Black
Sea Bass Aquaculture
by
Chip Cotton
Aquaculture is one of the oldest forms of agriculture known to man.
In China, people have been "farm raising" fish for many centuries
but only recently has the United States begun to culture fish on a large
scale. The culture of marine fish, or mariculture, has been particularly
slow to gain popularity in this country. For decades, harvesting fish
from the wild has been seen as the economically advantageous method
for fishermen, so there has been little demand for mariculture in the
United States. With the decline of world fisheries, this country, along
with the rest of the world, will have to turn to aquaculture in order
to support the current levels of fish consumption. In certain cases,
it has been proven that a cultured product, often younger, smaller or
faster growing than in the wild, can greatly improve market price of
that species. For example, cultured growth rates of the hard clam or
quahog (Mercenaria mercenaria) are significantly higher than
natural growth rates. The cultured product is a small, tender, desirable
clam as opposed to the wild clams, which may be large, tough and undesirable.
The availability of food in the wild is usually quite low for carnivorous
finfish, like the bottom-feeding, black sea bass. Cultured fish, however,
can be fed to satiation on a daily basis thereby greatly increasing
growth rates. Also, since the farmer determines the diet of the fish,
he can control the nutritional intake which influences health, flavor,
appearance and ultimately, marketability of the fish.
 Black
sea bass (Centropristis striata) is a protogynous hermaphroditic
serranid. In layman's terms this means that they can change sex (hermaphrodite)
and that they begin their lives as females and later change into males
(protogynous). Also, they belong to the Serranidae, or grouper, family.
Black sea bass are commonly found along the North Atlantic coast from
Maine to the Gulf of Mexico, primarily associated with live-bottom reefs,
sponges, wrecks and other similar structures. One of the most popular
bottom fish in North America, it is commonly sought after by both commercial
and recreational anglers. In Georgia, sea bass are possibly the most
conspicuous residents of the live-bottom reefs, such as Gray's Reef
National Marine Sanctuary. Other species often confused with C. striata
include C. ocyurus, the bank sea bass and C. philadelphicus,
the rock sea bass. Neither of these species reaches a marketable size
and therefore is not considered to be commercially valuable
Until recently, regulations were unnecessary for black sea bass due
to their large population size. The commercial demand for sea bass has
historically been low mainly due to the higher market price obtained
by their relatives, the groupers. Grouper populations have been heavily
depleted in recent decades, and as a result they have gone the way of
most other fisheries. As populations of top predators decrease, fishermen
begin to harvest lower predators and omnivores. This has resulted in
the harvest of more black sea bass. Also, in the past, sea bass have
not been highly prized by recreational anglers. But recently, due to
the increased numbers of anglers (both recreational and commercial)
in coastal and nearshore waters, the need for regulation has arisen.
The Fishery Management Plan for Black Sea Bass was approved by the Atlantic
States Marine Fisheries Commission in October 1996. This was the first
regulation designed specifically for black sea bass and it implemented
an 8-inch size limit on both commercial and recreational anglers as
well as some other gear restrictions. In February of 1999 that size
limit was increased to 10 inches along the Atlantic coast. What was
once a plentiful, relatively unimportant fish commercially is now heavily
regulated. Charter boat captains complain that the sea bass used to
be their "bread and butter." When a chartered fishing trip
ended unsuccessfully, captains could always count on being able to stop
at the nearshore reefs and load up on sea bass so their customers wouldn't
go home empty-handed. Now with the decreased numbers of sea bass and
the 10-inch limit, these captains find that catching large numbers of
legal size sea bass is difficult.
Previous
aquacultural research dating back to 1970 has focused primarily on spawning
and hatchery techniques for sea bass. This research includes work done
in Florida on a subspecies, C. striata melana, the southern sea
bass. The methodology of spawning and hatchery care is well documented,
but research is lacking in the growth of hatchery-reared fingerlings
to market size, about 2 pounds. Most conclusions of previous research
indicate that black sea bass is an excellent candidate for aquaculture.
