Ontogenetic Shifts in Prey Selection and Foraging Behavior of Young-of-Year Alligator Gar

The early life history of alligator gar (Atractosteus spatula) is poorly documented.  We performed laboratory experiments to quantify prey selection and foraging behaviors of alligator gar through early ontogeny (16 – 80 mm TL).  Alligator gar were simultaneously offered zooplankton, benthic invertebrates, and one of three densities of fish prey.  The smallest size groups of alligator gar consumed zooplankton almost exclusively, but selection for zooplankton declined with increasing alligator gar size, whereas selection for fish prey increased.  Benthic invertebrates were avoided by all size groups of alligator gar.  Selection of fish prey increased, whereas selection of zooplankton declined at higher densities of fish prey.  Alligator gar spent the majority of their time foraging at the surface of the water column, although the proportion of strikes in the middle and bottom of the water column increased with larger alligator gar sizes.  Increasing consumption of fish prey by larger alligator gar was associated with longer pursuit and strike distances, increased capture and handling efficiencies, and decreasing handling times.  These observations indicate that alligator gar undergo several functional and behavioral changes during early ontogeny that facilitate a rapid transition to piscivory, but that prey consumption patterns are strongly affected by prey density.