| Abstract/Description or Keywords |
In recent decades, the northern leopard frog (Rana pipiens) has declined across western North America. In British Columbia, surveys conducted in the 1990’s failed to detect leopard frogs outside of a single wetland in the Creston Valley Wildlife Management Area (CVWMA), near Creston, BC. Designated as “Endangered” by the Committee on the Status of Endangered Wildlife in Canada and protected under the Species at Risk Act, this population is in imminent threat of extinction. Between 2000 and 2005, the population of leopard frogs in the CVWMA was monitored using visual encounter surveys, nocturnal calling surveys, egg mass surveys, and Mark-Recapture techniques. Calling activity, egg mass counts, catch-per-survey hour, and Mark-Recapture population estimates indicate that the population of leopard frogs declined approximately 50% over this period. Although there is a high degree of uncertainly with the population estimates, we estimate the population in 2005 to be in the low to mid-hundreds. In part, we attribute the decline observed during this period to an outbreak of Saprolegnia that resulted in high egg mortality in 2001. Moreover, we observed chytrid-associated (Batrachochytrium dendrobatidis) mortality and observed numerous unhealthy animals with chytridiomycosis, which lead us to believe that chytridiomycosis is suppressing the population. In 2001, recovery actions for the northern leopard frog were initiated and included a captive rearing and reintroduction program, and to a lesser extent habitat enhancement. Between 2001 and 2005, 30,065 leopard frog hatchlings from 27 egg masses were collected and reared in captivity under artificial conditions. The objectives of captive rearing program were to achieve a survival rate greater than 50% and rear leopard frogs to a mean minimum body size of 30 mm snout-to-vent length (SVL) at metamorphs. To this end, we conducted controlled experiments manipulating diet and stocking density to help refine our husbandry techniques and found that the amount of protein provided in the diet had a profound effect on size at metamorphosis. In the final two years of the project, we exceeded our goal of 30 mm SVL at metamorphosis achieving SLV’s of 34.9 mm in 2004 and 32.1 mm and 2005. Average survival of leopard frogs in captivity for all years was 82%. In total, 10,147 leopard frog tadpoles and 14,487 leopard frog metamorphs were released into the wild. The objectives of the reintroduction program were to establish leopard frogs at two sites in their former range: one in the CVWMA and the second in the Bummer Flats Wildlife Management Area (BFWMA). In the spring of 2005, three egg masses were detected in the Leach Lake management unit in the CVWMA and numerous young-of-year were observed during fall visual encounter surveys. In 2004, restoration was conducted at this site to reduce the emergent vegetation (e.g. Typha and Scirpus) and create open water habitat for waterfowl. Restoration entailed drawing down the water, mowing the emergent vegetation, tilling the soil, and then re-flooding the wetland in late fall. The establishment of leopard frogs at this site indicates that habitat restoration may assist in recovery. The results of this project suggest that reintroduction and habitat restoration are viable methods for the recovery of leopard frogs in BC, however the population of leopard frogs in BC remains extremely vulnerable and recovery is confounded by B. dendrobatidis. We recommend that future recovery actions should focus on conserving the leopard frog population in the CVWMA and include habitat restoration and monitoring. If this population continues to decline over the next three years, we recommend establishing a captive breeding program. We also recommend that research should be conducted immediately to determine the prevalence and epidemiology of B. dendrobatidis. Finally, if a reintroduction program is resumed, we highly recommend that a reintroduction strategy be developed to address population viability, genetics, disease, monitoring, public education, and the facility operations, and that long-term funding be secured at the outset. In conclusion, we suggest that in the absence of recovery, the leopard frog will become extinct in British Columbia. |
