Observations of black bass (Centrarchidae) confined during angling tournaments: A cautionary note concerning dissolved oxygen

Delayed mortality in black bass (Centrarchidae) following angling tournaments is well documented. The causes of mortality are varied, but most involve stress from catching, handling and confining the fish. Blood chemistry values suggest that actual handling may be more stressful than the process of hooking and landing. During competitive tournaments, bass may be confined in boat livewells for up to 8 h. If levels of dissolved oxygen are limiting in such circumstances, stress can play a major role in delayed mortality of fish following release. During a study of pre- and post-release tournament-related mortalities of smallmouth bass, Micropterus dolomieu , and largemouth bass, M. salmoides , in Maine, the authors had the opportunity to examine conditions in livewells during confinement of fish. The objective was to examine dissolved oxygen and temperature in boat livewells under different tournament conditions, with and without the presence of fish. A pair of livewells in bass boats was monitored during each of three tournaments. In each tournament, anglers operated the aeration systems of the livewells in a different manner, thus allowing a comparison of the effectiveness of the three most common techniques on the dissolved oxygen levels in livewells. Although conditions in only one pair of livewells were examined during each tournament and fish were added at (typically) irregular intervals, these tests demonstrate the rapid depletion of dissolved oxygen during actual tournament conditions, when just a few fish are added.