An important method in the management of Asian carps is research. Research is on-going in this field to find more ways to prevent the arrival of, control, and eradicate these species. Scientists are focusing on a few key areas:
- Biology and behaviour of Asian carps in environments where they have already established (e.g. U.S. waters excluding the Great Lakes) or are predicted to arrive
- Social, economic, and environmental impacts of an establishment
- Methods of prevention, monitoring, and detection
- Methods of control
Biology and Behaviour
To understand the impacts of Asian carps, it is important to understand their biology and behaviour. Currently, there are no established populations in Canadian waters of the Great Lakes. A recent study has found that Grass Carp have spawned in the Sandusky River which flows into Lake Erie (Embke et al. 2016). To get a better understanding of the reproductive dynamics of Grass Carp, some were captured from western Lake Erie over a three-year period. Of the 60 captured, 86.7% were reproductively viable (Wieringa et al. 2016). Based on the bigheaded carps (Bighead Carp and Silver Carp) Risk Assessment of the Great Lakes conducted by Fisheries and Oceans Canada in 2011, we know that these species could survive in the Great Lakes and a single event that accidentally introduces a few adults has a high probability of leading to an established population (Cudmore et al. 2012, Cuddington et al. 2013).
Establishment of Asian carps in the Great Lakes could have devastating effects ecologically and socio-economically. In areas where they have already become established, they have negatively impacted not only the ecosystem but the commercial and recreational fishing industries as well (Kolar et al. 2007). It is expected that Asian carps could successfully establish in Lake Erie and reach biomass greater than native species with a similar function in the ecosystem (Wittmann et al. 2014).
To what extent do Asian carps impact native fish species?
Current research suggests that Bighead and Silver carp abundance is negatively impacting the body condition of native planktivores, such as bigmouth buffalo and gizzard shad, due to diet overlap (Irons et al. 2007). A Grass Carp invasion would lead to a reduction in biomass of aquatic vegetation, negatively impacting native species like largemouth bass and bluegill (Wittmann et al. 2014).
Prevention, Monitoring and Detection
There are methods for preventing, monitoring, and detecting Asian carps such as the electric barrier in Chicago, surveillance with traditional gears (i.e. electrofishing, netting) and the environmental DNA (eDNA) program. Currently, eDNA is used as an early detection method. It can detect genetic material that has been shed by organisms into their environment. New methods look to develop species specific markers to better detect Asian carps (Farrington et al. 2015). Many aquatic invasive species in the Great Lakes have used the Welland Canal as a pathway between Lake Erie and Lake Ontario, however; specific movement of fish between this canal is unknown (Kim and Mandrak 2016). It was determined using acoustic telemetry that 7 of 139 tagged fish (3.9%) moved between lakes Ontario and Erie through the canal, demonstrating that fish can move through the canal, but locks limit dispersal (Kim and Mandrak 2016).
How can we prevent Asian carps from entering the Great Lakes?
New research is being done to investigate more options for prevention. Bubble curtains are a tool that can be used to deter the movement of Asian carps. Bubble curtains use air bubbles to produce loud noises and movement within the water. This technique was found to deter 73-83% of Bighead and Silver carps in an experimental study (Zielinski and Sorensen 2016).
The use of carbon dioxide as a deterrent is also being studied. Bigheaded carps were found to avoid areas of higher carbon dioxide concentrations, and as the carbon dioxide spread throughout the study area they moved farther away from the source (Donaldson et al. 2016). Acoustic deterrents have been found to be effective in Asian carp management. Silver Carp exhibited a habitual behaviour to acoustic deterrents (Vetter et al. 2015). They reacted and moved away from the source a couple of times but eventually ignored it, suggesting that a complex sound stimulus would be effective in prevention and management of Asian carps (Vetter et al. 2015).
What is the most effective way to detect Asian carps?
Understanding how to detect Asian carps is essential in their control and management. Early detection of Asian carps provides the opportunity to respond quickly and control the situation. To better understand where we should be looking for Asian carps in case of arrival, Canadian scientists have modeled their habitat requirements and overlapped them with habitats in Canada to identify locations that are highly suitable for these species (DFO unpublished data). These results continue to be refined with new tools as new information becomes available to continuously identify at risk habitats. Studying the movement of Asian carps provides information on where and when to implement control and management efforts.
Using acoustic telemetry to monitor the direction, distance and timing of carp movement, recent research suggests that specific seasons (spring and early fall) and locations (backwater) are good target areas for control in the Wabash River in Indiana (Coulter et al. 2015). This research provides useful information that can assist with pre-existing detection methods.
It is important to study control methods that can effectively eliminate populations of Asian carps or prevent their movement, and ensure that any resulting damage is minimal. These methods should also work to ensure that native species are not negatively impacted.
Do native predators of Asian carps exist in North America?
A common issue with invasive species is that they have no predators in their new ecosystems. This is an issue for Asian carps as well. Juvenile carps are prey for native predatory fishes right after a spawning event, but as they grow bigger quickly, predation decreases (Anderson 2016).
