Hatchery 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.

中文翻译：

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可捕捞孵化场虹鳟的跑道分级对筒子架返回的影响

可捕捞的孵化场鳟鱼（即全长约250毫米；以下简称“可捕捞物”）的养成费用昂贵，因此，渔业管理机构努力修改饲养方式以最大程度地提高养殖比例钓鱼者捕获的库存捕捞物。我们在鱼种孵化场的鱼种大小和可捕大小上对鱼进行了分级，将鱼分为“头目”（此处是饲养场中较大的鱼，在分级过程中分开）和“刺鱼”（较小的鱼） 。我们假设（1）对可捕获领导者进行定级和立即放养，以及短期捕获并持续捕捞可捕获匕首，可能会增加匕首的生长，并导致更大的平均鱼类种群（相对于来自未分级航道的鱼类），可能会提高分级组的鱼笼总体回报率，并且（2）在饲养过程的早期对鱼种前导和匕首进行分级和分离可能会减少其余鱼种在饲养期间的竞争，从而有可能提高总体放养后的鱼产量整个组，无需在备货时进行可分级。我们发现，刚开始放养之前对可捕捞物进行分级会略微增加第一个放养期间的放养平均尺寸（与未分级的对照鱼相比），从而导致放养鱼的鱼架收益更高。但是，在整个放养期间，各组之间的饲料相同，分级鱼和对照鱼的平均放鱼尺寸几乎相同，垂钓者放回鱼架也是如此。在剩下的饲养期间，将鱼种分级以分开首领和匕首，对垂钓者的捕获也没有积极影响。我们的研究结果表明，生产级别的分级对增加匕首的生长无效，因此不会增加放养的总体规模。因此，在将放养到放养渔业中的孵化鳟鱼分级之前，不太可能实现垂钓者捕获的改善。