Research Document - 2004/085

Habitat-specific production rate estimates from 5 Canadian shield lakes

By Pratt, T.C.

Abstract

Estimating habitat-specific production rates is a difficult but crucial component of meeting Fisheries and Oceans Canada's policy of 'no net loss of productive capacity of fish habitats' as outlined in the Fisheries Act. In this study, an underwater visual technique was used to estimate habitat-specific littoral zone fish densities. Passive traps were concurrently fished in each habitat type, and the weight of captured fish was used, in combination with the available density estimates and estimates of habitat availability, to provide habitat-specific biomass estimates for each species. These estimates were converted into habitat-specific production estimates in one of two ways; by multiplying habitat-specific biomass estimates with published species-specific production:biomass ratios to determine habitat production indices (HPI), and by estimating actual habitat-specific production rates by conducting visual censuses and biomass estimates over two time periods. The underwater visual method for determining habitat-specific densities was validated by conducting a concurrent mark-recapture population estimate in the five study lakes. The visual abundance estimates successfully predicted 75% of the variation in the mark-recapture population estimates, indicating that the underwater visual method is capable of providing habitat-specific density, biomass and production estimates. Structurally complex habitats contained the highest fish densities and biomass, and provided the greatest potential for production. Given the high cost and variability observed in habitat-specific production rate estimates, the use of underwater visual methods for determining habitat-specific density estimates, in combination with published production:biomass ratios, provides the simplest and most effective method for estimating habitat-specific production.

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