Chapter 5: Procedures for Investigation of Freshwater Mollusk Kills
The goal of this chapter is to provide guidance to resource professionals to assist with the entire investigative process, from first knowledge of a mollusk kill incident to the kill assessment to preparation of a final report.
This chapter is divided into several sections. The first section provides background information on freshwater mollusks and an overview of kill investigations. In the second section, useful forms for the kill investigation are provided. The final section details procedures for investigating a freshwater mollusk kill, including initial notifications, what measurements to take, quantifying the magnitude of the kill, and preparing the final report. Chapter 6 provides methods for making a quantitative estimate of the total mollusk kill. This chapter draws from the fish kill guidance manuals developed by the American Fisheries Society (Southwick and Loftus 2003) and Meyer and Barclay (1990) and makes use of many of the same procedures, recommendations, and forms provided in those publications.
Freshwater mollusks, including mussels (Unionoida) and snails (Gastropoda), are widely distributed across North America. North America supports nearly 300 recognized species or subspecies of mussels (Turgeon et al. 1998; Williams et al. 2017) and more than 700 snail species (Johnson et al. 2013). Freshwater mollusks occupy a prominent niche in a variety of freshwater ecosystems, including fast-moving mountain springs, sluggish coastal streams, small creeks, large rivers, ponds, lakes, reservoirs, and wetlands. They are recognized as excellent indicators of water and habitat quality due to their sensitivity to many types of environmental perturbations. Mollusks provide a food source for several fish species, as well as aquatic and riparian mammals, birds, and reptiles. Snails have a profound impact on algal primary productivity, playing a pivotal role in nutrient cycling, and mussels remove large amounts of suspended solids and contaminants from the water column through their filter-feeding activity. Even the shells of mussels serve a purpose in the ecosystem, providing substrate and cover for invertebrates and cover and spawning sites for some small fish species. The commercial history of mussels in the button industry has been well documented (Thiel and Fritz 1993; Anthony and Downing 2001), and mussels continue to possess significant economic value in the international cultured pearl industry and in bead production.