If two anglers go out and catch their limit, does that mean the lake is packed with fish-and that it doesn't need stocking or experimental regulations? Of course not - no more than getting blanked would mean the lake was empty of fish.Just as the world isn't flat despite the horizon appearing to be straight a single observation by a few people isn't an accurate indication of a fish population's status. Their good fishing may be due to a hot bite, extraordinary skill, or just good luck rather than an abundance of game fish.The shortcomings of anecdotal evidence and casual observations are the main reasons we invest so much time and money gathering information using scientific, comprehensive lake and stream surveys.That's not to say firsthand accounts aren't valuable. But such information must be balanced with methodical, consistent surveys of fish populations, fish habitat, and fishing activity.Information from lake and stream surveys forms the foundation of every DNR fisheries management activity we do to improve fishing-from stocking fish to restoring aquatic plant habitat. Fisheries managers conduct these surveys by netting, seining, trawling, electrofishing, and analyzing water. This gives us long-term information on fish population size structure, fish reproductive success, species abundance, fish growth and movement, and habitat conditions. Added to this is information about angling success and preferences we get from creel surveys (interviews with anglers).Along with public input, survey information helps us decide when stockings is needed, whether experimental regulations are necessary, and how environmental conditions affect fish populations. Follow-up sampling and angler surveys determine if specific management techniques such as fingerling stocking or a slot limit are having the desired effect on a particular lake.As one fisheries manager puts it: "Without the lake and streams surveys, everything we did would be guesswork."
Lake and stream surveys
So important are lake and stream surveys that one-fourth of our $22 million yearly budget goes towards this work. Each year, field crews around the state survey several hundred lakes and several dozen streams or rivers. Most lakes are surveyed every three to five years, although Rainy Lake, Lake Mille Lacs, and other large lakes are monitored yearly. We now have a data-base of survey information for 4,500 lakes and streams-more than any other state-and biologists are adding new information each year.In the short term, surveys show the relative proportion of big and small fish, and whether each year's new generation of fish, called a year class, is relatively weak or strong. By accumulating many years of this information, we can see long-term trends and patterns, such as how quickly fish grow in various lakes or the gradual loss of important habitat.Survey techniques
Fisheries managers and their crews use various survey techniques appropriate for various fish species or sizes.- Gill nets: usually 250 feet long, these nets are used to capture walleyes, northern pike, and yellow perch. Live fish are released after workers take measurements and samples of scales (to be analyzed later to determine fish age). Dead fish are further analyzed for sex, stomach contents, and parasites.
- Trap nets: These smaller nets capture bluegills and other small fish.
- Trawls and shoreline seines: These small-meshed nets are used to capture young fish.
- Electrofishing equipment: Used in streams and rivers, this equipment uses an electrical charge to temporarily stun fish so they can be measured and weighed. It also is used in lakes to survey bass, crappies, and young walleyes.
- Trotlines and angling: These methods are used to survey catfish and other species that often can't be captured efficiently any other way.
- Water analysis: This is used to determine the percentage of dissolved oxygen in water as well as water fertility and clarity.