In Situ Swimming Behavior of Lake Trout Observed Using Integrated Multibeam Acoustics and Biotelemetry

Abstract

Multibeam echo sounder systems allow the in situ observation of swimming and foraging behavior and give insights into the ecology of fish at the individual level. In Lake Opeongo, Ontario, 16 adult lake trout Salvelinus namaycush were surgically implanted with ultrasonic tags, released, and studied by means of mobile fisheries acoustics. The transmitted pulses from the ultrasonic tags could be detected and displayed within the multibeam echogram in real time. Tagged lake trout were relocated on 131 occasions over 12 d, for a total of 11.7 h of echogram observations. From these events we observed and quantified the spatial relationships of individual lake trout to other fish targets, schools of cisco Coregonus artedi, and the surrounding habitat. We found that all but one tagged lake trout spent at least a portion of their time close to the lake's bottom, but interestingly, many made rapid vertical swimming movements into the water column. These burst vertical movements were sometimes targeted at schools of cisco, such attacks always occurring from below the schools. During such interactions, the lake trout showed distinct peaks in swimming speed when they were between 2.4 and 6.4 m from the schools; we interpret this as the range of their reactive distance in the field. Some of the lake trout were also found to travel alongside of or to actively swim toward other fish targets, whereas others were more solitary. This type of information, made possible by the integration of fisheries acoustics and biotelemetry technology, gives us a fuller understanding of the ecology of aquatic predators and their prey and provides the direct measurements needed to quantify the bioenergetics of lake trout in their natural environment.

Life at the top: Lake ecotype influences the foraging pattern, metabolic costs and life history of an apex fish predator

“…The apparent confirmation of the “constant satiation hypothesis” in our study is contingent on the assumption that our daytime observations of activity are dominated by foraging behaviours. Several lines of evidence support this assumption: (a) lake trout are the apex predator in our study systems and hence should not exhibit predator avoidance behaviours; (b) our observations were temporally well separated from the known spawning season and hence should not be confounded with reproductive behaviours; (c) our observations were focused on the final foraging period prior to spawning, when energy acquisition through foraging is a primary determinant of future reproductive success; hence, foraging should be a priority activity; (d) the shift in activity patterns from night to day is consistent with that expected when a visual predator resumes foraging in daylight (i.e., in all lakes, the proportion of resting state detections was higher at night and the median activity level was lower); (e) lake‐to‐lake differences in water temperatures selected by lake trout varied in concert with temperature preferences of primary prey: colder temperatures were selected in lakes (Lakes 373 and Opeongo) with pelagic cold‐water prey, while warmer temperatures were selected in lakes with warm‐water epilimnetic/littoral prey (e.g., Lake Louisa); and (f) in the active dataset, the distribution of daytime values for a typical individual is skewed left with a heavy right‐hand tail; this is consistent with the feeding behaviour typical of a predatory feeder like lake trout where foraging activity is dominated by “low”‐intensity prey search behaviours, interrupted by short‐term bursts of high intensity associated with attempts at prey capture; (e.g., Dunlop, Milne, Ridway, Condiotty, & Higginbottom, —a study of lake trout predation on cisco in Lake Opeongo).…”

Does habitat occupancy by lake trout and lake whitefish in large lakes match published thermal habitat envelopes?

“…This is surprising and contrary to their proximity with the lake bottom. Previous studies have demonstrated lake trout spend the majority of their time within close proximity to the lake bottom and coordinate prey encounters by attacking pelagic prey from below (Dunlop et al, ). Substrate characteristics appear to be irrelevant given this feeding mode.…”

“…Biotelemetry is one method to infer selection within a habitat envelope. This is achievable in smaller lakes (Plumb & Blanchfield, 2009) but technically challenging in large lakes (Dunlop et al, 2010;Morbey et al, 2006).…”

“…A difference in covariates between the two scales points to differences in factors governing habitat selection. The movement‐scale boundary was derived from the mean of 2‐hr locations of individual lake trout ( N = 6), fitted with ultrasonic transmitters, and tracked during July 2007 in Lake Opeongo using a multi‐beam hydroacoustic system (Dunlop, Milne, Ridgway, Condiotty, & Higginbottom, ). The average distance a lake trout travelled in 2 hr (313 m) was the basis for a circular radius (156.5 m) for movement‐scale sample sites.…”

Exploratory and Instantaneous Swimming Speeds of Amphidromous Fish School in Shallow-Water Coastal Lagoon Channels

“…several hours) collected using ad hoc sampling protocols (e.g. a mobile transducer along the channel to track the school or the methodology used by Dunlop et al (2010), which combines ultrasonic tagging with multibeam acoustic observations). However, the maximum observation time recorded during our study (34 s) did not allow us to apply such analysis.…”