Life on a seamount: Lake charr at Stannard Rock, Lake Superior, 2011–2015

Abstract

Lake Superior has four extant lake charr ecotypes including the ubiquitous lean (shallow-water form), the deep-water siscowet, and the less common, mid-depth redfin and humper forms. Stannard Rock is a distant seamount in Michigan waters that is a coveted recreational lean lake charr fishing destination. Lake charr at Stannard Rock were surveyed during 2011–2015 using gill nets set in waters <80 and ≥80 m to assess population status. All four ecotypes were found at Stannard Rock with leans being most abundant at depths <80 m and humpers and siscowets most abundant in waters ≥80 m. Few redfins were found. Total annual mortality was estimated to be 24% for leans, 18% for humpers, and 15% for siscowets. Population age and size structure of lake charr were broad with many fish older than 20 years and >700 mm. Asymptotic length was 891 mm for leans, 459 mm for humpers, and 938 mm for siscowets. Female length at 50% maturity was 547 mm for leans, 382 mm for humpers, and 453 mm for siscowets. Recreational fishery total harvest of leans peaked at 5,000 fish per year during 2011–2015. Overall, lake charr populations at Stannard Rock were healthy. Caution must be exercised because harvest levels were modest at Stannard Rock, which has a small area relative to nearshore lake charr habitat. These findings support the concept put forth by progressive recreational fishers that have advocated assigning Stannard Rock as a heritage fishery area with restrictive regulations to maintain its sustainability.