A substantial portion of the sea bass demand is in the live fish market
of the northeast United States. Fishermen trap sea bass and transport
them live to the market for sale to a largely Asian clientele. A resourceful
fisherman in McIntosh County came up with the idea that live sea bass
could be farm raised for a sizable profit. He came to the University
of Georgia Marine Extension Service for consultation and research was
begun to develop methods for culturing black sea bass in recirculating
tank systems. The method of trapping wild sea bass for culturing is
not a sustainable solution to the problem, so the Marine Extension Service
contracted a hatchery to spawn sea bass. The hatchery was to produce
fingerling size fish (1-3 inches long) for experimentation and ultimately
for the industry. The goal was to provide an economically viable and
sustainable method for culturing hatchery reared fingerling sea bass
to market size of about 900 grams.
Research is ongoing at the Shellfish Research Lab (SRL)
on Skidaway Island and initial results have been positive. The sea bass
have exhibited much higher growth rates in captivity compared to natural
growth rates. For example, a very liberal estimate of growth from a
5-gram fingerling to a 900-gram (2 pounds), marketable adult is one
and a half years, compared to the six or seven years it would naturally
take the fish to reach that size. Also, initial experiments were conducted
in flow-through tanks, which subjected the sea bass to often deleterious
water quality. They exhibited high resilience to poor water quality,
such as high ammonia, very high water temperatures (93 F), low dissolved
oxygen and high turbidity (cloudiness). This high growth rate, tolerance
of poor water quality, and the promise of high market prices for live
fish make the black sea bass an excellent candidate for a fish farmer.
Both research and marketing projections indicate that black sea bass
will prove to be an excellent species for mariculture. They are easily
grown, exhibit rapid growth in captivity and are quite hardy fish. Also
the live market demand for sea bass insures a substantial profit for
the product. Being a member of the grouper family, black sea bass has
a very desirable appearance and taste. For these reasons, the future
of black sea bass aquaculture in Georgia looks quite promising.
(Chip Cotton wrote this as a graduate student working with the MAREX
Shellfish Research Lab)
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Habitat
Heros
by
John "Crawfish" Crawford
A local TV station has an award they give to "Home town heroes".
The recipients are folks who make positive contributions to their communities.
We have some neighbors in surrounding communities who are unsung heroes.
I am speaking of a diverse group, in fact, they do not even all belong
to the same Phyla. But, they do make a positive contribution to their
respective biological communities. They are called keystone species.
You are, no doubt, familiar with some of these important species. But,
you may not realize just how valuable they are and just how many other
species depend on them.
 One
of the best known of these keystone species is the Beaver (Castor
canadensis). This industrious mammal helps control water levels
in and sometimes even helps creates wetlands themselves. The beaver's
damming of seasonal streams can mean life or death for numerous species
including insects, crustaceans, fish, amphibians, reptiles, birds and
mammals. Although trees are "eaten" or cut down by the beavers
during dam construction, wetland plants benefit greatly. Beaver ponds
are valuable reservoirs during droughts. In the southeast, with our
rich water resources this beaver accomplishment is not appreciated and
the species is even considered a pest. This is mainly because beaver
activity can flood commercial pine plantations. our financial well being
seems to take precedence over the needs of all other species.
A walk on any of Georgia's ocean beaches at low tide takes you over
the hidden realm of the Ghost Shrimp (Callianassa biformis),
another keystone species. It takes some imagination to "see"
this habitat and understand the shrimp's value. The visible evidence
of this important species is just small holes in the wet sand with "chocolate
sprinkles" scattered around the openings. The shrimp (more closely
related to hermit crabs) can be as much as six feet down with in its
extensive burrow system. It is not alone. Other species use this habitat
for their living space. Worms, copepods, crabs and even fish spend some
or all their lives here in these protected retreats. The pumping action
of the shrimp's abdominal appendages bring oxygenated water and food
for itself and their roommates. The large amount of fecal material pumped
outside the borrows enriches the beach community and provides food for
other species including crabs, sand dollars and even fish. Millions
of these secretive crustaceans inhabit our beaches and their contribution
to beach productivity is enormous.
The State of Georgia has honored one of our keystone species. The gopher
tortoise (Gopherus polyphemus) is Georgia's official state reptile.
