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Alien Fishery…

While exotic species grab the headlines, the truth is that most of the freshwater fish we think of as belonging to New England aren’t native at all.

Years ago, while walking along the shoreline of the Charles River in downtown Boston throwing a spinnerbait for summer largemouths, I was stopped dead in my tracks by the sight of two glowing, pinkish-white creatures milling about in the shallows. As I snuck closer, I saw it was a pair of fish that resembled the tropical cichlids I used to sell when I worked in a pet shop. Their behavior looked familiar too. For a few minutes, I watched the pair of 10-inch fish vigorously defend a small patch of bottom, chasing away two carp, a 2-pound largemouth and numerous bluegills. Typical cichlid spawning behavior, I thought. But could some sort of tropical cichlid really be spawning in the Charles?

tilapia caught on a fly rod by Roy Leyva in the Charles River

Bluegill? Tautog? Cunner? Nope. This tilapia was caught on a fly rod by Roy Leyva in the Charles River, and it’s not the only one. These fish were somehow introduced to the river, and even though they are native to the Nile River, they appear to be thriving in downtown Boston.

They wanted nothing to do with my spinnerbait, but I eventually got one to attack a bare bronze hook, and I snapped a few photos. Karsten Hartel, the Curatorial Associate in Ichthyology at Harvard’s Museum of Comparative Zoology—in other words, a man who knows a whole lot about fish—identified the fish to be a Nile tilapia, Oreochromis niloticus, a cichlid fish native to Africa and of a size and coloration suspiciously similar to those sold in Chinatown’s live fish markets. An aberration, perhaps, but the spawning behavior, and the fact that I’ve seen as many as a dozen of these fish at the same location in each of the last four years, lends credence to the hypothesis that they may in fact be surviving New England’s winters and reproducing, despite their tropical roots.

The tilapia episode is only the most recent chapter in the long history of nonnative fish introductions into New England waters, a story that dates back to the 17th century. While freak encounters in New England waters with tropical species such as piranhas, walking catfish, pacu, or that poster child of nonnative fishes, the northern snakehead, may get all the press, a look at established, reproducing species reveals that most of the freshwater fish that we tend to think of as native to New England were completely alien to our waters until the 1800s. According to Hartel, 47 percent of the primary freshwater fish species (fish that spend their entire lives in freshwater) reproducing in Massachusetts are not native to the state, but have been introduced by humans. Most of these introductions have not been accidental, but intentional, often undertaken by state or federal agencies to provide New England’s residents with a ready source of nutrition and sport.

northern snakehead

The northern snakehead, may get all the press but freshwater fish that we tend to think of as native to New England were completely alien to our waters until the 1800s

A survey of New England’s freshwater ecosystems prior to the 17th century would seem almost foreign to any freshwater angler used to targeting largemouth bass, northern pike, carp or virtually any other game fish. Small fish like darters, sculpins and especially minnows, dominated the fish diversity composed of 50 or so species. And the apex predators, depending on the locale, were yellow perch, brook trout and chain pickerel.

Before taking a closer look at the cast of interlopers, let’s define the terminology used to describe “alien” species. A nonnative species is, as you’d expect, a species not indigenous to a certain region. All of the nonnative species discussed here are introduced—that is, brought into the ecosystem by humans and not by a natural extension of their range. One type of nonnative species is an exotic species, a species not native to the country into which it was introduced. Another type is a transplant, which is a species moved within its native country into a watershed in which it is not native. The National Invasive Species Council (NISC) defines an invasive species as “a species that is nonnative to the ecosystem under consideration and whose introduction causes, or is likely to cause, economic or environmental harm or harm to human health.” Not all of New England’s nonnative fishes can be considered invasive, but there’s little doubt that each has in some way altered the environment in which it lives.

20.5-pound koi caught by Roy Leyva in Jamaica Pond in Boston

20.5-pound koi caught by Roy Leyva in Jamaica Pond in Boston

The first species on record as having been introduced into New England waters is the goldfish Carassius auratus, a close relative of the carp native to much of eastern Asia. They were brought to North America as early as the late 17th century by British settlers, who released them into neighborhood waters with the hope of adding the ornamental species to the local waters. In the late 1800s, the United States Fish Commission, a predecessor of today’s National Marine Fisheries Service, bred and raised the species, distributing them nationwide to meet demand for ornamental fish ponds and aquaria. Those initial introductions have been augmented over the centuries by aquarium releases and escapes from private ponds and other facilities, resulting in a wide diversity in the shapes and colorations of wild goldfish. They’re sometimes caught by anglers targeting carp and are a frequent site in more urban areas, their presence often betrayed by their bright orange hue.

