Blue-Grey Taildropper Slug Prophysaon Coeruleum
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COSEWIC Assessment and Status Report on the Blue-grey Taildropper slug Prophysaon coeruleum in Canada ENDANGERED 2006 COSEWIC COSEPAC COMMITTEE ON THE STATUS OF COMITÉ SUR LA SITUATION ENDANGERED WILDLIFE DES ESPÈCES EN PÉRIL IN CANADA AU CANADA COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows: COSEWIC 2006. COSEWIC assessment and status report on the Blue-grey Taildropper slug Prophysaon coeruleum in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vi + 27 pp. (www.sararegistry.gc.ca/status/status_e.cfm). Production note: COSEWIC would like to acknowledge Kristiina Ovaska and Lennart Sopuck for writing the status report on the Blue-grey Taildropper slug Prophysaon coeruleum, prepared under contract with Environment Canada, overseen and edited by Janice L. Smith, Co-chair, COSEWIC Molluscs Species Specialist Subcommittee. For additional copies contact: COSEWIC Secretariat c/o Canadian Wildlife Service Environment Canada Ottawa, ON K1A 0H3 Tel.: (819) 997-4991 / (819) 953-3215 Fax: (819) 994-3684 E-mail: COSEWIC/[email protected] http://www.cosewic.gc.ca Également disponible en français sous le titre Évaluation et Rapport de situation du COSEPAC sur le limace-prophyse bleu-gris (Prophysaon coeruleum) au Canada. Cover illustration: Blue-grey Taildropper slug — Photograph by K. Ovaska. ©Her Majesty the Queen in Right of Canada 2006 Catalogue No. CW69-14/464-2006E-PDF ISBN 0-662-43231-2 Recycled paper COSEWIC Assessment Summary Assessment Summary – April 2006 Common name Blue-grey Taildropper slug Scientific name Prophysaon coeruleum Status Endangered Reason for designation This species has a very small extent of occurrence (~ 150 km2) and area of occupancy (< 5 km2), and a continuing decline is projected in quality of habitat. It is found in remnant patches of older forest with a deciduous component. It is currently known from only 5 locations on southern Vancouver Island. Threats at these locations include heavy recreational use and the impacts of introduced plants and animals, including introduced invasive slugs and snails. Occurrence British Columbia Status history Designated Endangered in April 2006. Assessment based on a new status report. iii COSEWIC Executive Summary Blue-grey Taildropper slug Prophysaon coeruleum Species information The Blue-grey Taildropper is one of nine described species of taildropper slugs (genus Prophysaon) endemic to western North America. It is a small- to medium-sized slug (up to 45 mm long when extended) with a slender body. Distinguishing external features include blue-grey colour and parallel grooves and ridges on the back and sides of the tail. Internally, the slugs are distinguished from related species by features of reproductive anatomy. Distribution The species ranges from southern British Columbia south to Puget Lowlands in Washington State and through the Cascade Range into Oregon and northern California. Much genetic variation exists in the southern portion of the range. An isolated population exists in northern Idaho. In Canada, the species is known only from five sites on southern Vancouver Island, British Columbia. Habitat The Blue-grey Taildropper inhabits moist, coniferous or mixed-wood forests of varying age classes. All records from British Columbia are from within the Coastal Douglas-fir biogeoclimatic zone. In Washington State, the species is often associated with older forests. Required microhabitat features include abundant coarse woody debris or other cover, a deep forest litter layer, and shaded, moist forest floor conditions. Biology This species appears to have an annual life cycle, maturing and reproducing within one year. In British Columbia, specimens (all adults) have been found in late autumn only. The Blue-grey Taildropper feeds extensively on fungi, including species that form symbiotic mycorrhizal associations with roots of conifers. Like other taildropper slugs, this species is capable of self-amputation of the tail, an adaptation that is an effective anti-predator mechanism against invertebrate predators, such as ground beetles and carnivorous snails. iv Population sizes and trends The Blue-grey Taildropper slug was first documented from British Columbia in 2002, and due to its recent discovery virtually nothing is known of its population sizes and trends. These slugs tend to be solitary or occur in small groups at scattered locations. Only a few specimens have ever been found, although hundreds of localities on Vancouver Island and in the Lower Fraser Valley on the mainland have been searched for terrestrial gastropods over the past decade. The extent to which the slugs’ secretive habits, highly seasonal activity, and scattered distribution pattern contribute to their apparent rarity is presently unknown. Limiting factors and threats This species exists at the northern extremity of its geographic range in southwestern British Columbia. Most likely, its present-day distribution reflects the glacial history of the region and resettlement from the south after glacial retreat. Main immediate threats to populations include habitat loss, fragmentation, and degradation through human activities and land conversions. Additional threats include competition with exotic gastropods and predation by native and introduced animals. Forest habitats outside protected areas are shrinking at an alarming rate on southern and eastern Vancouver Island. Isolation of populations in remnant forest patches increases the probability of local extinctions. Population isolation is likely to be exacerbated by summer droughts, predicted for the region under global climate change scenarios. Special significance of the species At the localities where it occurs, the Blue-grey Taildropper might perform an important ecological role by dispersing spores of mycorrhizal fungi that form essential symbiotic associations with tree roots. Although it also feeds on green plant matter, it is unlikely to become a horticultural pest because of its low densities and association with forests rather than with open habitats. With its often-brilliant bluish colouration this species is attractive and could become an emblem of invertebrate conservation in British Columbia. Existing protection The Blue-grey Taildropper was placed on the provincial Red List of species at risk in British Columbia in 2005. Species on the Red List are species that are extirpated, endangered, or threatened in British Columbia. While not currently listed as an Identified Wildlife Species in British Columbia, the species could become a candidate for inclusion in a future version of the provincial Identified Wildlife Management Strategy. v COSEWIC HISTORY The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5th 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process. COSEWIC MANDATE The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens. COSEWIC MEMBERSHIP COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species. DEFINITIONS (2006) Wildlife Species A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and it is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years. Extinct (X) A wildlife species that no longer exists. Extirpated (XT) A wildlife species no longer existing in the wild in Canada, but occurring elsewhere. Endangered (E) A wildlife species facing imminent extirpation or extinction. Threatened (T) A wildlife species likely to become endangered if limiting factors are not reversed. Special Concern (SC)* A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats. Not at Risk (NAR)** A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances. Data Deficient (DD)*** A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b)