Alaska Department of Fish and Game
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Alternatives to Rotenone
There are other methods to remove invasive fish, but the alternatives are not as effective or efficient as rotenone. Some of these methods have serious limitations and impacts on habitat.
- Fishing Regulations: Increasing bag limits and allowing many different gear types (such as bowfishing) can be effective when anglers want to fish for the target species. Pike regulations in Southcentral Alaska are very liberal. However, many northern pike anglers prefer to keep large pike, and smaller pike are often released. Typically large pike are rare in shallow lakes in Southcentral that have invasive pike populations. This is because the largest pike are either harvested or die, and after the rearing salmonids have been consumed, the remaining small pike don't have a sufficient prey base to support their growth.
- Netting: Nets have been used to collect illegally-stocked pike in Southcentral. However, nets don't always catch all sizes of fish. Repeated netting is necessary to control pike, and these programs are labor intensive and costly. Nets are easiest to use in shallow, non-vegetated areas. Because pike prefer vegetated areas, nets must be placed in areas where nets are susceptible to damage and tearing. Nets may also catch non-target species of fish and wildlife. Netting can reduce populations of invasive fish, but this method can never eliminate them completely.
- Electrofishing: Specialized electrofishing equipment delivers an electrical current into the water. When fish encounter the current, the electricity stuns their swimming muscles. This causes fish to float to the surface where they can be easily netted. The equipment is very sensitive, and generating the correct electrical field is dependent on water clarity and lack of vegetation. Because pike prefer areas with dense aquatic plants, electrofishing has limited success for pike removal. Electrofishing loses its effectiveness in water deeper than six feet.
- Biological Controls: Biological controls may include introducing a predator that feeds on the unwanted species or a sterile fish to compete with fertile fish during spawning. However, introduction of nonnative fish would be against Alaska state law and ADF&G's stocking policy because of the potential for the new species to drastically change the existing fish community. Releasing sterilized fish to outcompete fertile spawners would take years to implement and may not be 100% effective.
- Environmental Controls: Draining the water out of a lake has been done in the Lower 48, but draining even a small water body is more difficult than it sounds. This method would not be possible for rivers or streams. Draining a lake requires many permits and, in populated areas, there are many questions that need to be addressed such as what happens to the property owner's shoreline, wells, leach fields, and more? Where will the displaced water go? How is incoming water, such as a stream or spring, controlled? What happens to the other wildlife? Success is also highly dependent on weather.
- Fish Fences: In Lower 48 streams, fish "fences" and other barriers are commonly used with rotenone to remove unwanted species upstream of the fence. This strategy is complicated in Alaska because most Southcentral rivers and creeks that have illegally-stocked northern pike also have salmon, trout, Arctic grayling, or Dolly Varden. A barrier could prevent the natural movements and migrations of these native fish. However, most barriers would not stop the movement of very small juvenile or larval pike.
- Percussion: Explosives and pneumatic pressure have been used in the past in some places. Explosives are extremely expensive, dangerous, kill all wildlife, and could significantly change the lakebed or shoreline. Permits for explosives are difficult to obtain. Any percussion must be very large and very close to the fish to rupture its internal organs or swim bladder. It is difficult to generate a large enough concussion in the heavy aquatic vegetation where pike tend to reside. Similar to netting, repeated treatments are necessary to reduce the pike, and it is doubtful it could eliminate undesirable fish 100%.
Completely draining a lake or using a piscicide like rotenone are the only proven methods to eradicate invasive fish, and rotenone is the most practical and efficient method.