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Old February 10th, 2005, 06:06 PM   #1
Dani
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AZ Game & Fish ABA Summer Night Tournament Mortality Study


Exerpt of full AZGF Tournament Mortality Study Report

Due to questionable results of the summer B.A.S.S. Federation Open, we included a second summer tournament, the ABA Summer Nights tournament, held from 5 p.m. on August 28 through 1 a.m. on August 29, 2004. This report provides the preliminary results. A final report will be published when data from all tournaments has been collected (December 2004).

This tournament was a 6-hour night tournament. Due to the high water temperatures, anglers were encouraged to circulate their live wells often and use ice to keep water cool. Tournament organizers also encouraged anglers to “fizz” any fish that were caught in deep waters.

For the delayed mortality experiment, 30 largemouth bass were selected at random from the tournament release tanks on August 29, 2004. Of the 30 fish selected at random, all were upright, but most were lethargic and some had visible hemorrhaging around the caudal fin. Anglers were very cooperative and allowed us to measure dissolved oxygen and temperature of their live-wells at the completion of the tournament. We were able to measure water quality from 14 randomly selected live-wells.

In addition, 30 control fish (not subjected to angling stresses) were captured by electrofishing the shoreline on the night before tournament fish were collected (electroshocking did not occur on the same day as the tournament due to logistical constraints). During the previous tournament, control bass were held in a recirculating live well for a period of over one-hour. For this tournament, we reduced handling stress on largemouth bass with ice-cooled water, constant aeration, and periodic recirculation. Control fish were not held in the live well for more than 30 minutes.

Fifteen tournament caught fish ranging from 12.7”–17.9” were placed in each of two holding pens. Additionally, 15 control fish ranging from 11.7”-19.1” were placed in each of two pens. The four rectangular holding pens measured 8 ft x 6 ft x 6ft. One pen containing tournament fish and one pen containing control fish were held at the surface, the remaining two pens were submerged to a depth of 20-28’ in a covered slip in Pleasant Harbor Marina. Surface water temperature was 81.7 F, while water temperatures at the depth of the submerged pens was 80.5 F. Bass were held in the pens for five days and monitored daily to check mortality and to remove dead fish. Following the experimental period of 5 days, 10 control fish and 8 tournament fish were transported to the AGFD Fish Health Lab in Pinetop, AZ to test for virus (especially Largemouth Bass Virus), and other pathogens and parasites.


Results

Water quality in anglers’ live-wells was generally good. Dissolved oxygen of over 4.0 mg/L is adequate for fish survival; nearly 30% (4 of 14) of live-wells had DO levels below the tolerable range. Water temperatures were equal to that of lake temperatures, which was expected due to recirculation practices. Anglers using ice had only slightly lower live-well temperatures than those not using ice.



For the 6-hour tournament, 136 largemouth bass were officially weighed-in. Initial mortality was recorded by tournament organizers and corroborated by AGFD; 12 fish (8.82%) were either reported dead at weigh-in or were dead prior to release. Delayed mortality for tournament caught fish was relatively high, as 23 of the 30 (76.7%) fish died. It is interesting to note that all 15 fish held in the submerged cage died, while 8 of the fish in the surface cage died. Only four control fish died (13.3%); 3 of which where held in the surface cage and 1 in the submerged cage. Of the fish that died during the experiment, 6 tournament fish and 0 control fish died within the first 72 hours. The table below describes initial and delayed mortality for the tournament, including control fish.



To accurately assess delayed mortality, and ultimately total mortality, there must be a correction made to account for mortality caused by holding fish in pens. In this study, mortality of control fish is attributed to being held in pens and is used to correct for delayed mortality. Therefore, when corrected for the 4 tournament fish that died, delayed mortality was 63.3% and total mortality was 66.6%.

All fish sent to the AGFD Fish lab tested negative for largemouth bass virus, bacterial infection, and external parasites.

Summary and Conclusion

During this experiment, bass were held for five days, rather than the six-day holding period used for previous tournaments at Lake Pleasant. We did this to more closely mimic summer tournament mortality studies completed in the Southeastern U.S. during 2002-2003.

The pre-release mortality experienced by fish during the ABA tournament (8.8%) was higher than during spring tournaments at Lake Pleasant, and only slightly higher than the mean initial mortality of southeastern tournaments (6.7%). Delayed and total mortality were high in this experiment (63.3% and 66.6%, respectively), but slightly lower than experienced in southeastern tournaments (74.4% and 75.9%).

We cannot explain the higher mortality experienced by tournament-caught fish held in submerged cages compared to surface cages, especially since the same pattern of mortality was not observed in control fish. Initially, we speculated that confinement and stress may be causing an outbreak of disease, possibly even Largemouth Bass Virus. However, all fish tested negative. Therefore, we believe that the total mortality of tournament-caught fish is related to the stress of tournament handling (being caught, handled, held in live-wells, carried in bags, weighed-in, and released).

Most tournament anglers took great care in an attempt to reduce initial mortality (using ice in live-wells, aeration, and recirculating water) and tournament organizers ran an efficient weigh-in (including fish holding tanks with fish conditioner, ice and aeration). This careful handling of fish is likely the reason for lower mortality rates than observed in southeastern U.S. tournaments. However, mortality rates for this, and probably other summer tournaments in Arizona are very high. Recent research by Shimano, Inc. has concluded that the stress of the weigh-in procedure may be the greatest cause of mortality for largemouth bass. Therefore, they have devised a new weigh-in system that ensures that stress in minimized during that critical period, which may be of interest to Arizona bass anglers.

Conclusions

We will reserve our final conclusions until the remaining tournaments have been completed. We would like to thank the tournament organizers and the participants for their cooperation with this study.

Last edited by Delw; February 10th, 2005 at 10:09 PM..
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