Survey and Assessment of Live Food Markets as an Invasion Pathway

Science Center Objects

Live food markets may be a source of the increasing number of non-native wild invertebrate and fish species, like Asian swamp eels and snakeheads. USGS is surveying such markets around the United States to identify and document species that might be of concern if released live into the wild to assess if the live food market is a possible invasion pathway. 

Surveying small market's assortment of fish and invertebrates

Scientist surveying small market showing an assortment of fish and invertebrates, some live and others on ice.

(Credit: Leo Nico, USGS. Public domain.)

The Science Issue and Relevance: A diverse array of live native and non-native aquatic and semi-aquatic animals are for sale in live food markets across the United States. However, the kinds and numbers of live vertebrates and invertebrates present in such markets are largely undocumented and the significance of live food markets as an invasion pathway is not adequately assessed. It is suspected that such markets are a source of the increasing number of non-native wild populations, including certain populations of highly invasive fish taxa like Asian swamp eels (family Synbranchidae) and snakeheads (family Channidae). The current project, a long-term study initiated in 2001, has shown that a wide diversity of live animals are imported into the U.S. and the kinds and numbers often change radically, a reflection of changes in availability and various other market and cultural dynamics. The current project has found that certain taxa in the international live food trade disappear or decline over years or decades, while other, previously undocumented taxa appear and become widespread within a relatively short period. Although many of the live animals are butchered on site upon purchase, some are potentially released into the wild.

Live periwinkle snails on display in a live food market in Texas

Many hundreds of live periwinkle snails on display in a live food market in Texas. Those in photograph were tentatively identified as Littorina littorea, a species native to Europe and now widespread in USA and Canada.

(Credit: Leo Nico, USGS. Public domain.)

Methodology for Addressing the Issue: The study intends to: 1) survey live food markets to identify and document the occurrence and market distribution of live fishes, turtles, frogs, and invertebrates, such as crabs and mollusks; 2) use the resulting survey data and the literature to estimate risk of establishment of each species encountered; and 3) provide an assessment of the live food market as a pathway of invasion. Accomplishing project goals requires: 1) locating metropolitan areas with food markets likely to carry live animals; 2) first-hand surveys of food markets, giving highest priority to areas with the greatest likelihood of having a variety of live food markets (including metropolitan areas not previously surveyed as well as those previously visited but requiring further attention); 3) continuous updating and modification of a database developed for the project that includes all records with associated details; and 4) determining the risk that a live non-native taxa present in a food market could establish a new wild population. Basic methods involve documenting the names and location of each food market included in the survey and photographing any live species present. For animals not easily identified on site, voucher specimens are purchased and preserved, and taxonomic experts consulted. The created database includes scientific and common names of all live animals encountered during surveys as well as details such as dates, names, and location of markets surveyed; abundance of live individuals observed; the native distribution of each species; and the observed species’ presence in the wild near the market.

Live Asian carp on display in a U.S. food market

Live Asian carp on display in a U.S. food market

(Credit: Leo Nico, USGS. Public domain.)

 

Future Steps: This project is expected to be completed in 2019. The number of markets surveyed annually has varied over the years because funding has been inconsistent. Regardless, this study is improving our understanding of the invasion risks associated with the live food trade and the frequent changes in the kinds of live animals imported. The researcher’s earlier work on live food markets led to a collaborative study with USGS parasitologist Dr. Rebecca Cole that revealed a high proportion of Asian swamp eels imported live from Asia carried Gnathostoma spinigerum nematodes, a known source of human gnathostomiasis in Asia and thus, a possible conduit for the disease’ introduction to the U.S. Future research may include the examination and assessment of the parasites of other live imported aquatic and semi-aquatic animals as well as other risks associated with animal imports. Information from this study is of interest to a wide variety of state and federal resource management agencies, especially those interested in the prevention of invasive species introductions.

Study Area: This is a national study that includes surveys of markets across the United States from New York and Florida to Hawaii.

Swamp eels imported live from Asia to a U.S. food market

Swamp eels imported live from Asia to a U.S. food market

(Credit: Leo Nico, USGS. Public domain.)