Orr 1 ECOSYSTEM HEALTH AND SALMON RESTORATION: A BROADER PERSPECTIVE BRUCE K. ORR Stillwater Sciences, Berkeley, California, USA ABSTRACT An understanding of healthy, naturally functioning riverine and riparian ecosystems, and especially of the processes that produce and maintain such systems, is critical in developing effective strategies for managing natural populations of salmon and restoring habitat in regulated river systems. This paper briefly reviews concepts related to ecosystem health, biotic integrity, ecosystem management, and watershed analysis and shows how they can be used to improve our understanding of the factors influencing chinook salmon populations and to help develop and prioritize habitat restoration efforts. INTRODUCTION The examples presented here are based on studies of chinook salmon in the Tuolumne River, California (USA). Ligon (1997) provides a more comprehensive discussion of the research program that was developed by EA Engineering, Science, and Technology (EA 1992) to analyze what had caused the chinook salmon population in the Tuolumne River to decline to current low levels and to find potential management solutions. Ocean, estuarine, and riverine ecosystems are all important at different times in the life cycle of chinook salmon. In this paper I discuss only the riverine ecosystem and its associated riparian or floodplain habitats. COMPONENTS OF HEALTHY RIVERINE ECOSYSTEMS Successful restoration of anadromous salmon populations is dependent on a variety of factors. One strategy for salmonid restoration consists of maintaining or restoring the integrity of the riverine ecosystem. This strategy requires identification of the key processes and characteristics existing in the natural (or unmanaged) ecosystem, and the development of various methods for restoring some or all of these key elements. In a river such as the Tuolumne that is managed for water supply and hydropower, the difficulty lies in balancing human uses of the river with maintaining ecosystem form and function. Restoration of the riverine ecosystem has benefits beyond those directly related to salmon, including: maintenance or enhancement of native fish species and other aquatic organisms, amphibians and terrestrial species that utilize riparian habitats;
floodplain flood storage capacity; and human aesthetic and recreational enjoyment of a river with high quality water and a well-developed riparian corridor. Orr 2 Attributes of healthy riverine ecosystems include intact ecological processes, physical structure (form), and function. Various indicators can be used to assess ecosystem health. For example, in the Tuolumne River one might use indicators related to physical processes and structure, such as flow regime, channel morphology, and substrate conditions (see McBain and Trush 1997), and biological characteristics such as the relative abundance of native versus non-native fish and other species, macroinvertebrate abundance and community structure, amount of riparian vegetation, and abundance of mature cottonwood and willow trees. Riverine ecosystems are strongly influenced by natural conditions, ecological processes, historical factors, and human land use activities in the associated watershed or catchment. These larger landscape-scale factors affect the five major ecosystem components (energy flow, hydrologic regime, water quality, habitat conditions, and biotic characteristics) that determine riverine ecosystem health. Table 1 summarizes the relationship of these ecosystem components to indicators of ecosystem health or biotic integrity (sensu Karr et al. 1986), potential natural and anthropogenic factors controlling the various components, and provides examples of alterations and ecological impacts caused by human activities in the Tuolumne River system. TWO EXAMPLES OF ECOSYSTEM COMPONENTS AFFECTING JUVENILE SALMON IN THE TUOLUMNE RIVER The following are two examples of factors controlling key components of the Tuolumne River ecosystem and the influence they have on the ecology of juvenile chinook salmon to help illustrate the relationships identified in Table 1. Many more factors have been examined as part of the ecosystem-oriented studies that have been conducted in the Tuolumne River system (see EA 1992, Ligon 1997). McBain and Trush (1997) provide additional examples of how natural and altered fluvial geomorphic processes affect physical habitat conditions in the Tuolumne River. MACROINVERTEBRATES AND FOOD FOR JUVENILE SALMON Fish populations are influenced by a variety of biotic and abiotic factors. Examination of potential limiting factors (such as food supply or spawning habitat) is essential to the development of programs for enhancing fish populations: determination of factors that are limiting to a target population can lead to increased project success rates and improved cost-effectiveness of proposed actions. For example, if the current food resources of the river are sufficient to support specified escapement goals, efforts at enhancement should focus on other factors, such as spawning gravel availability and outmigration success. If food limitation is perceived to be a problem, or may occur before escapement goals are reached, then enhancement of food resources (i.e., invertebrates) must be addressed in addition to other proposed enhancement measures.