Recent research has found Asian carps in the diet of River Otters in Illinois (Feltrop et al. 2016). If River Otters develop an affinity for Asian carps, perhaps they could be an effective biological control.
Other uses for Asian carps?
Since predation is not always effective on its own, other options need to be considered. Use of Asian carps as fertilizer, pet food, and for human consumption is being explored in the U.S.A.. In a blind test conducted by the Missouri Department of Conservation, Silver Carp was preferred 2-1 over tilapia and catfish (Phelps 2016).
Can pheromones aid in Asian carp control?
The use of pheromones has been studied in Sea Lamprey control, and is being studied for Asian carps as well. Asian carps were found to avoid alarm pheromone cues (i.e. pheromones of a predator) and be attracted to chemical cues of schooling and sex pheromones (Little et al. 2014). These results have implications for capturing and deterring Asian carp populations.
Climate change will influence the survival, establishment, spread, and impact of Asian carps should they arrive in Canada. Specifically, climate change will have direct impacts on temperature and precipitation in the Great Lakes Basin that will, in turn, improve the conditions for the survival, establishment, and spread of Asian carps. Increased temperature coincides with increased speed of maturation, and increased development leads to more rapid population growth. In addition, changes in temperature and precipitation will likely influence spawning success. Changes in temperature and precipitation could work synergistically to allow for greater population success of Black, Silver, Grass and Bighead carps.
Climate change will likely increase both variation and mean of air temperature that, in turn, will directly influence water temperatures. Greater variation in temperature means that there will likely be more extremes in both warmer and colder conditions. The mean annual temperature will also likely increase, which means that there will be more hotter, and fewer colder, days on average.
Chemical reactions can occur at different rates depending on weather. Metabolism, which is responsible for critical processes like growth and sexual maturation, is the sum of all chemical reactions in an organism. In other words, metabolism can be considered as the speed of living. Cold-blooded animals like fishes, whose body temperatures are controlled by the environment, will see their metabolisms increase in warmer conditions. If metabolism is the speed of life, fishes are living more of their lives on hot days than cold ones. Warmer conditions lead to faster growth which leads to larger body sizes and thus greater rates of survival. Asian carps are among the species that may benefit from warming temperatures because of their ability to accelerate the processes that take place in shorter timeframes and, therefore, survive predation or other threats in light of their size.
Asian carps may also mature at a faster rate with a warming climate as warmer air temperatures coincide with earlier sexual maturity. Reducing the number of years before reaching the age of reproduction shortens the generation time for these fishes and, as a result, a faster population growth. While increased metabolism is responsible for faster development and sexual maturity, adults will also be smaller because growth tapers off with age. Interestingly, smaller adult Asian carps produce fewer eggs. This is perhaps a single trade-off that could slow reproduction, but nonetheless, this alteration in time of maturity and development is concerning. As an example, Bighead Carp mature at different ages across environments depending on temperature: in lower latitudes, they mature at a younger age compared to colder environments at higher latitudes. Climates at lower latitudes may reflect the potential conditions that will result from climate change at higher latitudes. Based on this assumption, there are high abundances of Bighead Carp due to a younger age at maturity in the Mississippi River, and under future climate scenarios, we can expect the Great Lakes Basin to have a similar climate to that region. This could mean that populations of Bighead Carp, as well as other Asian carps, will mirror these population successes and prove problematic for the Great Lakes.
Higher temperatures will also have an impact on spawning. Increased high flows, in combination with increased temperature, would trigger earlier and more spawning events. Water temperature determines hatching time, and higher temperatures will lead to shorter hatching times which would provide increased opportunity for egg success. Additionally, higher temperatures as a result of climate change will increase the number of rivers suitable for spawning in the Great Lakes Basin.
Canada is warming at two times the global rate due to polar amplification. This means that warming is accelerated at higher latitudes. The impacts of this warming will be clear in the Great Lakes where Asian carps, if they become established, will see increased metabolism and development, decreased age of maturity leading to earlier reproduction, and increased population growth rates.
Warmer temperatures also have an impact on precipitation. Warmer air can hold exponentially more moisture than cold air, which can affect how much it rains. Increased precipitation is also linked to alterations in the polar jet stream patterns caused by climate change. “Blocking” patterns, where the jet stream is slowed in certain areas, could lead to higher precipitation from colder, moist air trapped in low pressure systems above the Great Lakes. This means that there is a higher likelihood of more extreme and extended precipitation events. This could impact Asian carps as their spawning success is highly dependent on flows. If the flows are too high, then the eggs will be washed out of the spawning tributary before hatching. Conversely, if the flows are too low, the eggs will drop out of suspension and fail to hatch on the substrate. Nonetheless, the net overall effect of more extreme precipitation events is an increasing number of successful spawning events.
The change in precipitation could lead to more reproductive opportunities, but equally, more flooding and opportunities to breach physical barriers, and more fertilizer runoff which will subsequently increase food availability. Overall, increased precipitation will likely be beneficial to Asian carps.
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