The Influence of Available Benthic Habitat Type on Predation Risk in Larval Least Brook Lamprey

Refuge habitats are important for stream fishes.  For habitat specialists, the loss of refuge habitats can impact populations in several ways, including an increased susceptibility to predation.  Understanding the links between predation risk, available habitat, and habitat stressors may be critical for management and conservation of declining species, such as lampreys (Petromyzontidae) with burrowing larvae (ammocoetes) that are benthic habitat specialists.  In this laboratory study, we experimentally examined the influence of habitat availability on predation risk in ammocoetes of the least brook lamprey (Lampetra aepyptera). Ammocoetes were placed in aquaria containing a predator species (yellow bullhead, Ameiurus natalis) and one of 3 substrates: fine sand (0.125-0.5 mm), coarse sand (0.5-1.4 mm), or silt/clay (< 0.063 mm).  Based on 10 trials with each habitat type, survival of ammocoetes was highest in aquaria with fine sand (mean = 80%) and lower in those with coarse sand (mean = 58%) and silt/clay (mean = 4%).  Based on experimental results, ammocoetes may bear elevated predation risk in streams with excessive silt/clay sedimentation.  Predation risk of ammocoetes may also be increased in benthic habitats with larger substrates (coarse sand or larger sizes), such as those expected in channelized streams.