Factors that Affect the First Year Growth of Chum Salmon Released from Japanese Hatcheries

• Main Author: Toshihiko Saito
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Chum salmon; first year growth; hatcheries; sea surface temperature; Bering Sea; Pacific
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.528.5262; http://www.npafc.org/new/publications/Technical Report/TR6/page 98-99(Saito).pdf

Increased abundance has been related to reduced adult size in a number of studies from the mid-1960s to the mid-1990s (Kaeriyama 1989, 1998, 1999; Ishida et al. 1993; Bigler et al. 1996). The authors suggested that density-dependent processes play important roles in regulating their ocean growth because these reductions in size occurred simultaneously in geographically widespread populations. However, salmon abundance is generally thought to be determined during their coastal residence period (e.g., Mueter et al. 2002). Accordingly, salmon abundance in the Bering Sea would be related to the abundance of survivors in the coastal waters. From this point of view, the density-dependent growth in the Bering Sea would also be related to the coastal events in different regions of the Pacific Rim. Thus, studies of density-dependent processes during the early ocean life of salmon are indispensable. In the present study, year-to-year variations in growth at age 0.1 (hereafter the first year growth) were investigated using age 0.3 chum salmon of 1977–1999 brood years returning to five rivers (Ishikari, Shari, Nishibetu, Tokachi, and Yurappu Rivers) in Hokkaido, Japan. The first year growth of individual fish was estimated by their scale increments at age 0.1 (i.e., radius at the first annulus). Scale measurements were conducted using a microscope ( × 25) equipped with a scale measurement system (ARP/W, Version 3.20. Ratoc system engineering Co. Ltd., Tokyo, Japan). The measurements were directly used as an indicator for the first year growth of individual fish. Although sample size varied from six to 114