Understanding the causes of salmon declines is critical to understanding long-term trends in salmon production, and to developing effective tools for forecasting future changes.

Understanding factors that control mortality and growth of juvenile salmonids during their first few months at sea is also critical.

1. The proportion of outmigrating Oregon Production Index hatchery coho salmon smolts that return to spawn has declined from 5-10% (in 1960s and 1970s) to less than 1% in the 1980s to present.

2. The long-term trend appears to be related to the regime-shift which took place in 1976-77; high survival was observed before the regime shift in the late 1970s and early 1980s, low survival thereafter.

3. The proportion of coho salmon surviving to return to spawn was correlated with the Bakun upwelling index during the 1960s and 1970s; since the early 1980s until present, there has been no correlation with the upwelling index.

• Need to understand what the Bakun upwelling index is telling us about "ocean conditions."

• Need to understand if wild and hatchery reared salmon have different growth and survival rates.

• Compare growth and survival of a few index stocks of salmon in different coastal oceanographic regions (e.g., compare juvenile salmonids that reside primarily south of Cape Blanco vs. north of Cape Blanco). Also, compare adjacent stocks (e.g., Siletz, Yaquina, Alsea) within a region to discriminate common ocean effects from natural stream habitat effects.

• Available evidence suggests that, for Oregon Production Index (OPI) coho salmon, much of the marine mortality occurs during the first few weeks at sea, when the juveniles are resident nearshore and in the continental shelf waters.

H₁

Mortality is due to predation by birds, mammals, and piscivorous fishes such as mackerel and Pacific hake; recent increases in predation rate may be due to increased abundances of predators.

H₂

Mortality rates are higher during periods of poor ocean conditions (i.e., if salmon which are just entering the sea encounter poor feeding conditions, their growth rates may be low, their condition may be poor, and thus their small size and weakened conditions may make them more susceptible to predation).

H₃

Wild fish have higher survival rates than hatchery fish because they have higher growth rates and are better at avoiding predators.

Beginning in 1997, all coho salmon produced in Oregon hatcheries will be marked (adipose fin clipped). This gives us the opportunity to compare hatchery and wild fish in estuaries and in the ocean with respect to a differential in the timing of migration to sea, dispersal at sea, distribution and abundance, food habits, growth, and survival. In the write-up which follows, the reader should keep in mind the opportunities provided by such a unique comparison.

Since the climate shift in 1976-77, the Bakun upwelling index has not been a very robust predictor of salmon survival. Although correlations between coho salmon survival and upwelling were good for data from the pre-1976 cool regime, there is no correlation for data during the present warm regime. This may be explained simply by the fact that we have not had a summer of high upwelling since 1976, so all of the data since the late 1970s fall within the lower quadrant (low upwelling and low survival). It may be that the signal-to-noise ratio is now too low to permit a useful correlation. The conclusion is that it is unclear how to interpret any correlation between salmon survival and upwelling. How does upwelling affect salmon survival? Directly by providing a large cool-water habitat, or by setting up favorable circulation patterns that are vital to salmon survival in some way? Indirectly by fueling biological productivity, thus enhancing levels of prey biomass? Is there a critical interaction between winds, circulation, upwelling and productivity in April/May when fish first go to sea? Are such interactions more important later in the upwelling season during the period of strong upwelling and maximum zooplankton abundance in July/August? In an interannual context, how is the Bakun upwelling index a measure of "good" vs. "poor" ocean conditions? Certainly a summer during which winds blew from the north every day would produce very different biological conditions in the coastal waters off Oregon than a "normal" upwelling season characterized by pulses in wind speed and direction.

Coastal upwelling off Oregon is characterized by active upwelling events having northerly winds blowing for 4-10 days duration that are interrupted by periods of calm or southerly winds. Seasonally integrated biological productivity in shelf waters is almost certainly higher under the condition of pulsed rather than continuous upwelling. What is the optimal set of pulsed events (e.g., 7 days upwelling, 4 days relaxed; 7 days upwelling, 7 days relaxed . . . .)?

