A Method for Culturing Mussels Using In-River Cages

Abstract

A variety of techniques have been used since the early 1900s to produce mussels for augmenting depleted populations, including the use of wire-covered crates to house fish bearing mussel larvae. Here we describe a modification of earlier techniques, which provides a viable, low-cost method for producing large numbers of mussels. Aluminum-framed cages covered with commercially available hardware cloth are used to confine glochidia-bearing fish. Juvenile mussels then excyst off the host fish, and fall to the substrate-covered cage bottom, which protects the mussels from predation until they mature into subadult mussels. To date, seven species of mussels totaling over 57,100 2- and 3-y-old mussels have been reared in these culture cages.

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A Method for Culturing Mussels Using In-River Cages
Tony R. Brady,* Doug Aloisi, Roger Gordon, Gary Wege
T.R. Brady
U.S. Fish and Wildlife Service, Natchitoches National Fish Hatchery, 615 S. Drive, Natchitoches, Louisiana 71457
D. Aloisi
U.S. Fish and Wildlife Service, Genoa National Fish Hatchery, S. 5631 State Highway 35, Genoa, Wisconsin 54632
R. Gordon
U.S. Fish and Wildlife Service, Jordan River National Fish Hatchery, 6623 Turner Road, Elmira, Michigan 49730
G. Wege
U.S. Fish and Wildlife Service, Twin Cities Field Office, 4101 E. 80th Street, Bloomington, Minnesota 55425
Abstract
A variety of techniques have been used since the early 1900s to produce mussels for augmenting depleted
populations, including the use of wire-covered crates to house fish bearing mussel larvae. Here we describe a
modification of earlier techniques, which provides a viable, low-cost method for producing large numbers of mussels.
Aluminum-framed cages covered with commercially available hardware cloth are used to confine glochidia-bearing
fish. Juvenile mussels then excyst off the host fish, and fall to the substrate-covered cage bottom, which protects the
mussels from predation until they mature into subadult mussels. To date, seven species of mussels totaling over 57,100
2- and 3-y-old mussels have been reared in these culture cages.
Keywords: freshwater mussels; endangered mussels; Lampsilis higginsi; culture; cages
Received: October 26, 2009; Accepted: January 11, 2011; Published Online Early: January 2011; Published Online: June
2011
Citation: Brady TR, Aloisi D, Gordon R, Wege G. 2010. A method for culturing mussels using in-river cages. Journal of
Fish and Wildlife Management 2(1):85–89; e1944–687X. doi: 10.3996/102009-JFWM-017
Copyright: All material appearing in the Journal of Fish and Wildlife Management is in the public domain and may be
reproduced or copied without permission unless specifically noted with the copyright symbol ß. Citation of the
source, as given above, is requested.
The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the
U.S. Fish and Wildlife Service.
* Corresponding author: tony_brady@fws.gov
Introduction
North America has the most diverse assemblage of
freshwater mussel species in the world with over 300
species recorded (Williams et al. 1993). Today over one-
half of these species are either extinct or imperiled due
to habitat losses from flow alterations, or impacts related
to human activities such as dredging and gravel mining
(Neves et al. 1997). Huges and Parmalee (1999) suggest
that this drastic decline in mussel populations began as
early as the 1800s with vast deforestation and the
resulting siltation devastating aquatic habitat. By the
1900s, mussels had gained commercial importance in the
pearl button industry, causing further declines in
populations due to overharvesting of mussel shells to
be turned into buttons (Knott 1980). A new threat has
emerged in the 1980s; colonization of the invasive zebra
mussel Dreissena polymorpha has caused localized
eradication of some mussel populations (Welke et al.
2000).
In the Upper Mississippi River, large increases in zebra
mussel populations have become problematic. Barge
and boat traffic aided in the spread of zebra mussels up
the Mississippi River by transporting zebra mussels
attached to their hulls, allowing them to reproduce in
previously uninfested portions of the Mississippi River.
