Category: Fish/Shellfish Research
Author(s): C. Jeff Cederholm, WDNR, David H. Johnson, WDFW, Robert E. Bilby, NMFS, Lawrence G. Dominguez, WDNR, Ann M. Garrett, Private Consultant, William H. Graeber, WDNR, Eva L. Greda, WDFW, Matt D. Kunze, Private Consultant, Bruce G. Marcot, United States Forest Service, John F. Palmisano, Private Consultant, Rob W. Plotnikoff, WDOE, William G. Pearcy, Oregon State University, Charles A. Simenstad, University of Washington, Patrick C. Trotter, Private Consultant
There are seven indigenous salmon and trout of the genus Oncorhynchus in Washington and Oregon (chinook, coho, chum, sockeye, and pink salmon, and steelhead and cutthroat trout), for this paper we will collectively call them salmon. Their habitat extends from the smallest inland streams to the vast North Pacific Ocean, an area of freshwater, estuarine, and ocean habitats in excess of 4 million km2 . Due to past commercial fisheries, habitat loss, hatchery problems, and more recently a changing ocean environment, salmon populations have shown substantial decline over the past several decades. Many salmon stocks in Washington and Oregon are now listed as either threatened or endangered, under the Federal Endangered Species Act.
Early in the 1900â€™s and up until relatively recently, commercial fishing permanently diverted massive quantities of nutrients away from Washington and Oregon rivers, and their respective fish and wildlife inhabitants. Recent calculations by Gresh et al. indicate that only 3 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. There have also been many other losses of salmon habitat during this period caused by: river channel clearing and channelization, log driving and splash damming, extensive land clearing, major water diversions, livestock grazing, mining runoff pollution, logging road associated erosion and removal of the old growth forest, filling and diking of wetlands and estuaries, hydro-electric dam development, urban runoff, water and sediment contamination with toxicant, and recently recognized human induced oligotrophication of waterways. Over fishing and habitat degradation, together with a background of a changing ocean environment, have cumulatively reduced stock resilience. A century of hatchery programs have failed to rebuild the wild runs, and in many cases, likely contributed to their further declines. Modern salmon management techniques have become highly sophisticated, however, they have not been able to keep pace with the salmon population declines.
The life history of anadromous salmon covers time spent in freshwater, estuaries, and the ocean. Freshwater habitats are mainly used for spawning, incubation and juvenile rearing; estuaries are where juveniles put on critical rapid growth and make important osmoregulatory adjustments as they transition between fresh and saline waters; and the ocean is where significant feeding results in most of the body mass of the returning adults. Throughout their life salmon feed on a wide variety of prey organisms, including many kinds of freshwater and marine invertebrates and fishes; and at the same time, are fed upon by a wide variety of invertebrate and vertebrate predators and scavengers.
Juvenile salmon are known to feed directly on salmon carcass flesh, salmon eggs, and aquatic macroinvertebrates that may have previously fed on salmon carcasses. Research has uncovered significant contributions of nutrient from spawning salmon to the collector-gatherer macroinvertebrate community. Caddisflies, stoneflies, and midges are involved in processing the microbially conditioned salmon carcass flesh. Increase in aquatic macroinvertebrate density from the introduction of salmon carcasses stimulates feeding by early life stages of select salmon species. Other stages of the salmon life cycle also contribute to the macroinvertebrate food base, such as some stonefly nymphs, when they scavenge dead pink and chum
Of this group of wildlife species, 9 species had a Strong-Consistent relationship, 58 a Recurrent relationship, 25 an Indirect relationship, and 65 had a Rare relationship (the tally is more than 138 because 19 species have more than one type of relationship with salmon). These species were further examined as to the life cycle stage of salmon to which they were linked. The five salmon life stages, and the number of wildlife species associated with each (in parenthesis) were: Incubation (23); Freshwater Rearing (49); Saltwater (63); Spawning (16); and Carcasses (83) (this tally of wildlife species totals more than 137 because 66 species of wildlife are associated with salmon at several life stages).
Salmon act as an ecological process vector, important in the transport of energy and nutrients between the ocean, estuaries, and freshwater environments. The flow of nutrients back upstream via spawning salmon and the ability of watersheds to retain them plays a vital role in determining the overall productivity of salmon runs. As a seasonal resource, salmon directly affect the ecology of many aquatic and terrestrial consumers, and indirectly affect the entire food web. The challenge for salmon, wildlife, and land managers is to recognize and account for the importance of salmon not only as a commodity resource to be harvested for human consumption, but also for their crucial role in supporting overall ecosystem health. It is also important that naive view of wildlife as only consumers of salmon be abandoned. Many species of wildlife for which hard earned environmental laws and significant conservation efforts have been established (e.g., grizzly bears, bald eagles, river otters, killer whales, beaver), play key roles in providing for the health and sustainability of the ecosystems upon which salmon depend. As the health of salmon populations improves, increases in the populations of many of the associated wildlife species would be expected. Salmon and wildlife are important co-dependent components of regional biodiversity, and deserve far greater joint consideration in land-management planning, fishery management strategies, and ecological studies than they have received in the past.