ESTIMATES OF POPULATION DENSITY AND DISPERSAL IN THE NATICID GASTROPOD, POLINICES DUPLICATUS, WITH A DISCUSSION OF COMPUTATIONAL METHODS

¹ Department of Zoology, Syracuse University, Syracuse, New York 13210
² Department of Biology, Yale University, New Haven, Connecticut 06520

1. Capture-recapture methods were used to assess population density and dispersal in Polinices duplicatus.

2. Preliminary surveys indicated an area of 1600 sq. m. as optimal for density estimations. This yielded capture rates averaging 147 per day and the number of each mark recaptured usually made up 7.7% to 19.3% of each sample.

3. Various computational methods are applied to the data, and their values discussed. These include simple and modified maximum-likelihood estimates (with measures of their variance), a serial census method weighted for sample size, and the classical Jackson-Fisher extrapolations of relative recapture frequencies, both "positive" and "negative."

4. The two maximum-likelihood methods yield average population estimates of 1018.4 and 10912, and the sample-weighted census method yields a value of 992.6. With capture rates and mark frequencies as in this study on Polinices, these relatively simple calculations are judged adequate.

5. These estimates are equivalent to a population density for Polinices duplicatus of 6250 (5313-7188) per hectare, or 2530 (2150-2900) per acre.

6. Recommendations are made regarding the value of different computational methods, if capture-recapture methods are applied to other marine benthic populations. Approximate population density, sample size, and the relation of samplingrate to population dynamics should be used to determine the appropriate procedure.