Monitoring restoration success: Assessing Marine-Freshwater Food Web Linkages Using Stable Isotopes Dr. Karen Wilson, University of Southern Maine Dr. Graham Sherwood, Gulf of Maine Research Institute Dr. Jonathan Grabowski, Gulf of Maine Research Institute Dr. Theodore Willis, University of Southern Maine – Aquatic Systems Group

Juvenile lamprey migrate to sea sea lamprey larvae Spawning sea lamprey AprilMayJuneJulyAugSeptOctNov estuary tidal brackish tidal fresh Mainstem or tributary ponds/lakes Elvers move upstream Mature adult eels leave freshwater Adult alewife Spawning ALE ALE YOY exit lakes ALE YOY Shad Spawning shad Shad YOY exit river shad YOY Salmon parr Adult salmon Spawning salmon Salmon smolt exit river Adult bluebacks Blueback YOY Spawning bluebacks Blueback YOY exit river Smelt YOY exit river Smelt ad smelt YOY Spawning Smelt Also in the lower river: Shortnose sturgeon Atlantic sturgeon Tomcod Striped Bass

Penobscot River Restoration Project

Food Web Restoration Indicators IndicatorRationale & desired outcomes Trophic levelsMore trophic levels = more diverse predator-prey interactions greater prey availability greater ecosystem complexity (i.e., more pathways for food web interactions) ConnectivityGreater reliance on prey from non-focal habitats (i.e., marine vs. freshwater) indicating increased marine-freshwater linkages See

Carbon and Nitrogen stable isotopes: “you are what you eat” Light (common) & heavy (rare) isotope forms differ by # of neutrons Heavy nitrogen ( 15 N) is more difficult to excrete, so is accumulated from prey to predator as it moves up the food chain Approximately 3 – 4 δ 15 N(‰) units between trophic levels (primary producer, primary consumer, secondary consumer, etc) Primary producers [plants] assimilate heavy carbon ( 13 C) under carbon-limited conditions, which vary depending upon habitat Animals do not distinguish between heavy & light carbon, so carbon reflects the original source of carbon in their prey

You are what you eat: 15N indicates trophic position 13C indicates habitat- in this case: –freshwater (lighter) –marine (heavier) Other critical advantage: stable isotope signatures of slow turn-over tissues integrate feeding relationships over many months

With increases in anadromous fish, particularly alewife, it is expected that: Spawning alewife add marine-derived nutrients through spawning, excretion & mortality, shifting freshwater 15 N signatures higher and enriching freshwater 13 C towards heavier (marine) values. YOY or juvenile alewife may become important forage for larger predators, increasing trophic position of some species (SMB, CP, cod, mackerel). Nearshore marine predators may consume out-migrating YOY alewife in greater numbers, shifting marine 13 C signatures towards lighter (freshwater) values.

Expectations: carbon river mouth  13 C( ‰ ) Marine carbon signature Freshwater carbon signature Before Restoration After Restoration freshwatermarine Distance from river mouth

Field collections Muscle tissue samples from common fish & top predators (bass, chain pickerel, cod, mackerel) –freshwater fish collected in collaboration with U. Maine Fish Index Surveys –marine fish collected in part in collaboration with MeDMR Tissue samples from food web base –primary consumers including snails (benthic algae) & mussels (phytoplankton) –secondary consumers (crayfish, crabs, insects)

Freshwater sites: Penobscot River and Tributaries

Penobscot River

Marine sites: Penobscot Bay A B C D E

RV ‘Gadid’ - GMRI September 2009

FV Robert Michael – ME/NH inshore trawl survey May 2010

del 13 C del 15 N Penobscot Bay Pushaw Stream Pen Riv Below VZD Pen GW Impoundment Pen VZ Impoundment SMB snail CP mussels snail Odonata SMB snail urchin brittle star mussel predatory snail sea star lobster cod, sculpin, crab, pollock WS eel bivalve Odonata bivave snail eel SMB RBSF WS YP RBSF YP GS PS eel FW Marine lamprey alewife blueback mackerel

Chain pickerelSMBMackerelAlewifeBlueback Cod Percent FW influence  Influenced by adult alewife? Influenced by juvenile alewife?

Connectivity Pushaw GWI VZDI Below VZD ABCDE River Mouth Del 13C Inverts_River Fish_River Fish_Bay Inverts_Bay

What’s next? Analyze new samples (more fish and inverts from Pen bay and additional tributaries) Comparison to Kennebec River system (2010) Re-sampling post dam removal

Mechanisms: high abundances of river herring Spring Fall Freshwater Marine Summer