Wednesday, February 1, 2012

North Fork Clackamas Update from ODFW Biologist Kathryn Kostow


Since 2000 the North Fork of the Clackamas has been a refugia for wild winter steelhead. No hatchery steelhead are released in the river and all hatchery adults are removed from the spawning population at the North Fork Dam. Recent work by ODFW biologist Kathryn Kostow has demonstrated that since the removal of hatchery fish from the North Fork the productivity of wild winter steelhead has increased significantly. She recently updated her anaylsis to include more recent years and found that the pattern remains, wild fish are doing better in the North Fork thanks to the removal of hatchery fish. Here is an update on her work.

Memorandum


Date: January 27, 2012
From: Kathryn Kostow
Subject: Update on Clackamas Steelhead

I have been hearing rumors that some people are casting doubts on the benefits of ODFW’s removal of hatchery adults above North Fork Dam on the Clackamas River. I’ve been told that this question came up during the recent Senate hearing on hatcheries, for example. The implication is that wild fish sanctuaries are not effective at protecting wild populations. This seems like an unfortunate interpretation that puts proposals like salmon strongholds and other wild fish sanctuaries at jeopardy.

This perspective is not supported by the facts in the Clackamas. Since my research provided the scientific support for this management action, I have been getting questions about it from a number of sources. The purpose of this memo is to provide everyone with the same update of the Clackamas data so that the facts are evenly understood.

The management action: As a refresher on the management action, it was implemented starting in 2000 and involved the removal of all hatchery adults at the dam, as well as the discontinuance of hatchery smolt plants above the dam. The hatchery programs were primarily for summer steelhead along with smaller numbers of hatchery spring Chinook, winter steelhead and coho. Hatchery programs for all species are still being implemented below North Fork Dam. The management decision was based on two studies of winter steelhead conducted by ODFW in the 1990s and ultimately published in Transactions of the American Fisheries Society . A “cliff notes” version was also published in the Osprey in 2006 . All three papers are attached.

What the data says:

The hatchery summer steelhead program started with an initial hatchery smolt release in 1969. The hatchery stock came from Washington (“Skamania” stock). By 1976 an average of 164,000 hatchery steelhead smolts were being released above the dam and an average of 70% of the steelhead adults passed above the dam were hatchery adults (Figure 1). Wild population abundance declined over this period to a low of only 109 fish in 1999.

Figure 1. Number of adult wild winter steelhead (blue, solid) and hatchery summer steelhead (red, dashed) passed above North Fork Dam on the Clackamas River.

A genetics analysis indicated that the hatchery summer steelhead were not interbreeding with the wild winter steelhead, so the hatchery fish were not posing genetic risks to the wild winter steelhead.

However, the hatchery summer steelhead adults were breeding among themselves, although at a reduced reproductive success compared to the wild winter steelhead. Since the hatchery adults out-numbered the wild adults, even with depressed reproductive success they were producing about half of the smolts out-migrating from the basin (Figure 2).

Figure 2. Relative proportion of parents, naturally-produced smolts and naturally produced adult offspring that were wild winter steelhead verses hatchery summer steelhead.

The hatchery fish depressed wild steelhead productivity by ecological effects since the hatchery and wild fish were not inter-breeding. This effect was demonstrated by Ricker and Beverton-Holt productivity models. In basic productivity models, the number of offspring produced is determined by the number of parents. Kostow and Zhou (2006) added additional interaction variables to the models to explore whether other factors besides the number of parents might influence the production of offspring. The hatchery variables included the number of hatchery adults passed and the number of hatchery smolts released. Several environmental variables were also explored including several flow scenarios and PDO (ocean productivity). The production of both smolt and adult offspring was measured. Twenty three different models demonstrated significant decreases in wild fish productivity due to the presence of hatchery fish above the dam. The number of winter steelhead offspring produced per parent decreased by an average of 50% while the capacity of the basin decreased by an average of 22% during the years that the hatchery program was implemented.

A simple version of the modeling, updated through 2011 adult returns (brood year 2005) is presented in Figure 3. This update used a similar approach to the discrete ‘‘high’’ and ‘‘low’’ hatchery fraction models used by Kostow and Zhou (2006). Two Ricker models are shown for the production of adult recruits under two observed scenarios. In the first scenario 0 – 12% (“low”) of the adults passed above North Fork Dam were hatchery adults. In the second scenario 31% - 92% (“high”) of the adults passed above the dam were hatchery adults. These simple models graphically demonstrate the reduction in capacity (height of the curves) and recruits/spawner (slope of the curves) that occurred as a result of the hatchery program. The updated data set validates the original results in Kostow and Zhou (2006).

Figure 3. The difference in wild fish productivity in the Clackamas when no to few hatchery fish were present (upper, blue line, square data points, BY 1958-74 and 2000-05) compared to the years when a large number of hatchery fish were present (lower, red line, diamond data points, BY 1975-99) as modeled by Ricker productivity functions.

The Clackamas research demonstrated impacts on population productivity, which is a different metric than population abundance. The abundance of a healthy population may fluctuate, but it does not chronically decline. A healthy population responds to a period of low abundance by increasing the number of offspring produced per parent. This productivity response returns the population to a larger size.

The wild winter steelhead population in the Clackamas appears to cycle under natural conditions (Figure 1, pre-hatchery years 1958-1974). This demographic pattern is likely due to large-scale environmental events. However, after the implementation of the summer steelhead hatchery program, when wild winter steelhead abundance in the Clackamas declined, the fish did not respond by increasing their productivity because the total abundance of steelhead was held artificially high by the presence of the hatchery fish. Kostow and Zhou (2006) determined that the carrying capacity of the river was regularly exceeded during the 25 years that hatchery adults were passed above North Fork Dam.

Thus over the three decades of the hatchery program, the production of both smolt and adult offspring chronically declined (Figure 4a and b). The decline has reversed when the hatchery fish were removed and the population appears to be returning to its typical cyclic pattern.

The population appears to be able to grow again, which should increase the chance for recovery of this ESA-listed species. Two factors, population grow rate and basin carrying capacity, will determine how rapid the population abundance will increase and how big it can become. Recent modeling results (still in progress) suggest that population growth could take as long 5 or 6 generations and will continue to be influenced by external factors that influence smolt-to-adult survival, such as migration survival, ocean productivity cycles, and harvest rates.

The basin should be capable of producing at least 50,000 winter steelhead smolts, based on observed historic (pre-hatchery) production levels. Smolt-to-adult survivals on the Clackamas average 7% (1958-2011 data). Given this survival, the expected maximum Clackamas adult abundance will be about 3,500 fish. In 2004 the run hit 3,100 adults while in 2010 the run hit 2,200 adults. Thus the population has already approached expected abundances since the removal of the hatchery program and is significantly improved over the low of 109 fish.

The Lower Columbia River Recovery Plan (ODFW 2010 ) indicates that adult abundance in the Clackamas should reach 10,655 fish in order for the population to be at “low risk” (ODFW 2010, page 154, Table 6.2). Since the habitat above North Fork Dam is in fairly good condition, the two options that could increase winter steelhead abundance to the “low risk” goal include substantial improvements in smolt-to-adult survival, or an increase in basin capacity which must be achieved by expanding the protected area in the Clackamas to include natural production areas below the dam.


No comments: