Night Moves: Alpena's Ichthyoplankton Sampling for
Early Detection of Aquatic Invasive Species
By Eric Stadig
U.S. Fish and Wildlife Service fish biologists, Stephen Hensler and Eric Stadig, from the Alpena Fish and Wildlife Conservation Office's Waterford Substation, recently completed their larval fish sampling cruise.
Armed with bongo nets and light traps aboard the R/V Kraken, the biologists searched for non-native species on Maumee and Sandusky Bays. Larval fish sampling concluded on both bays after sampling in the months of May, June, and July. This unique nighttime effort represents one of four portions of the Service's large-scale early detection monitoring program for invasive species using traditional and non-traditional gear types within the Great Lakes.
Ichthyoplankton, more commonly known as larval fishes, are planktonic, meaning they cannot swim effectively against currents under their own power. Early stage larvae swim poorly and are impacted by hydrodynamic conditions such as seiches. A seiche is a wave that swings back and forth in lakes, bays or gulfs, lasting from a few minutes to a few hours, as a result of seismic or atmospheric disturbances. Lake Erie is particularly prone to seiches because of its east-west orientation and shallow depths.
Lastly, larval fish are heavily influenced by light conditions, and are drawn to the surface by the moonlight. This behavior allows the larval fish to feed at the surface when their predators cannot see them as easily. This does, however, make them more susceptible to traditional sampling gear, such as bongo nets, during nighttime sampling.
The Alpena FWCO crew has seen their larval fish sampling pay off with numerous samples filled with larval fishes. These samples will be analyzed in collaboration with U.S. Environmental Protection Agency offices in Duluth, Minnesota and Cincinnati, Ohio. The sampled fish will be identified using both traditional taxonomic identification and genetic barcoding.
Genetic barcoding is particularly useful for early detection of aquatic invasive species, as results are automatically cross-checked against a global database of genetic codes for various types of species. The concept could provide an adaptation to fisheries monitoring plans worldwide.