Largemouth Bass Mortality and Related Causal Factors during Live-Release Fishing Tournaments on a Large Minnesota Lake

We quantified initial and delayed mortality of largemouth bass Micropterus salmoides during live-release fishing tournaments and identified probable causes of death in order to provide a biological basis for refining tournament guidelines and regulation. Mean estimates for two tournaments on Lake Minnetonka, Minnesota, were 1.42% weigh-in mortality, 3.35% 3-d delayed mortality, and 4.72% total mortality. Catch and total mortality rates during a May tournament were both over 1.5 times those of a September tournament, the difference presumably being related to reproductive behavior and condition. Tournament mortality of the population was minimal relative to other causes of mortality; total tournament mortality estimates for 1992 (11 tournaments) represented 2.3–6.3% of angling mortality and 1.3–3.0% of total mortality in Lake Minnetonka. Means of all water quality variables measured in live wells were significantly different from those of lake water, and relative differences were greatest for ammonia concentration. The percentage of dead fish in live wells was significantly and inversely correlated with pH, which may reflect effects of dissolved carbon dioxide, No relationship between mortality and live-well fish density, equipment, or holding techniques was detected. Our results suggest that most tournament mortality was due to the cumulative effects of sublethal stressors. Among other recommendations, we suggest that alternatives to traditional weigh-in tournaments during the spawning period be explored and that anglers maximize replacement of live-well water with lake water to reduce concentrations of metabolic waste products.