9458

• UCREFRP Catalog Number: 9458
• Author: National Park Service.
• Title: Workshop on Population Estimates for Colorado Pikeminnow and Humpback Chub.
• USFW Year: 2001.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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Schnabel Multiple-Census population Estimate

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Confidence limits

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In cases where the total number of recaptures in the study is small, say
less than 25, we do not expect the variance (l/N) to be normally distributed,
making it important to calculate confidence limits by alternative methods.
This can be done by using tables of Poisson distribution (see Ricker 1975) to
determine 95% (and 99%) limits for R, and then substituting these values into
the Schnabel population estimation equation to determine limits for N.

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Assumptions of the model

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These assumptions must be met to obtain valid estimates using the
Schnabel multiple-census population estimate:

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Marked fish do not lose their marks prior to the recapture period.

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Marked fish are not overlooked in the recapture sample.

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3)

Marked and unmarked fish are equally vulnerable to capture in the
recapture period.

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There is no mortality allowed during the study interval.

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Following release, marked animals become randomly mixed with the
unmarked ones, or recapture effort is distributed in proportion to the
number of animals in different parts of the population area.

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6)

There are no additions to the population during the study interval.

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Literature Cited

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Ricker, W. E. 1975. Computation and interpretation of biological statistics
of fish populations. Fisheries Research Board of Canada Bulletin 191.

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Van Den Avyle, M. J. 1993. Dynamics of exploited fish populations. Pages
105-135 in C. C.Kohler and W. A. Hubert, editors. Inland fisheries
management in North America. American Fisheries Society, Bethesda,
Maryland.

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