr growth could be in response to seasonal changes in food availability and temperature. Keywords: body weight, salmonids, seasonal change, specific growth rate 1. Introduction How individuals change in length and weight over time is of central importance in fish biology. Many studies have examined the growth history of lotic salmonids including masu salmon Oncorhynchus masou (Nagata, 1989; Nakano et al., 1991; Kiso et al., 1992; Mayama, 1992; Takami et al., 1998). However, knowledge about seasonal variations in growth history, particularly during winter in ice-covered northern streams, is still limited. Studies from other geographic populations, under different biotic and environmental conditions, are needed for a more general understanding of masu salmon growth. The aim of this paper is to examine the seasonal growth patterns of wild masu salmon parr in a subarctic river in northern Japan. 2. Materials and Methods The field study was undertaken in two tributaries of the Shoro River, Hokkaido (43.1 N, E), the northernmost island of the Japanese archipelago. No records describing artificial releases of masu salmon into the Shoro River are known. To follow seasonal growth patterns of wild masu salmon parr, fish were collected monthly from Aug 2007 to Nov 2008 (16 months) using a backpack electrofisher ( V DC, Smith-Root, Inc., Vancouver). During the winter, fish were collected by breaking through the ice. A total of 2,101 masu salmon parr were collected during the study. Captured fish was anesthetized using phenoxyethanol; fork length 1 Hokkaido National Fisheries Research Institute, Fisheries Research Agency, Kushiro , Japan. 2 National Salmon Resources Center, Fisheries Research Agency, Sapporo , Japan *Corresponding author. moritak@affrc.go.jp

2 88 National Taiwan Museum Special Publication No. 14 was measured to the nearest 1 mm, and body weight was measured to the nearest 0.1 g. Almost all fish were released immediately at their capture sites after being measured. However, 4.3% of individuals were killed for age determination using otoliths. Water temperature was measured at hourly intervals by fixing data loggers (Stow-Away TidbiT, Onset Computer, Massachusetts) on the stream beds. Air temperature at the nearest observatory (Nakateshibetsu, 43.2 N E) was obtained from the Japan Meteorological Agency ( Details of the Shoro River system were described by Nagasawa et al. (2009). The age of masu salmon parr was categorized as 0+, 1+, and >2 years old based on length frequency histograms. Although the fork length distribution of age 0+ and older fishes overlapped after September, it was possible to separate age categories from length frequency histograms to a certain extent. A small discrepancy between ages from length frequency histograms and otolith-determined age was observed for the 90 killed fish (the percent agreement was 97.8%). Fish aged >2 and 1+ collected in 2007 were excluded from the analyses due to small sample sizes. In a separate study, masu salmon parr older than age 1+ usually represented less than 2% of anadromous populations (Morita and Nagasawa, submitted). The specific growth rate was calculated for each sampling interval as 100 (lnw 2 lnw 1 )/(t 2 t 1 ), where W 1 and W 2 are average body weight at times t 1 and t 2, respectively. Emigrating smolts were excluded for the calculation of the specific growth rate after smolting period. 3. Results Both 2007 and 2008 year classes of masu salmon parr grew during the study period (Fig. 1). The newly emerged 2008 year class recruited in April Masu salmon parr increased in length and weight during the summer and either did not grow or decreased in both length and weight during the winter (Fig. 1). Age 0+ fish showed high specific growth rates during the early summer and moderate specific growth rates in autumn, whereas positive specific growth rates of age 1+ fish were observed only in May July (Fig. 2). Age 1+ fish ceased to grow after late summer and showed a remarkable negative growth rate after autumn (Fig. 2). Seasonal changes in specific growth rates generally corresponded to changes in temperature, but the peak growth rates occurred slightly earlier than temperature peaks (Fig. 2). In addition, in 2008, specific growth rates showed a sharp decrease in August but slightly recovered in September.

