BC Conservation Data Centre: Conservation Status Report
Staala gwaii
Haida Gwaii Slug
| Scientific Name: | Staala gwaii |
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| English Name: | Haida Gwaii Slug |
| Provincial Status Summary | |
| Status: | S2? |
| Date Status Assigned: | December 01, 2015 |
| Date Last Reviewed: | March 11, 2024 |
| Reasons: | This species endemic to Canada is known from only a few localities on Graham and Moresby Islands in Haida Gwaii and from Brooks Peninsula on northwestern Vancouver Island. Most localities are in subalpine tundra, but in Haida Gwaii, the species is patchily distributed also in lowland, coniferous forest. Although many localities are in protected areas, populations across the species? range continue to be threatened by climate change impacts, including more frequent and severe droughts and storms and encroachment of forest into subalpine habitats, and by browsing of introduced deer across Haida Gwaii. Logging is an additional threat to slugs within lower elevation forests outside protected areas. Cumulative impacts and interactions among climate change, deer browsing, and logging are likely but unknown. |
| Range | |
| Range Extent: | E = 5,000-20,000 square km |
| Range Extent Comments: | Haida Gwaii Slug occurs on Graham and Moresby islands on the Haida Gwaii archipelago and on Brooks Peninsula on northwestern Vancouver Island (COSEWIC 2013c). The BC Conservation Data Centre calculated the Extent of Occurrence (EO) as 3,828 square km (including the ocean) based on records up to 2015; COSEWIC (2013c) reported the EO as 3,453 square km when the ocean is excluded. No new localities have been reported since the preparation of the COSEWIC (2013c) status report (BC Ministry of Environment and Climate Change 2022). |
| Area of Occupancy (km2): | DE = 6-125 |
| Area of Occupancy Comments: | The discrete Index of Area of Occupancy (IAO), based on 2 km x 2 km grid cells placed on known occurrences is 52 square km, of which eight square km (i.e., two grid cells) are on Brooks Peninsula; however, additional suitable but unsurveyed habitat exists (COSEWC 2013c). If continuous stretches of alpine-subalpine areas between observations in Haida Gwaii are included, then the IAO in Haida Gwaii is 284 square km, and the IAO on the Brooks Peninsula overlapping potential habitat is 96 square km (COSEWIC 2013c), resulting in a total estimated IAO of 380 square km. |
| Occurrences & Population | |
| Number of Occurrences: | BC = 6 - 80 |
| Comments: | According to the provincial management plan (BCECCS 2022), the species is known from 13 sites, representing seven subpopulations (Moresby Island:3; Graham Island: 3, Brooks Peninsula: 1). Subpopulations are defined based on habitat connectivity and distance. Undocumented sites most likely exist, as survey coverage is incomplete and the slugs can easily be overlooked. The species was detected for the first time on Vancouver Island (Brooks Peninsula) in 2012. In Haida Gwaii, the species has been found only rarely and in low numbers in the coastal Western Hemlock biogeoclimatic zone, which covers much of the islands. However, potentially suitable habitat is present in rugged alpine and sub alpine areas, which are difficult to access and survey adequately. |
| Number of Occurrences with Good Viability / Ecological Integrity: | U = Unknown |
| Number of Occurrences Appropriately Protected & Managed: | C = 4 - 12 |
| Comments: | On Vancouver Island, Haida Gwaii Slug occurs in Brooks Peninsula Provincial Park. In Haida Gwaii, all six known occupied sites on Moresby Island are within Gwaii Haanas National Park Reserve and Haida Heritage Site (COSEWIC 2013c). The remaining five sites are on Graham Island on BC Crown lands used for forestry; two of these sites are within a recreational trail system (COSEWIC 2013c). |
| Population Size: | U = Unknown |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | B = High |
| Comments: | As part of the preparation of the COSEWIC (2013c) status report for the species, threats were assessed using the IUCN?CMP (International Union for Conservation of Nature?Conservation Measures Partnership) threats calculator. The threat analysis was still considered appropriate in the subsequent management plan (BC Ministry of Environment and Climate Change 2022). The overall threat impact is ?high?. The three primary threats are climate change and severe weather, natural system modifications, and biological resource use, mainly forestry activities. More frequent and severe droughts, temperature extremes, and severe storms associated with climate change are potentially harmful to the slugs. Over the long term, shifts in habitats and ecosystems, particularly in subalpine and alpine areas, would reduce habitat quantity and quality for the species. In Haida Gwaii, browsing on understory and ground vegetation by the introduced Sitka Black-tailed Deer has profoundly modified ecosystems, including microhabitats in the litter layer that the slugs depend on. Logging and wood harvesting is a potential threat to slugs inhabiting forested areas, particularly on Graham Island where several known localities and much potential habitat are within forestry lands. Logging drastically alters habitat structure at ground level, including the distribution and replenishment of down wood that provide refuges for the slugs. Movements of slugs among habitat patches are likely curtailed, leading to population isolation and increased risk of extirpation. All documented sites on Moresby Island are within a protected area in Gwaii Haanas National Park Reserve and Haida Heritage Site. |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | U = Unknown |
