Can filter-feeding Asian carp invade the Laurentian Great Lakes? A bioenergetic modeling exercise. Sandra L. Cooke and Walter R. Hill Institute of Natural Resource Sustainability, Illinois Natural History Survey, University of Illinois Andrea Guibord

Could planktonic food resources actually support the growth of Hypophthalmichthys molitrix (Silver carp) and Hypophthalmichthys nobilis (Bighead carp) in the Great Lakes?

What are these species? “Asian carp” is a catch-all name for four species of carp: Silver, Bighead, Grass, and Black.

Most worrisome: Silver Bighead

Young Bighead and Silver carp may consume up to between % of their biomass daily.

What do they feed on?

How did this species get here?

They entered the U.S. in the ’70s, back when fish farmers along the Mississippi River imported them for aquaculture

In the ’80s, massive river flooding carried the carp into the Mississippi River—and they’ve been slowly making their way north

Battling the Invader 75M 75M

Currently: Samples taken within 10 miles of Lake Michigan have tested positive for carp DNA. Lake Erie affected Once they make it into the lake, they’re expected to easily spread to the other Great Lakes within 20 years.

Purpose To develop bioenergetics models for bighead and silver carp using 1) empirically determined respiration rates 2) bioenergetic parameters (derived from literature on Asian carp and other species) These models were then used to assess the theoretical potential of both these species to colonize habitats in the Great Lakes based on plankton biomass and surface water temperature data.

Also taken into account: The theoretical analysis also took into account the possible effects of 1) thermal stratification 2) swimming costs on carp growth 3) movement estimates The hypothesis was that most open-water habitats of the Great Lakes will be much less likely to support the establishment of these carp species due to between- habitat differences in plankton biomass and temperature.

Methods Bighead and silver carp models were structured using the popular Wisconsin bioenergetics model.

Basic equations were utilized:

One more equation:

Temp dependent coefficient for tilapia was used as they are planktivorous filter feeders with thermal tolerances and feeding characteristics very similar to Asian carp. The team also assumed that Asian carp energy density was the same as adult tilapia.

Determining temperature dependence parameters of the consumption equation: Mean optimum temperature and maximum temperature above which consumption ceases utilizing values reported for Asian carp were calculated.

NOTE: Bighead and Silver carp filtration and consumption rates are highly variable. They are dependent not just on body size and temperature, but also on particle size.

Daily consumption requirements of bighead and silver carp for basic metabolic maintenance were predicted

These consumption requirements were predicted for different swimming speeds (Temperatures were kept consistent because the purpose was to assess the effects of body size and swimming speed on consumption)

Consumption rates Consumption rates were converted to energy requirements and expressed in terms of environmental prey densities.

To model the growth of carp feeding in different types of habitats within the five Great Lakes, the following four sources of data were compiled:

Phytoplankton Biomass

Zooplankton Densities

Zooplankton Biomass

Water Temperature

As a control, the model was also applied to several riverine sites to demonstrate that the model predicts positive growth in habitats where Asian carp have already invaded

Bioenergetics models were used to estimate expected growth of juvenile and adult carp in a region during a 30 day period

To assess the effects of temperature on growth rates, four open water habitats which are normally thermally stratified during summer were reviewed for 1) summertime plankton data 2) growth at surface temperature The sites were as follows:

Lake Michigan’s Southern Basin

Collingwood Harbor (Lake Huron)

Central Basin of Lake Erie

Nearshore zone of Sandy Pond (Lake Ontario)

The model was run at different temperatures from 4-24 degrees C for 30 days of feeding

Separate simulations at a constant temperature were run for each temperature in order to more effectively compare the growth of a feeding carp at each of the varying depths. (Carp growth in the warmer epilimnion)

Results: The specific consumption rate required to maintain a constant fish mass increased with swimming speed and decreased with fish size.

Silver carp specific consumption rates were slightly higher than big head carp.

Results: Energy requirements:

Although the differences between reproducing and non- reproducing adults were smaller at higher speeds because of the higher energetic costs of swimming A = silver B = Bighead Example: 2400g female spawning at 5% of it’s body mass at speeds from 0-4 cm per second

Results: Food Requirements

Environmental requirements are similar for non-producing Asian carp of different sizes because of the greater filtration rates of larger carp

