Enos Lake Limnetic Threespine Stickleback

Gasterosteus aculeatus

SARA Status
No Status
NS
Special Concern
SC
Threatened
TH
Endangered
EN
Extirpated
EX

SARA Status

  • No Status NS
  • Special Concern SC
  • Threatened TH
  • Endangered EN
  • Extirpated EX
COSEWIC Status
Not at Risk
NR
Special Concern
SC
Threatened
TH
Endangered
EN
Extirpated
EX

COSEWIC Status

  • Not at Risk NR
  • Special Concern SC
  • Threatened TH
  • Endangered EN
  • Extirpated EX

Description

Enos Lake Benthic and Limnetic Threespine Sticklebacks (Gasterosteus aculeatus) are one of several unique Stickleback Species Pairs that live in sympatry. Two species are sympatric when they exist in the same area and evolved together from a common ancestor. The two species of Enos Lake Sticklebacks descended from the marine Threespine Stickleback and evolved into separate species by living in different habitats. The benthic species lives in nearshore areas. The limnetic species lives in open water. The divergence from their common ancestor is thought to have occurred because of the limited competition and predation in their habitat after the last glaciation.

Habitat or environmental changes can disrupt mating barriers within a species pair and lead to a collapse of the pair into a single hybrid population. This hybrid population is sometimes referred to as a hybrid swarm. In Enos Lake, morphological and genetic studies suggest that Benthic and Limnetic Sticklebacks are no longer distinct species. They collapsed into a hybrid population in the late 1990s. This happened because of habitat changes following the invasion of American Signal Crayfish (Pacifastacus leniusculus).

The Enos Lake Limnetic Stickleback was a small, streamlined fish with a light-coloured belly and silver sides. It was typically smaller than the Benthic species. During breeding season, males would have red throats and blue backs. Enos Lake Limnetic Sticklebacks were more heavily armoured than the Benthic species. They had more bony rays in their anal fins and a greater number of gill rakers.

Habitat

The Enos Lake Stickleback Species Pair is found only in Enos Lake on Vancouver Island in British Columbia, Canada. Enos Lake is a small coastal lake that covers 17.6 hectares. Its maximum depth is 11 metres. There is no permanent surface drainage into the lake. An outlet drains the lake towards the northwest in the rainy season.

Enos Lake Limnetic Sticklebacks primarily lived in open water. Both the Limnetic and Benthic species nested in nearshore beaches. However, Enos Lake Limnetic Sticklebacks preferred to spawn in more open areas than the Benthic species. Natural light was necessary for the species to recognize their mates. Once emerging from nests, Limnetic fry used inshore vegetated areas for food and protection. They eventually moved offshore to open water. Both the Limnetic and Benthic species moved to deeper water habitats to overwinter.

After the introduction of American Signal Crayfish, inshore habitat changed drastically. The invasive crayfish removed almost all aquatic vegetation. This likely had a significant effect on the mating barriers between the Benthic and Limnetic species and promoted the collapse of the pair into a single hybrid population.

Threats

The American Signal Crayfish got established in Enos Lake in the 1990s. Following its invasion, aquatic vegetation disappeared from the lake and the number of Limnetic-Benthic hybrids increased in the lake. The species pair now exists as a single hybrid population. The American Signal Crayfish may have affected the Enos Lake Stickleback Species Pair through changing vegetated habitat, displacement from nesting habitat, predation and competition.

Current threats to the species include more invasive species, water use and land use. Additional introductions of species are possible. For example, Brown Bullhead (Ameiurus nebulosus),Largemouth and Smallmouth Basses (Micropterus salmoides and M. dolomieu), Pumpkinseed (Lepomis gibbosus), and Yellow Perch (Perca flavescens) may be spread by anglers and other members of the public. In most regions of British Columbia, the probability of invasive species becoming established after release to a new location is high or very high.

Existing water licences allow both water storage and diversion from Enos Lake. These have raised lake levels because of a dam at the outlet and increased annual drawdowns. This could threaten the species by reducing spawning and feeding habitat. Also, the Enos Lake watershed is currently being developed for residential use. Increases in sedimentation and loss of riparian habitat associated with these developments are a concern for the species. 

Further Information

The Enos Lake Limnetic Stickleback was assessed as Endangered in 2002 and reassessed as Endangered in 2012 by COSEWIC. The species was listed under the Species at Risk Act in January 2005. A Recovery Strategy that addresses the Paxton Lake, Vananda Creek, and Enos Lake Stickleback Species Pairs was posted in 2007. The Recovery Strategy identifies threats, population and distribution objectives and broad approaches to recovery for the six species.

Researchers have investigated the relationship between American Signal Crayfish and the Enos Lake Stickleback Species Pair. Stewardship groups also contribute outreach and education activities, and management activities to recovery the Enos Lake Stickleback Species Pairs. For example, the Nanoose Naturalists developed and submitted an Enos Lake Water Management Plan to the key landowner in the watershed. They also developed a management plan that addresses water quality for the Enos Lake Stickleback Species Pair.

This species is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available on the Species at Risk Public Registry.

To find out if this species is protected by provincial or territorial laws, consult the provinces' and territories' website.