Invasive goby larvae: first evidence as stowaways in small watercraft motors

Aquatic invasive species (AIS) are a major threat to aquatic ecosystems worldwide. Despite management efforts, human assisted dispersal continues to distribute AIS within and across waterbodies. An understudied translocation vector for AIS, especially for invasive fish, are the cooling systems of small watercraft motors. Here, we investigate the contents of boat motor cooling systems for the presence of invasive goby larvae in a collaboration with local boat owners. Because of the exclusively nocturnal drift activity of goby larvae, to collect samples we drove boats in the first hours after sunset. For an estimate of the translocation potential, we quantified drift density of goby larvae as well as boat traffic after sunset. We found a goby larva in a boat motor once in 30 boat drives of 1-2 hours duration each. Peak drift densities of goby larvae were 2.5 per 100 m3, which is comparable to previously reported data. Recreational boats were active after sunset throughout the reproductive season of invasive gobies and are therefore a realistic translocation vector for goby larvae. Additionally, evidence of fish and other animals inside boat motor cooling systems, gathered from online boating forums, demonstrates the potential of AIS transport in small watercraft. Translocation inside motors is especially likely for in-water transport of boats, which should be a management focus in interconnected aquatic systems.