Monitoring, Prevention and Response
There have been a few individual Bighead Carp and Grass Carp captured in the Canadian waters of the Great Lakes. Of the Bighead Carp, only three specimens have been collected, all in western Lake Erie, between 2000 and 2003. These are believed to have been intentionally released. There have been approximately 8 Grass Carp captured since 1985 in Lake Huron, Lake Ontario and Lake Erie but were found to be triploid (sterile). These likely escaped from populations being stocked in the United States. To date, no Silver or Black carps have been found in the Great Lakes.
Asian carps are highly invasive and threaten the native ecosystems that they are introduced into. Two of these species (Bighead, Grass and Silver carps) are of immediate concern due to the threat that they pose to the Great Lakes. These species currently inhabit numerous waterways throughout the United States including the middle and lower segments of the Illinois River, upper Illinois River and the Chicago Area Waterway System which are directly linked to the Great Lakes basin. This proximity could allow the invasive carps to spread into the Great Lakes unless effective measures are utilized to prevent this occurrence.
In 2002 electrical barriers were installed in one of the Chicago waterways to prevent the bigheaded carps from entering the Great Lakes. To date, only one Bighead Carp has been found on the other side of the barrier in that waterway.
Fisheries and Oceans Canada crews visited 24 locations in Lake Erie, Lake Huron and the Huron-Erie Corridor in 2013 to conduct early detection sampling. In 2014, DFO crews have conducted early detection sampling at 34 locations in Lake Erie, Lake Huron, the Huron-Erie Corridor, and scout sites in Lake Ontario and Lake Superior. These locations were selected based on prediction models which indicated that they have suitable habitats for Asian carp species. Locations were sampled at least once and those that were predicted by ecological models, to be at highest risk of invasion were re-sampled up to a maximum of three times between June and October. The number of sample sites at each location varied depending on the size of the location and habitat types available. Habitat information was recorded at each sample site. Crews conducted boat electrofishing and deployed gill nets, trammel nets, hoop nets, fyke nets, trap nets and bag seines. The fishes collected at each site were identified, counted, measured and returned to the waters from which they came. Any Asian carps detected are removed from the water and taken to the lab for further analysis. Upon capture of an Asian carp specimen, DFO staff will go immediately into response protocols. Response focuses intensely on capturing any additional Asian carps that might be in the vicinity of initial detection and does not include sampling the rest of the fish community.
Map of early detection monitoring locations in the near shore areas and tributaries on the Canadian side of the Great Lakes in 2013. Several sites at each location were sampled for early detection of Asian carps, surrogate species (buffalos, Common Carp) and the fish community using traditional fishing techniques including boat electrofishing, trap netting, fyke netting, trammel netting and bag seining.
A variety of sampling and removal tools are available to accomplish the plan objectives outlined above. They include traditional sampling gears (electrofishing, trammel nets, experimental gill nets, fyke or trap nets, tow nets, and seines), chemical pesticides (rotenone), high-tech sonic detection and imaging devices (sonic telemetry and hydroacoustics, DIDSON, and side-scan SONAR), and newly developed or developing techniques (eDNA, water guns, chemical barriers, and feeding attractants).
Electrofishing is a term generally applied to a process that establishes an electric field in the water in order to capture fishes by stunning them. When exposed to the field, most fishes become oriented toward the anode and as the density of the electric field increases they swim toward it. In close proximity to the anode, they are immobilized and float to the surface, allowing for the determination of abundance, density, and species composition. There are three types of electrofishing units that are generally used: backpack units, stream-side or shore units, and electrofishing boats.
Electrofishing is an important fish sampling tool incorporated in nearly every sampling action plan outlined in the CAWS. It is used to monitor for adult, juvenile and young-of-year Asian carps at fixed and random sites throughout the waterway and during response/planned intensive surveillance events and barrier maintenance actions.
Large-mesh trammel (a type of gill net) are frequently used in combination with electrofishing during fixed site monitoring and removal actions in Canada, the CAWS, lower Des Plaines River, and upper Illinois Waterway. These nets target large juveniles and adult Asian carp and are typically fished in deeper, side channel or offshore habitats not effectively sampled with electrofishing gear. The sizes of these nets vary depending on the need and range from 2-5 metres in height and 90-500 metres long. New net designs will be incorporated into sampling programs as they become available.
Hoop Nets, Fyke Nets, and Trap Nets
These three tools trap fishes inside mesh enclosures. The fish enter the passive gear through constrictions, referred to as tunnels or funnels. In hoop nets, the frames may be round, D-shaped or square, and are usually made from aluminum tubing. The tunnels are cones of mesh that are attached to a pair of hoops, so that when the net is set and the hoops are separated the narrow end of the tunnel points to the rear. The hoops can be held apart by spreader bars that are attached to the hoops, or by stretching the net between fixed points.
A fyke net is simply a hoop net to which wings and a lead are attached. Wings are short lengths of mesh with float and lead lines that are attached to the lateral margins of the first hoop and extend the longitudinal plane of the trap.
A trap net is similar to a fyke net, in that it has wings and a lead attached and a tunnel or tunnels though which fish enter, but it does not have rigid frames.
Bag Seines consist of a length of fine mesh strung between a positively buoyant line and a negatively buoyant line that is pulled through the water to encircle fish. A bag of the same mesh that extends behind the plane of the net is built into the midpoint, so that fish move into the bag as the net is pulled forward. A description of a seine normally includes its length, depth, the dimensions of the bag, and the mesh size and material. Sometimes the amount of floatation and weight on the lead and float lines is provided. Bag Seines can be used by wading (walking) or deployment from a boat. A single deployment and retrieval of a bag seine is usually referred to as a haul. In the simplest technique, two people walk in parallel through the water holding the seine forming a U-shape behind them. Seines are also deployed by keeping one end fixed and deploying the net in a semi-circle, either by wading or from a boat. The bag seine haul is collected by bringing the two ends together and pulling the net forward so that the encircled fish end up in the bag.
Bag seines are normally only used in water depths that are less than one half or two thirds the depth of the seine, so that the lead line remains on the bottom and the float line remains at the surface as the net is pulled forward. The netting process is easiest over smooth bottoms with no debris or obstructions, as the seine net can become snagged on rocks, logs etc., and often can only be freed by pulling the net backward off the object.
Gill nets consist of mesh with square openings fastened to a positively buoyant line at the top, often referred to as the float line, and a negatively buoyant line at the bottom, often referred to as the lead line because lead has traditionally been used to weight this line. Gill nets are typically stretched between two fixed points by attaching one end to an immobile object such as an anchor or a tree along the shoreline and then moving away from that point while laying the net out. Once the other end is reached, it is also attached to an immobile object and the net is left in place to capture fishes when they swim into it. Fishes are caught in gill nets when they become wedged in the openings in the mesh or become entangled in it. Therefore, the size of the openings, referred to as mesh size, is a critical parameter affecting efficiency. Experimental nets with mesh sizes from 19 – 50mm have shown promise as a monitoring tool for young-of-year and early juvenile fishes.