An Early Report on Salmon Carcasses

• “This river is remarkably Clear and Crouded with Salmon in maney places, I observe in assending great numbers of Salmon dead on the shores, floating on the water and in the Bottom which can be seen at the debth of 20 feet.  the cause of the emence numbers of dead salmon I can't account for So it is I must have seen 3 or 400 dead and maney living...”
• William Clark, journal entry for 18 October 1805

Salmon (genus Oncorhynchus)

Cederholm, et al.:

• "As the decline of wild salmon continues throughout the Pacific Northwest, it is logical to assume that the productivity of some freshwater and terrestrial ecosystems will also decline.  Decreased production could be self-perpetuating, as salmon stocks already in decline are likely to decrease further in a negative feedback loop." 
• Pacific Salmon and Wildlife, 2000, p 68

Cederholm, et al.:

• Recent calculations by Gresh et al. indicate that only three percent of the marine-derived biomass once delivered by anadromous salmon to the rivers of Puget Sound, the Washington Coast, Columbia River, and the Oregon Coast is currently reaching those streams.
• Pacific Salmon and Wildlife, 2000, p iv

First Concern

• The MDN or marine nutrient pump model has focused on the upstream movement of nutrients (N, P and calories, plus?) to the almost complete exclusion of all other nutrient fluxes:

Adult Salmon Migration

Adult & Juvenile Salmon

Hypothetical Example (>1 year in freshwater)

Hypothetical Example (<1 year in freshwater)

Mixing of Nitrogen Isotopes

• Measurements of Nitrogen isotopic compositions of stream reaches supplemented by salmon carcasses and reaches without supplementation show a pattern consistent with mixing of marine and terrestrial nitrogen.
• This is not the same as demonstrating that salmon account for a net addition of nutrients to the freshwater system.

Mixing Is Not Proof of Addition

Comparison of Models

Fluxes To Be Considered Natural

Fluxes Including Anthropogenic Impacts

Nutrient Fluxes

• near the mouth of the Columbia River

Nutrient Loadings

• Nutrient loadings can be reported different ways:
• kg N/sq meter of stream bed
• kg N/kilometer of stream
• g N/juvenile

Nutrient Inputs

Juvenile Production

Juvenile Nutrition

Summary

Interpretation

• For relatively small spawning runs – carcass additions should not be necessary the background flux should be sufficient.

Interpretation (continued)

• Carcasses are important ONCE there are juveniles present but the returning adults should be sufficient.
• The lowest nutrient availability per juvenile occurs at the peak spawning success (maximum number of juveniles survive).

Additional Implications

• A small class of spawners is expected to result in good survival and growth, which could result in a net export of nutrients with the smolts
• This possibility was noted by Scheuerell, Levin, et al., 2005, who concluded that this meant nutrient supplementation was especially important at low spawner densities

Potential Consequences of Applying the Wrong Model

• Increasing the density of salmon carcasses without a corresponding increase in the number of smolts moving downstream will lead to increased nutrient densities in the region where the carcasses are added and an increased spiraling flux of nutrients downstream (that is assuming that there is a longer residence time for nutrients in the stream in the absence of salmon than there is with salmon present and smolt migration).

Potential Consequences of Applying the Wrong Model

• The additional nutrients will support other species in the stream (e.g. resident trout and small fish or algae).
• These species will prey on fry or compete with juveniles more.
• Shift ecosystem from a salmon stream to a stream dominated by resident species.
• Raise nutrient levels to point that areas with adequate sunlight grow enough phytoplankton to create severe swings in dissolved oxygen (areas without sunlight could also become low dissolved oxygen due to bacterial utilization of carcass material).

Potential Consequences of Applying the Wrong Model

• 5) The nutrient spiral will add to any nutrient excesses caused by human utilization of the lower basin.
• Development of a TMDL for nutrients will require a reduction of inputs, which would require additional reductions from other sources to offset nutrient introductions for salmon restoration.

Distinguishing Between Restoration and Aquaculture

• An aquaculture model will result in the run returning to the level prior to intervention upon cessation of supplementation.
• A restoration model should lead to the condition that terminating human intervention will not result in a return of the salmon run to the levels before intervention.

Restoration versus Aquaculture

• If the activity qualifies as aquaculture, a wastewater discharge permit may be required
• If the activity is truly restoration, other oversight mechanisms can be used

Needs

• Flesh out the stick figure model I have presented with data on smolt out migration rates and natural nutrient fluxes.
• The impact of releasing masses of hatchery reared smolts needs to be included in any attempt to fully quantify the nutrient cycle. Do they die before exiting the stream and add nutrients or do they feed during the journey and mine the stream of nutrients?.
• The ecology associated with spawning salmon needs to be understood in greater detail.

The ecology associated with spawning salmon needs to be understood in greater detail.

• What characteristics distinguish starved from healthy from over-enriched photosynthetic and invertebrate communities.
• Develop criteria for when nutrient (or calorie) additions are required and when corrective actions to reduce nutrient inputs are needed which reflect conditions in the watershed, not just the observation that the spawning runs are depleted.

Suggestions (if salmon carcass placement is to continue):

• Concentrate the available carcasses (resources) in a few streams and use the others for controls.
• Measure productivity of supplemented and un-supplemented streams for several generations, then switch treatments for half of the control streams. The response should distinguish between whether the carcass placement functions as aquaculture or restoration.

Comment:

• The differences in juvenile lifestyles and one shot versus multiple spawning can be used to increase the understanding of the importance of salmon carcasses.
• There have been a number of studies of the impact of adding salmon carcasses or carcass analogs to streams which have not produced measurable results. There are two likely causes: the addition was small compared to the natural flux (i.e. the result was inherently not measurable) and nutrients were not the limiting factor, other considerations (e.g., rearing habitat) were more important to their survival and growth.

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