6/8/2018

The spread of zebra mussels

The Minnesota invasion

Data from USGS Nonindigenous Aquatic Species Information Resource

Impacts of the mussel invasion

  • Changes in water chemistry
  • Decreases in plankton densities
    • Decreases in native mussel populations
    • Changes in water clarity
    • Increases in plant cover

Managing the invasion

At high densities management options are limited

However, at low densities options depend on:

  • the spatial distribution of the population
  • the rate of increase of the population

Surveying mussels

We used divers to search for zebra mussels

Photo credit: Naomi Blinick

Photo credit: Naomi Blinick

Why shouldn't we just go out and start counting?

  • Difficult to control diver effort
  • Hard to reproduce
  • Useful for detecting presence but not for estimating density

Benefits of using a more formal survey design

  • Can control the amount of survey effort
  • Can revisit in following years
  • This means we can make comparisons across space and time

Existing designs

  • Discovery in low densities (timed searches)
  • High-densities (quadrat surveys)

But what about designs for moderate densities?

Application to MN

Lakes surveyed last year

Detectability is low

Why is detectability low?

Estimating detection

Distribution of detections

Estimating detection in Lake Burgan

Modeling zebra mussel density

\(P\) is the detection probability of detecting a zebra mussel

  • Observed density: \[\frac{X}{A}\]

  • Estimated density: \[\frac{X}{P\,A}\]

Density estimates

The observed density of zebra mussels in Lake Burgan was 0.08 mussels per square-meter.

The estimated density, corrected for detection, was 0.37 mussels per square-meter.

What we are doing this summer

Exploring tradeoffs in survey efficiency

Trying to survey more area (efficiently)

+

Acknowledgements

John Fieberg

Michael McCartney

Naomi Blinick

Leslie Schroeder

Sarah Baker

Aislyn Keyes

Austin Hilding