Observations of a Nuclear-follower Foraging Association Between Spiny Softshell Turtles (Apalone spinifera) and Fish in an Urban Drainage Canal in Louisiana

The nuclear-follower relationship is a specialized interspecific foraging association in which the nuclear species excavates the substrate while foraging, and follower species access food items flushed or uncovered by the nuclear species. We observed a nuclear-follower association between Apalone spinifera (Spiny Softshell Turtle) and fish (Micropterus salmoides [Largemouth Bass] and Lepomis spp.) in an urban drainage canal (Wards Creek) in Baton Rouge, LA, during June and July of 2020. Groups of Largemouth Bass and Lepomis spp. numbering 0-2 and 1-20, respectively, followed foraging Spiny Softshell Turtles. When foraging, Spiny Softshell Turtles were observed moving along the creek bottom, thrusting their probosces into and vigorously excavating the substrate. The accompanying fish then entered the cloud of suspended sediment to pursue and capture prey. Excavation of the substrate by Spiny Softshell Turtles appears to be the critical component of this nuclear-follower relationship, flushing or exposing prey that would otherwise be unavailable to fish. This nuclear-follower relationship is apparently one of commensalism, i.e., while fish probably benefit from increased foraging success, few if any benefits accrue to foraging turtles.