Zebra mussels colonize on bottom substrates (including
native mussels) in such large numbers that they inhibit
the respiration, feeding, and successful reproduction of
freshwater mussel populations. The federal 9-Foot
Channel Project, a series of locks and dams operated
and maintained by the U.S. Army Corp of Engineers that
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allows boats free access up and down the Upper
Mississippi River, was constructed in the 1930s to allow
for boat traffic to safely and effectively use the river for
recreation and cargo transport. The U.S. Fish and Wildlife
Service (USFWS; 2000) determined that the continuation
of the 9-Foot Channel Project for an additional 50 y
would jeopardize the continued existence of the Higgins
eye pearlymussel Lampsilis higginsii, a species listed as
endangered under the Endangered Species Act (ESA
1973). To ensure the continued existence of Higgins eye,
the U.S. Army Corp of Engineers was tasked to establish
five new and viable populations of Higgins eye in areas
of the Upper Mississippi River and tributaries where
zebra mussels were absent or at low densities. In 2000,
the U.S. Army Corp of Engineers established the
interagency Mussel Coordination Team to assist in
establishing these new populations.
The Mussel Coordination Team approached Genoa
National Fish Hatchery to assist in the recovery efforts for
Higgins eye because of their ongoing culture programs
for yearling largemouth bass Micropterus salmoides ,
smallmouth bass Micropterus dolomieu, and walleye
Sander vitreus, all of which are known hosts (Watters
1994; USFWS 2004) for the successful transformation of
Higgins eye larva, called glochidia. Almost all freshwater
mussel species require a fish host to attach to as larva to
complete their reproductive cycle. For most mussel
species, their larvae attach to the gills or skin of fish, and
live there until they are developed enough to feed on
their own. The time spent on the fish host is water-
temperature and species dependent.
The Mussel Coordination Team also asked Genoa
National Fish Hatchery to develop culture techniques to
produce large numbers of subadult mussels (age 1+) for
their recovery efforts. Mussel cages were designed by
modifying culture cages that were successful for
culturing mussels in the early 1900s (Howard 1922).
Mussels cultured in the cages are protected from large
predators such as mollusk-eating fish, and are provided a
natural food source from the river. Use of the culture
cages requires less maintenance through the course of a
growing season than lab-rearing mussels, which entails
algae culture to provide a food source and weekly
maintenance of culture systems (Barnhart 2006). Cage
culture ensures not only that the nutritional require-
ments of the species are being met, but the effect of
selection from intensive artificial culture is minimized by
rearing the mussels in a more natural environment.
Culture cages provide a means for harvesting subadult
mussels, which can be marked and transported to
relocation areas. The Genoa National Fish Hatchery and
Mussel Coordination Team have successfully used these
culture cages since 2002 to produce Higgins eye and six
additional species of mussels for other restoration
programs in the Upper Mississippi River Basin.
Methods
The mussel culture cage described here consists of
two parts; the wire-covered top and a detachable base
are combined for propagation and culture of mussels to
subadults, age 1, or older (Figure 1). A rectangular top is
used with a base fitted with an untreated plywood tray
designed hold a thin layer of substrate and to collect the
transformed mussels, allowing them to grow inside the
protective cage. These culture cages are designed to be
placed on the river bottom in waters deep enough not to
impede recreational uses of the Mississippi River or to be
suspended from a floating array.
The rectangular top has dimensions that are 24 in. 6
36 in. 6 18 in. high (Figure 1). Frames for the tops are
constructed of 0.75-in. 6 0.75-in. 6 0.125-in. angled
aluminum, and are enclosed with 0.5-in. mesh by riveting
hardware cloth to the frame. A door is created in the tops
by leaving one-half of the hardware cloth unattached. No
hardware cloth is attached to the bottom of the
rectangular top, to prevent mussels from being trapped
between the wire and the plywood tray.
The base is constructed of 1.5-in. 6 1.5-in. 6 0.25-in.
angled aluminum with inside dimensions slightly larger
than the outside dimensions of the top frame, allowing
the top to nest inside the base. The legs of the base are
made from 1-in. 6 1-in. 6 0.25-in. angled aluminum. The
leg ends are cut at a 45u angle, producing a sharp point
that can be driven into the river bottom to prevent the
cages from being overturned or washed away. Bases
intended for use in a floating array do not need legs. The
collection tray is made of 0.25-in. untreated plywood that
is riveted to the base frame and sealed with silicone
caulk. Tabs made from 3-in. 6 1.5-in. 6 0.25-in. angled
aluminum are welded to each end of the base frame
(Figure 1). Holes are drilled into the tabs to allow for
bungee straps to be hooked to the base and secured to
the top.
