Zebadiah Woiak | Geology Reports

USGS2017

Carbon dioxide as an under-ice lethal control for invasive fishes

Resource managers need effective tools to control invasive fish populations. In this study, we tested under-ice carbon dioxide (CO 2 ) injection as a novel piscicide method for non-native Silver Carp ( Hypophthalmichthys molitrix ), Bighead Carp ( Hypophthalmichthys nobilis ), Grass Carp ( Ctenopharyngodon idella ), Common Carp ( Cyprinus carpio ) and native Bigmouth Buffalo ( Ictiobus cyprinellus ). Fish were held overwinter in nine outdoor ponds (0.04 ha surface area; 340,000 L volume) treated with no CO 2 (control), 43.5–44.0 kg CO 2 (low treatment), and 87.5–88.5 kg CO 2 (high treatment). Ponds were harvested immediately after ice-out to assess survival and condition. Resulting survival in low (mean = 32%) and high (mean = 5%) CO 2 -treated ponds was significantly lower than untreated control ponds (mean = 84%). Lethal efficacy varied across species with no Bighead Carp, Silver Carp, or Bigmouth Buffalo surviving the high CO 2 treatment. External infections were observed more frequently after CO 2 treatments (means = 49–67%) relative to untreated ponds (mean = 2%), suggesting a secondary mechanism for poor survival. This study demonstrates that CO 2 can be used as a lethal control for invasive fishes, but effectiveness may vary by species and CO 2 concentration.

Biological Invasions↗

USGS2013

Use of classification trees to apportion single echo detections to species: Application to the pelagic fish community of Lake Superior

Acoustic methods are used to estimate the density of pelagic fish in large lakes with results of midwater trawling used to assign species composition. Apportionment in lakes having mixed species can be challenging because only a small fraction of the water sampled acoustically is sampled with trawl gear. Here we describe a new method where single echo detections (SEDs) are assigned to species based on classification tree models developed from catch data that separate species based on fish size and the spatial habitats they occupy. During the summer of 2011, we conducted a spatially-balanced lake-wide acoustic and midwater trawl survey of Lake Superior. A total of 51 sites in four bathymetric depth strata (0–30 m, 30–100 m, 100–200 m, and >200 m) were sampled. We developed classification tree models for each stratum and found fish length was the most important variable for separating species. To apply these trees to the acoustic data, we needed to identify a target strength to length (TS-to-L) relationship appropriate for all abundant Lake Superior pelagic species. We tested performance of 7 general (i.e., multi-species) relationships derived from three published studies. The best-performing relationship was identified by comparing predicted and observed catch compositions using a second independent Lake Superior data set. Once identified, the relationship was used to predict lengths of SEDs from the lake-wide survey, and the classification tree models were used to assign each SED to a species. Exotic rainbow smelt (Osmerus mordax) were the most common species at bathymetric depths <100 m with their population estimated at 755 million (3.4 kt). Kiyi (Coregonus kiyi) were the most abundant species at depths >100 m (384 million; 6.0 kt). Cisco (Coregonus artedi) were widely distributed over all strata with their population estimated at 182 million (44 kt). The apportionment method we describe should be transferable to other large lakes provided fish are not tightly aggregated, and an appropriate TS-to-L relationship for abundant pelagic fish species can be determined.

Lake Superior↗