A Population Study of Small Mouth Bass Using Mark

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A Population Study of Small Mouth Bass Using Mark
Recapture Technique

• Presented by
• Brian D. Beauerle
• Curran W. Wilkinson

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The Beauerle Pondin Bardstown, KY
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Background on the Pond

• Made in 1981
• Stocked in 1984 with bluegill, small-mouth bass,
  and channel catfish
• Average depth 14-20 feet
• Currently 6 feet below average water level

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Facts About Small Mouth Bass

• Average Length is between 10-20 in.
• Average weight is between 1-5 lbs.
• Cold-blooded schooling fish
• Prefer to be near bottom, where they feed on
  minnows, crayfish, and insects

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THE EXPERIMENT
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Background on the Experiment

• Three sample collections were performed the
  initial on 10/23, the following samples on
  11/13, 11/20 respectively
• Bait used artificial night-crawlers
• Fish were marked with clothespin-like tag
  inserted into flesh of lower lip
• All captured fish were marked for each sample
  also measured for approximate length

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Overview of Mark Recapture Models

• I. Closed population models
• a) Two samples - Lincoln-Peterson Estimator
• b) Several samples (kgt2) - Schnabel Estimator
• Assume no recruitment or losses during period
  of study

II. Open population models a) Jolly-Seber
Model (based on kgt2) Population size and
composition changes due to births, deaths,
and migration
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Schnabel Equation

• N ?(Mtnt)/((? mt)1)
• where
• nt of individuals caught in sample t
• mt already marked when caught in sample t
• Mt marked just before the tth sample
• variance of N is a function of recaptures,
  therefore precision
• of the estimate is increased by increasing nt
  and Mt

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Fundamental Assumptions of the Schnabel Estimator

• The population is closed (geographically and
  demographically)
• All animals are equally likely to be captured in
  each sample
• Capture and marking do not affect catchability
• Each sample is random
• Marks are not lost between sampling occasions

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THE RESULTS
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Results of Sample Collections

• Initial Collection (Oct. 23rd)
• Twenty fish were caught and tagged
• Second Collection (Nov. 13th)
• Eleven fish were caught, 3 of which were
• previously marked from the initial collection.
• Third Collection (Nov. 20th)
• Sixteen fish were caught, 4 of which were
• previously marked (2 from initial, 2 from Second)

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Analysis of Fish Distribution
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Fish Length Data
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Size of Small Mouth Bass
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Discussion/Conclusions

• The average length of captured fish was 10.44 in.
  
• Using the Schnabel equation, the estimated small
  mouth bass population (N) was calculated to be
  90.
• The calculated population size is only a very
  rough estimate. Factors that can affect this
  estimate include number of samples analyzed,
  weather, water temperature, etc.
• Most importantly, we have concluded without a
  shadow of a doubt that Brian is a better
  fisherman than Curran!

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JUST FOR FUN
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Two Talented Fishermen
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Trouble with the Pole
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Incognito Strategy

• Curran out-smarts even the brightest fish

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Draining the Weasel

• Sometimes you just
• have to go!!!!

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Draining a Bigger Weasel

• Following Brians
• example

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THE END