Species Profile

Giant Threespine Stickleback

Scientific Name: Gasterosteus aculeatus
Other/Previous Names: Giant Stickleback ,Gasterosteus sp.
Taxonomy Group: Fishes
Range: British Columbia
Last COSEWIC Assessment: November 2013
Last COSEWIC Designation: Special Concern
SARA Status: Schedule 3, Special Concern - (SARA Schedule 1 provisions do not apply)

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Image of Giant Threespine Stickleback

Giant Threespine Stickleback Photo 1



The Giant Threespine Stickleback is a freshwater fish, likely descended from the marine Threespine Stickleback (Gasterosteus aculeatus). Freshwater Threespine Sticklebacks typically have three dorsal spines, an anal spine, two pelvic spines and bony plates on the sides of their bodies. Key features of the Giant Threespine Stickleback’s appearance include its unusually large size (~80-85 mm length), a streamlined body, a greater number of gill rakers and bony plates on the sides of the body, longer pelvic spines, and black colouration with silver shading and dark flank bars. Breeding colouration of these fish is unusually dark compared to the more typical red breeding colouration observed in other stickleback species.


Distribution and Population

The Giant Threespine Stickleback occurs only within Mayer and Drizzle lakes on Graham Island, Haida Gwaii, British Columbia. The number of mature individuals is thought to be in the high tens of thousands for Mayer Lake, and greater than 100,000 for Drizzle Lake.



In general, the species likely requires: sustained productivity in open water and near-shore habitats, including natural near-shore vegetation; absence of invasive species; and gently sloping sand/gravel beaches. Mayer and Drizzle lakes are shallow, acidic, and darkly stained water bodies located in lowlands consisting primarily of Sphagnum spp. bogs and coniferous forest. Mayer Lake has three inlets (Cott, Woodpile, and Gold Creeks) and an outlet (Mayer River) flowing to the Pacific Ocean. Near-shore habitat typically consists of gently sloping sand or pebbles with patchy vegetation. Drizzle Lake has an inlet stream, and an outlet stream, which drains to the Pacific Ocean. The lake-bottom typically consists of sand and gravel, with some pebbles occurring closer to shore. Calcium levels are particularly low, and aquatic vegetation is sparse in this lake. The Giant Threespine Stickleback spends spring and summer in near-shore areas for spawning, and moves to deeper waters in winter.



The reproductive biology of the Giant Threespine Stickleback is generally thought to be similar to other freshwater Threespine Stickleback, where males build nests and provide care to fry. The male Giant Threespine Stickleback reaches maturity at approximately two (Mayer Lake) or three years (Drizzle Lake). The breeding season typically lasts from early May to mid-August. Males breed up to five times within a given breeding season. Females lay ~250 eggs in Mayer Lake and ~400 eggs per clutch in Drizzle Lake. Main predators in both lakes include Coastal Cutthroat Trout, and the Common Loon, among several other bird species. Giant Threespine Sticklebacks typically live up to four years in Mayer Lake and eight years in Drizzle Lake.



The key threat to the Giant Threespine Stickleback is the introduction of invasive species. Other threats include changes in predation regimes (e.g. from Coastal Cutthroat Trout and/or the Common Loon), human disturbance (e.g. forestry operations), and potentially habitat changes caused by introduced beavers



Federal Protection

The Giant Threespine Stickleback is being considered for listing under the federal Species at Risk Act (SARA) as Special Concern. More information about SARA, including how it protects individual species, is available on the Species at Risk Public Registry (http://www.sararegistry.gc.ca/).

Provincial and Territorial Protection

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.



PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.

4 record(s) found.

COSEWIC Status Reports

  • COSEWIC Assessment and Status Report on the Giant Threespine Stickleback Gasterosteus aculeatus and the Unarmoured Threespine Stickleback Gasterosteus aculeatus in Canada (2014)

    The Giant Threespine Stickleback has a mean adult standard length (SL) exceeding 75 mm, being almost twice the length of most other freshwater Threespine Stickleback. Although not unique, several other morphological features also set it apart from the "typical" freshwater form: it has a more streamlined shape; more gill rakers and robust body armour; and has an unusual colouration. The two confirmed populations of the Giant Threespine Stickleback appear to have evolved independently from one another, and each one appears to be at least partially reproductively isolated from the Threespine Stickleback that inhabits the streams connected to its lakes. The Unarmoured Threespine Stickleback is one of a few populations across the global range of Threespine Stickleback that exhibit extensive loss of defensive spines. Its three confirmed occurrences are characterized by the loss of one or more spines in the majority of fish. They appear to have evolved independently from one another. Both species contribute to the extensive morphological variation displayed by Threespine Stickleback from Haida Gwaii, and have intrinsic value as significant prey items in their ecosystems. They continue to provide significant insights into the processes involved in evolutionary change.

Response Statements

  • Response Statement – Giant Threespine Stickleback (2015)

    This freshwater stickleback is of unusually large size and is currently known to exist in two small lakes that are in relatively remote areas. The populations could, however, quickly become Endangered if invasive species were to be introduced as has been observed in other stickleback populations.

COSEWIC Annual Reports

  • COSEWIC Annual Report - 2013-2014 (2014)

    Under Canada’s Species at Risk Act (SARA), the foremost function of COSEWIC is to "assess the status of each wildlife species considered by COSEWIC to be at risk and, as part of the assessment, identify existing and potential threats to the species". COSEWIC held two Wildlife Species Assessment Meetings in this reporting year (October, 2013 to September, 2014) from November 24 to November 29, 2013 and from April 27 to May 2, 2014. During the current reporting period, COSEWIC assessed the status or reviewed the classification of 56 wildlife species. The wildlife species assessment results for the 2012-2013 reporting period include the following: Extinct: 0 Extirpated: 0 Endangered: 23 Threatened: 12 Special Concern: 20 Data Deficient: 0 Not at Risk: 1 Total: 56 Of the 56 wildlife species examined, COSEWIC reviewed the classification of 40 that had been previously assessed. The review of classification for 25 of those wildlife species resulted in a confirmation of the same status as the previous assessment.

Consultation Documents