Evidence of Positive Phototaxis in Paddlefish: Implications for Larval Sampling

Paired lit and unlit quatrefoil traps were used to examine the photic response of Paddlefish Polyodon spathula yolk-sac larvae (YSL) and exogenous-feeding larvae (EFL) under controlled conditions in a hatchery. One lit and one unlit trap were placed in two identical circular raceways containing approximately 10,000 YSL and EFL for 20 2-min trials. Lit traps captured nearly 10x more larvae than unlit traps for each cohort and accounted for 91% and 94% of total catch for YSL and EFL, respectively. This is the first documentation of this photic response in Paddlefish. A slight increasing trend in capture with length was noted for YSL, whereas EFL demonstrated a strong decreasing trend in capture, indicating a possible behavioral shift at 15-16 mm TL. The high proportional catch of lit traps among 1-mm length classes evaluated (≥79%) suggests that Paddlefish exhibit positive phototaxis and light trapping for Paddlefish larvae <20 mm TL may have potential to substantially increase catches in the wild. More efficient capture of larval Paddlefish in the wild using lighted traps might prove useful for documenting the presence of reproduction, for initial indications of year class strength, and as a source of fish for rearing in hatcheries and repatriation to the wild. However, much remains to be evaluated in controlled and wild settings, including responses to different light emissions, lower fish density, and higher turbidities common in rivers when and where wild Paddlefish spawn.