The sport of bass fishing has traditionally been a game of trial and error, with anglers making educated guesses as to the location of the bass. The sharing of successes and failures over time forms a “conventional wisdom” regarding where the fish are most likely to be found during the four seasons of the year. Professional bass tournaments have been a proving ground for developing cutting-edge bass tactics and have accelerated the learning curve for the wider fishing community. However, what if scientific analysis revealed that many of the established beliefs about bass behavior are incorrect?
Such was the task of Todd Driscoll and Jake Norman, fisheries biologists for the Texas Parks and Wildlife Department (TPWD) of the Jasper and Tyler offices, respectively, when undertaking a study of bass behavior recently submitted for publication in the North American Journal of Fisheries Management. The two-year tracking study is one of the few conducted on large reservoirs and the first to scientifically examine how bass use structural habitat.
The study was initiated by Driscoll and Norman, both avid bass anglers, in response to bass anglers within their management regions voicing concerns over declining fish catches from Toledo Bend and Lake Fork, both consistently ranked in the Top 10 in Bassmaster Magazine’s annual 100 Best Bass Lakes list.
TPWD’s electroshocking surveys, however, did not reflect angler experience. As Driscoll states, “Obviously, these are high-profile lakes, and we keep a close eye on populations through our electrofishing surveys, and those surveys weren’t showing a drop in bass populations. That was the driver for the studies.” In other words, if the bass populations were still intact, to what degree were fish utilizing the structural habitat and water depths traditionally targeted by bass anglers? Conversely, what proportion of the bass populations in these larger reservoirs occupy areas that receive relatively low fishing pressure?
The study/methodology
Per the TPWD publication, 43 largemouth bass on Toledo Bend and 37 at Lake Fork were implanted with radio transmitters and tracked over a two-year span. The studies were performed within large basins or tributaries that receive considerable bass fishing pressure: on Fork, Birch Creek was chosen as the study site, while massive Housen Bayou was selected on Toledo Bend.
As Norman points out, “Of course, telemetry has been utilized for fish studies for a long time, but often at the university level, and focused on much smaller impoundments because the fish are easier to relocate. However, no study has been done on bass behavior in reservoirs the size of Fork and Toledo Bend. I’d say it’s one of the first studies of its kind, and I think it’s sparked some interest in other state agencies using our methodology and analysis to answer similar questions from their anglers, as well.”
The bass in each reservoir were caught using rod and reel as well as electroshock methods, surgically implanted with a transmitter and immediately returned to the water after confirming the health of the fish. The bass were observed every two weeks using telemetry in conjunction with forward-facing sonar to record their exact location.
Findings
The telemetry data collected over two years reaffirmed much of what we already knew about bass behavior; however, it also revealed some surprises and a certain level of randomness in their behavior that is often difficult to explain, summarized in the following subheadings.
Flats vs. dropoffs
Both Toledo Bend and Fork are known for having a strong population of bass that live offshore apart from the spring spawning season. As expected, around 60% of the time the bass were found on “traditional” offshore structure: creek drops, ledges and points.
About 40% of the time, however, the bass in the study group were found on vast, nondescript flats with no discernable depth changes in the area.
As Driscoll points out, “The percent occurrence of bass over the flats for each reservoir was 46% at Toledo Bend and 37% at Fork. That, in my opinion, is the most surprising thing I saw. That’s a high number to me, as a biologist and an angler.”
“You might call it ‘no-man’s-land,’” Norman adds. “These big flats are areas that anglers wouldn’t typically target or even look at on a topo map and think, ‘That’s going to give me a high chance of success in catching bass.’ These areas [flats] are certainly off the beaten path and not heavily pressured by anglers.”
As to the possibility of increased fishing pressure moving the bass to these flats, Driscoll noted, “We just can’t answer that question with the data we have. My gut tells me much of it is just natural behavior in relation to the movement of threadfin shad schools. However, our biggest fish at either lake [both over 8 pounds] frequently occupied a big stump on a flat. It wasn’t out there feeding on shad at all. Now, why was it there as opposed to being out on traditional structure? We just don’t have a good answer.”
