This paper was written as part of the 2006 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.
Ecosystem Management–The Kenai River Estuary with an Emphasis on Herring Gulls
The estuary at the mouth of the Kenai River, on the Kenai Peninsula, is greatly changing due to human influences on this environment. In order to keep the diversity of organisms that live in this area, humans must learn to manage their way of living in order to prevent further destruction of this habitat. Several stressors occur at this location, which can be controlled if taking the proper precautions, and executing careful ecosystem management of this estuarine environment. This area is essential for the lifestyle on the Kenai Peninsula, and without this environment, would be impacted greatly. Obvious change in the biological community are noted from increased populations of herring gulls. In order to restore the ecosystem to a more natural state, a management plan for herring gulls, which includes a sustainable subsistence egg harvest, is proposed.
Our National Ocean Science Bowl Team is from Skyview High School, student population of approximately 600 students, which is located in Soldotna, Alaska on the Kenai Peninsula. (Figure 1 a and b) The population of the central Kenai Peninsula area is approximately 30,000 people.
Our community relies on both renewable and non-renewable natural resources for a major portion of its economy. The area is supported by the oil and gas industries; however, these industries have been in decline in recent years. Commercial fishing and tourism are also very significant economic contributors to the local economies. Combined, the sport, personal use, and commercial fishing industries have been worth over $100 million annually in some years to the economy (Tarbox, 2005).
The challenge for the 2006 Alaska Region Ocean Sciences Bowl was to develop a plan for implementing an ecosystem-based approach to management of a local marine resource. We chose the Kenai River estuarine ecosystem as it is an area of diverse plant and animal life that is an important part of the Kenai Peninsula. We selected herring gulls as this species is at artificially high levels of abundance and provides an opportunity for resource harvest in an eco-system context.
Estuarine areas by definition are dynamic environments, and the Kenai River estuary is no exception. For example, all salmon production in the Kenai River, between 10-20 million adult salmon returns in some years, is dependent on juvenile salmon migrating through this area and making a safe transition from freshwater to marine waters. Thousands of migratory birds, which nest in the far Arctic, stop to rest and feed in this locale while a local caribou population calves in the area.
However, this estuarine environment is under threat from a number of factors, which we will discuss in detail in this paper. We choose to look at the whole estuary initially, instead of focusing on a single species right away, because management biologists and decision makers have, in the past, focused on adult populations or the harvestable portion of those populations and failed to recognize the other critical life history stages of those resources or species that should be managed but are not because of lack of commercial or sport value. Examples of estuarine degradation along the Pacific coast of North America are stark examples of estuaries having their function and structure altered or significantly destroyed which resulted in the loss of those harvestable resources. Before we go into detail, we feel that a definition of eco-system management and how we intent to apply it is needed.
Ecosystem Definition and Management
The term ecosystem, short for ecological system, first appeared in a 1935 publication by the British ecologist Arthur Tansley. However, Tansley's colleague Roy Clapham, had already coined the term in 1930, when he was asked if he could think of a suitable word to denote the physical and biological components of an environment considered in relation to each other as a unit (Columbia Encyclopedia Sixth Edition 2005).
In ecology, an ecosystem is a community of organisms, plants and animals, living together with their environment, functioning as a unit. An ecosystem consists of a dynamic set of living organisms all interacting among themselves and with the environment in which they live (Canadian Forest Service 2003). An ecosystem's abiotic and biotic composition and structure is determined by the state of a number of interrelated environmental factors (Pidwirny 1999).
An ecosystem may be of very different size. It may be a whole forest, as well as a small pond. Different ecosystems are often separated by geographical barriers, like deserts, mountains, oceans, or otherwise isolated, like lakes or rivers. As these borders are never rigid, ecosystems tend to blend into each other. As a result, the whole earth can be seen as a single ecosystem, or a lake can be divided into several ecosystems, depending on the used scale. All ecosystems by definition have interactions between adjoining ecosystems and cannot be seen in isolation. There are marine organisms moving in and out of the estuarine ecosystem and tides bringing in nutrients and saline water. In the case of the Kenai River estuary, some hydrocarbon pollutants from the oil platforms might also be brought in but indications are that it is minimal. However, since many textbooks focus on estuaries as a specific type of marine ecosystem and to keep the focus as manageable as possible, the interaction from the marine environments should be downplayed.
