Dynamics of an Introduced and Unexploited Lake Whitefish Population in Lake Pend Oreille, Idaho

To evaluate the biological potential of a commercial fishery for lake whitefish in Lake Pend Oreille, Idaho, we estimated population attributes that regulate production and yield to constrain compensatory responses to exploitation.  The length-frequency distribution based on trap netting in autumn 2005 was unimodal with a mean of 448 mm, whereas the length-frequency distribution based on gillnetting in spring 2006 was bimodal with a mean of 390 mm.  The sex composition (proportion females) was skewed toward females (0.66; 95% CI = 0.63 – 0.70).  The shape parameter of the weight-length equation (β = 3.363) was similar to other unexploited whitefish populations and indicated that whitefish grew plumper as length increased.  The instantaneous growth coefficient for whitefish in Lake Pend Oreille (K = 0.12/year) was among the lowest recorded for unexploited whitefish across their range.  Maturation occurred at an age (6 years, range = 4–12 years) and length (383 mm, 340–440 mm) that was relatively high for unexploited populations of whitefish.  The instantaneous natural mortality rate (M = 0.167) was among the lowest observed among unexploited populations of the species.  Population density of adults was low based on total surface area (1.35 fish/acre; 95% CI = 1.11–1.78 fish/acre), but average based on area of expected habitat ≤ 230 feet deep (4.07 fish/acre; 95% CI = 3.35–5.35 fish/acre).  Density of juveniles and adults over area of expected habitat (11.93 fish/acre; 95% CI = 8.42–17.53 fish/acre) was within the range observed for unexploited populations.  Low natural mortality, slow growth, and late maturity of lake whitefish in Lake Pend Oreille indicate a high biological potential for fishery yield.