At Amistad Reservoir, Texas, the National Park Service (NPS) built a 46-m long release tube for convenient return of tournament-caught largemouth bass (Micropterus salmoides) to the reservoir following weigh-in. Several members of the public raised concerns to NPS that use of the tube might have been leading to increased tournament-associated mortality. We simulated two largemouth bass tournaments in August 2006 and March 2007 using volunteer anglers to compare six-day delayed mortality between fish returned to the reservoir via the tube and other methods. In summer, delayed mortality averaged 56% for boat-ramp hand-released fish, significantly lower than for fish released via the tube with chlorinated tap water running through it (89%). Initial mortality in the spring trial was 5%, significantly lower than in the summer trial (14%). In spring, delayed mortality was low across treatments (<12%), and did not differ significantly between treatments. We could not conclude that the release tube was primarily responsible for higher mortality, because chlorinated water used in conjunction with the release tube could have contributed to increased fish stress. The season in which a tournament is held seems to have more importance than use or non-use of the Amistad bass release tube in minimizing tournament- associated mortality. We recommend to the National Park Service that the use of the tube with chlorinated water be limited, especially in warm-weather months.