The "complexity" of the environment may be an important feature of continental shelf waters that is critical to salmon survival. For example, when studying a map of sea surface temperature taken during strong upwelling, one observes mesoscale variability in the form of fronts with complex shapes (sinuous ribbons rather than straight lines) and numerous small eddies. The productive habitat is larger in general, with upwelled water found all over the continental shelf and farther offshore. This complexity creates an enlarged habitat volume for juvenile salmon with many patches where salmon may forage. During weak upwelling, habitat is reduced in volume, there is little complexity (i.e., physical features may only parallel the coast) and juvenile salmon may become concentrated into a smaller volume nearshore. Since their predators may also be forced into a smaller volume, salmon may become more susceptible to predators.

Habitat complexity is influenced by basin-scale weather and climate patterns and freshwater discharge. Large-scale climate variations affect seasonal upwelling; duration, intensity, and timing of freshwater discharge from the Columbia River contribute to habitat complexity by influencing fronts.

The need to understand the linkages among scales was identified by several participants. In what ways do local upwelling dynamics respond to large-scale basinwide forcing? This is related to the problem of understanding what the upwelling index is telling us—if the upwelling index is a function of large-scale dynamics, whereas the biological response in nearshore waters is due to local winds, then the upwelling index may be providing little useful information about local production.

Beginning in 1997, all Oregon hatchery coho salmon will be marked (adipose fin clipped). This gives us the opportunity to compare hatchery and wild fish in estuaries and in the ocean with respect to studies of timing of migration to sea, distribution and abundance, food habits, growth, and survival. This also makes possible another experiment in which growth and survival of hatchery fish from different river systems can be compared. This would be made possible if the otoliths of hatchery fish were thermally marked by increasing/decreasing the temperature of hatchery pond waters for a day or two, so that a "check" appears on the otolith. Repeated three to four times over a 2-week period, four to five checks will be laid down. By varying the interval between checks among hatcheries, all the fish from a hatchery would carry the same code. One could select a few river systems, mark the fish, and compare growth/survival of fish from hatcheries from large vs. small rivers, northern vs. southern rivers, and rivers with and without estuaries, for example.

When planning a comparative study of survival and growth, a key question is where do salmon reside during their first few days at sea? If they remain in a zone very near to shore, then a very different set of variables will operate to modulate growth and survival as opposed to fish that immediately disperse over the entire continental shelf environment. Do salmon seek out specific oceanographic environments (just outside the surf zone, within cool upwelled water nearshore, mesoscale eddies or fronts, offshore in waters bordering the Columbia River plume)? Do wild salmonids occupy different habitats than hatchery salmonids?

Who are the key predators? Are mortality rates highest during the first few days at sea or are rates low but constant during the first few months? Studies of predation are straightforward but will require a large effort in order to give a definite answer to the question of who are the key predators. To obtain information on predator distribution, biomass, and feeding rates, an ambitious field program will be needed that involves acoustic as well as trawl surveys of potential piscivorous predators. The surveys should be conducted weekly during April/May to cover the first few weeks at sea, as well as at least a twice-monthly frequency during the summer months. When planning studies of predation by fishes on juvenile salmonids, one must keep in mind that salmonids are probably rare entities within the prey field of a Pacific hake or mackerel, for example. But, with sufficiently large sample sizes for predators, a predation hypothesis can be evaluated. The best places to conduct such studies may be where juvenile salmonids are most highly concentrated, such as near the mouths of larger rivers like the Columbia or near hatcheries that are near salt water such as in Barkeley Sound (Vancouver Island—see abstract by Hargreaves in this volume) or in Puget Sound. In addition, bird and mammal predator surveys may be required.

Given the changes in salmon survival that are associated with long-term climate variations, we need an assessment of how key oceanographic and biological variables may affect selected index stocks. The group agreed that new research should focus on comparing and contrasting responses of salmonids from a few different river systems. Growth and survival may have some stream dependency, thus there is the potential that interesting comparisons could be made following a research plan outlined above in the section on comparisons of stocks. Along these lines, discussion became centered upon another useful comparison of growth and survival, that of resident stocks vs. ocean migratory stocks to sort out mechanisms and scales of variability. Specific examples included coho salmon stocks in Puget Sound, some of which are resident and others of which migrate into the Pacific Ocean, returning to Puget Sound to spawn.

7. Need for coordinated efforts was stressed

The group discussed the need for a more coordinated approach to studies of relationships between upwelling, biological productivity, ecosystem structure, trophodynamic connection, and early life history of salmonids. The various comparisons outlined above would be best if carried out as a long-term study in a few index streams.