The primary issue for one wanting to manage an ecosystem is what the measures of success or failure are. Pautzke (2002) noted that ecosystem management principles include: (1) our ability to predict ecosystem behavior is limited; (2) ecosystems have thresholds and limits that affecting ecosystem structure; (3) if limits are exceeded changes are can be irreversible; (4) diversity is important in ecosystem functioning; (5) multiple time scales interact in and among ecosystems; and (6) components of ecosystems are linked.
We plan to apply these principles to the Kenai River estuarine area and identify those actions which are in violation of the above principles. We also intend to operate under the assumption that we know very little about this system and, therefore, we must work to maintain the structure of the system as measured by the relative abundance and types of organisms and plants while allowing the system to function and change at some natural rate.
The Kenai River and the Estuarine Environment
Amato (2005) indicated that officially, the Kenai River begins at the Sterling Highway Bridge in Cooper Landing (Figure 1b). From the 20 mile long, mile wide, boomerang shaped Kenai Lake, the river flows westward where it flows to its end at Cook Inlet. The Kenai also spills into Skilak Lake a fifth of it's way down from Kenai Lake. The Kenai River drains 2,162 square miles of the Kenai Mountains and lowlands (FEMA 1999). The average annual discharge is about 5,600 cfs (Scott 1982). A typical annual river cycle begins with a low flow of 800-1,700 cfs in late spring, April, and rises as a result of snowmelt and precipitation, reaching up to 17,000 to 20,000 cfs during August and September (Scott 1982). The river discharge decreases in late September to early October, and freezes over in late November to early December.
Through the last 12 miles of its 50 mile course from Skilak Lake to Cook Inlet, the river becomes estuarine, and dramatically changes in character. The Kenai River has always flowed into Cook Inlet or into a glacial melt water lake before that. As the glaciers melted the Kenai handled all the water by expanding its river valley with erosion. Large volumes of debris of rich melt water flowed into the Kenai from pre-glacial tributaries. The river maintained a braided flow pattern even while it was eroding away the riverbed. The Kenai cut back the valley walls as the channel shifted across the former flood plain. As the river grew deeper it also grew wider due to massive landslides and other forms of colluviums. All the debris from this process transported through the Kenai supplied a fan delta (Figure 2) that grew into the melt water body of Cook Inlet (Reger and Pinney 1996 and 1997).
Diurnal tides dominate the flow of the river, and the flow slows or reverses during incoming tides. The banks are low and covered with blue-gray, estuarine clay silt that is deposited during the twice, daily high tides. These tides cover the entire area once or twice a year (Figure 3).
Near the river mouth, the Kenai River cuts into a 25m high bluff that exposes sandy, pebble gravel. When undercut, these deposits quickly ravel back, producing a loose gravel apron at the base of the lower bluff face. Down stream the terraces on the outside of the meandering river collapse into the river as large blocks and are destroyed by river ice in the winter, which causes the river channel to be two to three times wider than upstream and have a more pebbly gravel covered bottom, (Reger and Pinney 1997).
The unique meandering loops imply that conditions making the loops exist only in this part of the river, and must have taken place over several millennia. The meandering is considered the result of unrestricted movement across the flood plain (Scott 1982). It is also possible that moving tectonic plates contributed to the meandering.
The ultimate source of the sand dunes at the mouth of the river is not known. The sands could have been carried down by the river, and then deposited by the waves and currents after the wind blew it from the beaches. Another theory is that the Kenai River migrated northward and cut into the thick, sandy sub estuarine fan complex there (Reger and Pinney 1997).
Vegetation of the Kenai River Estuary
There are three major types of plants that grow in the wetland areas of the Kenai River Flats. The first is Lyngbye's sedge (Carex lynbyei), which dominates the upper tidally influenced zone where the shore is protected from surf. Some inland areas have high Lyngbye's sedge cover, usually mixed with other plants. Lyngbye's sedge doesn't necessarily need saltwater influence, but it's a good indicator of wetland conditions. Organic matter doesn't accumulate around it, and it is flooded an average of two times per summer.
Ramensk's sedge (Carex rameskii) forms an almost single species dense stand in the protected tidal zone just below Lyngbye's sedge. This tidal zone is the first where ground is almost completely covered with vegetation. This zone floods an average of thirteen times a year.
