“Night Moves”: Larval Fish Sampling as Early
Detection of Aquatic Invasive Species
BY ERIC STADIG, ALPENA FWCO – WATERFORD, MICHIGAN SUBSTATION
sampling cruise. Credit: USFWS-Eric Stadig
U.S. Fish and Wildlife Service fish biologists, Stephen Hensler and Eric Stadig, from the Alpena Fish and Wildlife Conservation Office (FWCO) (Waterford Substation) completed another larval fish sampling cruise in July. Armed with bongo nets and light traps aboard the R/V Kraken, the biologists searched for non-native species on Maumee and Sandusky bays in western Lake Erie. This unique nighttime effort represents one of four portions of the Service’s large scale early detection monitoring program using traditional and non-traditional gear types within the Great Lakes.
Ichthyoplankton (a.k.a 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 condition such as seiches. 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, such as exhibiting diel vertical migration being 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 use of light traps was a major component for the Alpena FWCO
Ichthyoplankton sampling. They effectively sampled shallow areas
where the bongo net was unable to be used. Credit: USFWS-Eric Stadig
The Alpena FWCO crew is seeing their larval fish sampling pay off with numerous samples filled with larval fishes. These samples will be analyzed with collaboration with U.S. Environmental Protection Agency (EPA) offices in Duluth, Minnesota and Cincinnati, Ohio using both traditional taxonomic identification and genetic barcoding. Genetic barcoding is a 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.