BC Conservation Data Centre: Conservation Status Report
Rana pretiosa
Oregon Spotted Frog
| Scientific Name: | Rana pretiosa |
|---|---|
| English Name: | Oregon Spotted Frog |
| Provincial Status Summary | |
| Status: | S1 |
| Date Status Assigned: | June 01, 1996 |
| Date Last Reviewed: | January 14, 2022 |
| Reasons: | The very few occupied sites exhibit small population sizes and habitat areas. The frog's communal egg laying pattern make its eggs especially vulnerable to freezing and desiccation, an intrinsic limiting factor that increases the potential for catastrophic loss of annual breeding output. This species faces very high threats, including loss of wetlands and terrestrial habitat, alteration of site hydrology, pollution, disease and introduced species. |
| Range | |
| Range Extent: | C = 250-1,000 square km |
| Range Extent Estimate (km2): | 303 |
| Range Extent Comments: | Oregon Spotted Frog is found in extreme southwestern British Columbia, within the Fraser River Basin. COSEWIC (2011e) calculated the extent of occurrence to be 303 square km (COSEWIC 2011e). |
| Area of Occupancy (km2): | D = 6-25 |
| Area of Occupancy Estimate (km2): | 11 |
| Area of Occupancy Comments: | All sites are located within the Fraser River Basin, including Aldergrove, Maria Slough, Mountain Slough, Morris Valley and McLennan Creek. COSEWIC (2011e) calculated the index area of occupancy to be 40 square km (this calcuation did not include the McLennan Creek site). |
| Occurrences & Population | |
| Number of Occurrences: | AB = 1 - 20 |
| Comments: | This species is extant at four sites all within the Fraser River Basin in British Columbia: Maria Slough, Mountain Slough, Morris Valley and McLellan Creek. Four populations are now extirpated, Aldergrove (K. Lensky, pers. comm. 2017), Sumas Prairie, Nicomen Island, and Campbell Valley Regional Park in Langley. The species has not been found at the latter three sites during 1996-1997, 2000, or 2010 surveys (COSEWIC 2011e). |
| Number of Occurrences with Good Viability / Ecological Integrity: | U = Unknown |
| Comments: |
From COSEWIC (2011e): The current Canadian populations appear to have small effective population sizes, and inbreeding is probably occurring, although its extent and effects on viability are unknown. Spatial separation between sites/populations is significant. The viability of the populations is in doubt for at least two of the populations (Aldergrove and Maria Slough). None of the populations may remain viable over the long term (COSEWIC 2011e). As of 2017, the Aldergrove site is considered extirpated (K. Lensky, pers. comm. 2017). Prior to COSEWIC (2011e): Two of the three historically occupied (extinct) sites have been structurally compromised by infilling for agricultural use (Sumas Lake, Abbotsford and Nicomen Island, Mission) (Haycock 2000). The physical structure of the third historically occupied site (Campbell Valley Regional Park, Langley) has been altered by park infrastructure and natural succession (Haycock 2000, Haycock 2000b). Two of the three occupied (extant) sites have good viability (Mountain Slough, Aggasiz and Maria Slough, Aggasiz) although these sites may be altered in the future by natural succession caused by the rapid growth of the exotic reed canary grass (Phalaris arundinacae). The third occupied site (Maintenance Detachment Aldergrove, Langley) has poor viability and is rapidly declining due to a combination of hydrological dysfunction, exotic plants and animals and succession. Climatic conditions, such as extreme drought in the summer of 2002 and 2003, may also be a factor. |
| Number of Occurrences Appropriately Protected & Managed: | A = None |
| Population Size: | C = 250 - 1,000 individuals |
| Comments: | The size of the mature populations at the occupied sites can be estimated by doubling the number of egg masses encountered through exhaustive searches of occupied sites.The estimate is based on females laying a single clutch of eggs per year and the ratio of males to females is one to one. In 2010, egg mass counts of the extant sites resulted in an approximate population size of fewer than 500 adult frogs (COSEWIC 2011e). The Aldergrove population has declined quickly since monitoring began in 1997 and is now considered extirpated (COSEWIC 2011e, K. Lensky, pers. comm. 2017). The Mountain Slough population appears stable. The Maria Slough population has fluctuated and now may be declining. The Morris Valley population has limited data (COSEWIC 2011e). There is no information on the population size at McLennan Creek. In 2004 the size of the population for Aldergrove, Maria Slough, and Mountain Slough was 378 (Haycock 2005). |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | A = Very high |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | EF = Decline of 10-50% |
| Comments: |
