"Short-term Mortality of Smallmouth Bass Caught During a Live-Release Tournament at Lake Oahe, South Dakota"

By Jeffrey J. Jackson and David W. Willis, PhD
Department of Wildlife and Fisheries Sciences, South Dakota State University, Brookings SD 57007

ABSTRACT
Smallmouth bass (Micropterus dolomieui) caught during a fishing tournament at Lake Oahe, South Dakota, were held in floating cages for 48 hr to assess short-term mortality. This was a live-release tournament sponsored by the Bass Anglers Sportsman Society (BASS), and included a weigh-in. Thus, fish were held in boat live wells for as long as 7 hr. Of 61 legal-length (>30cm) smallmouth bass caught during the two-day tournament, three were dead at weigh-in (4.9%). No additional mortalities were observed at 24 or 48 hr [Mike's note: please read the prior sentence again...means no delayed mortality].

KEY WORDS
Smallmouth bass, fishing tournaments, hooking mortality

Bass (Micropterus spp.) fishing tournaments are a common occurrence on may lakes, reservoirs, and rivers in the U.S. (Schramm, Armstrong, Funicelli et al. 1991). The largemouth bass (Micropterus salmoides) is the principal species caught during most of these tournaments, but some tournament catches also include smallmouth bass (M. dolomieui). The popularity of bass fishing and the ecological importance of bass as piscivores in many systems have caused concern about the effects of bass tournaments on bass populations and other anglers (Schramm, Armstrong, Funicelli et al. 1991; Schramm, Armstrong, Fedler et al. 1991).

Hooking mortality and tournament survival have been more thoroughly investigated for largemouth bass than smallmouth bass. Green et al. (1988) summarized hooking and tournament mortality for largemouth bass. Although hooking mortality for smallmouth bass has been eveluated, we are aware of no literature citations that involve tournament survival. Clapp and Clark (1989) found mortality rates of 11% for smallmouth bass that were caught using minnows and 0% for those caught on spinners during controlled experiments in which fish were immediately released. Green et al. (1988) reported that smallmouth bass hooking mortality was "negligible" when fish were immediately released after being caught with artificial lures. However, smallmouth bass caught during tournaments may be retained in boat live wells for serveral hours before weigh-in.

Local interest and the paucity of data concerning smallmouth bass tournament mortality prompted the South Dakota Department of Game, Fish and Parks and South Dakota State University to assess smallmouth bass mortality during a live-release tournament at Lake Oahe, South Dakota.

METHODS
Smallmouth bass were collected during a tournament sponsored by the South Dakota Bass Anglers Sportsman Society (BASS) Federation at Lake Oahe, South Dakota. The tournament headquarters were located at the Spring Creek Marina, where weigh-ins and boat launching took place. The tournament was held 29-30 June 1991; a total of 68 anglers participated. Two anglers were assigned to each boat. BASS regulations required the use of only artificial lures; no live bait was allowed. The tournament was scheduled from 0630 to 1400 hr; however, inclement weather on 29 June caused a 1-hr delay.

Anglers were restricted to four fish per day with a minimum length limit of 30 cm (12 in.). All live fish were to be released after the weigh-in. A 57-g (2oz) penalty was assessed for any fish dead at weigh-in. A fish was classified as dead by tournament organizers when it lacked opercular movement.

After weighing, live smallmouth bass were placed into an aerated, 950-L, truck mounted transfer tank. Weigh-in procedures took approximately 0.5hr, and fish were then transported to floating cages in a protected cove at Spring Creek. Smallmouth bass caught during the first day of the tournament were placed in a steel mesh (13mm, bar measure) cage that was 1.2m deep x 1.8m long and 1.1m wide. Fish caught the second day were placed in a nylon mesh (19 mm, bar measure) cage that was 1.6m deep x 1.5m long x 1.0m wide. The total volume of both cages was 2.5m^3.

Initial mortality was defined as the total number of fish judged dead after weigh-in. Delayed mortality was determined by raising the cages at 24 and 48 hr and counting the number of dead fish.

RESULTS
Water temperature was 23C during the tournament, and air temperatures peaked at 31C the first day and 27C the second day. Wind speeds ranged from 16-32km/hr throughout the tournament. A total of 61 smallmouth bass (300 mm or longer) was caught during the tournament; fish ranged from 300 to 419 mm (total length). Smallmouth bass less than 300 mm in length were immediately released, and were not enumerated.

Two of the 41 smallmouth bass weighed the first day were dead, for an initial mortality of 4.9%. One of the 20 legal-lengh smallmouth bass catured on the second day was dead at weigh-in, for an initial mortality of 5.0%. The combined initial mortality for the two-day tournament was 4.9%. Delayed mortalities, measured at 24 and 48 hr, were 0.0% for both tournament days.

DISCUSSION
We found a mortality rate of 4.9% through 48 hr for smallmouth bass caught during the two-day tournament. This mortality rate was within the range reported by Clapp and Clark (1989), who reported mortality rates of 11% for smallmouth bass caught with live bait and 0% for bass caught with artificial lures and immediately released. Even though fish in our evaluation were held in live wells, mortality rates were relatively low at a water temperature of 23C. Holbrook (1975) found that total mortality of largemouth bass caught during tournaments and released after weigh-in ranged from 16 to 76%. However, Schramm et al. (1987) reported that mortality rates of tournament-caught largemouth bass can be less than 10% when careful procedures are used to handle fish during weigh-in.

The three fish deaths during this evaluation were caused by anglers removing hooks that had penetrated deeply into the throat or gills. Clapp and Clark (1989) reported mortality for three out of four fish that had been caught on minnows and deeply hooked. During our evaluation, one angler hooked a smallmouth bass deep in the esophageal region and instead of removing the hook had clipped the line, leaving the lure in place. This fish was still alive after 48hr. Weidlin (1988) found that the 20-day mortality for smallmouth bass (less than 305mm) that had swallowed hooks baited with live bait was 19-47% when hooks were removed. Mortality was reduced to 4% when the line was cut and hooks left in fish.

Our evaluation addressed only mortality of smallmouth bass that were kept by anglers and weighed by tournament officials. Thus, we do not know what impact the tournament might have had on sublegal (<300mm) smallmouth bass. However, tournaments held in Lake Oahe under conditions similar to this tournament should have little impact on populations of 300mm and longer smallmouth bass.

THIS STUDY HAS BEEN REPRINTED, WITH PERMISSION, IN ITS ENTIRETY. This can be validated by contacting Dr. David W. Willis at the South Dakota State University in Brookings, South Dakota.