Coastal Cutthroat Trout Maturity Studies in Southeast Alaska

Populations of wild coastal cutthroat and rainbow trout occur in streams and lakes throughout Southeast Alaska (SEAK) and are available to anglers year-round. During the late 1980s and early 1990s, biologists became increasingly concerned that these species were being overharvested and based on these concerns and public input new regulations were adopted by the State of Alaska in 1994. The cornerstone of the new trout regulations is a series of minimum size limits designed to protect 65% to (in areas with higher angling pressure) 100% of cutthroat trout from harvest until they have spawned at least once.  The objective of the study being presented was to estimate the proportions of female cutthroat trout that were sexually mature in typical lakes in Southeast Alaska and develop a means to evaluate if the objectives in the new regulations were being met or were too restrictive. Twenty-one lakes were selected for sampling that spanned the range of lake sizes, lake types (resident or anadromous), and fish sizes present in SEAK.  Sampling occurred between late-September and mid-November, which proved to be late enough in the fall to detect maturity of trout that were going to spawn the following spring. Each fish captured was measured, and the subset of fish that were sacrificed were weighed to the nearest gram, sexed, sampled for scales and otoliths, and later evaluated for sexual maturity.  Overall, 60% of all females sampled were mature in the 11-inch total length category, and 62% of the females were mature in the 12-inch length category. At lengths below 11 inches, anadromous cutthroat trout maturity rates quickly dropped. At 10 inches, only 28% of the anadromous females were mature.  Fecundity-at-length, and ovary weight and egg size in relation to maturity were also evaluated. Continuing efforts to develop management categories based on the relationship between physical parameters (i.e., size of lake, and resident vs. anadromous) and length-at-maturity will be presented. A brief description of techniques using non-destructive sampling to estimate maturity will be provided.