Feature Story                                            July 2013

Strange Vectors – The Unusual Ways That Species Are Introduced

By Monaca Noble (SERC)

When people think about the ways in which marine and estuarine species are moved around the world, hull fouling and ballast water are often the first mentioned, and rightly so, they are two of the largest and most important vectors for the transport of species. But there are many other vectors that contribute to the spread of invasive species. For example the importation and stocking of oysters has resulted in numerous introductions, including several species of tunicates, crabs, and at least one parasite, Loxothylacus panopaei. In some bays on the West Coast of the United States, oysters may be the most important vector in terms of the number of new species introduced. 

For this article we are focusing on the less well known vectors that have led to species introductions. For nearly all the introductions listed here the risks were not considered prior to the introduction or accidental release.

It Seemed Like a Good Idea at the Time

Multiflora Rose, photo courtesy of Paul Fofonoff.

Managers at the Department of Agriculture Soil Conservation Service thought they had the perfect plant to prevent erosion when they discovered Multiflora Rose (Rosa multiflora). A native to Asia, this fragrant plant was thought to be a great introduction because not only could it prevent soil erosion, but it was beautiful and thought to be good for wildlife. Billed as an attractive ‘living fence’, it was planted in the Chesapeake Bay watershed for erosion protection. Unfortunately, like many other introductions that seemed great at the time, it soon became a serious pest throughout the US, including the Chesapeake watershed where it is now regarded as a serious invader. Its impenetrable thickets choke out native plants and block movements of both animals and people.  

A Home Remedy Gone Wrong

During the summer of 2002 an Asian man purchased live snakeheads (Channa argus) to make a special soup for his sick sister (Washington Post article from 2002). When she recovered, he released them into a pond in Crofton, MD. When the snakeheads were discovered, all the fish in the pond had to be eradicated in an attempt to prevent the spread of the snakehead. Unfortunately, another population of snakeheads was discovered in the Potomac soon after and the fish is now established there. We don't know who released the Potomac population, but many people speculate that the fish were purchased for food, and then released.

Five Swans a Swimming

Five Mute Swims, photo courtesy of Paul Fofonoff

In the 1960s an estate along the Miles River in Talbot County, Maryland had 5 Mute Swans (Cygnus olor) from Europe. All had clipped wings and were meant to stay on the estate grounds adding ornamentation to the garden landscape. But in 1962 the birds escaped during a storm. Though not the first Mute Swans to be seen in Maryland, it is believed that these 5 birds were the start of today’s breeding population. By the 1980s their offspring had grown to ~ 400 birds, and by the late 1990s the population was in the thousands. As people became concerned about the impact of these birds on submerged aquatic vegetation and local waterfowl, control efforts began. These efforts have succeeded in reducing the population to a few hundred pairs but not without public protest from people who love seeing swans on the Bay.

Literary Introduction

Eugene Schieffelin was an eccentric New Yorker who loved birds and plays by William Shakespeare. In 1890 he imported ~80 Starlings (Sturnus vulgaris) from England and released them in Central Park, New York. He was a romantic and wanted to see all the birds mentioned in Shakespeare's plays in the park. The release of the Starlings was a huge success, the bird’s rasping, insistent call can now be heard across the US. While the birds may have enhanced Mr. Schieffelin’s enjoyment of Henry IV, their introduction has been costly to many, including farms that have seen damaged crops and feed consumed by millions of roosting birds.

Mr. Schieffelin was also responsible for first of many successful introductions of the House Sparrow starting with the release in New York City in 1852. Luckily his attempts to introduce bullfinches, chaffinches, nightingales, and skylarks were not successful.

Entrepreneurs and Ill Informed Refuge Managers

Nutria fur coat, photo courtesy of Kürschner from Wikimedia Commons

Nutria fur coats must still be chic in some parts as they are still fetching high prices online. In 1930s entrepreneurs in the US wanted in on the economic action of the South American Nutria fur trade and imported nutria (Myocastor coypus) for fur farms. Fur farms started popping up in places like Louisiana followed soon after by wild populations started by escapees. The first nutria in Chesapeake Bay were brought to the Fur Animal Field Station at Blackwater National Wildlife Refuge in Maryland in 1939. Managers were delighted to have the nutria control the marsh grass in the enclosures and make money from the sale of their fur. By 1979 nutria were well established along the Eastern Shore of Maryland and Virginia with isolated occurrences along the Potomac River and Patuxent Rivers. Today there is a limited market for the fur, and major control efforts are underway to eliminate Nutria and protect marsh grasses in areas like Blackwater National Wildlife Refuge.

My pet and mascot

The American Alligator (Alligator mississippiensis) was the mascot at the Naval Amphibious Training Base in Princess Anne County, VA and were depicted on the camp insignia. Before the sale of baby alligators for pets was outlawed by the Lacey Act and Endangered Species Act (1973), many servicemen showed their base pride by keeping pet alligators. Alligators are native to the Southeastern US from East Texas to Eastern North Carolina, but have been found abandoned in some unlikely places due to pet releases. Many alligators were released near the Naval Amphibious Training Base when they became too large to keep as pets. But the winters in the Chesapeake are too cold for alligators and few survive for more than a few years.