Aquatic Species at Risk - Enos Lake Stickleback Species Pair (Benthic and Limnetic Forms)

Description
Habitat
Threats
How Can You Help?
Further Information
Scientific Information

Description
The Enos Lake Sticklebacks are small (usually 35 – 55mm), lean fish with an elongated body that tapers to a slender tail. They possess lateral plates that provide some protection against predators. Two variety of this fish – the bottom dwelling “benthic” form and open water swimming “limnetic” form, have been identified by scientists. They both evolved from a common Three Spine Stickleback ancestor in marine environment. The limnetic form is more slender and has longer gill rakers than the benthic form. The benthic fish has evolved smaller eyes and a shorter jaw than the limnetic form.

These two distinct but closely related Sticklebacks (Benthic and Limnetic form) are commonly referred to as “Stickleback Species Pair”.

Habitat
The Enos Lake Stickleback Species Pair inhabits entirely in Enos Lake, situated north of Nanoose Bay on Vancouver Island, British Columbia. Habitat requirements for both Stickleback forms include deeper and shallow waters of Enos Lake. Both parts of the lake are productive and offer food sources for these fish. The aquatic vegetation, along with lake water quality, play an important role in keeping the separation of the two forms. Benthic forms build nests under the shelter of aquatic vegetation, while limnetic forms tend to build theirs in shallow, but open and unsheltered areas. Because of this nesting separation, both forms are able to breed in isolation, and little hybridizing happens between them. Invasive species can damage this delicate balance, as is evidently seen in Enos Lake. The invasion of freshwater crayfish caused the destruction of aquatic vegetation in Enos lake, which likely caused higher hybridization rate and loss of pure forms.

Threats
Primary threats to the Enos Lake Stickleback Pair include invasive species, impacts from water extraction, and land use.

As mentioned above, invasive species has been responsible for the higher hybridization and collapse the two Stickleback forms. Water and land use may also have major impact to the sustainability of Enos Lake Stickleback Pair, as they dictate the quality of the lake environment in terms of water level, water quality and healthy aquatic vegetations.

How Can You Help?

• Prevent invasive species from entering the environment: Many species of aquatic invasive can be transported with your boat, trailer, or fishing gear without you noticing. Once they enter the environment, these invasive species pose major risks to the delicate balance of a lake ecosystem. For more information please visit these websites:
  • Protect Your Waters.net (http://www.protectyourwaters.net/)
  • DFO Publication: STOP The spread of Invasive Species (http://www.pac.dfo-mpo.gc.ca/publications/docs/invasives-envahissantes-eng.htm)
    
    
• Respect the environment: Always put trash in trash cans, especially near rivers, lakes and beaches. Protect vegetation around lake shorelines, as it helps to prevent excessive sediments from entering into water.
• Record and report damage to fish habitat and pollution: Contact DFO’s Observe, Record and Report (ORR) phone line to report suspected environmental violation that damage fish habitat or cause pollution. (1-800-465-4336 or in Greater Vancouver: 604-607-4186)
• Participate in community consultations: Get involved in Community Working Groups or visit www.pac.dfo-mpo.gc.ca/saraconsultations
• Volunteer: This may include participating on committees, attending meetings, assisting at educational outreach events, distributing outreach materials, getting involved with a conservation organization or just simply telling a neighbour or a friend about this species.

The Enos Lake Stickleback Pair will get the protection it needs only if all Canadians work together to reduce threats. Find out more on how to best reduce these threats wherever possible, to better protect these species at risk and their habitat. For general information on conservation efforts, visit Habitat Stewardship Program for Species at Risk.

Further Information:
Benthic forms differ from Limnetic forms in a number of ways: they generally mature later, live longer and reproduce less often. Limnetic forms generally die after two years while Benthic forms can perhaps live as long as 7 years.

As adults, the Species Pair’s is also different; limnetics hunt primarily in the surface waters away from the lake shores for plankton, while benthics forage along the shallow margins of the lake for larger prey such as snails, dragonfly nymphs, amphipods, and chironomids.

Although pure benthic and limnetic forms of this Stickleback do exist as part of preliminary trial captive breeding program, currently these two forms have very likely collapsed into a hybrid swarm in Enos Lake. The invasive Signal Crayfish (Pacifastacus leniusculus) appears to be implicated in causing the collapse.

Total population size of the Sticklebacks in Enos Lake (Benthic and Limnetic form) was estimated in 2001. Since then, there have been increasing concerns over high rate of hybridization between the two forms. It is likely that true limnetic and benthic forms may have ceased to exist, and instead the population is present in the lake as a hybrid form.

A recovery strategy for the Enos Lake Stickleback Pair has been developed by Fisheries and Oceans Canada and the Province of British Columbia. The next step is development of an action plan to outline measures required to meet the goals and objectives of the recovery strategy.

Scientific Information:

Scientific Name: Gasterosteus spp.
Taxonomy: Fishes (freshwater)