Mapping Rocky Mountain ridged mussel beds with preliminary identification of overlapping Eurasian watermilfoil within the Canadian range

Joy Wade,Craig Stephen,Colin Robertson

doi:10.3897/natureconservation.42.51081

Joy Wade, Craig Stephen + Show 1 more

Open Access

https://doi.org/10.3897/natureconservation.42.51081

Copy DOI

Abstract

The Rocky Mountain ridged mussel (Gonidea angulata) is a bivalve species whose Canadian range is limited to the Okanagan Valley, British Columbia. In 2019, conflicts between habitat protection for the mussel and potential habitat alteration to control the invasive Eurasian watermilfoil (Myriophyllum spicatum) (milfoil), led to a decision to maintain the status of the mussels as Special Concern under Canada’s Species at Risk Act (SARA) rather than classify it as Endangered. Milfoil control can cause direct mortality and/or burial of the mussels, but there had been no systematic study of the impacts of milfoil control on mussel beds. The purpose of this study was to address knowledge gaps by delineating known mussel beds and potential overlap with milfoil to provide information for management decisions that balance the needs of native species protection and invasive species control. Rocky Mountain ridged mussels in three reference locations were enumerated using snorkel surveys. The presence and distribution of milfoil was documented in relation to five sites within these three locations. Milfoil was encroaching on one site, causing some changes to the substrate. At other sites, the differences in the depth and distribution of the mussel and the milfoil could allow milfoil control without damaging the mussel beds. It is recommended that, before milfoil removal near known mussel beds be undertaken, a detailed site evaluation be conducted to determine potential impacts. This study suggests presumed impediments to co-managing the mussels and controlling an invasive species should not preclude classifying the mussels as Endangered and affording protections under SARA.

Highlights

IntroductionFreshwater mussels (unionids) are one of the most endangered groups of animals in North America (Williams et al 1993; DFO 2017)
The Rocky Mountain ridged mussel (Gonidea angulata) is the only extant member of the genus Gonidea (Blevins et al 2016). It is a bivalve mussel species whose Canadian range is limited to the Okanagan Valley, British Columbia (BC)
Our results show that the perceived conflict between Rocky Mountain ridged mussel management and Eurasian watermilfoil control did not occur at all index sites and that standard methods of Eurasian watermilfoil control could be conducted within distances of less than 100 m from a mussel bed

Summary

Introduction

Freshwater mussels (unionids) are one of the most endangered groups of animals in North America (Williams et al 1993; DFO 2017). The Rocky Mountain ridged mussel (Gonidea angulata) is the only extant member of the genus Gonidea (Blevins et al 2016). It is a bivalve mussel species whose Canadian range is limited to the Okanagan Valley, British Columbia (BC). This area marks the northernmost limit of its patchy distribution which extends south to Napa County, California and from western Oregon and Washington, east to the Snake River Basin in Idaho and south to the Humboldt basin in Nevada (Blevins et al 2016). Some Washington, Oregon and Idaho populations are believed to be in decline (Blevins et al 2016). Comparison of the extent of occurrence (EOO) and area of watershed occupancy of these United States populations from occurrence prior to 1990 and from 1990–2015 indicates a decline in EOO by 28% and watershed area by 43% (Blevins et al 2016)

Objectives

Methods

Results

Discussion

Conclusion