3 Seasonal Growth Patterns of Wild Masu Salmon Parr in a Subarctic River 89 Fig. 1. Growth trajectories in (a) body weight and (b) fork length of masu salmon parr for the 2007 and 2008 year classes from Aug 2007 to Nov 2008 in the Shoro River. Sample sizes are provided near the data points. Error bars indicate standard deviations.

4 90 National Taiwan Museum Special Publication No. 14 Fig. 2. Seasonal changes in (a) the specific growth rate of masu salmon parr for the 2007 and 2008 year classes from Aug 2007 to Nov 2008 in the Shoro River and (b) hourly water and air temperatures as recorded by data loggers in a stream bed and the nearest meteorological observatory. 4. Discussion Somatic growth of masu salmon parr greatly varied among seasons. Most of their somatic growth occurred in the summer. Seasonal changes in parr growth could be in response to seasonal changes in food availability and temperature (cf. Utz and Hartman, 2009). Terrestrial and aquatic prey abundance are generally high in the summer, although seasonal patterns of prey abundance vary among rivers (e.g., Mayama, 1992; Nakano and Murakami, 2001; Rundio and Lindley, 2008). The growth rates of fishes initially increase with temperature, reach a maximum, and subsequently decrease with further temperature increases

5 Seasonal Growth Patterns of Wild Masu Salmon Parr in a Subarctic River 91 (Jobling, 2002). In an Appalachian brook trout (Salvelinus fontinalis) population, metabolic cost is highest in mid-summer, and energy intake (i.e., food consumption maintenance ration) is maximized in the early summer (Utz and Hartman, 2006, 2009). Consistent with our results, Takami et al. (1998) found that the specific growth rates of individually marked age 0+ masu salmon were high until July, declined in July and August, and increased in August and September. A mathematical study also indicated that growth rates of masu salmon parr change in one and three cycles annually (Kiso et al., 1992). Takami et al. (1998) suggested that the decrease in specific growth rate in summer could be due to thermal effects because high water temperatures may restrain feeding activity and the growth of juvenile masu salmon. Consistent with previous studies (Mayama, 1992; Takami et al., 1998; Kobayashi et al., 2007), we found that masu salmon parr cease to grow, and even decrease in weight, during the winter. Severe winters cause significant mortality for masu salmon (Mayama, 1995). Although our results suggest that winter is a severe season for masu salmon parr, our study was not adequate to address growth patterns during the winter. First, masu salmon parr often change their habitat along watercourses during winter (Inoue and Ishigaki, 1968; Kobayashi et al., 2007; Nagayama and Nakamura, 2007); therefore, the apparent growth trajectory at a given monitoring station may not represent the actual growth trajectory of a population. Second, if overwintering survival is size-dependent (Miyakoshi et al., 2003), winter growth would be overestimated. In conclusion, the growth rates of masu salmon parr change seasonally, and most of their growth occurs during summer. In addition to seasonal variation, parr growth could vary among localities and years (e.g., density-dependent growth; Nagata, 1989; Nagasawa et al., 2009). For a comprehensive understanding of the growth of masu salmon parr, it is necessary to survey whole river systems across seasons and years. Acknowledgements We thank M. Fukuwaka, N. Yamashita, K. Hattori, and J. Tsuboi for help with fieldwork. We also thank Mr. Konishi, Hokkaido Regional Forest Office, for permission to enter a state forest, and K. Ohkuma and Y. Okamoto, National Salmon Resources Center, for obtaining the sampling permit issued by the Governor of Hokkaido. This research was supported by a Grant-in-Aid for Young Scientists B (no ) from the Japan Society for the Promotion of Science. References Inoue, S. and K. Ishigaki Notes on the biology of juvenile masu salmon (Oncorhynchus masou) during winter in the Chihase River, Hokkaido. Jpn. J. Limnol., 29: (in Japanese) Jobling, M Environmental factors and rates of development and growth. In: Hart, P.J.B. and Reynolds, J.D. (eds.), Handbook of fish biology and fisheries. Vol. 1. Blackwell Science Ltd, pp Kiso, K., T. Akamine, S. Ohnishi and Y. Matsumiya Mathematical examinations of the growth of sea-run and fluviatile forms of female masu salmon Oncorhynchus masou in rivers of the southern Sanriku district, Honshu, Japan. Nippon Suisan Gakkaishi, 58: 1779-

