Figure 7-4. Klamath River fall chinook adult natural spawners, 1978-1992, including original and revised escapement floors set by the PFMC. NOT AVAILABLE IN ELECTRONIC FORMAT
The Klamath River Technical Advisory Team (KRTAT) serves the PFMC and KFMC in projecting Klamath fall chinook stock abundance in the ocean. The number of three year old chinook salmon is calculated by using a linear regression relationship that uses the number of two year old salmon (jacks) which returned to the river in the prior year (Figure 7-5). In some years the calculated number of three year olds can be off by a significant margin using this method. The number of four year old fall chinook salmon in the ocean are estimated from a projection based on a linear regression which uses the combined total of three year old fish harvested and those that returned to spawn (Figure 7-6). Pre-season estimates of four year old chinook has proved more accurate, as reflected by the closer distribution of all brood years to the regression line.
Figure 7-5. Regression using the number of two year old fall chinook salmon (jacks) to estimate the abundance of three year olds. NOT AVAILABLE IN ELECTRONIC FORMAT
Figure 7-6. Regression for prediction of Age 4 ocean fall chinook. NOT AVAILABLE IN ELECTRONIC FORMAT
After estimates are calculated, a model called the Harvest Rate Model (HRM) determines the allowable catches and resultant escapements based on allocations to the ocean and river fisheries. For several years the KMZ was managed as one large unit with harvest impacts of the commercial troll and ocean sport harvest modeled separately. In 1988, the KRTAT modified this approach andbegan separating fisheries by ocean area for more refined management within the range of Klamath stocks. The management of separate time/area cells is known as the Klamath Ocean Harvest Model (KOHM). The fisheries considered in the model are as follows:
1. Northern Oregon Troll Fishery: From Cape Falcon to Haceta Head,
2. Coos Bay Troll Fishery: Between Haceta Head and Cape Blanco,
3. KMZ Sport Fishery: Between Cape Blanco and Point Delgada,
4. KMZ Troll Fishery: Between Cape Blanco and Point Delgada,
5. Fort Bragg Troll Fishery: From Point Delgada to Point Arena, and
6. Southern California Troll Fishery: South of Point Arena.
Five time periods are considered annually in the KOHM: fall, spring, June, July and August. The combination of areas and times create a matrix of 30 time area management units in which fishing effort has been shaped to share as equally as possible in fishing opportunity over a wide area, while still protecting Klamath fall chinook salmon stocks (Figure 7-8).
Low Natural Spawning Escapement Triggers Over Fishing Report
The Magnusen Fishery Conservation and Management Act promotes "conservation and management measures that shall prevent overfishing while achieving, on a continuous basis, the optimal yield from each fishery." In Amendment X of the Act, a clear definition of "overfishing" is provided:
" Overfishing is an occurrence whereby all mortality, regardless of source, results in a failure of a salmon stock to meet its annual escapement goal or management objective... for three consecutive years, and for which changes in the fishery management regime offer the primary opportunity to improve stock status.
"Klamath Management Zone and Areas Used in Klamath Ocean Harvest Model Figure 7-8. Area managed as the Klamath Management Zone (KMZ) to protect Klamath fall chinook stocks and time/area cells used under the Klamath Ocean Harvest Model (KOHM).
Since Klamath fall chinook salmon have failed to meet the 35,000 escapement floor set by Amendment IX of the Magnusen Act for three consecutive years beginning in 1990, an overfishing committee was convened by the PFMC. While the report remains in draft at the time of this writing (PFMC, 1993a), preliminary findings are reviewed here to help understand the root causes of low fall chinook escapements to the Klamath basin in recent years. It is acknowledged in Amendment X that some factors leading to under-escapement may not have been related to harvest, and the committee's findings on factors other than fishing are also discussed.