From COSEWIC (2011e): Extrapolation from annual egg mass counts indicates a decline of approximately 35% from 2000 to 2010 within continuously monitored areas at three sites (Aldergrove, Mountain Slough, Maria Slough). The decline is 19% if the new expanded search in 2010 at one of the sites is included (Mountain Slough). This species was partitioned from its sibling species Rana luteiventris in 1997 (Green et al. 1997) and the sibling species is common and widespread throughout most of British Columbia. It is likely that many observations of the species may have been considered inconsequential and may not have been recorded. |
| Long-Term Trend: | U = Unknown |
| Other Factors | |
| Intrinsic Vulnerability: | B=Moderately vulnerable |
| Comments: | The species oviposits communally and therefore populations are subject to decline if episodic freezing and/or desiccation of eggs occurs, causing embryonic failure and subsequent reduced recruitment to sexual maturity. Communal laying is likely to facilitate the spread of pathogens between egg masses (Kiesecker and Blaustein 1997). |
| Environmental Specificity: | A=Very narrow. Specialist or community with key requirements scarce. |
| Comments: | Species usually associated with large wetlands with emergent or floating vegetation within a forested landscape (COSEWIC 2011e). Females require locations with rare combinations of water depth and exposure to the sun in the late winter in order to lay eggs (Haycock 2005). These locations are usually the ephemeral edge of the wetlands which is subject to higher rates of alteration relative to deeper portions of the wetland (Haycock 2005). Adults require warm, shallow wetlands with emergent aquatic vegetation in summer (Haycock 2005). Species over-winters in springs and seepages that do not completely freeze, or in low-flow channels or ditches, or bury into silty soils or vegetation (COSEWIC 2011e). |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | The effects of hydrological alteration by beaver and the creation or elimination of Oregon spotted frog habitat, is poorly understood and requires a range-wide assessment of variably-sized habitats that are occupied by the Oregon spotted frog. Specifically, populations of Oregon spotted frogs occupying small habitats may not be able to adapt to the immediate, negative hydrological effects of beaver dams. All life stages of the Oregon spotted frog must be surveyed at occupied sites to gain a better understanding of microhabitat utilization. For example, trapping data at NRS Aldergrove suggests that larval and juvenile frogs occupy wetland habitat immediately adjacent to oviposition sites. Additional data in this regard may further support the critical nature of oviposition sites, but equally as valuable, the importance of linking oviposition sites to active summer and overwintering habitats occupied by adults. Other research defining the relative importance of life stages in a sensitivity analysis may provide further support for the immediate completion of life stage surveys. The assumed threat of the bullfrog and the green frog must be further evaluated. Evaluation and control programs for both bullfrog and green frog populations must be developed and carried out at occupied sites as the interspecific relationship between either of the two exotic species and the Oregon spotted frog is not well-defined. The negative effects of encroaching vegetation, including exotic, invasive vegetation, should be further studied. Although it is strongly suggested that reed canary grass is a significant threat to habitat, tests of occupancy in cut and/or thinned stands should be considered so that practical and economically feasible control methods can be developed. An understanding of the role climate change has on both short-term and long-term hydrological alterations is needed. Specifically, links between annual recruitment and seasonal rainfalls, as well as the adverse affects that drought conditions will have on the population by congregating the frogs into smaller areas. Physical and chemical water quality analyses, including bacteriology, should be undertaken at sites occupied by the Oregon spotted frog in the near future. Further analysis will help develop criteria when selecting future introduction sites; this may be important when choosing sites adjacent to farmland. Further research is needed of disease-causing organisms (i.e. iridovirus), which may negatively effect wild and captive-reared populations. Consequences of inbreeding in population isolates should be established and procedures to 'de-isolate' fragmented populations should be determined (ie, what corridors/conditions might enhance intersite movements and does the distance/landscape between sites make this impossible?). The average distance between suitable habitat patches should be calculated along with a description of the land use and composition between these habitats. While conducting surveys, refinements should be made to the draft key indicators and the habitat assessment and recovery planning models. These tools will ultimately assist with refining recovery criteria, defining critical habitat and establishing self-sustaining populations by helping to determine the location of habitats that the Oregon spotted frog could potentially occupy if habitat improvements were made. |