Treasured by some, abhorred by others, the goldfish’s close relative, the common carp, is one of the most prominent nonnative species found in our waters, and one that can truly be called “invasive.” Native to much of the Eurasian landmass, the species was first brought to the United States in the mid-nineteenth century, both by private parties and the federal government. The real arrival of the common carp, however, is considered to be the shipment of 345 adults that the U.S. Fish Commission received from Germany in 1877. Breeding ponds were set up near Washington, D.C., and the fish were propagated and distributed throughout the country. The Commission envisioned introducing carp as an important food fish, due to their hardiness and general palatability, although they were admittedly “hardly equal to the high-priced delicate class of fish which includes the bass, trout, and shad.”


Carp were originally introduced as an important food fish, due to their hardiness and general palatability.

In the Commission’s 1883 Bulletin, C.W. Smiley spoke with optimism of developing carp farming as the harbinger in a nation-wide wave of aquaculture: “The cultivation of fish is destined to become as important among the American farmers and planters as the cultivation of cattle, sheep, swine, poultry, or of grains, fruits, and berries…The hardiness and wide range of diet and the rapid growth of carp especially fit it to be the precursor in fish farming.”

It took less than a quarter of a century, however, for the members of the Fish Commission to realize their mistake. By 1900, it was apparent that the carp, due to their habit of rooting in the substrate for food, brought with them a myriad of ecological complications. For example, their behavior uproots aquatic vegetation that provides important cover for juvenile native fishes as well as food for waterfowl. Their habits also significantly increase water turbidity, a problem for those species that prefer not to pass particles of muck over their gills in addition to water while breathing. Although anglers today might appreciate the fighting abilities of these overgrown minnows, the overall ecological consensus is pretty well summed up in a quote from the book Distribution, Biology, and Management of Exotic Fishes by Walter Courtenay and Jay Stauffer, Jr., published in 1984: “Overall…introduction of the common carp to U.S. waters would have to be considered a monumental mistake and one with which we must learn to live.”

Moving on to the salmonids, it might come as a surprise that neither rainbow nor brown trout are native to New England. Lake trout are native to some regions of northern New England, but are, for the most part, introduced as well, for example in Quabbin and Wachusett Reservoirs, where they were introduced by The Massachusetts Division of Fisheries and Wildlife (DFW) in 1952.

Rainbow trout

Rainbow trout were first introduced into Massachusetts in the late nineteenth century as a food and sport fish

Rainbow trout are a transplant from rivers and tributaries flowing into the northern Pacific Ocean on both the Asian and North American continents. They were first introduced into Massachusetts in the late nineteenth century as a food and sport fish and currently are known to reproduce in only about a dozen streams in western Massachusetts, although they’re stocked all over New England.

brown trout

The first brown trout that came to North America arrived in the form of eggs from Germany in 1883

Brown trout, indigenous to Europe, northern Africa and western Asia, are the only exotic species besides the carp that has been successfully established in many parts of the United States for sport fishing purposes. Voracious predators, the first brown trout that came to North America arrived in the form of eggs from Germany in 1883. They were reared by the New York Fish Commission and subsequently distributed to waterbodies in a number of states. Brown trout now reproduce in many New England waters. Indeed, those coveted holdover browns that so many freshwater anglers hope to capture have no business being in New England. And like carp, they can truly be considered an invasive species, competing directly with native species, especially brook trout, for food and habitat, as well as predating on a number of the indigenous fish fauna. Their negative impact on brook trout has been well documented among the sea-run populations of both species in the Falmouth-Mashpee area of Cape Cod.

white catfish

The white catfish is a common quarry or Charles River anglers. photo by Roy Leyva

Of the catfishes targeted by anglers in New England, only one of them, the brown bullhead, is indigenous to the region. The white catfish, a common quarry of anglers who frequent the Charles, Connecticut and Merrimack rivers in Massachusetts, is not native to waters of North America north of the Hudson River. It was introduced as a food and sport fish multiple times by the Massachusetts DFW during the first half of the 20th century, and is now established in a number of ponds and rivers, especially in Massachusetts, but also in Connecticut.

The yellow bullhead, most easily distinguished from the native brown bullhead by its pale, yellowish chin barbels (those of the brown bullhead are dark), is indigenous to the central and southeastern portions of the United States. Like the white catfish, it was introduced into southern New England rivers and ponds in the early twentieth century. Also a clear invasive, it directly competes with the native brown bullhead and in many cases outnumbers it. I’ve been fishing for catfish at night in the Charles River for many years, and although I’ve caught dozens of yellow bullheads, I have caught exactly one brown bullhead.

channel catfish

Chase Stokes’ Lake Champlain 33-inch channel catfish.