Table 1. Major ecosystem components influencing riverine ecosystem health, biotic integrity, and salmonid ecology. (Modified from Karr et al. 1986 and Naiman et al. 1992.) _ Orr 3 Ecosystem Component Indicators of Ecosystem Health and Biotic Integrity Potential Controlling Factors Tuolumne River Examples ENERGY SOURCES -Type, amount, and size of particulate organic matter entering stream -Sunlight available for instream primary production -Seasonal pattern of available energy -Latitude -Climate -Topography -Riparian vegetation Reductions in riparian vegetation have resulted in increased sunlight reaching stream and decreased particulate organic matter (leaves) inputs HYDROLOGIC REGIME -Water volume (instream flow) -Timing and duration of floods and low flows -Flood storage capacity -Basin geomorphology -Climate/precipitation -Human land use -Land cover -Dams and diversions Dams and diversions have altered magnitude, timing, and duration of flows; changes in land use and cover in watershed have also affected hydrology WATER QUALITY -Water temperature -Turbidity -Dissolved oxygen -Nutrients -ph -Chemical pollutants -Basin geomorphology -Human land use -Natural disturbances -Riparian vegetation Dams and diversions, land use patterns, and riparian habitat destruction have altered temperature regimes, sediment inputs, and increased nutrients and chemical pollutants HABITAT CONDITIONS -Substrate type, subsurface (hyporheic) conditions -Water depth and velocity -Spawning, rearing, and hiding sites -Habitat diversity (pools, riffles, runs, woody debris) -Basin and local geology and geomorphology -Dams and diversions -Instream gravel extraction -Hydrologic regime -Riparian vegetation Instream gravel extraction has created new habitat types favoring introduced species; riparian vegetation loss has reduced streambank stability and habitat structure provided by instream woody debris; habitat quality and quantity affected by altered flow regime BIOTIC INTERACTIONS -Natural biodiversity -Species diversity and abundance -Trophic interactions -Community structure -Introduced species -Biotic interactions (predation, competition, disease, parasitism) -Introduced species -Natural and anthropogenic disturbance -Habitat conditions Introduced predators (e.g., black bass) are a significant mortality factor for outmigrating juveniles; introduced warm water fish species may compete with natives; introduced water hyacinth affects summer low flow habitats
Orr 4 Food supply is one factor of many that may potentially limit fish populations. If fish survival or growth rates are low, or the condition of fish is poor, it is possible that food limitation is occurring, although other explanations are possible: inter- or intraspecific competition, disease, parasites, or suboptimal physical or chemical environmental conditions. The availability of food affects the growth rate, condition, and survival of juvenile salmon during both instream rearing and outmigration. Invertebrates are the primary food source for juvenile salmon. In a riverine system like the lower Tuolumne River, aquatic and terrestrial insects typically dominate the diet of juvenile salmon. Evaluation of the food resources available and assessment of whether the food supply is limiting requires sampling of invertebrates in both the rearing habitat (benthic and drift samples) and in the diet of the fish (stomach samples). In addition, benthic macroinvertebrates have been used as indicators of the general health of riverine ecosystems. Results of studies conducted by EA (1992) indicate that the Tuolumne River currently supports healthy aquatic invertebrate communities and that juvenile salmon are unlikely to be limited by food resources under present conditions. INTRODUCED SPECIES AND PREDATION ON JUVENILE SALMON Predation is often a major source of mortality for juvenile salmon, and it may be the reason why high spring flows have been correlated with larger recruitments. High flows can reduce predation on emigrating smolts by increasing turbidity, which can limit the predatory efficiency of sight-feeding fish such as black bass (largemouth bass and smallmouth bass), and by increasing velocity, which can both limit the predator's efficiency and access to smolts and decrease the exposure time of smolts to predation by decreasing their travel time. Studies conducted between 1987 and 1990 indicate that introduced predators (largemouth and smallmouth bass, and black crappie) are capable of significant predation, and may be the cause of an estimated mortality rate of 50-70 percent for smolts migrating out of the Tuolumne River during spring pulse flows. Analysis of the predator population data indicates that the greatest concentrations of predators is in the wide, deep, slow-moving, pond-like areas that are especially prevalent in the middle section of the river downstream of the major spawning areas. Because of their greater width and lower velocity, these areas probably result in slower than average outmigration rates and greater energy expenditure for juvenile salmon. These areas have resulted from instream sand and gravel mining operations. The predators using these habitats are species that were introduced in the late 1800s and 1900s to create a sport fishery. It is therefore likely that the present pattern and degree of predation mortality in the Tuolumne River is to a large extent a result of past sand and gravel mining and the introduction of piscivorous fish species. Evaluation of
