Predation Impacts of Round Goby on Zebra Mussels in the Great Lakes Megan Fencil

Static vs. Dynamic modeling In fisheries ecology, GIS is mainly used for descriptive mapping. Increased need for visualization of ecological models - spatially and temporally dynamic factors - interaction of species when they meet I’ll focus on predator-prey interaction of round gobies and zebra mussels Difficulties: Large number of assumptions Too many interaction effects to model Lack of data Water is a dynamic medium, so it’s properties change over time (temp, light penetrance, turbidity, food supply) Difficulties: (assumptions): population-based rather than individual model assumes all indivs act the same way (interaction effects): nature doesn’t follow orderly rules, so unexpected interactions can give different results than expected (lack of data): data based on presence/absence rather than numbers. So I’ll generate a range of numbers for the model and see how the model behaves at low and high densities of prey and predators.

Zebra mussel (Dreissena polymorpha) Native to Russia Introduced to U.S. in ballast water Negative impacts: clog pipes, foul ships, litter beaches, sink buoys, colonize native animals $5 billion cost in 10 years (U.S. Fish and Wildlife Service) Positive impact: improved water clarity from 6 inches to 30 feet! Filtering rapidly clears water of even the largest lakes Each can filter up to 1 gallon/day, despite tiny size 1 billion in lake erie, filter 1 billion gallons/day But, that water also holds food for native filter feeders

Zebra mussels spread very rapidly! 1st U.S. appearance in 1988: Lake St. Clair < 10 years: all Great Lakes, Mississippi, Tennessee, Hudson, and Ohio River basins Mostly spread by freighter ballast Recreational boats on trailers are only explanation for mussels reaching isolated lakes & quarries

Round goby (Neogobius melanostomus) Native to Black & Caspian Seas Introduced to U.S. in ballast water Negative impacts: Aggressively eat eggs & fry of native fishes Outcompete native species for nest sites Excellent sensory system gives an advantage (night) Very robust Spawn over long time period in summer Rapid population growth (20/m3 in Calumet Harbor = 20 fish in a bathtub) Males pugnaciously defend their nests Senses: can feed in complete darkness, better than natives Robust: can get into small crevices: eat trout eggs and get into ship’s ballast tanks Spawning: each female up to 5,000 eggs, guarded by males so they survive well. Don’t spill your bait bucket or take gobies home for aquarium!

Round gobies competitively displace native species Is there room for one more?

The spread of round gobies 1990: St. Clair River (channel between Lake Huron and Lake St. Clair) 1994: well-established in Lake Erie 1995: Lake Superior and Lake Michigan Ohio State University Preventing the spread: electric goby barrier Map modified from USGS website,2001

Interaction of gobies and zebra mussels Gobies eat up to 78 zebra mussels/day Gobies prefer small mussels near the substrate Mussels in goby-free waters are larger Gobies are main predators of mussels BUT, zebra mussels will not disappear due to gobies Negative effect of predation: mussels filter-feed and bioaccumulate toxins Sport fish (bass, walleyes, perch, trout) may be affected Most work done at Bowling Green State University by Dr. Jeff Miner and Great Lakes Science Center Once an invasive species is established, it can’t be eliminated BUT we can control its spread Mussels’ tissues absorb whatever toxins were in water. Gobies eat lots of mussels and absorb those toxins. Sport fish eat lots of gobies (can be significant bioaccumulation if goby density is high)

Work in Progress: Clarifying the problem with ArcGIS Apply a population growth model to overlaid distribution maps of mussels and gobies - Where do they interact? - What will be the effect on mussel population size? Population growth for prey (zebra mussels) population (Lotka-Volterra): dH / dt = r H - b1 H P H = number of prey P = number of predators r = rate of growth for prey population b1 = predation rate (coefficient expressing the efficiency of predation) Gobies and mussel have the potential to interact where their populations overlap. We’re not sure this is always the case, but it’s an assumption. Where gobies and mussels already overlap, they may already be regulating each other’s population sizes. How will a new introduction of either species affect the other?

Predicting the potential spread of invasives “Hitchhikers” are carried on/in recreational boats If they arrive at an new site, can they survive? Potential for invasion requires proper conditions: Light Depth pH Temperature Food supply Gobies and mussels will only co-exist if both of their habitat requirements are satisfied. If a boat’s ballast dumps invasives into this site, what are the chances they’ll survive? If a new site can only support mussels but not gobies, it might have more of a problem with mussels because they aren’t eaten. Overlay of layers can predict invasion success - Several currently uncolonized sites will be studied - Can they support zebra mussels and/or round gobies?