| Inventory Needs: | Discovery of additional occupied sites through an inventory of areas that have not been surveyed may have the effect of downgrading the species' status. Although the majority of wetlands in the near vicinity of historically and currently occupied sites have been surveyed, suitable habitat in other areas warrant further investigation. Separate inventory methodologies should be developed for occupied sites and newly surveyed sites. |
| Stewardship | |
| Protection: | From COSEWIC (2011e): Habitat protection is limited in Canada. There is some protection afforded to the habitat through federal and provincial fisheries legislation, as well as the federal Fisheries Act. This act controls activities that can cause harmful alternation, and the disruption or destruction of fish habitat. The British Columbia Water Act and the provincial Riparian Areas Regulation protect the in-stream environment and surrounding habitat, and apply to projects associated with specific activities that can alter wildlife or fish habitat. Limitations for development potential of the occupied wetlands as the Mountain Slough and Morris Valley sites are privately owned. Limited protection to the Maria Slough site as it is recorded to be on Provincial Crown Land, however, the land to the southeast side is located on First Nations Reserve Land, and the north side is private land. The Aldergrove site is federally owned by the Department of National Defence and access to the site is restricted which allows for some protection (note: this site is now considered extirpated (K. Lensky, pers. comm. 2017). |
| Management: | From COSEWIC (2011e): A recovery strategy has been drafted with five recovery implementation groups that have been formed: (1) habitat protection, management and restoration; (2) husbandry, invasive species and disease; (3) recovery planning; (4) science acquisition, information management and inventory/monitoring; and (5) outreach/stewardship. |
| Version | |
| Author: | Haycock, R., L. Westereng and L. Gelling |
| Date: | March 23, 2022 |
| References | |
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Corkran, C., and C. Thoms. 1996. Amphibians of Oregon, Washington and British Columbia - A field identification guide. Lone Pine Publ. Co., Edmonton, AB. 175pp.
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COSEWIC. 2011c. COSEWIC assessment and status report on the Oregon Spotted Frog Rana pretiosa in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. xi + 47 pp.
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Environment Canada. 2014q. Recovery Strategy for the Oregon Spotted Frog (Rana pretiosa) in Canada [Proposed]. Species at Risk Act Recovery Strategy Series. Environment Canada, Ottawa. 21 pp. + Appendix.
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Green, D. M., H. Kaiser, T. F. Sharbel, J. Kearsley, and K. R. McAllister. 1997. Cryptic species of spotted frogs, Rana pretiosa complex, in western North America. Copeia 1997:1-8.
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Green, D. M., T. F. Sharbel, J. Kearsley, and H. Kaiser. 1996. Postglacial range fluctuation, genetic subdivision and speciation in the western North American spotted frog complex, Rana pretiosa. Evolution 50:374-390.
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Green, D.M. 1999. British Columbia Amphibians: A taxonomic catalogue. B.C. Minist. Environ., Lands and Parks, Victoria. Wildl. Bull. No. B-87. 22pp.
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Haycock, R. 1998. Amphibian survey with special emphasis on the Oregon spotted frog, Rana pretiosa. Unpubl. rep. prepared for B.C. Minist. Environ., Lands and Parks, Wildl. Branch, Victoria. 230pp.
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Hayes, M.P. 1994. The Spotted Frog (Rana pretiosa) in western Oregon. Oregon Dep. Fish Wildl. Tech. Rep. No. 94-1-01. Unpubl. rep. 30pp. + figure and appendices.
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Keystone Wildlife Research Ltd. 2008. Appendix D: Terrestrial wildlife and vegetation assessment. Appendix D in BC Transmission Corporation. Interior to lower mainland transmission (ILM) Project Environmental Assessment Certificate (EAC) application. Vancouver, BC.
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Lensky, Kristina. Ministry of Forests, Lands and Natural Resource Operations. South Coast Region.
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Leonard, W., H. Brown, L. Jones, K. McAllister, and R. Storm. 1993. Amphibians of Washington and Oregon. Seattle Audubon Soc., The Trailside Ser., Seattle, WA. 168pp.
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Nussbaum, R. A., E. D. Brodie, Jr. and R. M. Storm. 1983. Amphibians and reptiles of the Pacific Northwest. University Press of Idaho, Moscow, Idaho. 332 pp.
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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. 2022. Conservation Status Report: Rana pretiosa. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Feb 10, 2025).