Dynamics of body size, age, and annual growth rate of Anadyr chum salmon Oncorhynchus keta in 1962–2010

Abstract

Interannual variability of body length, body weight, age structure, and seasonal growth rate of Anadyr chum salmon Oncorhynchus keta was studied using the monitoring data obtained in 1962-2010 in Anadyr River and Anadyr Firth. Body size of spawning adults has decreased significantly for the decade of 1990-2000s compared to the period of 1960-1970s, and the ratio of elder specimens was higher. Annual growth dynamics showed different patterns. Estimated from measuring intersclerite distances on scales, first year growth of Anadyr chum salmon samples collected in 1962 to 2007 was enhanced. After the first year, growth was reduced. The greatest reduction occurred in the third and forth years. Analysis of seasonal growth of scale evidences to the relaxation of the growth rates of Anadyr chum salmon after the first year of life pre conditioned by both the over wintering and foraging period. These data are in contradiction with the wide spread suggestion of decreasing of chum salmon body length during winter due to bad feeding conditions. According to the similarity of the dynamics of body length and growth rates of chum salmon and pink salmon O. gorbuscha observed for the last decades, we assume that this may be preconditioned by the same large scale limiting factors that affect similarly these salmon species inhabiting vast areas. Our data do not support the idea about high density population of chum salmon as a main factor affecting the productivity characteristics of this species in the northern Pacific Ocean in the second half of the 20th-beginning of the 21st century. Reasons for decrease of chum salmon body length are discussed.

Evidence for competition at sea between Norton Sound chum salmon and Asian hatchery chum salmon

“…This unexpected finding suggests that density-dependent effects involving abundance of hatchery chum salmon may have overwhelmed favorable growth conditions associated with warmer SST. Our results were consistent with other studies showing reduced length-at-age and delayed maturation of Japanese and Russian chum salmon during the past several decades in response to increasing abundance of hatchery chum salmon (Ishida et al 1993;Kaeriyama 1998;Zavolokin et al 2009). In contrast to total abundance of wild sockeye and pink salmon in the North Pacific Ocean, abundance of wild chum salmon did not increase after the ocean regime shift in the mid-1970s, possibly because the increasing abundance of hatchery chum salmon in the ocean led to reduced productivity of wild chum salmon Ruggerone et al 2010).…”

“…Hatchery chum salmon are much more numerous than other species of hatchery Pacific salmon. The large production of hatchery chum salmon in Asia was associated with a significant reduction in growth of Asian chum salmon (hatchery and wild) and delayed age-atmaturation (Ishida et al 1993;Kaeriyama 1998;Kaeriyama et al 2007;Zavolokin et al 2009). However, while some Russian scientists (Klovatch 2000;Zaporozhets and Zaporozhets 2004) claim that wild chum salmon in Russia have declined in response to increasing production of hatchery chum salmon in Asia, Morita et al (2006a) noted that there is little empirical evidence to support this claim.…”

Effect of population abundance and climate on the growth of 2 populations of chum salmon (Oncorhynchus keta) in the eastern North Pacific Ocean

“…GLS was the generalized least squares regression model. Growth indices included 1 st immature year (SW2), 2 nd immature year (SW3), and maturing (SW4) increasing body of growth studies on chum salmon populations from southcentral Alaska (Helle, 1979), western Alaska (Agler et al, 2013), Russia (Zavolokin et al, 2009), Japan (Kaeriyama et al, 2007), and Korea (Seo et al, 2006). Contrary to growth in the Asian populations, juvenile and maturing growth did not increase in the mid-1990s, indicating that productivity on the North American continental shelf remained relatively lower than that in the western Pacific Ocean.…”

“…Conversely, juvenile chum salmon released from Japan into the Sea of Okhotsk had lower growth from the late 1960s to the mid-1980s and higher growth from the mid-1980s to the mid-1990s, possibly because of reduced ice cover and warmer sea temperatures during summer and fall (Kaeriyama et al, 2007). Farther north in Russia, juvenile growth of chum salmon departing the Anadyr River was relatively stable from the early 1960s to the late 2000s, but slightly higher in the late 1990s (Zavolokin et al, 2009). The difference in the patterns in juvenile growth of chum salmon between the eastern and western Pacific Ocean populations indicates that conditions in the 1990s were more favorable for juvenile chum salmon in the western North Pacific than in the eastern North Pacific Ocean.…”

“…Our results are comparable to observed declines in body size of Hokkaido chum salmon in the mid-1980s that were linked to reduced growth during the 2 nd immature and maturing stages for years 1970-1994(Kaeriyama, 1998. Similarly, the reduction in the adult (mature) body size of chum salmon from the Anadyr River in Russia during the mid-1980s was linked to reduced growth in the immature and maturing stages (Zavolokin et al, 2009). Although the general trends in size at maturity from the 1970s to the 1990s were similar for different populations around the Pacific Ocean, the changes in adult size were linked to different developmental stages, namely the imma-ture and maturing life stages in the western Pacific and the juvenile, immature, and maturing life stages in the eastern Pacific.…”