Effects of Marine-Derived Nutrients on Productivity in Sockeye Systems

Collaborative Project Funded by Watersheds Initiative of the Gulf Ecosystem Monitoring (GEM) Component of EVOS IMS/UAF Bruce Finney Terry Whitledge Dean Stockwell Melanie Rohr ADF&G/Kodiak Steve Honnold Switgard Duesterloh Steve Thomsen

General Rationale for EVOS Initiative Marine-Derived Nutrients from Salmon may be Important in Aquatic and Terrestrial Ecosystem Processes Traced into Freshwater Plankton, Juvenile Anadromous and Resident Fish Traced into Riparian Vegetation and Terrestrial Animals MDN Fluxes are Linked to Ocean Processes Through Climate, Fishing, Oil Spills Ecosystem-Based Management Needs Data to Determine MDN Pathways, Ecosystem Importance and Monitoring Protocols Basic Research Needed!

Study Design: Sampling Sockeye (Karluk) and Control (Spiridon) Lakes 3 Year Study 9 Samplings/year (April - October) 2 Lake and 2 River (mouth) Stations at Each Lake Full Water Column Sampling (5 m intervals to bottom)

Karluk Spiridon Elevation (ft) Watershed area (10 6 m 2 ) Lake area (10 6 m 2 ) Volume (10 6 m 3 ) Mean depth (m) Residence time (yr) Anadromous YES NO Stocked Long-term limnological and salmon data available Site Characteristics

Study Design: Analyses Temperature, DO, pH, light TP, dissolved P, NO 3 -, Si Chlorophyll, POM, phytoplankton, zooplankton, juvenile and adult salmon Primary Productivity Stable Isotopes (  15 N,  13 C) on: POM, periphyton, zooplankton, juvenile and adult sockeye Exploratory Studies:  15 N,  13 C on terrestrial plants, bears, birds

Unique Study Relatively well-matched pair of lakes, except for salmon Previous Limnological and Paleoecological data show strong impact of MDN in Karluk Lake Detailed spatial and temporal sampling Measuring primary productivity Complete/integrated stable isotope analyses  15 N: enriched in salmon carcasses - tracer of MDN

Comparison of Limnological Profiles Between Lakes

Same for Early October

Summary Part 1 (Limnology): Similar physical regime Very different ratios of major nutrients Spiridon: P-limited Karluk: P, Si and N limited Consistent with MDN source MDN: high P, zero Si Higher algal standing stock in Karluk by ~ 4X

Comparison of seasonal cycles between lakes and rivers

River spawners Beach spawners

Surface

Summary Part 2 (Temporal perspective): Karluk Lake higher Chl a and primary productivity by ~ 5X  15 N higher in Karluk Lake and river phytoplankton (POM), zooplankton and juvenile sockeye relative to Spiridon Lake Differing seasonality: Late summer/early fall peaks in Chl a, primary productivity, biota  15 N and some nutrients in Karluk Temporal relationships suggests influence from the early, river spawning run of sockeye: reasonable lag between escapement at downstream weir, rivers and open lake stations Transfer into higher trophic levels indicated Data support hypothesis that MDN is main control

Thanks to: EVOS/GEM for funding Phil Mundy The dedicated field and lab personnel

Escapement/Lake area (1000s/km 2 )  15 N Zooplankton Sockeye smolts

Controversy? Two Views Salmon-derived nutrients are essential to freshwater and terrestrial ecosystems, and are key to the restoration and sustainability of salmon Salmon-derived nutrients are not that important, and the top- down effects of escapement on lake ecosystems is substantial

Salmon-Derived Nutrients - Productivity Feedback Freshwater Productivity Nutrients Spawner Abundance (escapement) Juveniles