Cutthroat Trout
Injury
Anadromous streams throughout the spill zone were oiled following the spill in 1989, and oil was sequestered in the intertidal
sediments at stream mouths and along shorelines. Subsequently, it was documented that cutthroat trout emigrating within the oiled
areas in 1989–1990 grew more slowly than those in the unoiled areas. When trout leave their freshwater spawning areas they feed
primarily in the nearshore environment, thus it is likely cutthroats were exposed to oil in this environment. The difference in
growth rates between trout in oiled versus unoiled streams persisted through 1991. It was hypothesized that the slower rate of
growth in oiled streams was the result of reduced food supplies or direct exposure to oil, and there was concern that reduced
growth rates resulted in reduced survival.
Recovery Objective
Cutthroat trout will have recovered when growth rates within oiled areas are similar to those for unoiled areas, after taking
into account geographic differences.
Recovery Status
Limited information exists regarding the current status of cutthroat trout. Recent exposure to lingering oil is unlikely, because
most of the bioavailable oil appears to be confined to subsurface intertidal areas, and not dissolved in the water column. Moreover,
distribution of cutthroat trout is patchy throughout the Sound, thus access to oil is restricted. However, the Sound is the northern
edge of cutthroat trout range and dispersal during marine migration is restricted, thereby increasing their susceptibility to habitat
alteration and pollution. Cutthroat trout populations in the Sound are small and geographically isolated from each other: These
characteristics suggest that recovery of a population would depend less on mixing with nearby aggregates than on the productivity of
the endemic population and the extent to which it was injured by the spill. Confounding factors such as sport fishing and habitat
alteration of spawning streams (e.g., through logging) may also inhibit successful recruitment of young into a population and
subsequent increase in numbers.
Given the ecological similarities in summer diet and foraging ecology along shorelines between cutthroat trout, pink salmon and Dolly Varden, and the absence of ongoing injury to those other two species, further research would be very unlikely to demonstrate any evidence of continuing differences between oiled and unoiled areas due to the spill. Thus, funding the additional research necessary to provide current growth rate and abundance data for this species is not a cost-effective scientific priority.
Cutthroat trout are VERY LIKELY RECOVERED. Additional study, with sufficient effort and scope to achieve powerful tests of the impacts of lingering oil, would be relatively expensive, would likely be unable to definitively demonstrate an effect, and any effects would likely be minimal. For these reasons, it is unlikely that additional research will clarify this species’ injury status.
Click HERE for more information on Trustee Council funded studies of Cutthroat Trout.