Smallmouth Bass Predation

Field Science — Through stocking, smallmouth bass now occur in Maine waters that still contain populations of native Atlantic salmon. Biologists and anglers are worried that these aggressive predators might further reduce numbers of already rare salmon through competition. In a lab study, biologists tested competition between age-0 fish of both species, using experimental stream tanks to evaluate behavior in several habitat configurations.*

Young salmon favored riffle habitat and were most active at night. Smallmouths, on the other hand, selected pool habitat more than riffle areas and were most active during daytime. In the presence of salmon, this preference was magnified. Though salmon shifted position somewhat after smallmouths were introduced to the experimental system, changes were not dramatic.

It seemed that the two species partitioned habitat spatially and temporarily, limiting competition between them. The researchers note that while studies in aquaria allow close monitoring of small fish using electronic sensors, the controlled setting eliminates natural ecological factors that might affect this relationship.

A companion study in natural stream habitat also found limited effects on salmon habitat use from age-0 smallmouths.** Competition was minimal most of the time, but more intense in warmer periods with lower flows. The researchers noted that competition might intensify if streams continue to warm due to climate change. In addition, predation risk from age-1 bass might alter behavior of juvenile salmon. As a result, they recommend focusing salmon recovery efforts in watersheds without smallmouth bass.

*Wathen, G., J. Zydlewski, S. M. Coghlan Jr., and J. G. Trial. 2012. Effects of smallmouth bass on Atlantic salmon habitat use and diel movements in an artificial stream. Trans. Am. Fish. Soc. 141:174-184.

**Wathen, G., S. M. Coghlan Jr., J. Zydlewski, and J. G. Trial. 2011. Habitat selection and overlap of Atlantic salmon and smallmouth bass juveniles in nursery streams. Trans. Am. Fish. Soc. 140: 1145-1157.