Monitoring Rusty Crayfish in Southern Ontario Streams and Rivers Scott Reid, Tom Brooke, Jane Devlin, Joe Nocera Applied Research and Development Branch
Background rusty crayfish first reported in 1960s: Lake of the Woods and a small number of south-central Ontario lakes spread to numerous lakes and rivers in other regions impacts in lakes: replacement of native crayfishes damage to macrophyte beds shifts in macroinvertebrate and fish assemblage composition
Monitoring Crayfish in Streams native and non-native crayfish have been monitored across hundreds of southcentral Ontario lakes no corresponding program for streams and rivers prevents defensible assessments of the status of native crayfish and the impacts of rusty crayfish in flowing waters limits opportunities for timely and effective remedial actions
Stream Monitoring: Study Objectives Objective #1: assess the effectiveness of stream sampling methods to detect native and non-native crayfish and characterize abundance Objective #2: examine differences in catchability related to size/reproductive form
Stream Sampling Approaches low equipment cost recommended for rusty crayfish detection (Hamr 2007) backpack electrofisher common stream fish sampling gear hand-picking bag seine suitable for wadeable habitats low risk of vandalism
Methods Field sampling removal sampling within closed units 20m length for hand-picking and backpack e-fishing samples 10m length for bag seine 15 replicates per gear type Data analysis population size & capture probability (P) were estimated using a generalized removal model (software: MICROFISH) 3-5 passes Flow block-nets
Results Species Detection six species collected from study streams rusty crayfish was dominant species: 65% of sampling units 90% of total number of individuals captured only species in four of eleven streams generally collected during first pass electrofishing most effective all six species detected seining least effective only three species captured often required multiple hauls for species detection
Population Size & Catchability 7 0.8 6 Mean density (#/m 2 ) 5 4 3 2 Mean Catchability 0.6 0.4 0.2 1 0 BP Hand Seine 0 BP Hand Seine
Results Crayfish Size/Form Size crayfish seined were generally larger capture prob. estimated for 33% of samples inconsistent pattern among size classes, and gear types Reproductive Form rusty crayfish sex ratio 1:1 capture prob. estimated for 40% of samples Frequeny (%) 60 50 40 30 20 10 0 60 50 40 30 20 10 0 60 50 40 30 20 10 0 Electrofishing 5 10 15 20 25 30 35 40 45 Hand-capture 5 10 15 20 25 30 35 40 45 Seining 5 10 15 20 25 30 35 40 45
Recommendations for Monitoring combination of seining with either handpicking or electrofishing would: permit a variety of habitat conditions to be sampled improve likelihood of species detection broad range of size classes additional information on fishes removal sampling not reliable for estimating population density frequent lack of depletion across sampling passes generally low estimates of capture prob.
Threat to Endangered Queensnake? Queensnake, Regina septemvittata medium-sized, semi-aquatic snake restricted distribution in SW Ontario freshly molted crayfish nearly 100% of its diet extremely vulnerable to changes in prey availability
Study Objectives and Approach Government Response Statement: identify prey species, distribution and abundance track invasions of rusty crayfish investigate rusty crayfish impacts may have on Queensnake and native crayfish Queensnake sites: rusty crayfish sites:
Sampling Method 10m 1m - study reach length: 15x channel width (max: 500m) - 10 shoreline transects evenly spaced along each study reach - 20 minute hand-picking search at each transect
Impact to Native Crayfishes Native Crayfish Abundance Native Crayfish Richness 140 2 120 Mean Count (±SE) 100 80 60 40 20 Mean Number of Species (±SE) 1.5 1 0.5 0 Rusty Crayfish Present Rusty Crayfish Absent 0 Rusty Crayfish Present Rusty Crayfish Absent white: all native species, grey: O. propinquus Mann-Whitney Test: p < 0.001
Variation in River Crayfish Fauna 2 C. r. 1.5 1 CA 2 (19%) 0.5 O. p. O. r. 0 C. b. -0.5 O. v. -1-1 -0.5 0 0.5 1 1.5 CA 1 (56%) Correspondance analysis of log (x+1) transformed crayfish abundance
Distribution of O. propinquus O. propinquus is the primary Queensnake prey % composition at native-only sites = 91% % composition rusty crayfish sites = 12% Relative influence of rusty crayfish and habitat: Generalized Additive Modeling (GAM) lo(or.count) -6-4 -2 0 2 4 Rusty Crayfish Ohio EPA Qualitative Habitat Evaluation Index 0 50 100 150 200 OR.Count probability of occurrence was negatively to rusty crayfish abundance O. propinquus less likely to occur at site with higher conductivity other habitat measures unimportant lo(pc2) -2 0 2 4 Conductivity -2-1 0 1 2 3 PC2
Implications for Queensnake? predictable pattern of species replacement after rusty crayfish introductions is expected to occur in other parts of its distribution, Queensnake exclusively feed on other crayfish species and genera (Cambarus vs. Orconectes) selection reflects dominant species suitability of rusty crayfish as prey: dependent on timing and duration of moulting behaviour of freshly moulted crayfish
Acknowledgements Invasive Species Partnership Fund Ausable Bayfield CA, Grand River CA, Upper Thames River CA, Nature Conservancy, Clinton MNR district office Collaborators: Jane Devlin, Tom Brooke, Dr. Joe Nocera, Scott Gillingwater, Eric Snyder, Keith Somers