Estimation Methodology and Harvest Management Contributions
The preliminary findings of the overfishing committee are that problems with estimation methodology and harvest management methods have contributed to under-escapement of natural fall chinook spawners (PFMC, 1993a). Pre-season estimates of three year old chinook available for harvest in 1989 through 1991 were high when compared with post season estimates (Figure 7-9). The committee (PFMC, 1993a) concluded that over-estimation of three year old fish allowed overfishing in 1991 and led to under escapement in that year. The prediction of abundance of three year old fall chinook in the ocean from 1985-1992 has been very imprecise, ranging from 31% to 210% of post season estimates (PFMC, 1993a).
Figure 7-9. Estimates of Age 3 Klamath fall chinook salmon before and after fishing seasons from 1985-1991 (Parker, 1993). NOT AVAILABLE IN ELECTRONIC FORMAT
Over estimation of stock abundance has also been shown to be a principal cause of overfishing of Oregon coho and Puget Sound stocks (PFMC, 1992a; 1992b). Estimates for abundance of three year old fall chinook salmon in 1992 showed that escapements below 35,000 could be expected but a fishery was carried out despite this knowledge.
"In 1990, errors in accurately modeling time-and-area fisheries in the ocean were the principal cause of the escapement shortfall" (PFMC, 1993a). The efforts to model fisheries in the Fort Bragg and Coos Bay areas have usually under-predicted impact rates, particularly on fully vulnerable four year old fall chinook salmon (Table 7-3). The seasons in these areas have been partially closed or allowed only short periods of access but the technique appears to have been ineffective in reducing impacts (PFMC, 1993a). The problem seems to arise because of the unpredictable way that fishing effort shifts in response to time and area closures. In 1990, the Coos Bay area had much greater fishing effort during openings than predicted and the catch rate of Klamath fall chinook was much higher than anticipated. The inability to predict impacts of very limited seasons has contributed to a chronic under-estimation of impacts on fully vulnerable 4 year old Klamath fall chinook salmon (Table 7-4). Only in 1992, when commercial salmon trolling was virtually closed in areas managed using the KOHM, did impacts not exceed the target.
Table 7-4. Preseason estimates of impact of ocean salmon fisheries on Age 4 fall chinook
compared to post season estimates, 1988-1992 (PFMC, 1993).
Year Preseason Target Post Season
Estimate
1988 39% 45%
1989 37.5% 43%
1990 37.5% 61%
1991 16% 22%
1992 8% 4%
Harvest Rate Much Higher For Klamath Sub-basin Stocks
The PFMC Salmon Framework Plan in Amendment IX of the Magnusen Act calls for a 33-34% harvest rate for each brood year, as well as a minimum escapement of 35,000 fish in years of low abundance. Fall chinook salmon for the entire Klamath/Trinity River are managed as an aggregate, but the overfishing committee found that some sub-basin stocks had chronically low escapement rates. Coded wire tagged fall chinook juveniles released as fingerlings from Iron Gate and Trinity River Hatcheries are thought to fairly represent vulnerability to harvest of natural chinook stocks from Klamath sub-basins above Weitchpec and from Trinity River sub-basins, respectively. Analysis of coded wire tag data from fingerlings released at the hatcheries show that stocks from the two basins may have substantially different escapement rates (Table 7-5).
Escapement rates of 33-34% are required for sustained yield even for fish returning to healthy habitat; therefore, low escapements related to harvest threaten the long term productivity of some Klamath fall chinook stocks. Some Klamath sub-basins, such as the Shasta and Scott Rivers, are known to have very poor habitat conditions so may have even greater vulnerability to overfishing. The overfishing committee recognized that the failure to meet the escapement rate for Klamath sub-basin stocks, including all tributaries above the Trinity River, constituted a problem (PFMC, 1993a). Solutions discussed by the committee included reducing ocean harvest rates and shifting the timing of Indian net harvest to target Trinity River Hatchery fish.
Table 7-5. Escapement rates of Klamath sub-basin and Trinity River sub-basin fall
chinook stocks as calculated from survival of hatchery releases of fall chinook fingerlings.
Brood Year Klamath Stocks Trinity Stocks
1979 14% 33%
1980 23% 69%
1981 46% 63%
1982 33% 41%
1983 22% 40%
1984 16% 31%
1985 12% 47%
1986 18% 46%
1987 35% 46%
1988 65% 64%