Using Partial Counting Fences and a Two-Sample Stratified Design for Mark–Recapture Estimation of an Atlantic Salmon Smolt Population

Abstract

A mark-recapture experiment was conducted in which a two-sample stratified design was used in estimating the number of Atlantic salmon Salmo salarmigrating as smolts out of the Conne River, Newfoundland. The Conne River is one of the largest Atlantic salmon-producing rivers in insular Newfoundland, with an average adult escapement of 8,582 fish during the period 1986–1988. Two partial fish-counting fences, located 10 km apart, were used to catch downstream-migrating smolts. About 5,000 smolts were tagged with numbered Floy streamer tags and released at the upstream trap; 20% of marked fish were subsequently recaptured in the downstream trap. Depending on the choice of stratification interval used, estimates of the unmarked population ranged from 64,676 to 68,130 smolts. Confidence limits were less than ±8% of the population estimate. The use of the partial fish-counting fences is described and promoted for experiments of this nature. Streamer tags proved quite successful for short-term marking of Atlantic salmon smolts.