Fish Hatchery Management - fisheries & aquaculture

80 FISH HATCHERY MANAGEMENTFIGURE 29. Muskellunge fry being sample-counted for inventory. (courtesyWisconsin Department of Natural Resources.)(4) Several samples (at least five) should be taken. If the calculatednumber of fish per pound (or weight per 1,000) varies considerably amongsamples, more samples should be taken until there is some consistency inthe calculation. Then the sample values can be averaged and applied to thetotal lot; all samples should be included in the average. Alternatively, thecounts and weights can be summed over all the samples, and an overallnumber per pound computed. Larger samples are required for large fish.Even with care, the sample-count method can be as high as 15-20% inaccurate.some fishery workers feel it is necessary to weigh as much as lzo/oof a population to gain an accuracy of 5-10%. Hewitt (tgag) developed aquarter-sampler that improved the accuracy of the sample count method(Figure 30).In the total-weight method, as the name implies, all of the fish in a lotare weighed, thus sampling error is avoided. Initial sample counting mustbe conducted during the first weighing to determine the number of fish inthe lot, but this is done when the fish are small and more uniform in size.This method involves more work in handling the fish, but is the most accuratemethod of inventorying fish.