Illegal Angling Harvest of Walleyes Protected by Length Limits in Alberta

Abstract

The sport fishery for walleyes Stizostedion vitreum in Alberta, Canada, has declined severely because of high angling pressure relative to the low productivity of northern fisheries. Following extensive public consultation, highly restrictive length and bag limits were implemented on all walleye fisheries, clearly increasing the opportunities and temptations for anglers to illegally harvest fish. An estimate of illegal harvest was derived from data gathered at 29 sport fisheries in Alberta from 1991 to 1998. The technique involved counting protected-length fish in anglers' creels and comparing these numbers to the numbers of protected-length fish released. I avoided anglers' exaggeration of released walleye numbers by comparing the ratios of the lengths of fish caught by test angling to those of fish retained and reported by anglers, as recorded by creel clerks. The average illegal harvest level was high; 18.4% (range = 0.2–68.8%) of protected-length walleyes caught were kept. Illegal harvest was lowest at fisheries with catch-and-release regulations and highest at fisheries managed with slot-length limits. Of particular importance to fisheries managers, illegal harvest was inversely related to catch rate, thereby creating a strong depensatory response to a fishery decline. Other indices of compliance (creel clerks' reports of illegal harvest, the percentage of protected-length fish in anglers' creels, and angler infraction rates) were less useful indicators of illegal harvest. To counteract the negative effects of illegal harvest, managers should (1) avoid using length limits at lakes expected to have high illegal harvest levels, (2) use slot-length limits only at lakes where catch rates are expected to be high, and (3) not rely on low infraction rates or low percentages of protected-length fish in creels to imply high levels of compliance.