Species Profile

Unarmoured Threespine Stickleback

Scientific Name: Gasterosteus aculeatus
Other/Previous Names: Charlotte Unarmoured Stickleback,Charlotte Unarmoured Sticklebacks,Charlotte Unarmoured Threespine Stickleback ,Gasterosteus aculeatus,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 Unarmoured Threespine Stickleback

Unarmoured Threespine Stickleback Photo 1



The Unarmoured Threespine Stickleback, also known as the Charlotte Unarmoured Stickleback, is a small (~65 mm length) 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. A key feature of Unarmoured Threespine Stickleback’s appearance is the loss of one or more of the typical dorsal spines, and the reduction or absence of bony plates on the sides of their bodies.


Distribution and Population

The Unarmoured Threespine Stickleback occurs only within Boulton, Rouge, and Serendipity lakes on Graham Island, Haida Gwaii, British Columbia. The number of mature individuals is thought to be in the high thousands for Rouge Lake, the low tens of thousands for Serendipity Lake, and the low hundreds of thousands for Boulton 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. Boulton, Rouge, and Serendipity lakes are small, shallow, acidic water bodies, surrounded by Sphagnum spp. bog and scrub coniferous forest. Boulton Lake is mainly fed by groundwater seepage and has an intermittent outlet to the Pacific Ocean. The lake-bottom consists of varying materials including thick organic ooze, sand, and gravel. Its water is relatively clearer than Rouge and Serendipity lakes. In Boulton Lake, adult females are primarily found in open waters in spring and summer, while adult males typically remain near shore to nest; both sexes move to deeper water in the winter. Rouge Lake is smaller, shallower, and more acidic than Boulton Lake; its lake-bottom consists primarily of organic ooze and sand. Serendipity Lake is similar in size, depth, and acidity to Rouge Lake; its lake-bottom consists primarily of thick organic ooze. Both Rouge and Serendipity lakes are mainly fed by groundwater seepage; their outflows are blocked by beaver dams.



Little is known of the reproductive biology of the Unarmoured Threespine Stickleback; however, it is thought to be similar to other freshwater Threespine Sticklebacks. Unarmoured Threespine Sticklebacks reach maturity at approximately three years of age, and females lay clutches of 100-300 eggs each. Likely predators include macroinvertebrates such as leeches and nymphs, the Common Loon, Belted Kingfisher, and several species of grebes and mergansers. Unique aspects of their biology include an unusual tolerance of acidic water, and a symbiotic relationship with parasites found in Rouge Lake. Threespine Sticklebacks typically live to between two to three years of age.



The key threat to the Unarmoured Threespine Stickleback is the introduction of invasive species. Other threats include changes in predator regimes, human disturbance (e.g. rural and industrial activities), erosion, severe winter conditions and potentially, habitat changes caused by introduced beavers.



Federal Protection

The Unarmoured 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 – Unarmoured Threespine Stickleback (2015)

    This morphologically distinctive small-bodied freshwater fish is currently known to exist in only three very small lakes that are in a relatively remote area. 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