dc.description.abstract | During aquatic suction feeding, the predator opens its
mouth and rapidly expands its buccal cavity, generating a
flow field external to the mouth. The rapid expansion of the
buccal cavity produces high fluid velocities and
accelerations that extend only a short distance from the
mouth (about half of one mouth diameter), and only persist
for several milliseconds. Therefore, the predator must
precisely time its strike to locate the prey within the narrow
region of high flow, during the brief period when flow is at
its peak. With flow being the agent for transferring force to
the prey, the predator may enhance these forces by
producing higher water velocities and faster acceleration at
the mouth, but also through increasing the strike’s
accuracy, i.e. locating the prey closer to the mouth at the
instant of peak flow speed. The objectives of this study
were to directly measure forces exerted by bluegill Lepomis
macrochirus on their prey and to determine how bluegill
modify force output. Bluegill were offered ghost shrimp
tethered to a load cell that recorded force at 5000·Hz, and
feeding sequences were synchronously recorded using
500·Hz video. Peak forces exerted on attached 20·mm
shrimp ranged from 0.005·N to 0.506·N. In accordance with
the short duration of the strikes (average time to peak gape
of ~13·ms), the forces recorded were brief (~12·ms from
initiation to peak force), and force magnitude declined
rapidly after peak force. Statistical analysis indicated that
rate of buccal expansion, and prey size, but not strike
initiation distance, significantly affected peak force. These
observed variables were used with results from flow
visualization studies to estimate the flow at the prey’s
location, which allowed the calculation of drag, pressure
gradient force and acceleration reaction force. The
relationship between these calculated forces and the
measured forces was strong, indicating that the model can
be used to estimate forces from strike kinematics. This
model was then used to study the effects of strike initiation
distance on peak force and on the rate of increasing force.
Comparisons of model output to empirical results indicated
that bluegill time their strike so as to exert an average of
~70% of the peak possible force on the prey, and that the
observed strike initiation distance corresponded to the
distance that maximized modeled force on an attached
prey. Our results highlight the ability of bluegill to produce
high forces on their prey, and indicate that precision and
visual acuity play important roles in prey acquisition,
beyond their recognized role in prey detection. | en_US |