It is listed in our state as a "threatened species" which
means it is close to becoming endangered. State reptile or not, this
species is in trouble and a number of other species along with it. The
"gopher", as it is known over it's range, has the unique habit
of digging burrows as life long retreats. These borrows can be very
long and deep. Some "gopher burrows"measure over thirty feet
long and up to 12 feet deep. The temperature and humidity in the depths
of these holes stay constant year-round. The Gopher's habitat is sandy
soil areas on the coastal plain known as sandhills. Unfortunately, much
of this habitat is turning into residential communities and tree farms.
Neither of which the tortoise can survive. And when it goes so do its
"dependents".
Gopher burrows are home and refuge for many species. At least 32 species
of arthropods call these "cave like" holes home. Gopher Frogs,
Red-tailed skinks, diamondback rattlesnakes and another threatened species,
the Eastern Indigo Snake, utilize these climate controlled habitats.
Burrowing Owls, foxes, opossums, raccoons and rodents also have lived
in them. In short, the gopher tortoise makes life possible for numerous
other species of animals. There is evidence that the tortoise's feeding
activity may improve growing conditions for native grasses. Humans also
have utilized the gopher. Unfortunately, they have done soby making
a quick meal of an animal that grows slowly.
The last keystone species I would like to discuss is one of the most
important and misunderstood, the American Alligator (Alligator mississipiensis).
We often hear that the alligator has made a quite a comeback as well
as exaggerated tales of its threat to humans. Its numbers were decimated
by hide hunters, but protection under the Endangered Species Act gave
it a chance for recovery. They are once again numerous in southern wetlands,
rivers and swamps but, so are humans ... much more numerous. And, we
are far more dangerous to the gators than they are to us.
 The
alligator's value to the ecosystem does not result from the fine leather
products that can be made from its hide. Nor is it the novelty dishes
restaurants serve out of its meat. The stuffed gator heads sold at fairs
and flea markets are small change compared to its real value. Even the
cash tourist spend to see gators at wildlife parks can't compare. Their
real value is something much more basic: they dig holes. We call them
"gator holes". The gator hole's value to the ecosystem is
most apparent during the dry times of year. During drought years, this
becomes even more evident. Alligators dig large depressions in the bottoms
of ponds and marshes. They maintain these pools even when the rest of
the pond or swamp has dried up by digging down into the groundwater
level. Fish, frogs, salamanders, birds and mammals all utilize these
"wells". In fact, the Okeefenokee Swamp alone has over 40
species of fish that depend on gator holes for survival. On our barrier
islands, where fresh water is limited to rain-filled sloughs, gator
holes are the only place for deer and other animals to drink or wait
out the drought.
We can easily understand the value of drinking water for wildlife or
even the fact that fish need water in which to live. But, the value
to the ecological balance goes even further. When the rains come again,
those fish will breed and spread out over the whole refilled pond. They
will feed on insects (more fish... fewer mosquitos). Birds will feed
on the fish and we can enjoy their beauty. It is a lot more complicated
than this, but you get the idea. The alligators also create "trails"
which allow fish, etc to move around the wetlands. This is especially
important in vegetation-filled fresh-water marshes like the Okeefenokee
Swamp or Everglades National Park. Alligators "patrol" under
wading bird colonies which are usually in trees surrounded by water.
This prevents predators, like the raccoon, from having easy pickings
on the eggs and young birds. Of course, alligators are happy to eat
young birds that fall from the nest. Good security comes at a price.
There is definitely a positive relationship between alligator protection
and successful nesting of our wading birds including the endangered
wood stork.
The removal of a large alligator from a natural pond system can destroy
the entire ecological balance making it much less hospitable, not only
us, but countless other species as well. Even though alligator populations
have increased, the size structure is tilted towards small and medium
specimens. Large gators (over 12 feet) excavate largerr and deeper "gator
holes" which can withstand severe droughts. The math is convincing:
larger "holes" mean greater numbers of animals benefit and
survive droughts, and the ecological balance is improved.
There are many other keystone species and our understanding of their
place in the scheme of things is only just beginning. We can learn how
to live in closer harmony with our environment by studying our "habitat
hero" neighbors.
John
"Crawfish" Crawford is one of MECA's senior educational faculty
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Marine
Polychaetes- A Lively Spawning Event
By
Maryellen Timmons, Ph.D.
