Analysis of a potential mechanism that may have facilitated the spread of the invasive round goby Ne

1
Analysis of a potential mechanism that may have
facilitated the spread of the invasive round goby
(Neogobius melanostoma) in Lake Erie

• Josh Waldman1 and Christopher J Winslow2
• Biological Sciences Department
• Ecology, Evolution, and Conservation Biology
• Bowling Green State University

1 - jwaldma_at_bgnet.bgsu.edu 2 - cjwinsl_at_bgnet.bgsu.
edu
2
Background/Rational

• The unintentional introduction of the round goby
  to Lake Erie in the mid 1990s has resulted in
  modified community dynamics
• Novel competitive and predatory interactions
• Previous research has documented
• Diet overlap (goby share prey with native
  fishes),
• Habitat overlap,
• Behavioral interactions/modifications,
• And consumption of native fish eggs.
• However, diet analysis indicates that round goby
  is currently an important prey species for
  predatory fishes
• Goby compose 65 of smallmouth bass diet (Knight
  et al. 20003).

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Driving Question?

• Question How was the round goby so successful at
  spreading throughout Lake Erie given that it is
  heavily preyed on by native fishes?.
• Hypothesis The round goby constituted a novel
  prey item, upon initial introduction, that wasnt
  instantly incorporated into fish diets until goby
  densities increased sufficiently to cause a diet
  shift in native fishes.
• Goal To determine the density of RG, or length
  of time, it will it take for a naïve, native fish
  (smallmouth bass) to consume a novel, invasive,
  prey.

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Methods(Multiple modifications, with
justification)

• Fine tuning
• Many field experiments take a tremendous amount
  of time to design and adjust before publishable
  data is collected.
• The experiments run and the data collected during
  this REU provided
• Needed design modifications
• Preliminary data
• A solid foundation for future experiments capable
  of producing publishable data
• Multiple design approaches are provided in this
  PowerPoint (following four slides)
• Design required a tremendous amount of
  modifications because of unforeseen challenges.

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Methods (General)

• For each trial we controlled for several
  variables (those items in red were changed as we
  altered methods for improved design)
• Density and type of prey,
• Number and type of shelters,
• Fish acclimation time,
• Water depth,
• Time aloud to forage (i.e., trial length),
• And size (i.e., length) of fish (round goby and
  smallmouth bass).
• We changed methods midway through the experiment
  to better mimic real world conditions.
• Included in the following slides are initial
  methods (Method 1) and modified methods (Method
  2).

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Methods(1 of 2)

• Tanks 3.2m in diameter x 1.8m deep.
• Benthic surface area 8m2.
• Tanks filled to a depth of 1.2m (9500L).
• Smallmouth bass, our single predator
• was always between 20-25cm.
• Smallmouth bass was either
• Obtained from Lake Erie HAD EXPERIENCE with
  round goby.
• Obtained from large river had NO EXPERIENCE with
  round goby (NAIVE) .
• Round goby, our prey, stocked at 6 fish per m2.
• Surface area 8m2, therefore, forty-eight goby per
  trial.
• 48 gobies matches conservative estimates in Lake
  Erie (based on current literature and personal
  observations).
• The 48 gobies were split into three size classes
  (16 per size class)
• lt74mm, 75-94mm, and 94-130mm.
• Shelters (N18)

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Results from Method One

• Two fish were consumed after two trials.
• Both prey were consumed by the same predator
• Tables 1 (Below)
• Both goby were eaten from mid-size range.

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Methods (2 of 2)

• After two trials, under Method 1, not enough fish
  were consumed to allow statistical analysis.
• Therefore, we altered the design to facilitate
  more consumption.
• Decreased density of goby from 6m2 to 3m2.
• 24 fish total, eight from each of the previously
  mentioned size classes (Method 1).
• Added emerald shiners as an alternate prey to
  better mimic real world conditions (i.e., prey
  choice in the wild).
• To ensure equal probability of predator to
  encounter and consume both prey we provided cover
  for shiners (rebar baskets in the open water).
• Goby readily used brick shelters while shiners
  hid in baskets.
• Cages were covered with a non-transparent
  material on two sides and mesh, permeable to
  emerald shiners but not predator, on remaining
  sides.
• Brick shelters Reduced from
• N18 to N9.
• Kept same dimensions.

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Results from Method Two

• 10 RG were eaten across four trials (i.e., four
  SMB).
• Bulk of the fish were eaten by one fish trial 3
  (consumed seven of eight fish).
• The predator also fed heavily on shiners.
• On average, five out of eight shiners were
  consumed per trial.
• Tables 2 (Right).

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Results Continued.

• Trials one and two from Method 1 had so few fish
  consumed it was impossible to draw conclusions
  regarding diet preference.
• 68 of the SMB diet consisted of shiners (i.e.,
  32 goby).
• When goby were consumed, more were chosen from
  the smallest size class.
• Bias toward small gobies may be because they are
  unable to procure shelter (i.e., hide from
  predators).
• Small gobies are likely out competed by larger
  gobies for available shelters.

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Preliminary Conclusions

• The results suggest that the preferred diet of
  naive predators does not include high numbers of
  round goby only 32 of diet.
• However, the presence of a few goby in the diet
  suggests that a prey switch is possible and
  warrants additional trials.
• Increasing the density of goby presented to naive
  smallmouth bass in future trials may elicit a
  diet shift.
• Repeating trial with same smallmouth bass may
  allow us to determine if there is a temporal
  component to diet shift.

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REU Importance

• Despite the low number of trials completed the
  REU aided in modifying the experimental design.
• REU provided
• Needed design modifications,
• Preliminary data,
• Justification for pursuing the question further
  given more support and time.
• The REU enhanced the undergraduate education.
• It introduced undergrad, Josh Waldman, to
  hands-on, meaningful research.
• Was intellectually stimulated
• Made Josh an active participant in the creative
  process and in the activities inherent in field
  research.

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REU Importance Continued.

• After completing the undergraduate experience, we
  feel that Josh has been exposed to and
  accomplished all of the goals of the program
• Developed written and verbal communications
  skills,
• Gained a sense of collaboration and teamwork,
• Feels better prepared for graduate school,
• And found some research strengths and interests.