Geology topics

Michael J Hansen

Publications and source records attributed to Michael J Hansen.

2 recordsLinked to original sources

USGS2021

Distribution

The lake charr Salvelinus namaycush is restricted in its native distribution to oligotrophic fresh waters of northern North America largely within the extent of the Pleistocene glaciations. It is the only freshwater species in northwest North America that does not occur in Siberia. A GIS-based native occurrence map linked to the HydroLAKES database does not extend the lake charr range but provides more comprehensive occurrence data than previous maps. The total waterbody area of lakes occupied by lake charr (451,304 km 2 ) is 40% of the total waterbody area across the range. Lake charr occur from 42.020901 latitude in the south to 74.420800 in the north and from −62.700000 longitude in the east to −161.173090 in the west. Lake charr lakes range in surface area from 3.4 to 8,210,000 ha (mean = 9715 ha; median = 191 ha), maximum depth from 2.7 to 614 m, and elevation from sea level to 2035 m ASL (mean = 381 m; median = 366 m). Glaciation, water temperature, dissolved oxygen, depth, and nutrient content are the main variables associated with lake charr native distribution in lakes. Life history variation, physiology, and ecological opportunity are the most likely drivers of lake charr dispersal and colonization.

Book chapter↗

USGS2021

Life history and population dynamics

Lake charr Salvelinus namaycush life history and population dynamics metrics were reviewed to evaluate populations inside ( n = 462) and outside ( n = 24) the native range. Our goals were to create a database of metrics useful for evaluating population status and to test for large-scale patterns between metrics and latitude and lake size. An average lake charr grew from a 69-mm length at age-0 ( L 0 ) at 89 mm/year early growth rate ( ω ) to 50% maturity at 420 mm ( L 50 ) at age 8 ( t 50 ), and then continued to grow toward a 717-mm asymptotic length ( L ∞ ). L 50 was positively correlated to ω , whereas t 50 was inversely correlated to ω . Lake charr grew slower toward larger size and older age in northern latitudes and larger lakes than in southern latitudes and smaller lakes. Population density (number/ha) and yield density (kg/ha) decreased with lake size, and yield and total annual mortality ( A ) decreased with latitude. Native populations grew slower ( ω ), were heavier at 500 mm ( W 500 ), matured at shorter L 50 , grew to a shorter L ∞ , and suffered lower annual mortality A than non-native populations. Our review and database should be useful to managers and researchers for quantifying lake charr population status across the species range.

Book chapter↗