The most common plants found along the Kenai Lowland shores are alkaligrass communities which include Hulten's (P. hultenii), creeping (P. phyganodes) and nutka (P. nukaensis). This zone floods an average of fifteen times per summer.
Bird Use of the Kenai River Estuary
Davis (2005) conducted informal surveys of the estuary during the 1990s. He found that in the spring thousands of shorebirds and waterfowl use the area to rest and feed and documented greater than 100 bird species using the Kenai River estuary. Peak migration periods were from mid-April to late May for shorebirds and waterfowl.
Hoffman (2005) recently conducted limited surveys from April 2003 — March 2004. The surveys were limited to assessment of impacts from a proposed bluff erosion control project, and, therefore, did not include the entire estuarine area.
Gulls were the most numerous species of bird found during Hoffman's observations, the majority being herring gulls (Larus argentatus), whose numbers peaked in July with thousands observed in a breeding colony on the wetlands across from the bluff. Breeding is possible on the wetlands during the summer due to the lower tides during this time of year. Observations taken on May 14, 2003 indicated that 20% of the herring nests contained one egg. By August 21, 2003 nearly 90% of the herring gulls had fledged. Peak use by herring gulls was concluded to be from early May until the end of August. The birds migrate south to British Columbia and the western United States in the winter.
Blokpoel (2001) reported that herring gulls typically lay 1-2 eggs per clutch. Younger birds tend to lay late in the season. Herring gulls usually breed in their 3rd or 4th year and juveniles do not return to the breeding area until time to breed. If all the eggs are lost early, the birds will lay additional eggs to replace the lost eggs.
Davis (2005) has noted that the herring gull population has increased dramatically over the last 20 years, doubling or more. Population levels have been estimated at 5-10 thousand birds during the peak of the season. One potential reason for this is that the gull colony feeds extensively on the discharge of salmon waste from processing plants in the area. It has been estimated that an average of 5 million pounds of fish waste are discharged annually into the Kenai River by fish processing plants (Shields 2005). This abundant food supply is thought to increase gull survival and breeding success. Examples of this have been documented in Quebec where census of herring gull colonies increased from 650 to 8000 nesting pairs between 1925 and 1975, increased further to 14,000 pairs by 1988 but then decreased dramatically by 1993. The decline appears to related to a decrease in the amount of fish waste as a result of the decline of the commercial cod fishery (Blokpoel 2001).
Herring gulls have been known to displace other nesting and feeding species in the area (Davis 2005). When a herring gull population is dense, the gulls will drive all other birds from their feeding areas (Blokpoel 2001). Herring gulls have been known to drive terns and puffins from breeding grounds in competition for space. In some areas it has been necessary to cull gull numbers to maintain breeding populations of these other bird species (Yptenc 2005). Within the Kenai River estuary, Aleutian terns and Arctic terns have nesting sites which herring gulls are impacting.
Herring gulls are probably a significant source of marine nutrients to the wetlands of the estuary. By feeding on salmon waste the birds transport, via feces, marine nitrogen and other nutrients to the terrestrial environment. Larger gull populations also tend to increase predation on downstream salmon smolts and upstream migrating smelt and other species. In addition fish and invertebrates, herring gulls will consume clams, floating dead animals, and the young of other nesting birds (Blokpoel 2001).
It has been suggested by Davis (2005) that bald eagle (Haliaeetus leucocephalus) populations that concentrate in the estuary may also be artificially high in the spring because of the increased gull population. Eagles have been observed feeding on the abundant gulls available in April and May, prior to the entry of major fish populations into the Kenai River (Tarbox 2005). This higher eagle population may also be impacting the ability of migratory shorebirds to rest and feed in the area.
Bald eagles are most numerous from April and May and are reduced in abundance in the summer and winter. This may be due to the absence of breeding sites and abundant food available in other areas of south central Alaska during these time intervals (Hoffman 2005).
Harbor seals (Phoca vitulina) and beluga whales (Delphinapterus leucas) are frequent users of the Kenai River estuary. Over 40 harbor seals have been counted at one time hauling out on the shoreline of the Kenai River, near RM3. In addition, over 40 beluga whales have been counted in the Kenai River during the spring and fall months. These times correspond to when fish numbers start to increase. Migration of juvenile salmon to the sea from the Kenai River can number in the millions while adult salmon and other species are entering the river in the spring. The adult salmon migration continues in the late fall making a food source available for these marine mammals.
