Alternatives to Rotenone
There are other methods to remove invasive fish, but the alternatives are not as effective or efficient as rotenone and rarely result in complete removal. 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 increase pike harvest. Pike regulations in Southcentral Alaska are very liberal and in many areas in southcentral it is illegal to release a live pike after capture. Typically, anglers prefer to capture larger pike but when high harvest occurs it eventually reduces the average size of the pike available. Young pike, up to four years old, have been shown to consume the most juvenile salmonids and can deplete salmonid populations. This loss of a rich food source can further limit pike growth and is often referred to as often “stunting”. To date, angler harvest alone has not been shown to be an effective tool to eliminate pike populations.
- Netting: Nets have been used to remove invasive northern pike in Southcentral. However, nets don't always catch all sizes of pike, particularly small pike. Repeated netting is necessary to control these pike populations, 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 fished in or near those areas which can be problematic due to entanglement and net damage. Nets can also catch non-target species of fish and wildlife. Netting can reduce populations of invasive fish, but this method can rarely eliminate them entirely.
- Electrofishing: Specialized electrofishing equipment delivers an electrical current into the water. When fish encounter the current, the electricity causes the fish to briefly lose control of its swimming muscles so they can be easily netted. The equipment is very sensitive, and generating the correct electrical field is dependent on water chemistry and lack of vegetation. Because pike prefer areas with dense aquatic plants, electrofishing has had 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 stocking 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 to remove unwanted fish has been done in the Lower 48, but in most cases draining even a small water body is usually impractical. This method is not possible for rivers or streams and most lakes. Draining a waterbody 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, water rights, leach fields, including planning where 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 Barriers: In Lower 48 streams, fish "fences" and other barriers are commonly used with rotenone to remove unwanted species by preventing their escape. 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.