Zebra mussel shells were found in the filter of an air conditioning unit of a 35-foot cabin cruiser boat that was purchased new and moored at Roosevelt Lake since 2005. However, state authorities found no live mussels or any other compelling evidence that invasive mussels have made their way into this popular recreation and fishing lake in central Arizona.
“Quite simply, we just don’t yet know the origin of the very few invasive mussel shells found in this boat,” said Tom McMahon, invasive species coordinator for the Arizona Game and Fish Department.
The cabin cruiser was undergoing routine maintenance when an astute marine mechanic discovered the shells in the water filter of an air conditioning unit. The air conditioner utilizes lake water.
McMahon said physical inspections of the boat’s hull, the surrounding docks, and throughout the marina have shown no evidence of any invasive mussels. Biologists have also examined water samples collected from the Roosevelt Lake marina for the presence of veligers, the name for the microscopic mussel larvae. No veligers have been found in these samples or any previous samples collected from Roosevelt in 2009. Divers from the marina will also be checking underwater structures and habitat as well.
McMahon said what makes this discovery even more puzzling is that the cabin cruiser in question was apparently shipped to Roosevelt straight from the manufacturer in Maryland five years ago. However, the boat could have been exposed to other waters during field testing or sales activities prior to shipping to Arizona.
“We are very confident that these shells did not originate in Arizona, but were most likely transported to Roosevelt Lake within the interior of the boat in 2005 and probably not viable. The Arizona Game and Fish Department, along with the Salt River Project, will continue to survey Roosevelt and other waters in the state for quagga and zebra mussels,” says McMahon.
Zebra and quagga mussels are freshwater, bivalve mollusks that typically have a dark and white (zebra-like) pattern on their shells. They are alien to North America, but have invaded many waters in the east. Although quagga mussels have been found in the lower Colorado River and in lakes Mead, Mohave, Havasu and Pleasant, no zebra mussels have been discovered in Arizona.
Despite some minor morphological and ecological differences, both invasive mussel species are very similar and pose a significant threat to the environment and our water infrastructure systems. They are both generally quite small, only about 1/2 of an inch or less in length. These mussels can clog boat intakes and the grates and pipes for water delivery systems. It is estimated that invasive mussels in North America have cost industries and businesses billions of dollars.
On a positive note, McMahon said it was good that a marine mechanic at Roosevelt was able to alert the Game and Fish Department to the presence of these shells. “Our first and best line of defense for invasive species is the public, especially the boating public.”
Furthermore, it is illegal to transport or move live, viable invasive mussels in Arizona. A new law, the Aquatic Invasive Species Interdiction Act of 2009, prohibits the transport, release, placement or movement of these invasive mussels into waters of the state. Violators could be fined up to $500 per occurrence
This all reinforces why it is necessary to always clean, drain and dry your boat after every outing on any lake. “Please do your part. Wash and dry your watercraft so you; Don’t Move a Mussel,” says McMahon.