You may have noticed swarms of worms in the rivers, by your docks, or
heard about them from a friend. They seem innumerable, but make no mistake,
you are seeing worms, billions of them! So what are they, and what are
they doing? These worms are most likely one of our common species of
worm, Nereis succinea, also called the clam or blood worm. It
is a marine relative of the common earthworm called a polychaete. Polychaetes
are segmented just like the earthworms, however, they have parapodia
(analogous to legs) that extend outwards from each segment. These parapodia
have bristles (called setae) that, along with muscular contractions,
help the worm move forward. Unlike the common earthworm, whose muscular
contractions move from front to back, the marine polychaetes have muscular
contractions that move from the rear forward. These contractions actually
produce forward movement!
This
worm is a benthic (bottom-dwelling) organism commonly found among oyster
beds and along docks, crawling around other organisms such as sea squirts,
barnacles, and algae. It can be found in all benthic habitats except
the outer beaches. The clam worm, Nereis, provides an important
nutritional resource for our fish populations. If you look at the head
of the worm you can see that it has two formidable jaws, as well as
two rings of hard small teeth in its pharynx (just behind the mouth).
These come into play when feeding; the worm protrudes its pharynx and
its jaws come forward.
Surprisingly the clam worm feeds on surface detritus and is a very generalized
feeder. The jaws are used for protection as well as for feeding. Reproduction
in marine polychaete worms often can be quite spectacular by human standards.
In Samoa a polychaete worm called "Palolo" (genus Eunice
) spawns according to the lunar cycle. One week after the October and
November full moons the worms swarm to the surface at dawn and create
an image of wriggling brilliant colors covering the surface of the water.
This massive spawning is an image not soon forgotten. The Samoans collect
the brilliantly colored worms, eat some on the spot, and then have a
large feast afterwards. They don't actually collect the worms, they
collect the reproductive portions of the worms called epitokes. The
adult worms will produce a gamete-filled (containing eggs or sperm)
tail portion which will be released to the surface. The adult worms
in Samoa actually dwell in mucus-lined burrows in the crevices of the
reefs. Though just a reproductive portion of the worm, the epitokes
do have small eyes, and can be up to one foot in length! Once on the
surface, the tails (epitokes) will explode, and the gametes will be
released en masse when the sun rises. The epitokes are brightly colored;
the females are blue (and better tasting!), while the males are greenish
blue.
Here
in Georgia our spawning version of the Palolo worm is just as spectacular.
During March, April, and May, our local clam worms also follow a lunar
cycle and rise to the surface for a spawning event. Our clam worms,
however, have formidable jaws even on the reproductive individuals.
These reproductive males and females, called heteronereids (hetero from
the Greek meaning different, as in two different sexes) are brilliant
red, white, and black during spawning and look like small fish wriggling
at the surface of the water. After the spawning event the fertilized
eggs become part of the plankton, and are in turn food for other species
such as crab, shrimp, and oysters. Our clam worm is not a burrower like
the Samoan version and can be found if you look closely at the organisms
attached to a dock. If you happen to come across a spawning event, take
a good long look, or quickly collect some to view, since the event doesn't
last long!
Dr.
Maryellen Timmons is one of MECA's senior education faculty
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A
Right Whale in the Wrong Place
by John Crawford
I first learned
about the state marine mammal of Georgia when a newborn male right whale
washed ashore on Little Saint Simons Island early in January of 1982.
I was part of the team that did the necropsy on this endangered species.
The infant was approximately 15 feet 4 inches long and about 200 lbs.
It was probably stillborn since no milk was found in its stomach and
the intestines contained meconium (a fetal bowel accumulation) that
is usually expelled soon after birth. Little did I know that years later
I would be helping with the necropsy of a large adult male who was possibly
this infant's father.
Sometime around the 26th of 1996, one of the rarest animals on the planet
was swimming slowly along the coast of Georgia on a course it had undoubtedly
followed many times before. It was in the right place heading north
for a summer of feeding in the plankton-rich waters off New England.
Unfortunately, by coincidence, it picked the wrong time. "Lindsey,"
as he was known to researchers, a healthy Northern Right Whale, Eubalena
glacialis, was killed by a collision with a large vessel. Lindsey
first became known to whale researchers when he was photographed in
1985. In 1986 He was entered into the identification catalog and given
the number 1623.