Fish and Invertebrates
There have been four studies on the fish and invertebrates in and near the Kenai River mouth (Bendock and Bingham 1988a and b; Breakfield 2005, and Willette et al 2004). Thirty-one taxonomic groups of animals have been found in the Kenai estuary. Nineteen occur in marine habitats, eight are anadromous, and four usually occur in the estuaries, but can also be found in freshwater or coastal marine habitats (Bendock & Bingham 1988; Breakfield 2005). Some of the fish include: chinook salmon (Onocorhynchus tshawytscha), sockeye salmon (O. nerka), coho salmon (O. kitsutch), Pacific lamprey (Lampetra tridentate), Arctic lamprey (L. japonica), and longfin smelt (Spirinchus thaleichthys).
The Kenai River estuary supports an aquatic detritus food web in winter and a combination of detritus and grazing food webs in summer and fall. Autotrophic productions during the winter decreases due to the lack of sunlight, and the low temperatures. The appearances of finfish that eat zooplankton, insects, and other fishes in June indicate development of a grazing food web but detritivory was still important, the grazing food supply was most likely from autochthonous inputs of organisms from nearby freshwater and marine habitats, because high turbidity in the estuary limited autotrophic production (Willette et al. 2004).
Stresses on the Kenai River Estuary
Philosophically, when resources and their use are altered some change in the ecosystem is expected. Therefore, whether it is the actual harvest of an organism or the alteration of habitat, which causes a change in plant and animal diversity or the rate of change in the system the net effect may be the same. For example, in the Kenai River watershed the removal of beetle killed spruce trees by logging for economic gain or the removal of the trees by burning for fire control may have similar consequence on the watershed. Species diversity changes, not through harvest, but by habitat alteration and management.
These non-direct impacts on plant and animal populations are significant for ecosystem management. Therefore, we decided to identify these factors in the Kenai River estuary and to assess their impact on the function and structure of the system.
Figure 4 defines the location of these and individual areas will be described below.
Sources of pollutants in the Kenai River, upstream of the estuary enter the area via river flow (Figure 4 -#1). For example, hydrocarbons and salted sand from winter road maintenance combine with oil and gas from recreational users ultimately impact the lower river. It has been estimated that 200-300 gallons of gas enter the Kenai River from boat traffic in July (Kenai River Watershed Forum 2003). In contrast, pollutants from the marine environment (Figure 4-#2 and 6) also enter the system via tidal flows. Upstream influence from this source can be to river mile 8.
The Bridge Access Road (Figure 4 -#3, 8 and 9) carries hundreds of motorists over the Kenai River and Kenai River flats to Soldotna and Kenai every day. Impacts to plants and animals come from a variety of sources. Pollutants associated with road runoff can enter both the terrestrial and aquatic environments. In addition to runoff, litter is common along the highway. Of more significance is that the road acts as a barrier to water flow (sheet flow) from one side of the highway to the area. This has resulted in a drying of the area downstream of the highway and a change in plant communities. Direct impacts to animals include collisions with vehicles and bird use of the area has been altered (Figure 4-#11). For example, Erikson (2002) found that individuals walking along the road (Figure 4-#8) way caused fright responses in white-fronted geese (Anser albifron) 50-90 meters from the road, Canadian geese (Branta canadensis) 50-70 meters, and sandhill cranes (Grus canadensis) 80-120 meters.
The Kenai River estuary is influenced by the waste from the fish processing that are located adjacent to the river (Figure 4 - #4). Shields (2005) indicated that on average 16 million pounds of salmon are processed by these facilities annually. Of this approximately 5 million pounds are ground and discharged directly into the river (Davis 2005). As noted, Davis (2005) has hypothesized that this food resource has allowed the breeding herring gull population to double in size. Further the addition of 5 million pounds of organic material is having an unknown impact on the aquatic environment.
Areas where people live and are building houses (Figure 4-#5 and 13), for example the City of Kenai, are additional sources of stress to the system. Impacts associated with urban development include road and yard runoff of pollutants, stabilization of naturally eroding banks to allow development, and waste discharge.
