Munching on Invasives: New Zealand Mudsnails in the Diet of the Federally Endangered Tidewater Goby

This study documents predation by the federally endangered tidewater goby, Eucyclogobius newberryi, upon the invasive New Zealand mudsnail, Potamopyrgus antipodarum, in Big Lagoon, California, USA. Close to 400 tidewater goby were collected monthly from April 2009 to August 2010.  Mudsnails were found in the digestive tract of tidewater goby ranging in size from 14 mm to 52 mm TL, corresponding to post-settlement and nearly maximal sizes of this species. The presence of shell fragments and complete absence of intact shells in the hind gut suggest full digestion and energy extraction from this hard-shelled prey.  Consumed snails ranged in size from 0.39 mm to 4.0 mm, and the average size of ingested snail increased with fish length (p < 0.001). New Zealand mudsnails were found in over 80% of individuals during the summer and fall of 2009, when the estimated population size of E. newberryi was several million. This suggests that tidewater goby exert substantial predation pressure upon New Zealand mudsnails and take advantage of these readily available novel prey items.