ESTIMATING CRAYFISH DENSITY IN LAKES USING QUADRATS - MAXIMIZING PRECISION AND EFFICIENCY

We provide a method to estimate the number of quadrat samples needed t o obtain precise crayfish densities at a site or transect for two quad rat sizes (1 and 10 m2). We based the analysis on data from a survey o f 61 depth-transects from 31 lakes representing a gradient in crayfish density. There was no significant difference between density estimate s obtained with different quadrat sizes for six transects where both q uadrats were used. Fewer samples were needed with the large quadrat, b ut it was more efficient to use a 1-m2 quadrat at densities above 0.3 crayfish.m-2 because less effort (i.e. diving time) was required to co llect the requisite number of samples. There was a linear relationship between density estimates by quadrat and timed counts (a more rapid m ethod to estimate crayfish density), but timed counts were less accura te.