No abstract

Four behavioral experiments conducted in both the laboratory and the field provide evidence that adult sea lamprey (Petromyzon marinus) select spawning rivers based on the odor of larvae that they contain and that bile acids released by the larvae are part of this pheromonal odor. First, when tested in a recirculating maze, migratory adult lamprey spent more time in water scented with larvae. However, when fully mature, adults lost their responsiveness to larvae and preferred instead the odor of mature individuals. Second, when tested in a flowing stream, migratory adults swam upstream more actively when the water was scented with larvae. Third, when migratory adults were tested in a laboratory maze containing still water, they exhibited enhanced swimming activity in the presence of a 0.1 nM concentration of the two unique bile acids released by larvae and detected by adult lamprey. Fourth, when adults were exposed to this bile acid mixture within flowing waters, they actively swam into it. Taken together, these data suggest that adult lamprey use a bile acid based larval pheromone to help them locate spawning rivers and that responsiveness to this cue is influenced by current flow, maturity, and time of day. Although the precise identity and function of the larval pheromone remain to be fully elucidated, we believe that this cue will ultimately prove useful as an attractant in sea lamprey control.

We developed a new approach for directly quantifying selection parameters for fishing gear using a dual underwater video camera apparatus and employed the method to estimate gill net retention probability for walleye (Sander vitreus). The method allows observation of fish behavior around fishing gear and estimation of the absolute probability of fish encountering, contacting, or being retained by the gear. We demonstrated the applicability of this method by quantifying the probability that walleye were retained in multifilament nylon gill nets after contacting the nets. Walleye with total lengths 2.49 times the perimeter of the mesh were most likely to be retained, and retention probability peaked at 0.60 (95% confidence interval 0.41–0.90), meaning 40% of walleye that were the ideal size for a given mesh escaped after contacting the net. Our empirically derived retention curve exhibited a steep ascending limb and strong positive skew because of walleye morphology and the tendency for larger walleye to be captured by tangling. Most walleye that avoided capture did not fully enter the mesh or backed out of the mesh after they became temporarily wedged or tangled.

The behavior of sexually active brook trout Salvelinus fontinalis and brown trout Salmo trutta was observed on spawning redds in a small Minnesota stream to characterize the nature and frequency of interactions between the two species. Twelve redds were continuously monitored for 24 h with underwater video cameras; a total of 270 h of videotape was analyzed. Fifteen spawning events were observed, four of which involved individuals of different species. Male brown trout and brook trout attended females of both species. Female reproductive behavior was similar whether attended by conspecific or heterospecific males. No diel rhythms that would temporally isolate species during spawning were evident. Our results suggest that brook trout and brown trout spawning behaviors do not contribute to reproductive isolation of the two species and that disruptive interactions between them may be common. These interspecific sexual interactions may play a role in species replacement.