Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—Recent studies have shown that anadromous fish deliver ecologically significant quantities of marine-derived nitrogen (N), phosphorus (P), and organic carbon (C) to lakes, rivers, and streams of the Pacific Northwest. These marine-derived nutrients (MDN) can influence the ecological functioning of receiving streams through nutrient release and food availability. In Idaho, populations of anadromous salmon have declined dramatically with many formerly salmon-bearing streams now receiving no MDN supplementation. In order to assess how the loss of MDN may influence Idaho streams and rivers, we examined the current nutrient status of streams and rivers in Idaho with particular emphasis on the limiting role of N and P. We also generated a range of estimates of the historic and current affects of MDN on selected basins of the Salmon River, Idaho. Our analysis indicates that 25–50% of Idaho’s streams are potentially nutrient limited. Further analysis suggests that N and P limitation occurred in an approximately equal number of streams. Historic contributions of MDN to the Salmon River had varying potential to influence N and P availability, ranging from undetectable to resulting in a doubling of N availability. The level of influence depended upon location within the basin and the choices made regarding some simplifying assumptions. Finally, we discuss the effectiveness of artificial fertilization as a means of compensating for lost MDN and suggest that a spiraling approach be used to design and monitor fertilization treatments.

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—Positive numerical responses in steelhead <em>Oncorhynchus mykiss </em>and coho salmon <em>O. kisutch </em>juvenile abundance and size, smolt yield, and smolts per spawner were obtained from watershed restoration in the Keogh River on northern Vancouver Island, British Columbia. Annual increases coincided with treatment and were compared with data from an untreated neighboring watershed (Waukwaas River). The steelhead population, now apparently capable of thriving, was below replacement recruitment prior to the addition of inorganic nutrients and instream habitat structures, the key components of several restoration activities. Annual increases in summer densities of steelhead juveniles were recorded as the rehabilitation treatments progressed from 1997 to 2000. Estimation of steelhead parr densities indicated a 3.8-fold increase over pretreatment or internal untreated values; increases in sites with both inorganic nutrient briquettes and habitat structure additions were 2.5–1.9 times higher than sites with nutrient additions or habitat structures alone. Average size-at-age of juvenile salmonids, by autumn, significantly increased through the years of rehabilitation treatment and compared with fish in the Waukwaas River. Steelhead smolt yield in 2000 increased to 2,338 fish, the highest yield since 1993, but lower than the historical average (>6,000) due to low escapement. Current yield was an improvement over the historic low (<1,000 steelhead smolts, 1998). Coho smolt yield increased to 74,500 or 20% above the historic average (62,000 smolts; 1975–1999), well above the record low counts of 1998 (22,000), but below the historic maximum yield (105,000; 1981). A significant increase in steelhead smolt recruitment at low escapement, from less than 2 to greater than 50 smolts per spawner, was observed over the last four brood years (1995–1998). The assessment now shifts to further benefits to smolt yield, which will require evaluation to 2004.

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—Based on the information presented at the Restoring Nutrients to Salmonid Ecosystems conference in Eugene, Oregon, in April of 2001, it will be necessary to substantially increase and achieve salmon spawner escapement goals in order to meet ecosystem productivity potential. Modeling of recovery rates shows that achievement of even the currently identified spawner escapement goals (much less ecosystem recovery) in less than 50–100 years is unlikely, unless there are substantial shifts in management thought and practice. To speed recovery, it is necessary to achieve consistent rates of increase in spawning escapement not seen in current management activities. Until actual spawner escapements approach levels necessary to support ecosystem function, it will be necessary to utilize alternative methods such as the distribution of salmon carcasses, carcass analogs, or the use of fertilizer to provide the nutrients needed to assist its salmonid population recovery. In addition to restoring absolute numbers, the size and age structures of the fish populations need to be restored in order to successfully utilize the available environment. Simply increasing escapements and resultant nutrient levels, however, is insufficient. Stream flows, whether average, flood, or low, need to be stabilized. Instream and riparian habitats need to be stabilized and restored; this would include allowing normal flood paths to be followed.

