The Influence of Hatchery Rearing Practices on Salmon Migratory Behavior: Is the Tendency of Chinook Salmon to Remain within Puget Sound Affected by Size and Date of Release?

Abstract

The marine migrations of Pacific salmon Oncorhynchus spp., and especially Chinook salmon O. tshawytscha, vary greatly in duration and spatial extent. In Puget Sound, Washington, most Chinook salmon migrate from freshwater to the coastal waters of the Pacific Ocean before returning to spawn in their natal streams. However, some leave freshwater but remain in the semi‐estuarine waters of Puget Sound until they mature and then return to freshwater to spawn. The objective of our study was to determine the effect of rearing conditions and hatchery location on the prevalence of this alternative pattern of marine distribution by hatchery‐produced Chinook salmon in Puget Sound. We used coded wire tag recovery data to analyze the effect of release region, age, size, and date of release on the proportion of fish showing resident‐type behavior, defined as recovery in Puget Sound fisheries outside the period when maturing salmon return from the coast. Based on 226 different release groups from 26 hatcheries throughout Puget Sound from 1972 to 1993, 24% of the fish recovered were classified as residents, though this is not an actual estimate of the percentage of fish displaying this distribution pattern. The best single predictor of residency was release region, suggesting that where fish enter the marine environment had the largest influence on whether they adopted resident behavior or migrated directly to the ocean. The overall best model included an interactive effect between release region and size at release, revealing that the propensity of large fish to remain resident varied significantly among regions. The actual mechanisms that create the diversity of distribution patterns are still unknown, but the effects of rearing conditions and release location provide useful information for the management of these salmon populations.

Residency, partial migration, and late egress of subadult Chinook salmon (Oncorhynchus tshawytscha) and coho salmon (O. kisutch) in Puget Sound, Washington

“…Following Chamberlin et al (2011), we defined movements as discrete detections between individual receivers. These movement data were summarized by receiver type (offshore-deep, onshore-deep, and onshore-shallow) and tested for circular uniformity among hours by using Rayleigh tests with R package circular, vers.…”

“…Coho and Chinook salmon in Puget Sound are ecologically similar and both exhibit partial migration (i.e., residency). The factors affecting residency, inferred from coded wire tagging data, were similar for the 2 species (Chamberlin et al, 2011;Rohde et al, 2014), and both species tended to be caught as residents in the natal basin where they entered Puget Sound. We therefore combined data from this study and that by Rohde et al (2013) to compare directly the movement patterns of individual residents of these species in Puget Sound.…”

“…Few detections occurred in the Whidbey Basin as well. These areas are not devoid of resident Chinook salmon (Chamberlin et al, 2011) or coho salmon (Rohde et al, 2014), but both species tend to remain in one basin unless they leave Puget Sound entirely. There were several significant differences between the movements of the 2 salmon species.…”

“…Similar to the analysis of acoustically tagged coho and Chinook salmon, analysis of coded-wire tagging data also revealed differences and similarities that shed light on the phenomenon of residency (partial migration) of salmon. Residency seems much more prevalent with Chinook salmon (O'Neill and West, 2009;Chamberlin et al, 2011) than with coho salmon (Rohde et al, 2014), although it is not possible to precisely estimate the fraction for either species that adopts this behavior. However, the proportions of subyearling and yearlings adopting resident behavior were positively correlated between the two species among years, as well correlated with environmental variables (Rohde et al, 2014), suggesting common influences on behavior.…”

“…Analysis of coded-wire tag data indicated that an estimated 29% of hatchery Chinook salmon subyearlings and 45% of yearlings entering Puget Sound remained as residents (O'Neill and West, 2009). Subsequent analyses based on similar data but reflecting a different analytical approach also revealed that many Puget Sound Chinook salmon adopt a resident marine distribution pattern (Chamberlin et al, 2011). This pattern occurs but is less common with coho salmon (O. kisutch; Rohde et al, 2014).…”