Title: Sockeye Salmon Overescapement
Project Year and Number: 1992: FS27
Principal Investigator (PI): Dana Schmidt, Alaska Department of Fish & Game
Research Location: KEN/KAP
Restoration Category: Damage Assessment
Abstract: This study is a continuation of the oil spill damage assessment program initiated in 1990. Recent findings have suggested major economic damage to commercial, subsistence, and sport fisheries may result from overescapement. The continuing program is essentially identical to the previous study plans with minor modifications. These modifications are highlighted in the following revised plan.
Commercial fishing for sockeye salmon in 1989 was curtailed in Upper Cook Inlet, the outer Chignik districts, and the Kodiak areas due to presence of oil and subsequent contamination of catches in the fishing areas from the Exxon Valdez oil spill. As a result, the number of sockeye salmon entering four important sockeye producing systems (Kenai/Skilak, Chignik/Black, Red, and Frazer Lakes) and two less important lake systems (Akalura and Afognak or Litnik Lakes) greatly exceeded levels thought to be optimal. Sockeye salmon spawn in lake associated river systems. Adult salmon serve an extremely important role in the ecosystem, providing food for marine mammals, terrestrial mammals, and birds. Additionally, carcass decomposition serves to charge freshwater lake systems with important nutrients. Juvenile salmon which rear in lakes for one or two years serve as a food source for a variety of fish and mammals. Sockeye salmon are also an important subsistence, sport, and commercial species. The ex-vessel value of the commercial catch of sockeye from these lake systems has averaged about $42 million per year since 1979, with the 1988 catch worth $115 million. Sockeye salmon returns to the Kenai River system support some of the largest recreational fisheries in the State.
Overly large spawning escapements may result in poor returns by producing more rearing juvenile sockeye than can be supported by the nursery lake's productivity (Kyle et al. 1988). In general, when rearing fish abundance greatly exceeds the lake's carrying capacity, prey resources are altered by changes in species and size composition (Mills and Schiavone 1982, Koenings and Burkett 1987, Kyle et al. 1988) with concomitant effects on all trophic levels (Carpenter et al. 1985). Because of such changes, growth of juvenile sockeye is reduced, mortality increases, larger percentages holdover for another year of rearing, and the poor quality of smolts increases marine mortality. Where escapements are two to three times normal levels, the resulting high juvenile densities crop the prey resources to the extent that more than one year is required to return to normal productivity. Rearing juveniles from subsequent brood-years suffer from both the poor quality of forage and from the increased competition for food by holdover juveniles (Townsend 1989). This is the brood year interaction underlying cyclic variation in the year class strength of anadromous fish.
This project will examine the effects of large 1989 spawning escapements on the resulting progeny for a select subset of the above mentioned sockeye nursery lakes. Three impacted lake systems where the 1989 escapements were more than twice the desired levels (Kenai/Skilak in Upper Cook Inlet; Red and Akalura Lakes on Kodiak Island) were selected. Tustumena Lake in Upper Cook Inlet and Upper Station Lake on Kodiak did not receive a large escapement and will be examined as controls. This study is necessary to obtain a more timely assessment of impact as adult sockeye, produced from the 1989 escapement, will not return until the 1994/1995 season. Further, total return data are not available for individual Kodiak sockeye systems due to the complex mixed stock nature of the commercial fisheries and the inability to estimate stock specific catches.
In addition to continuing previously identified activities, several new activities are proposed to ensure study results are valid. The Red River system is being evaluated based on fry and smolt production of Red Lake. Estimation of spawner distribution outside of Red Lake will be completed by establishing an adult weir on Red River immediately below the lake. In addition, the very low numbers of out migrating smolt estimated by the current mark recapture method has raised some doubt about violating assumptions of the technique. Approximately 60% of the river flow is intercepted by the traps but recapture efficiency remains below 10%. This indicates avoidance by the marked fish, violating the assumption that all fish have the same probability of being captured. If avoidance rate is great, then significant biases may occur. A full smolt weir is proposed to enumerate smolt and verify the current smolt mark recapture method.
On the Kenai River system, additional smolt samples will be collected from the Russian River to verify the aging techniques. The current method is suspect because age classes known to be produced from the Russian River do not appear in the smolt traps further downstream. Smolt trapping will also be continued into July to insure current projections of smolt production failure from the Kenai River lake systems are not an artifact of some unknown sampling bias. Finally, a late fall fry sampling period will be conducted on the major Kenai Peninsula lakes. Approximately 50% of the weight gain from fry to smolt on the Kenai River system occurs outside of the current sampling regime. If poor survival occurs because of limitations in rearing habitat quality during this period, these data are crucial for determining the validity of density of fry causing decreased over wintering survival.
Prince William Sound
Fish - Salmon
|Fields of Expertise||
Proposal: View PDF (31 KB)
Funding Recommendations: View
Funding Detail For: 1992
Quarterly Project Tasks For: 1992
Annual Report: 1992: Not Applicable
Final Report: View
Publications from this Project: None Available
More information may be available for this project under other years:
We continue to populate our database to make all of our project information available online. If you would like more information on any project listed below, please contact us and we can search our files for the information you request.
|Project Number||Proposal||Annual Reports||Final Report||Data|
|1991: FS27||Not Available||
||See Project FS27||See Project FS27|
|1990: FS27||Not Available||
||See Project FS27||See Project FS27|