On Tuesday, the US Geological Survey (USGS) reported evidence of Asian carp spawning further up the Mississippi River than expected. Eggs and embryos from the invasive Asian carp turned up in samples taken from the upper Mississippi River, near Lynxville Wisconson in 2013, 250 miles further upstream than previously reported. Worse, the fact that the eggs and embryos were found at that latitude means the spawning took place even further north of the site where they found. Cindy Kolar, a scientist for the USGS, said that scientists had been looking for background information on fish around Lynxville before the invasion of the Asian carp, and were not expecting to find the carp itself.
Asian carp is a term applied to a group of related fish, including the two that were definitively identified by the USGS in the Lynxville samples: the bighead carp (Hypophthalmichthys nobilis), and silver carp (Hypophthalmichthys molitrix). Eggs from grass carp (Ctenopharyngodon idella) might also have been present in the samples. Originally cultivated to control weeds and parasites in water systems in the 1970s, the Asian fish escaped from aquaculture operations in the US Southeast, and have been heading further north since then.
To an ecologist, Asian carp are a pain in the neck. The carp can grow to 110 pounds, outclassing predators. It over-eats plankton and vegetation, imperiling the ecosystem they invade, threatening the survival of other species, and crowding out game fish. The carp has cost Federal and State governments hundreds of millions of dollars in measures aimed at keeping the Asian carp from spreading further up the Mississippi, and especially to keep them from moving into the Great Lakes via the Chicago Waterway. The city of Chicago has proposed $18 billion in February to keep the carp out of the Great Lakes because of their threat they pose to the aquatic ecosystem and to recreational activities.
Asian carp are edible, and they have been farmed in Asia, where they are prized as food, for a millennium. They haven’t caught on in North America as food quite as much, because of the association with common carp, which is not a favored food fish. To control their spread in the U.S., biologists are encouraging people to catch and eat the carp.
Invasive species are a perennial problem for ecologists for a number of reasons. When a species is transplanted from its natural habitat to a new ecosystem – especially where it has no natural predators, the species may over-proliferate, leading to a population explosion. The transplanted species will then out-consume the species that were already there, disrupting the local food web, and sometimes resulting in a population crash due to mass starvation. Often, a transplanted species will prey on the native species or their young, threatening them with extinction.
At this point, scientists do not know how the carp got so far up the Mississippi. Standing in the way of their northward progress is a series of dams – at no point should the water have been high enough for the carp to jump over them, according to Kolar. She speculates the fish may have been inadvertently carried in bait buckets. It is important to understand how the fish got so far north in order to halt their spread. Worries about the Asian carp spreading further up the Mississippi are “warranted.” Kolar says, pointing to changes in fish populations where the carp has invaded.
By Laura Prendergast