Changes in density, age structure and age-specific mortality in two western pearlshell (Margaritifera falcata) populations in Washington (1995–2006)

✍ Scribed by Lee C. Hastie; Kelly A. Toy

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 153 KB
• Volume: 18
• Category: Article
• ISSN: 1052-7613
• DOI: 10.1002/aqc.879

✦ Synopsis

1. Two western pearlshell (Margaritifera falcata) populations in western Washington were surveyed in 1995 and re-surveyed in 2006. Significant declines in mussel numbers had occurred in both streams during the past decade.

2. In Bear Creek, overall density dropped from 56.0-6.9 mussels m À2 , and in Battle Creek, overall density dropped from 80.7-13.4 mussels m À2 in 2006.

3. Large numbers of empty shells were found in Bear Creek in 2006, indicating high levels of mortality. A disproportionate loss of large, old mussels resulted in a forward shift in modal age class, from 51-60 years to 31-40 years.

4. In Battle Creek, survival appeared to be higher, although significant numbers of shells were found in places. A lack of juvenile mussels indicated recruitment problems, possibly due to habitat degradation following colonization of the stream corridor by beavers and/or a lack of migratory host fish.

5. Effective remedial actions for the Bear Creek and Battle Creek M. falcata populations are required within the next 5-10 years and 50 years, respectively, in order to ensure their long-term survival.