Paxton 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

Paxton 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 Paxton 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 probably occurred because of the limited competition and predation in their habitat. Habitat or environmental changes can disrupt mating barriers within a species pair and lead to the collapse of the pair into a single hybrid population. Hybrids occur naturally at a low rate.

Paxton Lake Limnetic Sticklebacks are approximately 65 millimetres in length and smaller than the Benthic species. The Limnetic species has a streamlined body, narrow mouth, and many long gill rakers. Both species have delicate fins, spines on their back and sides, and plate-like armour to protect themselves from predators. Paxton Lake Limnetic Sticklebacks have variable body colour, ranging from silvery to mottled green and brown. Sexually mature males may develop red coloration on the throat, or in some cases turn completely black.

Habitat

The Paxton Lake Stickleback Species Pair is only found in Paxton Lake on Texada Island, British Columbia, Canada. The Benthic and Limnetic species exist as separate designatable units. The population size of the Limnetic species is is thought to be over 100,000.

Paxton Lake Limnetic Sticklebacks primarily live in open water. Both the Limnetic and Benthic species nest in nearshore beaches. However, Paxton Lake Limnetic Stickleback prefer to spawn in more open areas than the Benthic species. Natural light is necessary for the species to recognize their mates. Both Benthic and Limnetic fry use nearshore habitat with aquatic plants to feed and hide. Juvenile Paxton Lake Limnetic Stickleback are common around steep, rocky and open shoreline. They eventually move offshore to open water. Both the Limnetic and Benthic species move to deeper water habitats to overwinter.

Threats

Primary threats to the Paxton Lake Stickleback Species Pair include invasive species, water management, habitat loss or degradation from land use, collections for research, recreational activities and disease.

Stickleback Species Pairs have specific needs and are very sensitive to changes in habitat and environmental factors. Changes can disrupt the mating barriers between the Stickleback Species Pair and collapse the species pair into a single hybrid population. Invasive species may disrupt the simple fish communities required by the Paxton Lake Stickleback Species Pair. In recent decades, introduced species caused the extinction of at least two Stickleback Species Pairs.

Water management and land use affect the Paxton Lake environment. Water level reductions from water extraction could directly reduce habitat. Land uses, such as mining, forestry and development around Paxton Lake, could reduce riparian cover, increase pollution, and increase sedimentation. Riparian vegetation is important for regulating water temperature and food availability. Sedimentation and pollution can alter aquatic vegetation and water clarity, which could decrease mate recognition and increase hybridization.

Finally, the Paxton Lake Stickleback Species Pair has been the subject of intensive genetic research because of its evolutionary significance. In 2008, scientific collection guidelines were created to reduce impact on the species.

Further Information

The Paxton Lake Limnetic Stickleback was assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada in May 2000. This status was reconfirmed in April 2010. The species was listed under the Species at Risk Act in June 2003. 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. An Action Plan for the Paxton Lake and Vananda Creek Stickleback Species Pairs was proposed in 2016. It describes critical habitat and identifies ways to implement recovery measures.

Government agencies, stewardship groups (e.g. Nanoose Naturalists and Texada Stickleback Group Association), and universities such as the University of British Columbia and Michigan State University, continue to carry out research to fill knowledge gaps on the Paxton Lake Stickleback Species Pair. They also contribute to outreach and education activities, and management activities to recovery Stickleback Species Pairs.

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.

Paxton Lake Limnetic Threespine Stickleback

Photo Credit: G. Velema. Upper: Paxton Lake Limnetic Threespine Stickleback and lower: Benthic Threespine Stickleback

Photo Credit: G. Velema. Upper: Paxton Lake Limnetic Threespine Stickleback and lower: Benthic Threespine Stickleback

Scientific Name: Gasterosteus aculeatus
SARA Status: Endangered, Schedule 1
COSEWIC Status: Endangered (April 2010)
Region: British Columbia

Region map

Region map, British Columbia

Did You Know?

Stickleback Species Pairs are regarded as a scientific treasure because they are among the youngest species on earth. They evolved after the last glaciation, less than 13,000 years ago. They are considered remarkable research subjects for the persistence of biodiversity.

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