The Asian Carp Invasion

On my walks around Landen Lake this week (a small suburban lake north of Cincinnati), I have been repeatedly reminded that the Asian carp invasion is a significant problem throughout the Mississippi River watershed.  Introduced in the 1970s to control aquatic vegetation and to filter sewage water, they escaped containment areas during floods and have spread throughout most of the U.S.  Favoring shallow, sluggish waters, they often attract our attention as they thrash about, their dorsal and tail fins breaking the surface.

Represented by four species (grass, black, silver and bighead carp) these large fish are very prolific and soon dominate the aquatic ecosystems that they colonize; black carp, which feed on mollusks, threaten native snail, mussel and clam populations while the others reduce the availability of plankton and vegetation vital to native fish, amphibians and aquatic reptiles.  As video enthusiasts know, silver carp also pose a threat to boaters, jumping into the air (and into boats) in response to the sound of outboard motors.

Concerned that Asian carp will enter the Great Lakes and disrupt the ecology of their fisheries, efforts have been made to block carp migration along canals that connect those Lakes with streams of the Mississippi watershed; "electric fences" have been used with some success but carp also spread as eggs or fingerlings on boat hulls, via the use of live bait, during floods and perhaps even on the legs of wading birds.  Taking advantage of the carp bonanza, some companies are culling them to produce pet food or fertilizer; vultures also partake of the bounty, feasting on dead carp that were stranded by shrinking lakes or rivers.

Eulachon

Eulachon are small marine fish (8-9 inches in length) that feed on plankton in the eastern Pacific, from Alaska to northern California.  In late winter, they move into estuaries and coastal rivers to spawn; most adults die after this process.  Fertilized eggs, which sink to the gravel beds, hatch in a month and the fry head to sea; there they will live in offshore waters for 3-5 years before returning to spawn.

Heavily laden with fat, the spawning eulachon are known as candlefish (since dried specimens can be lit like candles) and were called "salvation fish" by Native Americans of the Pacific Northwest since their calorie-rich bodies provided vital nutrition during the leans months of late winter and early spring.  Of course, Steller's sea lions, dolphins and sea birds also welcome their spawning runs.

Unfortunately, eulachon have all but disappeared from the coastal rivers of northern California, Oregon and Washington and their numbers have decreased significantly farther north.  Global warming, overfishing, water pollution and altered river sediments (due to hydroelectric dams) are all thought to be playing a role in the population decline of this smelt.

Atlantic Needlefish

One of the more interesting predators along our seawall is the Atlantic needlefish.  These streamlined, long-jawed fish dart about a barnacle-encrusted rock pile at a bend in the wall, snaring small fish with their numerous sharp teeth; young needlefish, tiny replicas of the adults, hunt in schools, feeding on a host of marine invertebrates.  The needlefish themselves are potential prey for larger fish, inshore sharks and dolphins.

Found along the western coast of the Atlantic Ocean, from Maine to Brazil, these distinctive fish favor shallow, calm, brackish waters near mangroves, marinas, piers and seawalls.  Tolerant of freshwater, many travel up coastal rivers and some have been found as far inland as the Tennessee River watershed (having traversed canals from Gulf Coast streams).  Spawning occurs in May or June, the eggs harboring tendrils that attach to aquatic vegetation.

While Atlantic needlefish are officially listed as gamefish (adults may reach 2-3 feet in length), they are more often caught accidentally and are generally used as bait.  Some of us, not inclined to drown worms for recreation, simply enjoy watching these "saltwater gar" as they zoom about the shallows of Sarasota Bay.

Convict Fish

Of all the fish that congregate along our seawall on Sarasota Bay, sheepshead are among the most common.  Often called "convict fish" due to their prominent black and silver stripes, sheepshead are medium-sized marine fish, found along the western Atlantic Coast from Nova Scotia to Brazil; their numbers are especially high in southwest Florida.

Favoring inshore, brackish habitats, sheepshead are best found near mangroves, piers, jetties, seawalls and tidal creek inlets.  They are omnivorous predators, consuming small fish, crustaceans, aquatic insects, a host of marine invertebrates and some aquatic plants.  Come March and April, sheepshead move offshore to spawn but still prefer to gather near human structures or natural reefs.

Members of the porgy and seabream family, which is represented by more than 120 species worldwide, convict fish are prized for their mild, white flesh and are commonly placed in aquariums due to their attractive markings.  Natural predators include a variety of inshore sharks and large fish.