Use of Visual Census for Estimating Population Size in Northern Pike (Esox lucius)

A stratified systematic sampling regime was used to survey numbers of northern pike (Esox lucius) (age 1 yr or older) on five different 2-d sampling periods during the summer months (June, July, and August) in Roi Lake, Alberta, a small, deep, meromictic lake with a simple basin morphometry and high water clarity. The final combined estimate was 180 ± 39 northern pike (23 pike/ha of lake surface). Detailed underwater observation within a specified area was used to assess depth distribution, sample independence, and reaction of northern pike to the presence of the observer. Northern pike selected depths of less than 1 m, and this distribution pattern was constant throughout the summer months, justifying the stratified methodology utilized in the population estimate. Samples were 92% independent, and the reaction of pike to a diver contributed an estimated 4% error to the accuracy of the estimate.