Vulnerability of Early Life‐Stage Lake Whitefish and Cisco to Invasive Nearshore Predators

ABSTRACT In recent years (post 2010), the recruitment of populations of cisco ( Coregonus artedi ) in the Great Lakes and surrounding inland lakes has generally increased. Conversely, recruitment of lake whitefish ( C. clupeaformis ) populations is declining, in some cases at alarming rates. Differential survival of the two species is likely set during early life stages and may be partially explained by differences in avoidance behaviours, particularly in the presence of more recently introduced nearshore predators, like round goby ( Neogobius melanostomus ) and rainbow smelt ( Osmerus mordax ). We evaluated the predation success of three sizes of round goby (small, 59–59 mm total length (TL)), medium, 82–92 mm TL and large, 111–132 mm TL) and one size of rainbow smelt (130–144 mm TL) consuming lake whitefish and cisco at various early life stages—larval, early juvenile and juvenile. Controlled predation trials were conducted and recorded for 30 min. to examine foraging behaviours of potential predators and avoidance patterns of the two coregonine species at the three early life stages. Round goby capture success and attacks per pursuit were primarily related to coregonine life stage (i.e., size), but medium and large round goby had higher success with captures and/or predation efficiency on early juvenile and juvenile lake whitefish than cisco. The number of attacks per pursuit by rainbow smelt was higher on juvenile lake whitefish than cisco, which did not lead to different capture rates. Juvenile cisco exhibited stronger anti‐predator response (i.e., tighter group cohesion) than juvenile lake whitefish, which could contribute to lower predation success and/or lower efficiency by introduced predators. Our results suggest that round goby (> 65 mm TL) may have an impact on survival of early juvenile and juvenile lake whitefish, and rainbow smelt may have a larger impact on juvenile lake whitefish than cisco during times of spatial overlap in late spring. Predation by these two invasive fish species in the Great Lakes has the potential to at least partially explain recruitment differences between lake whitefish and cisco.