It is hot here! Or at least much hotter than what I am used to. It was 95 degrees Fahrenheit which is cool weather for those native to Nevada. The first day I was here it was the running joke that I thought it was hot out because it gets to be about 120 degrees Fahrenheit when it really warms up. Still, I managed to get sunburned through multiple applications of waterproof SPF 70 sunscreen. I was wondering how anything survives out here, and then I learned about the Quagga mussels which have completely taken over everything in Lake Mead. After diving in the lake, I saw for myself that Quagga mussels are definitely the most abundant creature down there and cling to any available hard surface, littered trash and all. Due to the warm water temperature of the lake and abundant sunlight, these Quagga mussels are thought to reproduce year-round instead of just seasonally, as in other areas of the country. Research is still being done, but this may be one of the factors contributing to why they have been so successful here and able to spread throughout the lake in just 3 years.
Lake Mead is a reservoir that was created by the construction of the Hoover Dam in 1936, and it became the first National Recreational Area in 1964. Today, the Lake Mead dive team conducts a wide range of diving operations here. They are involved in maintenance dives such as moving docks, recovering sunken boats and cars, and setting anchors. They conduct biological research with the endangered Razorback Suckerfish and Bonytail Chubs as well as the invasive Quagga mussels. Also, they participate in body recoveries and Remote Operated Vehicle (ROV) operations in addition to surveying underwater cultural resources.
During my time at the lake I helped out with biological and cultural research. For the first day of diving, Boat Captain Tom Culler took us out to a floating platform at a site called Rufus Cove. Park divers Bryan Moore, Ross Haley, and I used a device that downloads data from temperature loggers that have been tethered to a chain at intervals from the surface to a depth of 50 feet. The information gathered will be used to determine the tolerance of the mussels at different temperatures. Then, on the second and third dives we went down to gather small rocks that will be sealed with a glossy acrylic paint to be used as an educational tool and visual representation to help curtail the spread of the mussels. Also, we gathered more mussels off of another chain to be sent to Texas Christian University in order for them to conduct research about temperature requirements for reproduction. These mussels had to be packed up and sent overnight in order for them to arrive there alive. Bryan Moore found that sending them in water actually killed them, so we put them in a cooler filled with wet burlap to make sure they survived.
Since this is my first time diving in a lake I had to get used to a few things. First, there is a significant thermocline. The water is about 73 degrees Fahrenheit at the surface and drops about 10 degrees at around 25 feet deep. At about 50 feet deep the water temperature is around 55 degrees Fahrenheit. The dive team wore two piece 7mm wetsuits to stay warm at depth, but since I was frying most of the time out of the water, I just wore half of the 7mm suit I wear in California and warmed up quickly at the surface. I wasn’t used to all of the silt either; I went to touch the bottom and ended up submerging my forearm in gelatinous goo. However, one nice thing about diving fresh water is that you don’t have to rinse your gear out afterwards, and it also dries quickly in the hot air!
On the second day we made a dive in Lake Mohave on some artificial habitats that had been set up for game fish to live in. The water was much clearer and we observed the structures to see if the fish were using them. We saw largemouth bass, bluegill, green sun fish, carp, and catfish. Also, we checked to see if Quagga mussels were colonizing on the structures as well, which they were. Next, we went to another part of the lake in Cottonwood Cove to survey the underwater cultural resources located there. The walls of an old gold mill were located underwater there and we checked to see the deterioration and how the mussels had affected the site.
That day, one of the divers, Ross Haley, who serves as the Wildlife Branch Chief for the Resource Management division, got a call to help out at Dry Tortugas in Florida and left the next day. Dry Tortugas National Park is preparing for potential impacts from the Gulf of Mexico oil spill and as a resource advisor, Ross will help to organize cleanup and wildlife resources projects.
On my last day, I got the chance to go to University of Nevada Las Vegas to work with graduate lab assistant, Scott Rainville, to see what is being done with the mussels we collected. They had quite a few specimens stored there for conducting research. I helped contribute to a project that looks at the size and health of the mussels according to their depth and location. They can also see how often they are spawning by checking how many adults and juveniles are in the population. After isolating the mussels from the rocks, we sorted them into piles according to size and then got exact shell length and width measurements using calipers of at least 6 mussels from 12 different size groups. Then, we removed the meat from the shells and put them into separate piles to be dried and weighed. This information will be used to determine the health and nourishment of the mussels by how much meat they have inside. Next, I rinsed the rocks and poured the water through a filter. The contents from the filter were then put under a high power microscope to look for small juvenile mussels. The images from the microscope were displayed on a computer monitor and special software was used to measure the shells of even the tiniest mussels.
In Lake Mead, the infestation of Quagga mussels seems to be beyond the point of eradication. The main goal now is to prevent the spread of Quagga mussels to other bodies of water. Boats that are moored in the marinas must be decontaminated before leaving as they may potentially have adult mussels, which can live up to 30 days out of the water, attached to them. Those who bring their boats in for the weekend will most likely only have a few larval mussels that will die before they could get to another lake. Still, it is important for them to clean, drain, and dry their equipment before leaving in order to ensure that the invasive mussels do not contaminate other lakes.
To learn more about the invasive Quagga mussel visit: www.nps.gov/lake/naturescience/zebramussel.htm
Thank you to Bryan Moore, Ross Haley, Tome Culler, and Scott Rainville