Along these lines, it was recognized that we need to develop a strategy for funding long-term studies of salmon ecology, and that the best approach may be to form an international steering committee made of representatives from the western states (including Alaska) and Canada at a minimum.

Apart from the specific process studies outlined above, the group discussed the need for modeling studies, retrospective analyses of existing data sets, monitoring, and development and application of new technologies. Such work should precede process studies because these activities would provide a richer context for hypothesis-based field process experiments.

Coupled physical-biological models are ideal tools to apply toward the problem of understanding how the Bakun upwelling index is related to local production and how the upwelling index is related to large-scale forcing. Ideally, the physical model should be a 3-D model capable of resolving mesoscale features such as eddies, jets, and riverine plumes. The biological component could initially be a simple NPZ model (Nutrient—Phytoplankton—Zooplankton) imbedded in the physical model. The ultimate goal would be to build more complex biological models that include individual-based models of salmon.

The role of predators as consumers of juvenile salmonids can be evaluated initially through modeling. Predator-prey models should be explored that have as input data the abundance of predators, feeding rates of predators, abundance of prey (juvenile salmonids), and abundance of alternative prey. Initially these can be viewed as back-of-the-envelope calculations to determine which predators appear to be the most significant. Once identified, more careful modeling could be initiated to determine whether any top-down regulation occurs in salmon populations.

Analyses of relations among salmon survival and growth and various time and space scales of meteorological and ocean variables can be done with retrospective comparisons of salmon survival and local forcing, survival vs. large-scale forcing, and salmon growth (using scales) compared to local variables vs. comparisons to basin-scale variables. Large scale/long-term retrospective studies are possible using the COADS and MOODS data sets and by accessing climate data from the NOAA/National Climate Data Center. Oceanic and terrestrial time series are now of sufficient length that it is possible to examine the coupled oceanic-atmospheric-terrestrial system to examine, for example, effects of regime shifts on ocean temperature, coastal weather, changes in rainfall, changes in stream flow, and salmon survival in streams and in the ocean.

Too few coastal institutions carry out continuous routine measurements of key oceanographic variables in continental shelf waters. Apart from long time-series of physical parameters such as sea level, sea surface temperature, wind speed/direction, and surface atmospheric pressure measured at buoys and shore stations, there is little information on year-to-year or interdecadal variations in the abundance and distribution in time or space of plankton, small pelagic fishes, or salmon predators. We must begin to take regular measurements of biological oceanographic variables that relate to ocean productivity, "ocean conditions," or salmon survival. The group agreed that such work needed to be coordinated so that a standard set of measurements were made at common intervals along onshore-offshore transects in key geographic regions. Transects should be located in regions that characterize different oceanographic provinces, such as south of Cape Mendocino, between Mendocino and Cape Blanco, off central Oregon (Newport), near the mouth of the Columbia River, off the central Washington coast, off Vancouver Island, and off central Alaska. Without long-term biological data it will not be possible to truly understand the biological significance of the Bakun upwelling index, nor will it be easy to differentiate between the terms "good ocean conditions" and "poor ocean conditions."

Technology exists for the mass-marking of coho salmon in hatcheries (use of rapid changes in water temperature to produce checks on the otoliths). Such technology is used by the Prince William Sound hatcheries to mark pink salmon. Marking of fish in this manner is very inexpensive. The value is that it permits comparisons of survival and growth of coho salmon as a function of river system.

The group expressed an interest in the development of improved methods of tracking individuals (and stocks) using "smart" archival tags. These tags would record or possibly transmit in real-time the position and depth of an individual fish through its lifetime. RNA/DNA ratios and lipid biomarkers need to be evaluated to develop measures of relative condition of wild and hatchery fish at sea, in relation to food supply or the origin of fish.

Coastal radar systems such as CODAR or OSCR are sufficiently developed to be applied to long-term study of mesoscale and smaller scale (1-km resolution) variability in upper ocean circulation patterns. With these systems it may be possible to monitor frontal genesis so that the distributional patterns of juvenile salmon at sea can be studied in relation to high-resolution charts of circulation and fronts. If radar data could be supplied in near real-time, sampling at sea could be coordinated with known location of fronts, eddies, and jets.

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