Spring survey shows positive results after smallmouth kill; TWRA says larger, older fish “likely” affected most

COLLECTING DATA-The TWRA uses electrofishing boats like the one shown here to survey the population of smallmouth here on Dale Hollow. (photo courtesy tnfish.org)

COLLECTING DATA-The TWRA uses electrofishing boats like the one shown here to survey the population of smallmouth here on Dale Hollow. (photo courtesy tnfish.org)

By THOMAS P. WEAVER, HORIZON Editor

DALE HOLLOW-Despite taking a hit during the fish kill of the summer of 2012, data from a Tennessee Wildlife Resources Agency’s (TWRA) recently released report showed the smallmouth bass population was still alive and well here on Dale Hollow Lake even though fishing results have been somewhat below anglers’ normal expectations of the world-class fishery.

The report explained the TWRA’s spring electrofishing (shocking) surveys yielded “very good catch rates” of smallmouth bass “for all size classes,” which they explained “were some of the highest obtained within the last decade.”

With that positive also came somewhat of a negative as the report explained “past electrofishing surveys have shown more fish towards the upper end of the slot (smallmouth over 20” long) than was represented in 2013 surveys.”

TWRA Region 3 reservoir fisheries biologist/manager Mike Jolley said it was “likely that the larger/older fish would have been more susceptible to various stresses” associated with the fish kill of a year ago.

“Older and weaker fish in the population are typically the first ones to succumb to stress,” Jolley said in the report.  “In Dale Hollow Reservoir, a 21-inch (smallmouth) is typically eight to nine years of age, according to the last age and growth data on record.

“This age is at or near the top of the life expectancy for smallmouth bass in Dale Hollow Reservoir. In fact, the majority of the smallmouth bass observed in this die-off were older fish and within the protected slot range (16-21 inches).”

That fact has also been evident in summertime night tournaments this year as only a handful of smallmouth over 21” have been carried to the scales.

Besides the good news of the electrofishing surveys of this spring showing “an impressive catch rate” between 27.02 (April) and 23.8 (May) smallmouth bass per hour–compared to the 10-year average of 17.7 per hour, the report also said “no sick or poor smallmouth bass were observed.”

The survey results are definitely good news for anglers here, but the TWRA did say the numbers may not necessarily mean good fishing results.

“Smallmouth bass ranging in size from 5-21 inches were collected and multiple year classes were represented which is reflective of past successful spawns,” the report said, “(but) electrofishing catch rates do not always guarantee however that fishing will be great (because) too many other influences can affect fishing success.

“But this data provides great measurements of fish populations in reference to spawning success, growth, annual mortality and density which in this case offers great hope for anglers and biologists.”

As previously reported in the HORIZON, after ruling out any virus, bacteria, parasites, and other diseases that could have resulted in “long-term consequences” for the lake’s prized species, TWRA’s report pointed to possible environmental and other factors that may have contributed to the die-off.

Jolley said the possible environmental factors “could include, but are not limited to, non-favorable oxygen levels at desired depth ranges which can change daily, harmful algal blooms (HAG’s), change in flow regimes affecting water layers and changes in reservoir retention time or other water quality issues.”

The article also reported Jolley saying the smallmouth kill could have been “likely caused by the record drought” or a byproduct of “higher than average temperatures which in some cases were record setting” last summer.

The report also detailed other possible factors in the die-off as the effect of a 60% increase in fishing pressure since 2000 and the possible adverse effects of fishing tournaments being held when the water temperature rises above 75 degrees.

Visit www.dalehollowhorizon.com for the two previous stories about the smallmouth kill or visit http://tn.gov/twra/region3/dhollowfishkill.pdf for Jolley’s complete report including graphs showing details of this spring’s electrofishing surveys.