Searching for 60-pound mussels

Zebra mussels and Quagga mussels — their closely-related cousins — make their living by filter-feeding on algae and small zooplankton, the building foundation of the aquatic food chain.When zebra mussels was first seen in Lake Erie in the late 1980s, some of the scientists who investigated the history of zebra mussel expansion throughout Europe found documentation of significant reduction in productivity after the mollusks became established.The amount of non-mussel biomass that a body of water could support averaged about 1/3 less than before the invasive species arrived. The cost of reduced productivity to us means fewer fish are available to harvest by commercial and recreational fisheries.Throughout the Great Lakes, ecosystem effects have become plain to see with the naked eye. Visibility from double to quadruple the former water clarity is an obvious indicator that the mussels are filtering particles of algae, zooplankton and mud that formerly clouded the water.A group of researchers assembled through the Great Lakes fish commission have confirmed through the consolidation of their research that the quagga mussels in Lake Michigan are impacting the prey fish populations, namely alewives through the suppression of the lower food chain by their filter-feeding.Mussels have been found to consume and/or compete with multiple size ranges of zooplankton, including water fleas such as Daphnia; Cladocerans, and their larvae called Nauplii; and invasive spiny water fleas. They also consume and/or compete with larval fish for their preferred zooplankton prey, such as rotifers, flagellates and bacteria.Fewer copepods and water fleas leave less prey for opossum shrimp, an important prey for adult alewives.Invasive filter-feeders can impact the growth and survival of larval fish, including prey fish and sport fish alike. As a result of lower prey densities, Salmon populations in Lake Huron collapsed and Lake Michigan's are presently noticeably declining.It is hard to say how many mussels are in the Great Lakes, but one estimate that has been published says 750 trillion.Luckily, they do not get to be 60 pounds, but some species of Asian carp do. Two of the four species, namely the Silver carp and Bighead carp filter feed on the same algae and zooplankton as the mussels are quite effectively doing already.The other two species of escaped Asian carp, the Grass carp and Black carp, which can weigh up to 150 pounds, are not regarded to be as much of a threat, as they consume plants and mollusks respectively.A report published in the Transactions of the American Fisheries Society in January 2016 predicted that once planktivorous Asian carp get into Lake Erie, they will eventually become 34 percent of the total weight of all fish in the lake.Bighead carp have been known to reach 88 pounds and feed mostly on zooplankton. Silver carp, the ones seen leaping out of the water as motorboats approach, can grow to 60 pounds on a steady diet of phytoplankton (algae).According to the study, Walleye, Yellow perch and Steelhead trout populations would decline — because of competition with their primary prey fish for planktonic food items, namely gizzard shad and emerald shiners. The plankton feeding Asian carp would directly consume sport fish larvae in the spring through their filter feeding activities.Smallmouth bass numbers may be one species that could increase, because of the availability of juvenile carp in shallow water that could be utilized as prey.Seen in Lake Erie since 1984, Grass carp are not perceived to be as big of a threat as the Silver and Bighead carp. Still, feral populations could negatively affect native fish populations, ecosystem integrity, sport fisheries and waterfowl health through the reduction of beneficial vegetation, increasing turbidity and destroying fish spawning beds. Their maximum weight is reported to be up to 100 pounds.Last year, the Ohio Division of Wildlife worked with seven agencies to practice and perfect their cooperative Asian carp rapid response plan sampling techniques using trammel netting and electrofishing.They were able to capture eight Grass carp in the Sandusky River ranging from 26-to-41 inches long and 6-to-28 pounds. Their population has not increased to troublesome levels yet.This week, they paired up with about a dozen U.S., state, Canadian and provincial agencies and universities to sample in the Sandusky and Maumee rivers.They came up with 27 Grass carp from the Sandusky River, near Fremont and three from the Maumee River near Blue Grass Island this year.Some were over 40 inches — but no 60-pound filter feeders have been found ... yet.