Foraging behavior of bay anchovy larvae, Anchoa mitchilli

Foraging behavior of the bay anchovy larvae, Anchoa mitchilli was characterized by silhouette video photography. Swimming speed, pause frequency and duration, burst duration, reactive distance (RD), horizontal and vertical reaction angle (HRA, VRA), and length of the predation cycle were estimated over a range of sizes and stages of development. First feeding larvae displayed a distinct pause-travel search behavior that included horizontal rotation of their body to the right or left to scan a new volume of water. Pause duration was affected by light intensity in small larvae and significantly decreased in length of time as larvae grew (ANOVA, p < 0.01). Duration of swimming bursts between pauses was short (mean = 0.13 ± 0.03 s). Average swimming speeds increased with size from a mean of 0.50 ± 0.39 BL · s- 1 (body lengths) at first feeding to 2.25 ± 1.27 BL · s- 1 at 12 mm SL. Mean RD of bay anchovy larvae at 10 lux and corrected for vertical angle was 0.65 BL and increased to 0.92 and 1.00 BL at 100 and 250 lux, respectively. The average RD increased in the presence of turbidity from 0.65 to 0.83 BL at 10 lux. Reducing light (250, 100, 10 lux) affected the foraging behavior of the largest larvae (14-19 mm SL) especially at 10 lux where only one attack was observed with or without turbidity. The Horizontal attack angles (HRA) of larvae ranged from 0-114° with 78% of attacks taking place at angles between 20 and 70° while vertical reaction angles (VRA) of larvae ranged from 12-90° with 77% of attacks occurring at < 50°. The average length of the predation cycle decreased with increasing larval size from 2.4 s down to 1.34 s for larger larvae. Bay anchovy larvae frequently aborted attacks (33%) after reacting and approaching prey. Attack success was high even for small larvae (mean = 83%) and approached 100% in the largest size class.