Document: MIC-3-56-9

Differential antipredatory responses of two similar species of fish to introduced brown trout.

NANNINI, M.A.* and M.C.BELK

Brigham Young University, Provo, UT 84602 ¹

Abstract:
Escape response was measured for two native species of fish, leatherside chub (Gila copei) or redside shiner (Richardsonius balteatus), to a simulated attacking brown trout, an introduced predator. An octagon shaped arena was set up with a diameter of 58 cm. The center of the arena contained a 10 cm diameter clear Plexiglas holding chamber that could be retracted through the bottom of the chamber. A single individual of either species was placed in the holding chamber. Once the prey had acclimated and was facing within a 45o angle of where the trout would come out, the Plexiglas holding chamber was lowered and a trigger was tripped, releasing the simulated trout. Directly over this arena, a Panasonic digital video camera was set up, which recorded the entire sequence of events. Later the tape was reviewed and 3 responses were measured. These included speed (the distance from the position of the fish when it first reacted to the position of the fish when the attack was over/time), direction (the angle between the fishes initial position and where it ended up with 0 being directly toward the trout), and reaction distance (the distance between the predator and prey when the prey first reacted to the predator). The size of each fish was also measured to account for differences in responses of these variables due to the size of the fish. Leatherside chub and redside shiner differed significantly for all 3 variables. Redside shiner tended to move toward the predator while leatherside chub tended to move away from the predator. Redside shiner had a longer reaction distance than leatherside chub, meaning that redside shiner reacted to the predator when the predator was further away. Finally, leatherside chub had a significantly faster speed than redside shiner. Though the two species differ in their reaction to an attacking predator it is unclear which strategy is more effective. Are redside shiner slower because they react quicker to the predator and thus don't need to move fast? Are leatherside chub faster because the predator is closer to them when they react and does this increased speed make up for the difference in reaction distance? These questions should be tested in experiments that measure mortality of these species in the presence of brown trout and look for differences in mortality between these two species.

Keywords: Predator, Escape response, Fish

This abstract is being presented at: 1:15 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.