  Using the recently-installed Fast-Ion Deuterium Alpha (FIDA) spectrometer,
the effects of low-frequency (20-50 kHz) chirping energetic particle modes with
toroidal mode number n \geq 1 on the fast-ion population in MAST plasmas are
considered. Results from the FIDA diagnostic are presented and discussed in the
light of the present theoretical understanding of these modes, known as
fishbones, in plasmas with reversed shear. Measurements of the fast-ion
population reveal strong redistribution of fast ions in both real and velocity
space as a result of the fishbones. Time-resolved measurements throughout the
evolution of a fishbone show radial redistribution of fast ions with energies
up to 95% of the primary beam injection energy. Correlations between changes in
the FIDA signal and the peak time derivative of the magnetic field perturbation
are observed in a limited range of operating scenarios. The transient reduction
in signal caused by a fishbone may in some cases reach 50% of the signal
intensity before mode onset.
