The Effect of Raceway Grading on Return to Creel for Catchable‐Sized Hatchery Rainbow Trout

Abstract

AbstractHatchery trout of catchable size (i.e., about 250 mm total length; hereafter termed “catchables”), which are stocked into put‐and‐take fisheries, are expensive to raise, so fisheries management agencies strive to modify rearing practices to maximize the proportion of stocked catchables that anglers catch. We graded fish in production‐level hatchery rearing units at both fingerling and catchable size, dividing the fish into “leaders” (herein, the larger fish in a rearing unit, separated during a grading event) and “laggers” (the smaller fish). We hypothesized that (1) grading and immediate stocking of catchable leaders and short‐term retention and continued feeding of catchable laggers might increase lagger growth and result in a larger average size of fish being stocked (relative to fish from ungraded raceways), potentially improving overall return to creel for the graded group and (2) grading and separation of fingerling leaders and laggers early in the rearing process may reduce competition between smaller and larger fish for the remainder of the rearing period, potentially improving overall poststocking return to creel for the entire group without the need for catchable grading at the time of stocking. We found that grading catchables just prior to stocking slightly increased the mean size at stocking (compared with ungraded control fish) for the first stocking period, which resulted in slightly higher return to creel for stocked fish. However, across the entire stocking period and with equal feed between groups, mean size at release was nearly identical between the graded and the control fish, as was return to creel by anglers. Grading fingerlings to separate leaders and laggers for the remainder of the rearing period also had no positive effect on angler catch. Our findings suggest that production‐level grading is ineffective at increasing the growth of laggers, so it will not increase overall size at stocking. Consequently, improvements in angler catch are unlikely to materialize from grading hatchery trout prior to stocking them into put‐and‐take fisheries.