Tides (Figure 4- #6) play an important role in the estuary and are unfortunately a further source of contaminants. From a natural function, when the tide rises, it moves up into the estuary causing the height of the river to rise as well. The rising water reaches up into areas where there are decomposing plants and washes them into the river, where they float, sink to the river bottom, or are carried out to sea. Plant matter can also be carried down from upriver. This action contributes to the detritus food web in the estuary. However, tides also bring contaminants into the system from the marine environment. These include oil and gas from vessels leaving the port of Kenai, waste from discharges into the environment from both point and non-point sources.
A public boat launch (Figure 4- #7) has altered both aquatic and terrestrial environments. Impacts with roads and vehicular traffic are similar to those noted above. In addition, wetlands have been filled, to create the road and parking areas.
Selection and Management of Herring Gulls
We recognized from the start of this project that there are far too many stressors in this area that a species specific management plan can solve. However, in using our principles, we have focused on developing a management plan for herring gulls that should help restore the natural function and structure of the estuary, provide a benefit to native cultures, and be sustainable.
We do not know the interactions of the estuary in enough detail to make species specific evaluations of our plan. We do know that if the system is allowed to operate in a natural state (ecosystem integrity) it should continue to provide the functions so critical to healthy populations of plants and animals. Therefore, the imbalance in the system caused by the increasing herring gull colonies needs to be examined and a practical management plan for herring gulls defined.
The objective of this management plan is to reduce the number of herring gulls by one half. This will approximate the population level to what it was in 1980. This is based on Davis (2005) observations. In addition, the fish processing plants were processing only one third the harvest of today's salmon production (Tarbox 2005).
Techniques to reduce gull numbers could include any or all of the following: (1) transport waste out of the system via pipe or barge to offshore Cook Inlet or via truck to another area; (2) we could cull the birds via hunting or controlled harvest; and (3) we could selectively harvest the eggs prior to hatching.
It is very possible that by reducing the herring gull numbers, other scavengers might move in. Other efforts should be pursued as well. Reduction of the fish waste is also desirable. A long pipeline or barging of the fish waste is possible. We have no cost accurate cost estimates, but feel it would be the responsibility of the fish processors to absorb the cost. Focusing on the herring gull population seems to be the easiest option for the greatest probability of restoring balance.
Culling the gulls in the spring as the gulls return from their wintering areas is possible but would probably significantly impact migrating waterfowl and shorebirds that rely on this area for resting and feeding. This would not be an ecosystem approach. Therefore, we decided to create a new subsistence or educational harvest of herring gull eggs. Herring gull eggs have been harvested commercially in the past and presently are in the diet of Native Alaskans (Blokpoel 2001). For example, Fall and Utermohle (1999) reported that 62% of households in the village of Nanwalek, Alaska used gull eggs during the study year 1997-1998. A total of 191 pounds of gull eggs were harvested. In addition to this use pattern Native Alaskans are harvesting geese eggs in Anchorage, Alaska to control geese populations in this urban area.
Initially, we have set a target harvest level of eggs at 1000-2000. This is based on the estimate of 3500 birds in the spring prior to hatching (Hoffman 2005). We have assumed that at least 4000 birds (2000 breeding pairs) were present in the area since Hoffman (2005) did not survey the entire estuary. This would translate to 2000 to 4000 eggs for the colony. Therefore a harvest of 1000-2000 eggs should significantly reduce the population over time. At least one egg would be left in each nest to prevent breeding pairs from laying additional eggs. This also should prevent over-harvesting and an unacceptable population decline.
We envision this harvest to be managed jointly by both State and Federal agencies as are geese and other migratory bird species. The harvest would be controlled by a permit system, which limits the number and time people can enter the area. Disruption of the breeding colony will be kept at a minimum.
We would expect that the following should occur to provide ecosystem integrity: (1) gull numbers should be reduced to no more than one half of the present population; (2) existing Arctic and Aleutian tern breeding colonies should be maintained and even expanded back to original locations; (3) predation on migrating salmon smolts should be reduced; (4) spring concentration of bald eagles may be reduced; (5) nutrient transfer to adjacent wetlands from bird feces will be reduced but not eliminated; (6) competition with other seabirds and gulls for feeding areas should be reduced; (7) predation on other nesting bird species should be reduced; and (8) reduced numbers of migrating gulls should reduce impacts on other ecosystems along their migration route.
We feel that the Kenai River estuary integrity will be enhanced with this management plan.
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