U.S. Dept Commerce/NOAA/NMFS/NWFSC/Publications

Hydroelectric development on the Columbia and Snake Rivers has created conditions which adversely impact juvenile salmonids (smolts) as they migrate seaward. The dams themselves exact their tolls directly by killing fish passing through turbines and spillways. Indirectly, the impoundments created by dams affect smolt survival by altering natural spring flow patterns resulting in delayed migrations and protracted exposure of smolts to predators. In drought years, smolts run the additional risk of mortality due to deteriorating environmental conditions, particularly increased water temperature.

To expedite the migration of smolts through the river system, particularly in low flow years, the Northwest Power Planning Council established a Water Budget Program. This program calls for strategic releases of water from storage reservoirs in an effort to flush smolts through the system. However, young salmon may not fully respond to such efforts if they are not physiologically prepared to migrate. There is evidence that coho salmon (Oncorhynchus kisutch) migrate at different rates depending on their level of physiological development within the transformation from parr to smolt. Juveniles in the more advanced stages of smolt development exhibited the highest migration rates.

In 1988, the National Marine Fisheries Service initiated a pilot study to determine the feasibility of manipulating physiological development and associated migratory behavior of juvenile spring chinook salmon (O. tshawytscha). Results from that study were encouraging. A treatment group, exposed to a photoperiod cycle advanced by 3 months, developed earlier physiologically and migrated slightly faster than a corresponding control group. These positive results led to an expanded research effort in 1989.

The second year of research, funded in part by Bonneville Power Administration, was conducted at Dworshak National Fish Hatchery. The basic study design included four treatment groups and a control group (approximately 2,300/group). The experimental groups were reared in hatchery raceways under controlled light and temperature conditions. The controls were reared under ambient outdoor light conditions. The treatments were as follows:

1)

18-week exposure to a 3-month advanced photoperiod cycle, and during the final 14 days, the water temperature was increased from ambient (4.5�C) to 11�C.

2)

14-week exposure to a 3-month advanced photoperiod cycle.

3)

18-week exposure to a 3-month advanced photoperiod cycle.

4)

18-week exposure to a 4-month advanced photoperiod cycle.

Physiological development was evaluated using gill Na⁺-K⁺ ATPase and thyroid hormones as indices. Members from each group were tagged with passive integrated transponders (PIT tags). PIT-tagged individuals provided detailed information regarding migratory behavior. A portion of the control group and the 18-week/4-month advanced treatment group were also freeze branded. The brand enabled us to visually identify each group at hydroelectric index sites and to sample fish for physiological data. Mark-recovery data were obtained at Lower Granite and Little Goose Dams on the Snake River and McNary Dam on the Columbia River.

At this time, physiological assays are still being processed; consequently, only mark-recovery data from PIT-tagged fish are available to characterize migratory behavior. Results indicate that fish from all four treatment groups migrated faster inriver than fish from the control group (Table 1, Fig. 1). Consistently, Treatment 1 yielded the fastest migration. Fish from this group were exposed to a 3-month advanced photoperiod cycle for the longest time (18 weeks) and subjected to a temperature increase for 14 days prior to release. The median travel time for that group was 7, 8, and 9 days earlier than the controls at Lower Granite, Little Goose, and McNary Dams, respectively (Table 1). Based on the median travel time, fish from the Treatment 4 group exhibited the least effect, yet still arrived 5, 4, and 5 days earlier than the control group at the same three dams, respectively (Table 1, Fig. 1).

The effect of photoperiod treatment, with or without an accompanying temperature increase, is also apparent in terms of the percent of marked fish recovered. Overall, fish from all the treatment groups were recovered in higher proportions than fish from the control group (Table 2, Fig. 2). Treatment 1 displayed the most pronounced response with 57.8% of the tagged fish recaptured. This was significantly higher (p < 0.001) than the 47.2% observed for control fish, and equates to a 22.5% increase in fish collected in the bypass system.

Increased recovery could be due to improved survival or increased guiding efficiency at the recovery sites. Shorter inriver migration times resulting in reduced exposure to predatory fish could account for some increased survival and hence increased recovery of treatment fish. Alternatively, treated fish may be guided into bypass systems in greater proportion than untreated controls—we have additional evidence which suggests that yearling chinook salmon which were more advanced in terms of smolt development are also more susceptible to guidance by submersible traveling screens. Improved fish guidance means that fewer fish pass through the turbines, thus avoiding mortality associated with those devices. Also, because more fish are collected in the bypass systems, more fish are available for barge or truck transport around hydroelectric dams. The extent to which either increased survival or increased fish guiding efficiency accounts for the observed high recovery proportions of treated fish is uncertain. Nevertheless, regardless of the mechanism, a benefit is realized. Higher fish survival during inriver migration means that more fish enter the ocean. All other things being equal, adult salmon contribution should increase.

The next phase of research will attempt to assess the benefits of these treatments in terms of adult contribution. Inriver evaluations similar to those described will be coupled with a coded-wire tagging effort to measure adult contribution to the various fisheries and hatcheries. To date, all of the research has been conducted at a single hatchery. Future investigations will include additional hatchery sites in the Snake-Columbia Basin.

Q:

Was your temperature boost constant or were the fish acclimated and then maintained at the higher temperature?

A:

Acclimated over 24 hours and then maintained.

Q:

If we don't match peaks of release, aren't we exacerbating a bad situation if we only have so much water on the low flow years—by trying to shift timing to earlier releases?

A:

Possibly. Maybe one could delay releases to maximize responses for survival. In the upper drainages, transport programs attempt to separate species and stocks and treat them differently. One could do this in a variety of ways. We will be looking at this year's data to see if various treatment groups reacted differently to flows.

Q:

Have you matched daily flows with treated fish and controls?

A:

We have the data, but they are not yet analyzed.

Q:

Are there size effects?

A:

We are still looking into this; we have only preliminary data.

Q:

Would a sharp peak with faster migration be desirable within the transportation program? It appears that this is already crowded.

A:

Possibly this could be worked out with the Fish Transportation Oversight Team.

Q:

Would the photoperiod acceleration have any effect on saltwater transition?

A:

We don't know. It should be a benefit, but we await adult return data which could show this. We can do a lot toward changing these fish and adapting them to a more efficient passage or transportation system. Each complements the other, and we need a holistic approach.

Q:

In the percentage recoveries, the photoperiod treatments alone showed no differences from the controls, only when temperature was a part of the treatment. How about all temperature and no photoperiod treatment?

A:

I agree that it looks like this, but one photoperiod alone did show a significant difference. We also had a temperature-only group, which I did not show, but it did not even do as well as the controls.

Table l. Travel time and migration speed of PIT-tagged spring chinook salmon released at Dworshak National Fish Hatchery on 29 March 1989. Recovery sites were at Lower Granite, Little Goose, and McNary Dams.

*Fourteen- or 18-week exposure to 3- or 4-month advanced photoperiod cycle, with and without increased temperature (T).

Table 2. Number and percentages of PIT-tagged spring chinook salmon from Dworshak National Fish Hatchery which were recovered at Lower Granite (LGR), Little Goose (LGO), and McNary (MCN) Dams, 1989.

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Figure 1. Median travel time of experimental groups from release at Dworshak National Fish Hatchery to recovery at Lower Granite (LGR), Little Goose (LGO), and McNary (MCN) Dams. Data are based on recovery of PIT-tagged fish.

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Figure 2. Recovery of PIT-tagged fish from experimental groups released at Dworshak National Fish Hatchery. Data presented are for all tagged fish recovered at all three recovery sites.

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