The channel catfish, although not as prevalent as its other two nonnative relatives, was also introduced into a number of Massachusetts’s waters in the early 20th century. Interestingly, the species’ introduction into the Charles River resulted not from intentional stocking but from the release of several albino specimens sold in the aquarium trade, which subsequently bred and resulted in a full-blown population.

Northern pike and tiger muskie—the latter a hybrid of the pike and muskie—aren’t native to New England either, besides the Lake Champlain population of northerns. Pike were first stocked in western Massachusetts in 1950, and since then have been stocked in over 40 lakes and ponds in Massachusetts alone. Interestingly, the U.S. Fish Commission had considered introducing pike into non-indigenous waters 75 years earlier, but had decided against it, as James Milner noted in the 1872-1873 Bulletin: “This fish, the merits of which are sometimes defended in regions where it is the principal species, is not only very destructive of other fishes, but is of indifferent flavor and full of bones.” By 1950, evidently, its qualities as a sportfish outweighed these deficiencies. For the same reason, over 430,000 tiger muskies have been stocked in Massachusetts waters since they were first introduced in 1980. Needless to say, both of these carnivorous ambush predators significantly alter the ecosystems in which they live, preying on a variety of smaller or juvenile fishes—although many of those small fish aren’t native to New England either!

Of all the introduced species, the most widespread and perhaps the most surprising of the lot are the transplants of the family Centrarchidae, the sunfishes. The family, which is endemic to North America, includes such high-profile players as largemouth and smallmouth bass, bluegills and black crappie, but only a few of the smaller species such as the pumpkinseed are native to New England. The bluegill, while native to parts of Vermont, isn’t indigenous to the rest of New England, but was introduced in the early 20th century as a game fish. It’s now one of the most abundant freshwater fishes in many parts of New England, present even on Martha’s Vineyard. The rock bass, whose native range begins west of the Hudson River, was introduced into Massachusetts in the early 1900s, primarily in the western portion of the state. Black crappie is another popular, nonnative centrarchid that was introduced into many parts of New England during the first half of the 20th century.

smallmouth bass

The native range of smallmouths doesn’t extend east of New York, but the species was introduced to the New England area by state agencies and private parties for sport-fishing purposes as early as 1850.

And then, of course, there are the largemouth and smallmouth bass, two of the most prominent freshwater game fish in the New England area, but interlopers nonetheless. The native range of smallmouths doesn’t extend east of New York, but the species was introduced to the New England area by state agencies and private parties for sport-fishing purposes as early as 1850. Largemouths were introduced in Massachusetts during the second half of the 19th century by the state’s fisheries commission, to “provide angling opportunities during the summer months.” Today, largemouth bass are found all over New England, rivaling the bluegill in abundance.

It’s rather ironic to think about the numerous anglers I’ve listened to over the years who lament the lack of quality largemouths in a given body of water. The culprit, they invariably claim, is the chain pickerel, which they charge with consuming juvenile bass and outcompeting it for limited food resources. Yet in reality, the exact opposite is likely true, resulting in the prevalence of invasive largemouth bass in waters that formerly hosted prodigious populations of native pickerel. These are good for fishermen who detest the “slime darts,” I suppose, but ironic all the same.

Largemouth bass

Largemouths were introduced in Massachusetts during the second half of the 19th century by the state’s fisheries commission

To round out the list, several species of minnows, including the fathead minnow and bluntnose minnow, are native to central parts of North America but have been introduced into New England waters through anglers’ release of unused live bait from their shiner buckets at the end of an outing—sensibly enough, dubbed “bait-bucket introductions.” Although not always a significant part of the ecosystem they inhabit, in some cases these species become a major presence, for example, the bluntnose minnow in the Quabbin Reservoir, where it’s the most common minnow.

For better or for worse, today’s New England freshwater habitats bear next to no resemblance to what they did prior to European colonization. As Karsten Hartel noted in a brief conversation with me a few months back, very little was done to assess the impact of nonnative species in the years following their introduction into New England waters, so how exactly the region’s ecosystems were affected might never be fully known. But as Courtenay and Stauffer mention, “Impacts should not be judged solely on what the exotic [or transplant] can do for man, but also on what the exotic can do to water quality, native biota, and habitat.”

To be sure, what’s done is done, and the irreversible establishment of so many nonnative fishes in our waters is a foregone conclusion—although annual stockings do of course continue. But at the very least, it’s an interesting exercise to consider that more often than not, the fish that’s tugging—hopefully—at the end of your line is no more at home in New England waters than those Nile tilapia that looked so out of place as they cruised the banks of the Charles.

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