Orr 5 restoration strategies for these sites is currently underway. AN ECOSYSTEM APPROACH TO SALMONID HABITAT RESTORATION In-channel restoration of aquatic habitats is unlikely to be successful unless the adjacent riparian zone or other portions of a watershed that affect the aquatic system are explicitly considered during restoration planning and implementation (National Research Council 1996). Terrestrial components of the environment have a profound influence on stream ecosystems. For example, terrestrial features affect the routing of water, sediment, nutrients, and woody debris within a watershed and its stream network. Human land-use practices, including construction of dams and diversions, can significantly alter such processes. Riparian vegetation can strongly influence the biological, chemical, and physical components of the aquatic ecosystem (Naiman et al. 1992, National Research Council 1996). Because of the important influence of riparian vegetation on the characteristics and biological productivity of riverine systems, effective restoration of aquatic habitats also requires protection or restoration of riparian habitat structure and processes. An integrated approach to evaluating potential habitat conservation, enhancement, or restoration sites on the Tuolumne River is currently being pursued by the Tuolumne River Settlement Agreement Technical Advisory Committee. Fundamental to this approach is the recognition of the need to fit protection and restoration efforts (or more precisely >rehabilitation=, sensu National Research Council 1996) to conditions currently existing in the managed river system and not to a pristine reference condition that is unachievable under current hydrologic and land use regimes (see McBain and Trush 1997). A nested set of criteria is currently being used to prioritize sites based on ecosystem function, riparian vegetation characteristics, and management constraints (J. Bair, McBain and Trush, personal communication). Ecosystem function criteria (significant potential to maintain or improve habitat value for salmon; potential for selfmaintenance by natural regeneration or recruitment; provision for long-term viability and improvement of the integrity of the riverine ecosystem; provision for connectivity of lotic and riparian habitats; and high flood storage capabilities) provide the initial filter for the screening of sites. The next tier involves riparian vegetation characteristics (which are partly nested within ecosystem function) such as provision of unique habitat, presence of naturally regenerating native woody riparian plants, older age classes and structural diversity, high species diversity, and evidence of complex interactions between vegetation and dynamic alluvial features. The final tier focuses on management constraints to assess the feasibility of site protection or restoration based on cost, access, compatibility with water and land use needs, availability of plant and construction materials, and potential for landowner cooperation, conservation easements, or purchase.
Orr 6 Once preservation and restoration projects have been implemented, monitoring is required to evaluate the effectiveness of this approach and of specific restoration strategies. Only through the feedback, evaluation, and adjustment processes of adaptive ecosystem management can we hope to reduce the uncertainties and risks involved in actively managing river systems to achieve a sustainable balance between human uses and ecosystem health (see Moyle and Yoshiyama 1997 for more on the application of adaptive management to the Tuolumne River). CONCLUSIONS The use of a broader perspective provided by the ecosystem management and watershed analysis approaches is critical to the development of long-term management solutions for restoration of salmonid populations and the riverine ecosystems that support them. A focus on restoring key elements of a healthy riverine ecosystem should yield benefits such as protection or enhancement of natural biological diversity, ecological integrity, and human recreational opportunities, in addition to bestowing direct benefits to chinook salmon. However, the ultimate success of restoration efforts for anadromous salmon may also depend on developing appropriate strategies for salmon management in the estuarine and ocean ecosystems. REFERENCES EA Engineering, Science, and Technology. 1992. Fisheries Study Report. Report of Turlock Irrigation District and Modesto Irrigation District Pursuant to Article 39 of the License for the Don Pedro Project. Vol. 2. Karr, J.R., K.D. Fausch, P.L. Angermeier, P.R. Yant, and I.J. Schlosser. 1986. Assessing Biological Integrity in Running Waters: A Method and Its Rationale. Illinois Natural History Survey, Special Publication No. 5. Ligon, F.K. 1997. Forensic ecology: a research program to enhance salmon production in the Tuolumne River. Water for a changing global community, IAHR Proceedings, San Francisco, CA, USA Moyle, P.B. and R.Y. Yoshiyama. 1997. The role of adaptive management in restoring chinook salmon to the Tuolumne River. Water for a changing global community, IAHR Proceedings, San Francisco, CA, USA McBain, S. And W. Trush. The fluvial geomorphology of the Tuolumne River: the physical foundation for the riverine ecosystem and its implications for salmonid restoration. Water for a changing global community, IAHR Proceedings, San Francisco, CA, USA Naiman, R.J., T.J. Beechie, L.E. Benda, D.R. Berg, P.A. Bisson, L.H. MacDonald, M.D. O=Connor, P.L. Olson, and E.A. Steel. 1992. Fundamental elements of ecologically healthy watersheds in the Pacific Northwest Coastal Ecoregion. In: R.J. Naiman (ed.), Watershed Management: Balancing Sustainability and Environmental Change, Springer-Verlag, New York. National Research Council. 1996. Upstream: Salmon and Society in the Pacific Northwest. National Academy Press, Washington, D.C.
Orr 7 KEY WORDS Tuolumne River chinook salmon ecosystem management ecosystem health biotic integrity predation macroinvertebrates riparian ecology habitat restoration introduced species watershed analysis