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—Pacific salmon <em>Oncorhynchus </em>spp. are important components of numerous food webs throughout their life history, yet we know very little about the historic and current abundance of these life history stages. We used past cannery records, recent harvest and hatchery records, and salmon life history information drawn from the literature to construct a simple bioregional model of historic and recent salmon abundance at egg, fry, smolt, ocean adult, and spawning stages for five species of Pacific salmon from Alaska to California. We found a historic-to-recent bioregional decline in salmon biomass in all life history stages. Recent salmon egg, fry, smolt, ocean-going adult, and escapement biomass estimates for northwestern North America are 74%, 55%, 59%, 86%, and 35%, respectively, of historic levels. Recent high productivity in Alaskan waters, however, masks a precipitous decline south of Alaska, where recent egg, fry, smolt, ocean-going adult, and escapement biomass levels are 34%, 23%, 50%, 40%, and 15% that of historic levels. Adult production and harvest levels are no longer sufficient measures of salmon management success. Researchers need to quantify and elucidate the ecosystem effects of historic biomass changes in life history stages of Pacific salmon on a watershed basis. Fisheries managers must set and meet specific targets for salmon life history stage abundance—from egg to spawning adult—to restore and maintain ecosystem function.

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—Snake River sockeye salmon <em>Oncorhynchus nerka </em>once inhabited five prealpine lakes in the Sawtooth Valley, Idaho, but are presently reduced to the Redfish Lake stock. Declining returns to Redfish Lake in the 1980s prompted the National Marine Fisheries Service to list Snake River sockeye salmon as endangered under the Endangered Species Act, and a multi-agency effort was initiated in 1991 to prevent their extinction. The recovery effort focused on the development of a captive broodstock coupled with evaluation and enhancement of nursery lake habitats. Large populations of nonendemic kokanee salmon <em>O. nerka </em>and the oligotrophic conditions of these lakes raised concerns about overstocking sockeye salmon and causing the collapse of macrozooplankton populations. To minimize these risks and to improve sockeye salmon forage production, the Shoshone- Bannock Tribes initiated a 4-year nutrient enrichment program in Redfish Lake. Liquid fertilizer (20:1, N:P by wt) was added weekly during the growing season from 1995 to 1998 to the surface of Redfish Lake with Stanley Lake (unfertilized) acting as a control. During the fertilization of Redfish Lake, Secchi depth decreased by 13% and compensation depth by 24%, while increases were observed for surface chlorophyll <em>a </em>(106%) and primary production (117%). Uniformity of phytoplankton communities throughout the experiment indicated that the Redfish Lake food web was efficient (without major carbon sinks) and improved forage conditions for macrozooplankton. Total macrozooplankton biomass increased 31%, and <em>Daphnia </em>spp<em>. </em>biomass increased by 225%, simultaneous to a 26% increase in <em>O. nerka </em>density. Also, during fertilization, overwinter survival of supplemented sockeye salmon increased 192% in Redfish Lake. However, meteorological conditions were partly responsible for these changes. In unfertilized Stanley Lake, during the same time periods, Secchi depth declined 27%, and compensation depth was reduced by 28%; chlorophyll <em>a </em>increased 16%, primary production increased 14%, and zooplankton biomass was stable. These changes highlight the importance of climate (meteorological forcing) and the need for a control when attempting to identify impacts from lake fertilization. Disproportionately larger increases in Redfish Lake chlorophyll <em>a</em>, primary productivity, and zooplankton biomass relative to observed changes in Stanley Lake provide evidence for the efficacy of nutrient supplementation in Redfish Lake.

