355 



Abstract— Recent research demon- 

 strated significantly lower growth 

 and survival of Bristol Bay sockeye 

 salmon (Oncorhynchus nerka) during 

 odd-numbered years of their second 

 or third years at sea (1975, 1977, 

 etc.). a trend that was opposite that 

 of Asian pink salmon (O. gorbuscha) 

 abundance. Here we evaluated sea- 

 sonal growth trends of Kvichak and 

 Egegik river sockeye salmon (Bristol 

 Bay stocks) during even- and odd- 

 numbered years at sea by measur- 

 ing scale circuli increments within 

 each growth zone of each major 

 salmon age group between 1955 and 

 2000. First year scale growth was 

 not significantly different between 

 odd- and even-numbered years, but 

 peak growth of age-2. smolts was sig- 

 nificantly higher than age-1. smolts. 

 Total second and third year scale 

 growth of salmon was significantly 

 lower during odd- than during even- 

 numbered years. However, reduced 

 scale growth in odd-numbered years 

 began after peak growth in spring 

 and continued through summer and 

 fall even though most pink salmon 

 had left the high seas by late July 

 (10-18% growth reduction in odd vs. 

 even years). The alternating odd and 

 even year growth pattern was consis- 

 tent before and after the 1977 ocean 

 regime shift. During 1977-2000, 

 when salmon abundance was rela- 

 tively great, sockeye salmon growth 

 was high during specific seasons com- 

 pared with that during 1955-1976, 

 that is to say. immediately after entry 

 to Bristol Bay, after peak growth in 

 the first year, during the middle of the 

 second growing season, and during 

 spring of the third season. Growth 

 after the spring peak in the third 

 year at sea was relatively low during 

 1977-2000. We hypothesize that high 

 consumption rates of prey by pink 

 salmon during spring through mid- 

 July of odd-numbered years, coupled 

 with declining zooplankton biomass 

 during summer and potentially cyclic 

 abundances of squid and other prey, 

 contributed to reduced prey availabil- 

 ity and therefore reduced growth of 

 Bristol Bay sockeye salmon during 

 late spring through fall of odd-num- 

 bered years. 



Manuscript submitted 7 April 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



14 December 2004 by the Scientific Editor. 



Fish. Bull. 103:355-370 (2005). 



Seasonal marine growth of Bristol Bay 

 sockeye salmon (Oncorhynchus nerka) 

 in relation to competition with Asian pink salmon 

 (O. gorbuscha) and the 1977 ocean regime shift 



Gregory T. Ruggerone 



Natural Resources Consultants, Inc. 

 1900 West Nlckerson Street. Suite 207 

 Seattle, Washington 98(19 

 E-mail address GRuggeronein'nrccorp.com 



Ed Farley 



National Marine Fisheries Service 

 11305 Glacier Highway 

 Juneau, Alaska 99801 



Jennifer Nielsen 



Biological Resources Division 

 U.S. Geological Survey 

 Anchorage, Alaska 99503 



Peter Hagen 



Alaska Dept. of Fish and Game 



P.O. Box 25526 



Juneau, Alaska 99802-5526 



Competition among Pacific salmon 

 {Oncorhynchus spp.) for food resources 

 in the North Pacific Ocean and Bering 

 Sea is a potentially important mech- 

 anism affecting salmon growth and 

 population dynamics. Reduced growth 

 at sea may lead to delayed matura- 

 tion (Rogers, 1987), lower reproductive 

 potential (Groot and Margolis, 1991), 

 or greater risk of predation (Juanes, 

 1994). 



Density-dependent growth in the 

 ocean has been observed among sock- 

 eye (O. nerka), pink (O. gorbuscha), 

 and chum salmon (O. keta), which are 

 the most abundant species among Pa- 

 cific salmon (Rogers 1 ; Eggers et al. 2 ). 

 Density-dependent growth may occur 

 during early marine life (Peterman, 

 1984) or during the homeward mi- 

 gration period when the potential for 

 high growth rate (Ishida et al., 1998) 

 may be influenced by high concen- 

 trations of salmon (Rogers and Rug- 

 gerone, 1993). 



Since the early 1970s, salmon 

 abundance in the North Pacific Ocean 

 has increased, whereas body size for 

 many populations of all salmon spe- 

 cies has declined (Bigler et al., 1996). 

 However, greater abundance of adult 

 sockeye salmon returning to Bristol 

 Bay, Alaska, was associated with in- 

 creased growth during the first and 

 second years at sea, followed by rela- 

 tively low growth during the third 

 year at sea, and greater adult size at 

 a given abundance (Ruggerone et al.. 



1 Rogers, D. E. 2001. Estimates of 

 annual salmon runs from the North 

 Pacific, 1951-2001. Report SAFS-UW- 

 0115. 11 p. School of Aquatic Sciences, 

 Univ. Washington, Seattle, WA. 



2 Eggers, D. M, J. Irvine, M. Fukawaki, 

 and V. Karpenko. 2003. Catch trends 

 and status of North Pacific salmon. Doc. 

 no. 723, 34 p. North Pacific Anadromous 

 Fisheries Commission (NPAFC), 889 

 Pender Street, Vancouver, Canada. 



