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Scientific Investigations Report 2012–5016


Dispersal of Larval Suckers at the Williamson River Delta, Upper Klamath Lake, Oregon, 2006–09


Introduction


Deltaic marshes at the mouth of the Williamson River were once among the most important habitats for larvae of the endangered Lost River sucker Deltistes luxatus and shortnose sucker Chasmistes brevirostris, due to their location downstream of known productive spawning grounds. In 1996, The Nature Conservancy purchased the property surrounding the mouth of the Williamson River and began a large-scale restoration project that would ultimately reconnect the Williamson River with 2,500 ha of land that had, prior to the 1940s, composed the wetlands of the Williamson River Delta (hereafter referred to as the Delta). In October, 2007, the levees around the northern half of the Delta, referred to as Tulana (fig. 1), were breached mechanically and with a series of explosions to reconnect it to Upper Klamath Lake, flooding approximately 1,500 ha of former agricultural land. Then in November, 2008, roughly 1,000 ha of land in the southern half of the Delta, known as Goose Bay (fig. 1), was flooded through mechanical removal of several large sections of levee. A primary goal of this restoration project was to restore the function of these wetlands as nursery habitat for the endangered Lost River and shortnose suckers, endemic to the Upper Klamath Basin.


Lost River and shortnose suckers are long-lived (as much as several decades), iteroparous lake dwellers that typically travel into the tributaries to spawn in the early spring (Scoppettone and Vinyard, 1991; Terwilliger and others, 2010). Upper Klamath Lake is the current population stronghold for both species. Large numbers spawn in the Williamson River between river kilometers 10 and 17.5 (the delta apex is at about river kilometer 5.6), in the Sprague River upstream of the confluence with the Williamson River, and as far upstream as river kilometer 120 (Ellsworth and others, 2011). In addition, a small cohort of Lost River suckers spawn at lakeshore spring areas along the eastern edge of the lake (Janney and others, 2008). After the larvae leave the gravel at the spawning grounds, they immediately begin drifting downstream at night with the river flow (Cooperman and Markle, 2003; Ellsworth and others, 2009). Before restoration, the travel time between spawning grounds and Upper Klamath Lake was as short as 1 day, resulting in many larvae entering the lake prior to caudal fin formation and yolk sac absorption (Cooperman and Markle, 2003). Age-0 sucker habitat use has been described as consisting of nearshore, vegetated areas as well as deeper, open water areas of Upper Klamath Lake and can vary depending on water quality conditions (Reiser and others, 2001; Cooperman and Markle, 2004; Crandall and others, 2008; Burdick and Brown, 2010; Burdick and Vanderkooi, 2010). 


The restoration of the Delta created myriad complex pathways connecting the lower 3 mi of the Williamson River channel to Upper Klamath and Agency Lakes, which should increase the travel time to the lakes for many of the larvae (Markle and others, 2009). The increase in emergent vegetation associated with wetland restoration at the Delta is expected to provide sanctuary from wind turbulence (Cooperman and others, 2010), ample feeding and growing opportunities (Crandall and others, 2008), and predator protection (Markle and Clausen, 2006; Markle and Dunsmoor, 2007). All of these, in combination with the increase in time between swim-up and entry to the lakes, could potentially contribute to a strong year class formation and aid in recovering these species.


It is of interest to stakeholders to know if the restoration has been successful and to what extent larvae are using the Delta, as well as the differences in the size and age of sucker larvae that are found in the lakes after having spent time in the newly restored wetlands. Collecting fish samples in an area as large as the Delta and surrounding lake habitats is resource intensive, and cannot be done with the spatial and temporal resolution required to resolve the true variability in the system. With properly defined boundary conditions, numerical models that simulate the transport of larvae are a useful means of augmenting net catches by providing information at temporal and spatial scales that otherwise is unattainable. A model can both help biologists visualize what is happening over the large area of the Delta, and, where model simulations differ from direct observations, can provide guidance as to where assumptions about larvae behavior that are embodied in the model have broken down. Furthermore, once confidence in a model is established, it can be used to predict how larval transport might differ under different scenarios for the active management of the system, primarily in terms of the lake elevation, for a given Williamson River flow and meteorological conditions.


The application of models to the dispersal of larvae in marine environments has received much attention in the literature in the past several decades. These studies are designed with one of three problems in mind: (1) connectivity—the movement of larvae between geographically separated populations (Hare and others, 2002; Nahas and others, 2003; Paris and others, 2009; Watson and others, 2010), (2) adaptive sampling—the real‑time modification of sampling strategies in order to most effectively sample a population (Pepin and others, 2009), and (3) recruitment prediction—the number of fish reaching a defined size, age, development stage, or suitable nursery habitat (Reyns and others, 2006; Hinckley and others, 2009; Mariani and others, 2010). Examples of models applied to the problems of freshwater dispersal are fewer (Beletsky and others, 2007). Marine larval dispersal typically takes place over larger spatial scales and longer time scales than are pertinent to the problem of the dispersal of sucker larvae through the Delta. Marine applications typically include vertical as well as horizontal variability. In this study, done in cooperation with the Bureau of Reclamation, the relevant concepts that have been developed for marine larval dispersal were adapted to a large, shallow lake with a complex spatial geometry in which the currents are primarily wind driven. In analogy to the recruitment prediction problem in the marine environment, the goal is to understand how the physical reconfiguration of the landscape at the Delta and environmental conditions (Williamson River flow, lake stage, and meteorology) determine the distribution of a larval cohort after it leaves the spawning grounds (that is, the number of fish that will occupy the habitat on both sides of the Delta before entering the open waters of the lake).


First posted April 2, 2012

For additional information contact:
Director, Oregon Water Science Center
U.S. Geological Survey
2130 SW 5th Avenue
Portland, Oregon 97201
http://or.water.usgs.gov

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