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—We observed that the aquatic animals, especially macroinvertebrates, colonized chum salmon <em>Oncorhynchus keta </em>carcasses in six rivers of five coastal districts in Hokkaido, northern Japan, 1997–2000. Fifty-six taxa of aquatic macroinvertebrates were found with the carcasses. Taxa and number of the macroinvertebrates were different among rivers and districts. Three taxa, Gammaridea (Amphipoda), <em>Hydatophylax </em>spp. (Trichoptera: Limnephilidae), and Chironomidae (Diptera), were widely and abundantly found. <em>Hydatophylax </em>larvae were more abundant on the carcasses, in comparison with the streambed, in some sites. The maximum number of macroinvertebrates colonizing a carcass was observed near an estuary site of the Shiretoko District, 747 on average of <em>Eogammarus </em>spp. (Gammaridea).

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—A solid briquette fertilizer for use in the Pacific Northwest streams and elsewhere was identified from a variety of slow-release formulations (26 were tested with varying N:P₂O₅:K₂O ratios and binders) using indoor trough and controlled field experiments. The use of a slow-release fertilizer is an innovative method for adding inorganic nutrients to nutrientpoor (oligotrophic) streams to increase autotrophic production and aid in the restoration of salmonid populations. A series of indoor trough experiments demonstrated that the majority of samples containing binders of molasses, hydrated lime, vegetable oil, bentonite, starch, acrawax, candle wax, and Daratak® XB-3631 (unpolymerized Saran™) dissolved too slowly. The fastest dissolution rates occurred with fertilizer briquettes having no binder or vegetable oil. Further trough and field studies using fertilizer with no binder and vegetable oil as binder examined the effects of varying N:P₂O₅:K₂O ratios. Dissolution rates were varied by using different percentages of magnesium ammonium phosphate (MagAmP; its formula 7:40:0 N:P₂O₅:K₂O) and urea (46:0:0). Optimal continual nutrient release for a period of four months was achieved with a fertilizer formulation of 17:30:0 (percent by weight N:P₂O₅:K₂O), with a ratio of 75% MagAmP to 25% urea, and containing no binder. The dissolution rate for this product ranged from 4.6% to 6.6% per week (for field and trough experiments, respectively) in water of 0.15 m/s average velocity. These studies indicate that a slow-release fertilizer product can be manufactured to last approximately four months when applied in the spring to stimulate autotrophic production in nutrient deficient streams, thereby increasing forage and salmonid production.

Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity

<em>Abstract.</em>—During 1997–2000, chum salmon <em>Oncorhynchus keta </em>spawners and their predators and scavengers were observed in lower Kennedy Creek, a small south Puget Sound, Washington stream. Chum salmon occupy 5.2 km of main Kennedy Creek and a small tributary called Fiscus Creek. Spawning escapements within this stream averaged 39,000 fish annually during this study. Active spawning began in late October and was over by mid- December. Direct consumption of live and dead salmon was observed or inferred from animal signs over the spawning period. Salmon carcasses and tissue fragments could be found scattered along the streambed from October through March, and bones remained year round. Live spawners, carcass flesh, and eggs were consumed by 30 species of birds, mammals, invertebrates, and fungi, including 9 previously undocumented species. High carcass densities allowed selective feeding for some consumers and opportunistic feeding for others. Apparent preferences for eggs by several consumers suggested another important role for naturally spawning salmon. Varied thrush <em>Ixoreus naevius</em>, otter <em>Lutra canadensis</em>, and song sparrow <em>Melospiza melodia </em>showed preferences for salmon eggs, and a cougar <em>Felis concolor </em>killed live salmon and fed on them. Some consumers coordinate successive utilization of carcasses, such as the gull <em>Larus </em>spp., terrestrial beetle <em>Agyrtidae</em>, raccoon <em>Procyon lotor</em>, fly maggots, and mice. Water samples taken from the anadromous areas of these creeks and from the estuary in Totten Inlet showed elevated levels of dissolved ammonium, nitrate, and nitrite. Benefits to chum fry were inferred.