Example Projected growth of non-swimming Bighead and Silver carp feeding on plankton in different regions of the Great Lakes was negative in nearly all open- water regions of Lakes Michigan, Huron, Ontario and Superior. Location Time of year, water temperat ure (°C) Phyto. wet mass (mg L −1 ) Zoop. wet mass (mg L −1 ) Predicted % biomass gain or loss over 30 days Reference s 10 g BC10 g SC2400 g BC2400 g SC 1.Open-water habitats near wetlands are indicated after the site name (wet), zooplankton samples excluding rotifers are noted in the reference column (NR), and negative growth values are highlighted in boldface. Lake Michigan southern basin, nearshore May, −15−9−9−3−3−3−3 C. E. Cáceres unpubl. data (zoop); Ga rdner et al., 2004(Chl a)Ga rdner et al., 2004 Jul, −29−30−6−6−10 Sep, −20−23−4−4−9−9

Energy expenditure pxNE pxNE

Positive Growth projected Greenbay, Western Lake Erie, and all of Lake Erie during the spring, the embayment regions of Sodus Bay and Sandy Pond in Lake Ontario and select wetlands.

Maximum distances Table 4. Maximum distance that can be travelled, based on bioenergetics models, by juvenile (10 cm, 10 g) and adult (60 cm, 2400 g) bighead carp (BC) and silver carp (SC) over 30 days in different habitats at different times of year (Spr = spring; Sum = summer). Open-water habitats near wetlands are indicated after the site name (wet) Location Time of year; water temp. (°C) Maximum distance of travel over 30 days (km) 10 g BC10 g SC2400 g BC2400 g SC Lake Michigan Green Bay Apr Jun Lake Superior Chippewa Park (wet) Jul – Pine Bay (wet)Jul –2.4– Hurkett Cove (wet) Jul –2.9– Lake Huron Collingwood Harbour Jul –2.6– Lake Erie West basin Spr, Sum, Central basinSpr, East basinSpr, Lake Ontario Sodus Bay embayment Jul Sandy Pond embayment Jul Frenchman’s Bay (wet) Jun Rivers Middle MS River (Chester) Aug, Middle MS River (Grand Tower) Oct, Upper MS RiverSum, Missouri RiverSum, The maximum distance that carp could travel in different Great Lakes habitats without losing biomass over 30 days ranged from km for 10g bighead and silver carp and km for 2400g carp.

Growth Simulations Growth simulations at different temperatures suggest that carp would generally have higher growth rates at lower temperatures. However, carp were projected to lose biomass at surface temperatures – modeled growth was positive at low temperatures at <8 Celsius in all four habitats.

Wrap -Up Modeling results indicate that the low concentrations of plankton in many open water regions of the Great Lakes cannot support growth of Silver and Bighead carp.

Threat? The threat appears to be small. However, results indicate that more productive regions such as Green Bay, the western basin of Lake Erie and other embayments and wetlands may contain sufficient plankton to meet energetic requirements at certain times of the year at certain temperatures.

Additionally: Simulations predict that carp could still travel up to 40 km over a 30 day period while maintaining body mass.

Likelihood of Asian Carp to become established in most near shore or offshore pelagic habitats of Lakes Ontario, Michigan, Superior or Huron is slim – however: Could indirectly affect these ecosystems should they become established in adjoining embayments and wetlands.

Although carp growth predicted to be negative in the four testing sites, this could change as a result of the following circumstances:

1.) When modeled at surface temperatures of degrees C, growth may be positive if carp were to feed in deeper and colder water where zooplankton reside during the day.

2.) Veliger larvae may serve as a food source should the carp move into an area with zebra mussels. (Lack of plankton vs. veliger as a food source)

3.) Changing temperature and increased nutrient inputs could increase plankton biomass or other zooplankton and phytoplankton community structure.

4.) Possible zooplankton swarms

5.) Extreme wind gusts, gyres, other physical phenomena = possible patches of zooplankton (could be sufficiently dense - although temporary)

Lack of rotifer data missing info may underestimate potential carp growth Ex: Mississippi and Illinois rivers studies show diets of Bighead and Silver carp dominated by rotifers. This study suggests that carp modify their diets based on prey availability Note: Rotifers make up 5- 20% of zooplankton biomass in the Great Lakes

Important implications: If Asian carp were to enter the “plankton desert” of Lake Michigan via the Chicago Sanitary and Ship Canal, study shows that the likelihood is slim (but not impossible) that they would derive sufficient energy from plankton to support the energetic costs of travelling to the next “plankton oasis”

Analysis suggests a greater risk of Asian carp invasion through: Inadvertent use of bait Canadian live fish markets in close proximity to productive harbors and embayments of Lakes Ontario and Erie

Modeling results also suggest positive growth possible in the Lake Michigan region at Chicago gateway. (despite low plankton rations)

Important to emphasize: Bioenergetics models are only one component of what should be a more extensive approach to assessing the invasion risk of Asian carp.