How many fish can be sustainably harvested from an Alberta lake? To answer that question, you need a basic understanding of biological economics. Let’s start by asking some straightforward questions:
- How many fish are in a lake?
- How many fish do you want to be there?
- What is the annual interest rate (the surplus population growth rate)?
- How necessary or important is reinvestment of fish back to the population?
In Alberta, we are getting pretty good data to answer those questions. Standardized fish population assessments, such as index netting on lakes and electrofishing on streams, provide solid data on fish numbers. Consultation with conservationists, Indigenous peoples and sport anglers tells us how many fish should ideally be there. Biological sampling for age, maturity and growth data is telling us about the environment’s interest rates and reinvestment needs.
An example of this work would be if biologists net a lake and learn the density of adult walleye is about three per hectare. To meet the needs of conservation and fisheries (both indigenous and sport), the density should be at least eight walleye per hectare. The annual interest rate is usually between five and 10 per cent. This means the population can grow at a rate of three adults x 5 per cent/year, or about 0.15 walleye per hectare annually. A lake that reports numbers like these needs all of the walleye produced to be reinvested to build up the population to meet the needs of conservation and peoples.
Now, let’s fast forward a few years. The lake now has eight walleye per hectare, or what biologists would determine as adequate numbers for conservation. At an interest rate of five per cent, the population has an annual surplus of 8 x 5 per cent or 0.4 walleye per hectare. In certain good years (e.g., 10 per cent) or at very productive lakes, that might be as high as 0.8 walleye per hectare. Excellent! More money in the bank means you can spend more, and more fish in the lake means you can harvest more!
Alberta biologists are developing better methods for counting fish and gaining long-term data on age and growth (productivity) of these fish. Now that we understand the key pieces of the fish economics budget, we are able to tailor the harvest to meet the goals for conservation and for the fishery. The amazing walleye fisheries at lakes like Lac Ste. Anne, Fawcett Lake, and Pigeon Lake are proof that a well-managed budget benefits everybody!