He was named Lindsey after a Daniel's Head, Nova Scotia fisherman who
"adopted" the research teams during the summer of 1988. Lindsey
proved on numerous sightings to be an "Alpha" male, who was
often spotted in the middle of courtship groups, having pushed other
males out of the way to get next to the female.
 On
January 30th, 1996, a private vessel reported sighting Lindsey's floating
carcass about 10 miles off of Blackbeard Island. After a small vessel
made several vain attempts to tow the whale, the Marine Extension Service
vessel, Georgia Bulldog, managed to begin moving Lindsey towards Harris
Neck National Wildlife Refuge. Moving slowly, Captain Lindsey Parker
of the Georgia Bulldog managed to maneuver the whale up a narrow creek
to the refuge. Waiting at Harris Neck was a large group of U.S. Fish
and Wildlife Service and Georgia Department of Natural Resources personnel.
Also in attendance were members of the press and curious onlookers.
It took several hours, two bulldozers, a huge CAT backhoe and quite
a bit of skill to pull Lindsey's 40-ton body out of the water. Once
the hawsers were removed, the public was allowed to approach the whale.
Awe was apparent on every face. This was the largest animal most of
us had ever seen.
Once the whale was on land, the necropsy team began its work. Barb Zoodsma
and Mike Harris (GA DNR) coordinated the stranding response team. Because
it was nearly 6 PM, not much was accomplished the first day. However,
biologists did measure the blubber thickness during that evening and
night. They also tested the satellite transmitter and tagging technique.
The main necropsy effort, scheduled for 9 AM the next morning, was headed
up by Bob Bonde of the US Fish and Wildlife Service.
Most available staff from MAREX headed south to Harris Neck to assist
in the necropsy efforts. Once suited up (in complete foul weather gear
and boots) we took measurements, removed blubber, collected isopods,
exposed the tiny ear opening, fleshed out bones, and hauled tons of
flesh away from the huge animal. Photographs and video footage were
taken and should prove very useful in our educational program.
Late in the day, we discovered the cause of death. As we removed the
scapula, we saw that it was chipped and the ribs under it were fractured.
Then we began trying to measure the impact area by uncovering the bruised
flesh and blubber. As we exposed the back of the gigantic skull we could
see into the brain case. The skull had been crushed. Lindsey died instantly,
and the ship probably did not even know it hit something.
This has been a bad year for right whales. The week after Lindsey died,
a dead female was reported floating about 40 miles off Fernandina Beach,
Florida, but was too far offshore and no attempt was made to reclaim
it. On February 19, an 18-foot infant right whale was spotted floating
about 20 miles off Cumberland Island by Georgia DNR during an aerial
survey of the coastal waters. This baby was taken to the veterinarian
hospital at the University of Florida, Gainsville, for necropsy. It
is feared that collision with a ship was again the cause of death.
The northern right whale has been an important part of this country's
history. Its oil and baleen were vital to our cultural and industrial
development before the advent of fossil fuels and plastics. We have
never given credit where it was due. Declaring this species the state
marine mammal of Georgia is a step in the right direction, but most
Georgians do not realize that our coastal waters and those of northern
Florida are the right whale's only known calving grounds. With less
than 350 of these magnificent animals in existence, we must find ways
to pull them back.
John Crawford
is one of MECA's senior education faculty
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Living
Precariously in the Food Chain
by Dr. Randy
Walker
Sunlight is the ultimate source of energy for life on earth. Sunlight
provides the fuel for photosynthesis. Plants use photosynthesis to capture
the energy from the sun and convert the energy to matter. Herbivores
feed off of the plants and the carnivores prey upon the herbivores.
Animals such as sharks that feed on other animals are called predators,
while animals eaten are referred to as prey. The flow of energy through
plants to predators is referred to as a food chain. Food chains may
become quite complex depending upon the number of organisms present
in a habitat. For instance, a simple food chain would be a whelk, a
marine snail, that preys on oysters. Oysters, marine bivalves, filter
the water and consume single celled marine algae called phytoplankton.
