The influence of lake attributes and predatory bass on the distribution of northern crayfish (Orconectes virilis) in central New Hampshire

Introduced species influence the dynamics and structure of freshwater systems; understanding the variables that shape introduced species’ distributions can aid in anticipating their spread. We examined multiple factors that may influence the distribution of northern crayfish (Orconectes virilis (Hagen, 1870)), an introduced species, in New Hampshire, USA. Sampling occurred July to August 2010 in 20 lakes. We tested catch per unit effort (CPUE) and body size of crayfish against lake trophic status, size, depth, and shoreline development, as well as substrate type. We also compared CPUE and body size in the presence or absence of known predators, smallmouth bass (Micropterus dolomieu Lacepède, 1802) and largemouth bass (Micropterus salmoides (Lacepède, 1802)). Crayfish body size was not strongly associated with any tested variables, nor were there significant correlations between lake-level parameters and CPUE. CPUE increased with rocky substrates and decreased with macrophyte cover. We also found significantly lower CPUE in lakes with bass predators; this could be due to consumptive effects directly lowering crayfish abundance, nonconsumptive effects of bass on crayfish behavior, or both. Our work provides a baseline for future surveys examining northern crayfish or bass expansion in New Hampshire and highlights a variable that could be important as this crayfish colonizes additional locations outside its native range.

New crayfish species records from the Sipsey Fork drainage, including Lewis Smith Reservoir (Alabama, USA): native or introduced species?

As part of a study of aquatic faunal community changes along riverine-lacustrine transition zones upstream of Lewis Smith Reservoir in northwest Alabama, USA, we collected crayfish from 60 sites in the Sipsey Fork, Brushy Creek, and selected tributaries (Black Warrior River system). After finding two unexpected and possibly-introduced crayfish species, we expanded our investigation of crayfish distributions to include crayfish obtained from stomachs of black bass (Micropterus spp.) caught at seven sites in the reservoir. To explore what crayfish species were in the drainage historically, we examined museum databases as well as stomach and intestinal contents of a variety of preserved fishes that were caught in the Sipsey Fork and Brushy Creek drainages upstream of the reservoir in the early 1990’s. Of the seven crayfish species collected, one, Orconectes (Procericambarus) sp. nr ronaldi, was not previously reported from Alabama, and another, O. lancifer, was not reported from the Black Warrior River system prior to the study. Three are known or possibly introduced species. Upstream of the reservoir, the native species Cambarus obstipus, C. striatus, and O. validus were common. The same three species were found in fish collected in the 1990’s. Orconectes perfectus was found only in the reservoir but may be native to the drainage. Orconectes lancifer was in the reservoir and in stream reaches influenced by the reservoir. Evidence points to O. lancifer being introduced in the drainage, but this is uncertain. Orconectes sp. nr ronaldi was found in a relatively small portion of Brushy Creek and its tributaries, in both flowing and impounded habitats, and may be introduced. Orconectes virilis is introduced in Alabama and was found only in stomachs of fish collected in the reservoir.