7/27/2019 Asian Carp Ecological Modeling

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Projected Harvest Levels for Controlling Asian Carp Populations in the Illinois River

Bio 325: Ecological Modeling and Conservation Strategies

Chris Ives, Rick Sykes, Will Travis, & Shawn Swaney

Background:Over the past several decades, invasive Asian carp populations

have been increasing at harmful rates in the United States.

Originally imported as a method of controlling aquatic plant and

phytoplankton, their high fecundity rates and lack of natural

predators resulted in a dramatic population increase. The species

of major concern are the s ilver carp (Hypophthalmichthys molitrix)

and the bighead carp (Hypophthalmichthys nobilis), both of which

feed on phytoplankton in rivers and lakes. As the carp consume

phytoplankton, they consequently disrupt the basis of the food

web, making Asian carp a direct threat to native species and

commercial businesses that rely on the environment. Harvesting is

a currently proposed method of population regulation.

Objective:The current model evaluates the necessary methods required to

regulate the Asian carp population in the Illinois River so they do

not reach the Great Lakes, which would result in a total collapse of

Great Lakes fisheries and connecting waterways. We examine the

harvesting proportions needed to manage the Asian carp

populations and eventually result in their local extinction in the

Illinois River.

Methods:A model was developed using Vensim programming to simulate

natural conditions for population growth of Asian carp in the

Illinois River. The model (see Fig. 1) was designed in a stage-based

fashion to observe the natural effects and mortalities of carp

during development. The analysis of the model proceeded as

follows:

1) A deterministic model was run looking at different growth rates

at a given harvest proportion. This allows for an examination of

an ideal harvest proportion of the population to drive the

species out of the area. All survivorship and mortality data were

collected from external biological references.

2) The model was run incorporating environmental stochasticity.

Asian carp require specific river conditions in order to lay eggs

and have the eggs survive to the first stage of juvenile

livelihood. Data were taken from the USGS database to

determine the percentage of days during the breeding months

that meet the minimal requirements for reproduction. From

these data, we included water velocity, water temperature for

laying eggs and water temperature for egg survival to juvenile.

Following model analysis and data collection, all results were

compiled in order to determine optimal harvest levels for Asian

Carp.

Results/Discussion:A) Figure A illustrates the difference between running the

model with stochasticity and without stochasticity(deterministic). In the deterministic run, all populations continue

to grow until 55% of carp are harvested. As expected, when

harvest levels are increased, the carp populations are driven

toward extinction. On the other hand, the stochastic run yielded

a more rapid population decline toward extinction. Model

simulations were conducted at harvest proportions of 30%, 60%

and 90%. The data displayed are average values of extinction

years through 100 independent simulations.

B) Figure B compares the breakdown of 100 stochastic

simulations at harvest proportions of 30%, 60% and 90%

respectively. At 30% harvest the majority of populations go

extinct within 75 years. Yet, there were simulations that still

yielded a population of carp after 100 years. However, at 60%

harvest all populations were extinct by 30 years and most before20 years. Finally, at 90% harvest all populations were extinct by

10 years.

Conclusions:Based upon the collected data, it can be concluded that optimal

harvest levels reside around 60%. At this rate, all populations are

guaranteed to be extinct within 30 years. A correlation exists

between harvest proportion and time to extinction. Thus, harvest

levels can be varied according to the needs of the environment

being evaluated.

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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

YearstoE

xtinction

Harvest Proportion

Average Years to Extinction for Varying Harvest

Proportions for Deterministic and Stochastic Models

Deterministic

Stochastic

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5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100+

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ofExtinction

Number ofYears to Extinction

Extinction Pattern for Varying Harvest

Proportions for Stochastic Model

Harvest Proportion = 0.3

Harvest Proportion = 0.6

Harvest Proportion = 0.9

B

References:For more information on the Asian carp problem in the IllinoisRiver, visit www.asiancarp.us

Fig. 1