Variation in Native Micro-Predator Abundance Explains Recruitment of a Mobile

Invasive Fish in a Naturally Unstable Environment

Przemyslaw G. Bajer, Christoper J. Chizinski, Justin Silbernagel, and Peter W. Sorensen

University of Minnesota bajer003@umn.edu

Thank you! • Brett Miller • Mary Headrick • Brian Moe • Jordan Wein • Jake Osborne • Reid Swanson

Global Invasive Species Data Base

• World’s worst invasive fish

Why so invasive? Combination of life history & environment

• Evolved in large, seasonally-unstable ecosystems • Strong tendency to migrate to adjacent shallow areas to spawn

Recruitment hypothesis • Common carp evolved to overcome recruitment bottlenecks

by moving to peripheral “predator-free” areas to spawn

Such strategy might be especially effective in highly interconnected and ecologically unstable regions

Study 1: Effects of ecological instability (winterkill) on carp recruitment

• Large-scale survey of lakes in S-Central Minnesota (19

lakes) • 3 years • Winter oxygen measured each year • Springtime abundance of adult carp

– Mark – recapture – Fecundity and propagule pressure (eggs/ha)

• Summertime abundance of YOY carp • Summertime abundance of native predators

– 4 dominant species, bluegill, black crappie, green sunfish, black bullhead

• AIC logistic regressions to predict presence of YOY carp

Bajer et al. Biol. Inv. 2012

AIC models showed that presence of YOY carp can be explained by the lack of bluegill sunfish, with other variables playing a minor role

Variables in the model AIC ∆AIC wi

BGS, GSF 45.36 0 0.19

BGS, BCP, GSF 46.21 0.85 0.12

BGS, BCP 46.25 0.89 0.12

BGS 46.40 1.03 0.11

BGS, PCP, Propagule 46.84 1.48 0.09

BCP (Best model without BGS) 50.14 4.77 0.02

GSF 54.70 9.34 0.00

BBHD 55.12 9.75 0.00

Propagule 55.21 9.84 0.00

With bluegills

Without bluegills

Bajer et al. Biol. Inv. 2012

YOY carp were inversely correlated with bluegill sunfish

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Bajer et al. Biol. Inv. 2012

Study 2: Can the lack of recruitment in normoxic lakes be explained by predation on carp eggs by bluegills (native fish)?

• A controlled experiment in 4 lakes – 2 hypoxic – 2 normoxic

• Carp spawning monitored daily • Ovulating females collected • Carp eggs fertilized, attached to yarn • Clumps of yarn placed within spawning areas

– Unprotected – Coarse mesh – Fine mesh

• Eggs counted daily until larvae hatched • Nested ANOVA • Native fish diets analyzed in one lake

Carp eggs in normoxic lakes survived only if protected by mesh that excluded fish

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Open Control Coarse mesh

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Bajer et al. Biol. Inv. 2012

Bluegill sunfish was the main egg predator

• 87 fish captured in carp spawning areas • Bluegills comprised 61% • 82% bluegills had eggs in the stomach • On average 83 eggs/fish

Conclusions

• Bluegill sunfish (and other sympatric predators) can control carp recruitment if sufficiently abundant

• Predation on carp eggs (and larvae) is key

Broader implications

• Management – Sustainable management is possible (Example –

Riley chain of lakes 2006-2012)

• Ecology – First direct evidence that native predators can

control invasive fish – Our results might explain why carp are invasive in

some regions/ecosystems but not in others

Achilles’ heel? – ongoing tests

Replicated lake-enclosure experiments • 70’ x 70’ impermeable enclosures • Lake Casey 2011 -- 4 enclosures • Lake Staring 2012 -- 4 enclosures • All fish removed (as much as possible) • Every other enclosure stocked with

bluegills

Replicated lake-enclosure experiments • Each stocked with carp eggs in May

– ~150,000 eggs each

• Abundance of YOY carp estimated in June-August – CPUE 2011 and 2012 – Mark-recapture 2012 only

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Preliminary results More tests 2013, AIS center, shallow lakes, grad student?