Tracking Bluegill Research
September 08, 2011
The earliest telemetry studies, dating to the mid-1950s, focused on mid-size and large fish, as radio and acoustic tags were bulky, largely due to batteries used to power them. Advances in electronics and battery technology have expanded the range of fish studied with this insightful technique, and more bluegill research has been done, following the first such study at Smith Mountain Lake, Virginia, published in 1978.
South Dakota Studies
Researchers at South Dakota State University have led the way in recent bluegill movement studies. Dr. Craig Paukert, now Unit Leader at the Missouri Cooperative Fish and Wildlife Unit, tracked big bluegills at Pelican Lake in Nebraska as part of his Ph.D. dissertation research. Pelican Lake, located in the Valentine National Wildlife Refuge in northcentral Nebraska, is regionally acclaimed for the quality of its bluegill fishing.
Pelican Lake: This 820-acre lake is about 3 miles long by 1/2 mile wide and shallow, with average depth less than 4 feet and maximum depth of 9 feet. Patches of emergent vegetation grow throughout the basin, particularly reeds, bulrushes, and cattails. Paukert and his team implanted transmitters in 60 bluegills from 8 to 103â„4 inches in length and noted locations and habitat from April through September. They also tracked some fish over 24-hour periods.
Throughout the 6-month study, bluegills moved an average of 62 yards per hour, though individuals varied greatly. A couple speedsters moved up to 3/4 of a mile in just an hour. Overall, Pelican Lake bluegills were most active in mid-summer and least active in April and September, when movements were primarily around dusk. Females also tended to move more than males, though there was no size difference between sexes.
From May to August, 24-hour tracking showed bluegill movement rather constant, which seemed to indicate that they were feeding opportunistically day and night. The effect of temperature on movement wasn't clear. While movement was limited in April, when the lake averaged just 46°F, movement also was less in August and September when the water was close to 70°F.
Bluegill core home ranges were largest in April, averaging 7 acres, though Paukert noted that over 90 percent of radio-tagged 'gills seemed to move rather randomly. This core home range was defined as the area encompassing at least half of all locations. Core home ranges varied considerably among individual fish as well, ranging from 0.02 to 67 acres.
Unlike fish in some other lakes, bluegills here didn't make regular inshore-offshore migrations, likely because the lake's shallow basin offered similar habitat throughout, with cattails growing in the middle of the lake. On a seasonal basis, however, fish were closest to shore in April and June, and farthest from shore in late summer.
In this weedy shallow lake, it wasn't surprising that bluegills occupied submergent and emergent vegetation in all months and throughout the day and night, though they also were found in open water. There were, however, differences in vegetation use between males and females. Females didn't show preference for any type of vegetation or open water, while males more often occupied emergent plants like bulrushes, reeds, and cattails during April, June, July, and August. An earlier lab study had determined that the deeper body of male bluegills is more efficient for foraging in vegetation, while slender females with longer snouts are better suited to feeding in open water.
Enemy Swim Lake: Graduate student Eric Weimer conducted a year-round tracking study at Enemy Swim Lake, a 2,150-acre glacial lake in northeastern South Dakota, also focusing on large bluegills (over 8 inches). This mesotrophic lake averages 16 feet and gets as deep as 28 feet. Though they don't grow as large as at Pelican Lake, the population is high-quality, and has attracted increased angling pressure since 2000. From that year through 2004, fishing effort for bluegill quadrupled, while the catch rose from 10,000 to over 100,000 fish. Ice-fishing pressure has risen even faster since 2002.
Similar to Pelican Lake, bluegills selected dense and moderate vegetation as habitat during fall, the spawn season, and summer. In winter, they favored dense vegetation only, while moderate vegetation was selected in spring. They avoided unvegetated areas throughout the study. During fall and winter, fish favored the tallest vegetation available, and during winter, many bluegills occupied a shallow weedy bay, remaining there until ice-out.
Weimer theorized that fish used thick vegetation as feeding areas, finding abundant macroinvertebrates, including insect larvae, among the stalks. He noted that the density and size of predators, particularly pike and largemouth bass, were probably not sufficient to force bluegills into weedy sanctuaries to avoid predation.
Findings on distance from the shoreline by season differed from the Pelican Lake study. At Enemy Swim, 'gills were located farthest from shore in spring, and closest in summer. At Pelican, they were farthest from shore in mid-summer, and an intermediate distance from shore during spring. It's likely that habitat factors, such as vegetation, as well as structural features like points and humps affect habitat selection, and distance from shore, in itself, has little meaning from an ecological or angling perspective.
During winter, bluegills occupied the smallest core home ranges, while ranges were largest in summer and fall. Movement peaked during the spawning period, and there was little difference in activity between males and females, similar to Paukert's findings at Pelican Lake.
While Weimer didn't locate bluegills in deep water during any season, that result could have been influenced by the nature of his radio transmitters. Their high-frequency pulses were difficult to detect in water deeper than 16 feet, so more fish may have moved into deeper water in summer to feed on open-water zooplankton or benthic invertebrates such as insect larvae.
Weimer also compared the spots anglers were targeting bluegills to the exact locations and habitat types occupied by radio-tagged fish. At Enemy Swim, most bluegill fishing takes place in July and August. Total catches and harvest were about twice as high during summer as in winter. Bluegills spawn in June there, and fishing might be expected to be excellent. But Weimer theorized that the excellent walleye fishing at that time tempted many anglers from the bluegill bite.
He noted that bluegill anglers generally fished close to, but not precisely on, concentrations of bluegills in all months. Notably, anglers targeted winter bluegills in shallow Indian Bay where they were indeed concentrated. In June, anglers were found fishing adjacent to bluegill spawning areas, including some in Indian Bay. In mid-summer, however, many bluegills evacuated this bay and spread into the main lake, though the bulk of anglers remained behind.
When ice-fishing, anglers tended to fish too deep, where vegetation was thinner, while most bluegills seemed to seek the thickest weeds. Weimer noted that winter anglers fished areas that were more conducive to trouble-free fishing, as weeds would foul their lines. In summer, as well, anglers tended to fish deeper and in more open areas than bluegills favored.
From these studies, the message seems clear — in various environments, big bluegills occupy weedy areas. Other investigations have found them in offshore habitats during summer and winter, but they're more difficult to locate in those areas, and more likely to move about with planktonic food sources.
Anglers have many tools to probe thick vegetation, particularly dipping or dabbling softbaits on jigs or livebaits weighted with lead shot. Target pockets or holes within weedbeds, as bluegills tend to exploit the edges of thick vegetation where they can focus more clearly and maneuver better. Ice fishing in weeds is an art, particularly if you use sonar, as the signal, so clean and bright in open water, is scattered and unreliable. But persistence pays off for big 'gills.