The tops and bases are assembled onsite by attaching
the top to the base with 14-in. bungee straps. Bungee
straps are hooked to the tabs and stretched to hook onto
the top. River sand is placed on top of the plywood tray
in the culture cage at a depth of #1 in. to provide
substrate for the transformed juveniles. Inoculated fish
are placed into the assembled cage and the door is
Figure 1. This photo shows the top and base of a mussel
culture cage. Note that the top is secured to the base using
bungee straps.
Mussel Culture Cages T.R. Brady et al.
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secured shut with plastic cable ties. Fish are released
from the cages by cutting the cable ties, folding back the
hardware cloth doors, and allowing the fish to swim out
of the cages. The cage door is again secured with cable
ties to prevent any potential disturbance inside the cage.
Culture cages are monitored for mussel production
either at the end of the first growing season or midway
through the second, by removing the cages from the
river, separating the top from the base, then sieving the
contents of the base to harvest any mussels that were
produced. A three-tier sieve is used to sort the mussels
from the sediment in the cages (Figure 2). The top tier
has a mesh size of 0.5 in., the middle-tier mesh size is
0.25 in. and the bottom-tier mesh is 0.125 in. The bottom
tier has legs welded to it that extend up to receive and
hold the other two tiers.
Cages were modified to meet challenges encoun-
tered in the production of other mussel species. The
need for one cage modification was evident for the
production of endangered winged mapleleaf Quadrula
fragosa. The winged mapleleaf uses channel catfish
Ictalurus punctatus as their fish host. Confined channel
catfish cluster together and their combined swimming
actions can remove large amounts of the sand and
mussels from the plywood tray. A dual-top system was
developed, which uses a smaller, 4-in.-high, rectangu-
lar top that sits on the base. A full sized top, fully
enclosed in hardware cloth, sits above the smaller top
and is bunged to the base. The dual-top design can
also be used in situations when resource managers
prefer that host fish not be released into the water
body. Once the fully enclosed top is removed, the smaller
top is secured to the base with the bungee straps. Other
modifications, such as using a smaller mesh hardware cloth
(0.25 in.), have been used to house smaller host-fish
species such as minnows and darters.
A floating array can be used to suspend culture cages
when the river bottom is subject to high bed-load
movement or anoxic conditions during the growing
season (Figure 3). The floating array is constructed of
1.5-in. 6 1.5-in. 6 0.25-in. angled aluminum, and is 12 ft
long and is 6 ft high. Fifty-five–gallon plastic barrels are
used as floats and are housed at the top of each end of
the array. Outside railings, 3.3 ft high, are placed 1.5 ft up
from the bottom to keep the cages inside the array.
Bottom railings, 1.9 ft apart, support the weight of the
cages. These floating arrays are designed to hold four
rectangular cages.
Results
The use of the culture cages has proven a viable tool
for large-scale production of freshwater mussels.
Culture cages both placed on the bottom and in
floating arrays have been successfully producing
mussels in the Upper Mississippi River for 8 y. Mussels
cultured in cages have been tagged and used in
recovery and restoration efforts in four states. These
Figure 2. A three-tier sieve used to sort mussels from culture sediments.
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subadult mussels have also been used by universities
and research organizations to advance mussel conser-
vation. To date, these cages have cultured seven mussel
species, totaling over 57,100 individuals, to the subadult
life stage, (Higgins eye pearlymussel [n = 48,270];
winged mapleleaf [n = 31]; snuffbox Epioblasma
triquetra [n = 1,001]; fat mucket Lampsilis siliquoidea
[n = 3,900]; plain pocketbook L. cardium [n = 480];
black sandshell Ligumia recta [n = 3,200]; mucket
Actinonaias ligamentina [n = 220]).
Acknowledgments
We would like to thank the U.S. Army Corp of Engineers
St. Paul and Rock Island Districts and the U.S. Fish and
Wildlife Service’s Twin Cities Ecological Services Office for
funding for this project.
This project also would not have been successful if it
were not for the vision of the following people and
agencies: Todd Turner, Kurt Welke, Pam Thiel, Dave
Heath, Mike Davis, and the Minnesota and Wisconsin
Departments of Natural Resources. We would like to give
special thanks to Jeff Lockington and Dan Kumlin for
their countless hours of metal fabrication, and to all the
volunteers that have helped in cage assembly. Finally we
would like to thank the editors and anonymous
reviewers for their comments of previous versions of
this paper.
Any use of trade, product, website, or firm names in
this publication is for descriptive purposes only and does
not imply endorsement by the U.S. Government.
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unwanted sediment deposits in the cages.
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