| Comments: | Prolonged droughts have occurred on Haida Gwaii and northern Vancouver Island in 2016, 2018, and 2022 (Government of BC 2024). Such droughts may have adversely affected Haida Gwaii Slug populations by restricting the periods when slugs are active and the amount of food and reproductive opportunities are available. |
| Long-Term Trend: | U = Unknown |
| Comments: | Since European settlement, natural vegetation of Haida Gwaii has been regularly modified by three main factors: post-industrial human population expansion, forestry, and browsing by the introduced Sitka Black-tailed Deer (COSEWIC 2013c). Climate change is another factor that is predicted to alter habitats and ecosystems (COSEWIC 2013c). Nothing is known of population fluctuations or trends of Haida Gwaii Slug. A decline in population size is projected if alpine and subalpine habitats shrink as a result of climate change (COSEWIC 2013c). |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | Poor dispersal ability makes the slugs vulnerable to disturbances and limit recolonization after extirpation, as well as colonization of new habitats that may become available. The slugs' dependence on very moist microhabitats and refuges also increases their vulnerability. |
| Environmental Specificity: | D=Broad. Generalist or community with all key requirements common. |
| Comments: | This species has been found in shaded, moist forests and in open-canopy subalpine-type habitats and krummholtz formations (COSEWIC 2013c). The species appears to be most common in open, subalpine habitats, characterized by scattered, stunted trees, swales of low shrubs and grasses, and near-saturated ground often with a moss cover (COSEWIC 2013c). In Haida Gwaii, these habitats can occur as low as approximately 200 m above sea-level. More typically this species occurs at an elevation between 600 ? 800 m above sea level. In Haida Gwaii, the slug has been found in all three biogeoclimatic zones present on the islands: Coastal Western Hemlock in the lowlands, Mountain Hemlock at higher elevations, and non-forested Alpine Tundra at highest elevations. On Vancouver Island, the Haida Gwaii slug has been found at elevations between 300 and 450 m on a rugged ridge top on Brooks Peninsula in krummholtz habitat (COSEWIC 2013c). The habitat is similar to subalpine habitats of the species in Haida Gwaii. |
| Other Rank Considerations: | This species is endemic to Canada, where it occurs only within a few sites along the west coast of BC. It is an unusual (to gastropods) northern endemic thought to have survived past glaciations in ice-free refuges in Haida Gwaii and Brooks Peninsula (Ovaska et al. 2010). |
| Information Gaps | |
| Research Needs: | Research on the impact of grazing by non-native Sitka Black-tailed Deer and long-term effects of climate change on slug habitats are priorities for his species (BC Ministry of Environment and Climate Change 2022). |
| Inventory Needs: | In British Columbia, surveys targeting terrestrial gastropods have focused largely to the southwest, including Vancouver Island; the central and north coast have received less survey effort (COSEWIC 2013c). In Haida Gwaii, survey effort specifically targeting terrestrial gastropods includes surveys by R. and T. Forsyth (1995-2008) and those by Ovaska, Sopuck, and the coworkers from Biolinx Environmental Research Ltd. (2000-2006). Most sites were visited only once, two sites were surveyed intensively and repeatedly by Biolinx Environmental Research Ltd (COSEWIC 2013c). However, further inventory is needed including revisits of known sites to assess persistence of the species (BC Ministry of Environment and Climate Change 2022). Much of the potentially suitable habitat on Haida Gwaii especially in alpine - subalpine areas and montane forests, has not been surveyed for gastropods, and additional sites and populations probably exist (COSEWIC 2013c). |
| Stewardship | |
| Protection: | There are a limited number of former glacial refugia in Canada, and these habitats cannot be easily recreated or restored; the slugs are unlikely to re-colonize areas due to their poor dispersal capabilities. Therefore, protection of habitats with extant populations is vital (BC Ministry of Environment and Climate Change 2022). |
| Management: | |
| Version | |
| Author: | Ovaska, K. and L. Sopuck; Forsyth, R. and L. Gelling |
| Date: | March 08, 2024 |
| References | |
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COSEWIC. 2013c. COSEWIC assessment and status report on the Haida Gwaii Slug Staala gwaii in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. x + 44 pp.
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Government of B.C. 2024. British Columbia Drought Information Portal. Website (accessed February 2024).
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Ovaska, K., and L. Sopuck. 2005b. Surveys for terrestrial gastropods in Pacific Rim, Gulf Islands, and Gwaii Haanas national park reserves. Prepared for Parks Canada Coastal British Columbia Field Unit, Victoria, BC. 133pp.
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Ovaska, K., Chichester, L., and Sopuck, L. 2010. Terrestrial gastropods from Haida Gwaii (Queen Charlotte Islands), British Columbia, Canada, including description of a new northern endemic slug (Mollusca: Gastropoda:Stylommatophora: Arionidae). The Nautilus 124(1):25-33.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2024. Conservation Status Report: Staala gwaii. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 3, 2026).