Genetic management guidelines for captive propagation of freshwater mussels

Journal of Shellfisheries Research, August, 2006 by Jess W. Jones, Eric M. Hallerman, Richard J. Neves

Guideline 7: Reduce domestication selection during propagation and culture of juvenile mussels by mimicking natural life history processes, such as fish hosts, diet, temperature regimes, and habitat of a targeted species as closely as possible in the hatchery.

Laboratory Protocols to Prevent Mixing of Mussel Species

The establishment of laboratory protocols to prevent the inadvertent mixing of species or other management units is important to protect the integrity of genetic resources. Most propagation facilities rearing juvenile mussels for augmentation or restoration are cultivating multiple species and populations from different drainages. For example, at the Freshwater Mollusk Conservation Center at Virginia Tech University, juveniles of 6-9 endangered mussel species are produced each year, representing species from several major river drainages. In these situations, separate tank systems are required for holding host fish and for grow-out of juveniles from different drainages. Because juvenile mussels are small (~200-1,000 [micro]m) for the first 60 days of life and can easily attach to laboratory equipment used for handling juveniles, such as sieves, siphons and Petri dishes, these items also should be kept separate for each lot and disinfected regularly. All hatchery personnel should be trained in field and laboratory protocols to reduce the risk of unintentional mixing of cultured populations.

Guideline 8: Protocols to prevent mixing of species or other management units through inadvertent exchanges of juveniles on laboratory equipment are needed to protect genetic resources of freshwater mussel populations.

Release of Propagated Juveniles

A suite of factors should be considered before juvenile mussels are released to the wild. Such planning is especially important for critically endangered populations with small effective population sizes ([N.sub.e]). Small populations (e.g., n = 500-1,000 and [N.sub.e] < 50-100) warrant special attention if they serve as a source for augmentation or reintroduction. First, production and release of thousands of juveniles from a small number of adult females into a small (n < 1,000) recipient population can significantly decrease [N.sub.e], because of unequal contributions of progeny from only a few progenitors (Ryman & Laikre 1991). Therefore, a target number of offspring should be established for release into a small population prior to augmentation. Excess progeny could be released at adjacent shoals or at other acceptable sites. Second, selection of suitable release sites should be based on at least the following criteria: (1) biological requirements of the species, such as presence of fish hosts; (2) habitat quality and (3) thorough assessment of localized and upstream threats to release sites. Third, juveniles should be released at the earliest life-stage possible that will maximize survival in the wild. There is a trade-off between how long juveniles are reared in the hatchery, to increase survival rate relative to juveniles reared naturally and continued exposure to the hatchery environment and the associated extent of domestication selection (Miller & Kapuscinski 2003). Exposure to natural environmental patterns and selective forces at an early life stage may prove most beneficial to ensure fitness in the wild of hatchery-reared juveniles. Fourth, juveniles should be released under moderate-to-low flow conditions to allow settlement at the selected site on the river bottom, and at the appropriate time of year (spring-summer). Fifth, release methods and sites should be selected to increase the range and connectivity of localized demes and populations. For example, juveniles could be released at suitable sites between known locations of upstream and downstream demes. Sixth, as propagation technology improves and juveniles are grown to larger sizes, juveniles should be marked with a tag or chemical stain to facilitate monitoring efforts (see Eads & Layzer 2002).