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Alex Wertheimer Researchers at ABL have recently measured the straying rates of several pink salmon populations in Southeast Alaska. A project based from the Little Port Walter Research Station examined natural straying rates for two wild stocks to compare the rates with straying rates of pink salmon exposed to oil during the embryo stage (Fig. 1).
Figure 1. Southeast Alaska Straying averaged 5.1% for the juveniles that were not exposed to oil (Thedinga et al. 2000). Estimated straying rates were 9.2% for the intertidal stock and 3.7% for the upstream stock. Fish marked with coded-wire tags tended to stray more than fish marked with pelvic fin-clips. Although tagging appeared to influence straying, incubation and initial estuarine environments appear to be major determinants of the natural straying of pink salmon. The frequency of observed strays was higher for oiled groups than for the control group, but exposure to oil did not result in significantly higher straying rates (Wertheimer et al. 2000). Fish exposed to the low oil dosage had an estimated straying rate of 9.2%, compared to 5.3% for the control; but the high dosage straying rate was 5.7%, and thus did not indicate a dosage-specific response. This result may have been influenced by the higher mortality associated with increased exposure (Heintz et al. 2000): survival from fry to adult return was 27% lower for the low-dose treatment and 47% lower for the high-dose, relative to the control group. At the higher dose, straying may be less because fish impaired by the oil during embryonic development were more likely to die before sublethal effects such as increased straying behavior could be expressed. In another study examining pink salmon straying, pink salmon fry from Auke Creek were marked with coded-wire tags and otolith thermal marks at the Auke Creek facility (Mortensen et al. 2002). Adults returning to Auke Creek and neighboring streams were sampled for these marks and for otolith thermal marks from the Gastineau Hatchery. No effect of coded-wire tags was observed in this study. Estimated straying rates were 4.4% and 6.7% for early-run and late-run Auke Creek pink salmon, and 6.9% for Gastineau Hatchery pink salmon. The observed straying and run-composition estimates for the Auke Creek return indicated a substantial movement of adult pink salmon among local streams, which may promote rapid colonization and recovery of reduced populations.
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