6 92 National Taiwan Museum Special Publication No Kobayashi, M., K. Shimoda and K. Takeuchi Winter behavior of juvenile masu salmon (Oncorhynchus masou) in the stream of southwestern Hokkaido. Sci. Rep. Hokkaido Fish Hatchery, 61: (in Japanese with English summary) Mayama, H Studies on the freshwater life and propagation technology of masu salmon, Oncorhynchus masou (Brevoort). Rep. Hokkaido Salmon Hatchery, 46: (in Japanese with English summary.) Mayama, H Overwintering life of juvenile masu salmon in stream. Tech. Rep. Hokkaido Salmon Hatchery, 164: (in Japanese.) Miyakoshi, Y., H. Hayano, M. Fujiwara, M. Nagata and J.R. Irvine Size-dependent smolt yield and overwinter survival of hatchery-reared masu salmon released in fall. N. Am. J. Fish. Manage., 23: Nagasawa, T., K. Morita and J. Tsuboi Longitudinal distribution and changes in the fish fauna of a mid-scale river, Shoro River system, eastern Hokkaido, with notes on signal crayfish. Jpn. J. Ichthyol., 56: (in Japanese with English summary.) Nagata, M The occurrence of bimodality in the length frequency distribution and its relation to growth and density in a juvenile masu salmon population in a Hokkaido stream. Physiol. Ecol. Japan, Spec., 1: Nagayama, M. and F. Nakamura Juvenile masu salmon in a regulated river. River Res. Applic., 23: Nakano, S., T. Kachi and M. Nagoshi Individual growth variation of red-spotted masu salmon, Oncorhynchus masou rhodurus, in a mountain stream. Jpn. J. Ichthyol., 38: Nakano, S. and M. Murakami Reciprocal subsidies: dynamic interdependence between terrestrial and aquatic food webs. Proc. Natl. Acad. Sci. USA 98: Rundio, D.E. and S.T. Lindley Seasonal patterns of terrestrial and aquatic prey abundance and use by Oncorhynchus mykiss in a California coastal basin with a Mediterranean climate. Trans. Am. Fish. Soc. 137: Takami, T., T. Aoyama, M. Nagata, M. Miyamoto, S. Ohkubo and H. Kawamula Individual growth and life-history divergence of juvenile masu salmon (Oncorhynchus masou) in a northern Japanese stream. Sci. Rep. Hokkaido Fish Hatchery, 52: Utz, R.M. and K.J. Hartman Temporal and spatial variation in the energy intake of a brook trout (Salvelinus fontinalis) population in an Appalachian watershed. Can. J. Fish. Aquat. Sci., 63: Utz, R.M. and K.J. Hartman Density-dependent individual growth and size dynamics of central Appalachian brook trout (Salvelinus fontinalis). Can. J. Fish. Aquat. Sci., 66:

7 Seasonal Growth Patterns of Wild Masu Salmon Parr in a Subarctic River 93 河野生櫻鮭條紋幼魚在亞北極區河川的季節成長模式 森田健太郎 1 森田晶子 1 永永亨 2 摘要 本研究調查棲息於日本北部亞北極區河川中野生櫻鮭條紋幼魚之季節性體長與體重的變化 野生條紋幼魚的成長率隨季節變化, 變異極大 在夏季幼魚的體長和體重急速增加, 然而在冬季, 魚隻不但不增加體長和體重, 甚或負成長 專一成長率 (specific growth rate;sgr) 和溫度的改變相倚, 但最高 SGR 卻比最高溫早些些出現 條紋幼魚季節性成長之改變, 可能反應出可利用食物的季節性變化與溫度之升降 關鍵詞 : 體重 鮭科魚類 季節變化 特異成長率 1 水產綜合研究中心 - 北海道區水産研究所 日本 2 水產綜合研究中心 - 鮭鱒魚中心 日本

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