In last month’s blog post, we dove into how the invasive sea lamprey entered the Great Lakes System, and the catastrophic effect they had on fish populations. While we touched on how rigorous control methods have reduced sea lamprey populations by up to 90 percent, going into exactly how sea lamprey control is done is also important. In this follow-up post, we’re taking a look at the three main methods of sea lamprey population control: lampricides, barriers, and traps.
During the 1950s and 1960s, scientists were searching for a way to chemically target and kill sea lamprey, while not affecting other species in the area or damaging the ecosystem. With time and rigorous testing, they discovered two compounds that did the job most effectively: TFM and Bayluscide.
Both TFM and Bayluscide target sea lamprey at their larval stage, when they’re most vulnerable to lampricides. At this stage, larvae burrow into the bottoms of the streams and tributaries of the Great Lakes, after which point they swim into the Great Lakes as parasitic juveniles. Sea lamprey larvae tend to prefer specific areas of streams, and will stay buried anywhere from three to five years before swimming out into the Great Lakes. Because of the wide range of time larvae might spend in those streams, TFM and Bayluscide treatments happen at regular intervals of every three to five years, and only in areas scientists have determined the larvae are present.
Before any TFM or Bayluscide are released in streams and tributaries of the Great Lakes, rigorous sampling of a tributary or stream is done. This ensures that the compounds are spread in the correct areas, and in a manner most suitable for that particular body of water. TFM and Bayluscide have been the top control methods for sea lamprey, breaking down harmlessly in just a few days after treatments so that these chemicals don’t accumulate in our environment. However, methods for reducing sea lamprey populations past the larval stage also exist in the form of barriers and traps.
|Years Treated With Lampricide
|2017, 2012, 2011, 1996
|2018, 2015, 2011, 2006, 1999
|2018, 2016, 2013, 2012, 2008, 2004, 1999
|2018, 2016, 2013, 2012, 2008, 2003, 1999, 1995
|2013, 2005, 1996
In order for sea lamprey to reproduce, adults need to swim upstream into tributaries of the Great Lakes. Physical barriers in these tributaries, both purpose-made sea lamprey control barriers and other structures like hydro dams, form a network of blockades that prevent sea lamprey from accessing vast amounts of spawning habitat. Before the discovery of lampricides, barriers were the main defence against sea lamprey, and today they still play a key role in population control. Custom-built barriers stop sea lamprey, but allow other fish to pass by.
Adult sea lamprey are poor jumpers, but have a suction mouth that can help them pass through difficult terrain. Sea lamprey barriers, therefore, are usually built with a two-to-four foot drop in them, and a horizontal lip along the crest of the barrier. Adult lamprey aren’t able to clear the jump, and the lip prevents them from being able to cross the barrier using their sucker mouths. Jumping fish, meanwhile, are able to harmlessly pass. In order for non-jumping fish to pass through, some sea lamprey barriers have ‘trap-and-sort’ systems where creatures caught by the barriers are sorted, and fish are moved upstream while lamprey are removed.
Traps are the final method used to control sea lamprey, and focus on two separate lamprey populations: juvenile sea lamprey leaving streams and tributaries to swim into the Great Lakes, and adult sea lamprey leaving the Great Lakes to spawn. Catching both these groups is of vital importance for reducing the amount of sea lamprey that are harmful to fish, as well as preventing the population from increasing.
Juvenile sea lamprey are often caught using removable methods such as nets, and removed from streams before they are able to reach the Great Lakes. Adult lamprey, meanwhile, are often caught in traps that are built into barriers.
The future of sea lamprey control
While sea lamprey populations in the Great Lakes have been reduced by 90 percent, population control is always going to be necessary. Lampricides, barriers, and traps are all important control methods. Nevertheless, scientists continue to look for ways to make control even more effective.
Currently, scientists are looking into the use of pheromones to guide sea lamprey towards or away from certain areas, as well as investigating whether sea lamprey have the potential to become resistant to TFM or Bayluscide. Additionally, as we move towards returning the Great Lakes’ tributaries and streams to their natural flow patterns, barriers and traps are being re-designed in order to protect these areas while being less disruptive.
Sea lamprey will likely always be part of the Great Lakes ecosystem, and controlling their population will continue to be important if we want to stop history from repeating itself.