Driscoll did offer a teaser regarding data being compiled for a second part of the study that’s yet to be released, stating, “We did two figure eights over the tops of the offshore fish [with the outboard idling], as most anglers do when scanning with sonar. The boat and motor noise moved 40% of the fish off of their location. That could explain some of the decline in catch rates from these traditional offshore areas — the fish were simply displaced off of that structure — and could explain why anglers aren’t seeing as many fish on sonar. If the boat gets within, say, 30 feet of a fish and it gets pushed off from the approaching boat, you’ll never see it [on sonar].”
Small home ranges
One might assume that impoundments as large as Toledo Bend and Fork would find the bass populations moving great distances with the freedom to roam for miles or in search of new foraging opportunities.
Driscoll and Norman both dispel that notion, with Driscoll stating, “We saw very little movement of bass in either reservoir; they typically stayed confined to less than 120 acres throughout the year. They essentially swam large circles within these home ranges. It tends to reinforce [the idea] that the size of the lake is irrelevant to overall fish movement. Toledo Bend is 186,000 acres, but those bass had similar home ranges as studies performed on 2,000-acre lakes.”
Norman continues, “We had some fish [at Fork] that didn’t leave a few tree stumps for months at a time, so they were contained within a 30- to 50-acre pocket or section of the creek. During spring, of course, they would move up to a little secondary point or an isolated spot in a pocket to spawn, and in the summer or winter, they may pull out a little deeper to a channel or drain. Some might just roam throughout standing timber or in the very back of the pocket. But ultimately the bass were mostly confined to a very small area, and that’s where they stayed all year.”
To illustrate the head-scratching behavior of some bass within a given population, Driscoll recalls, “Now what’s also interesting, even though very few fish moved outside of a small home range, a small percentage of them moved a lot. They were oddballs and they moved a great distance.”
The study details how five of 43 largemouth bass in Toledo Bend and five of 37 bass in Fork were found well outside their original embayments, with one particular bass at Toledo Bend having relocated nearly 7 miles within 11 days of prior observation. “We couldn’t find any reason for them to move considerable distances like this, as there was no biological reason for them to relocate [due to plenty of habitat and food availability],” noted Driscoll.
Seasonal migration
Hand and glove with their findings on the small home range is the concept of seasonal movement of a bass population. For example, for years, anglers have operated under the assumption that a significant number of bass migrate into the backs of creeks during the fall of the year. TPWD’s telemetry study on both reservoirs did not find that to be the case. As Driscoll emphasizes, “None of our observed fish reflected that behavior — zero.”
As Norman adds, “Perhaps that lack of fall migration is something specific to the lowland reservoirs we have here in the southeastern U.S., but we didn’t see that movement at all. The shad and other baitfish may move to and from the backs of creeks in higher concentrations, but there was by no means a mass migration of bass into the backs of the same creeks [in the fall].”
As Driscoll theorizes, “My personal opinion is [that] the bass we catch in the backs of creeks in the fall are resident fish that simply become more active with the presence of the baitfish movement into these areas.”
Regarding the seasonal movement of bass throughout the summer, Norman observes, “Just as interesting to me was their summertime behavior. We caught some of our study fish with a rod and reel on popular summertime offshore humps and released them right back in a matter of minutes. They stuck around these offshore areas for about a month and, afterward, they left the offshore humps and never returned.
“The point being,” states Norman, “many of these fish didn’t remain on what we’d consider ‘prime’ offshore summertime structure. In fact, most of these offshore fish [in the study population] relocated shallow for a good chunk of the summer and positioned on boat docks in 2 to 6 feet of water. Most of them stayed on the same stretch of two to three docks the entire summer. The big schools of bass remained offshore, but certainly not all the fish are doing the same thing [throughout the summer].”
Depth
The study did confirm the depths most anglers target when searching for bass offshore. Driscoll noted that, “At Toledo Bend and Lake Fork, nearly all of our relocated bass were in traditional depths commonly targeted by bass anglers. Ninety-eight percent of our total fish relocations were in areas with bottom depths of 30 feet or less.”
Driscoll is quick to point out, “I want to caution everyone to not overgeneralize these findings to highland reservoirs with steep shorelines. I suspect that bass in these reservoirs more frequently suspend in areas with bottom depths considerably deeper than 30 feet. We’ve had a lot of contact from other state agencies to perform similar studies on these different classifications of reservoirs to understand their specific fish populations better. At the end of the day, a state fisheries agency’s primary concern should be angler satisfaction.”
Originally appeared in Bassmaster Magazine 2024.