Marine algae utilize sunlight to grow. Thus, energy moves from the sun
to the algae, to oysters, and to the whelk. A more complex food chain
would be the algae supporting the oyster, which is eaten by the whelk,
which in turn may be eaten by the horse conch, which could be eaten
by a stingray, which may be eaten by man. The horse conch could feed
directly off of the oyster. Man of course also can eat the oyster, whelk,
or horse conch.
 In
the coastal waters of Georgia, four different species of predatory whelks
occur. Whelks belong to the family Melongenidae. The whelk species are
: the knobbed whelk, Busycon carica; the lightning whelk, Busycon
sinistrum; the pearwhelk, Busycotypus spiratus; and the channeled
whelk, Busycotypus canalicatum. The knobbed whelk is the most
abundant species and supports an offshore fishery in Georgia.
Whelks are predators, but they are also scavengers. Whelks will prey
on a wide range of species, but concentrate on marine bivalves such
as oysters, clams, mussels, scallops and arks. They will also eat dead
animals such as dead fish or crabs. Whelks are slow moving snails, so
they can not hunt down a fast moving fish or crab. But if something
else killed the crab or fish and left parts of it behind, whelks will
feed off the recent or decayed remains.
In Georgia, whelks generally occur in the subtidal areas or in underwater
areas below the lowest tidal level. However, in spring and fall, whelks
can be seen migrating onto the intertidal flats, areas exposed at low
tide, in search of oysters and clams. A whelk moves by crawling along
on its large massive muscular foot. During summer and winter when the
whelks cannot survive the high and low air temperatures, they remain
in subtidal areas. In the subtidal areas, whelks search for the various
species of arks to feed upon.
Arks, the subject of my initial quest, are a primitive form of marine
bivalve which feed on phytoplankton as an oyster does. Arks belong to
the family Arcidae and numerous species occur in the coastal waters
of Georgia. The three larger sized and more abundant species are: the
blood ark, Anadara ovalis; the incongruous ark, Anadara brasiliana;
and the ponderous ark, Noetia ponderosa. The blood ark occurs
inshore to just offshore, the incongruous ark lives in sand along the
coastal beaches to approximately 2 miles offshore, and the ponderous
ark inhabits muddy-sand bottoms primarily in offshore areas. The blood
and ponderous arks occur in muddy-sandy to muddy bottoms. All species
reach a shell length of approximately 2.5 to 3 inches. Generally, the
incongruous ark has a clean white to yellowish colored shell. This ark
is the species commonly found washed up along our coastal beaches. The
blood and ponderous arks are covered with a brown to black hairy-like
outer covering called a periostracum. The periostracum helps to keep
the animal from sinking in mud bottoms and is believed to act as a predator
prevention device. The periostracum, which is slippery when wet, helps
to keep the whelk from holding the ark in its muscular foot.
Whelks will prey on marine bivalves in two ways. If the bivalve is small
enough or has a thin shell, the whelk will crush the shell in its large
muscular foot. If unable to crack the shell, the whelk will hold the
prey in its foot. The whelk will then continuously rub the bivalve’s
shell at its margin against its own shell along its shell’s outer
whorl. By continuously scraping the bivalve shell, a small thin hole
will form along the margin of the shell. When the hole is wide enough,
the whelk will insert its proboscis through the hole into the bivalve
shell. Within the proboscis is series of teeth called a radula. The
radula is used to shred the animal which is then passed to the whelk’s
mouth and ingested.
Arks use byssal threads during their early life history in order to
keep from being washed away with the currents. As very small juveniles,
the size of a sand grain, many marine bivalves have the ability to attach
to solid objects by cementing numerous tiny threads produced from a
gland located in their foot to various objects located on the sea bottom.
Many bivalves only use byssal threads for the first few weeks of life.
Some species of arks and scallops use byssal threads only during three
to six months of their juvenile stage of life. A few bivalves species
such as mussels may use byssal threads throughout their life. Arks generally
attach to any item found on the bottom, including worm tubes, rocks,
oysters, dead shells, adult arks, etc.
Last summer, while trying to collect live blood arks to perform some
growth studies, I was informed that I could collect some small, live
arks from the beach on St. Simons Island. I did indeed find the arks.
The easiest means of collecting them was to find a knobbed whelk which
could easily be located in the surf by hand or foot. By pulling up the
foot long whelk, we found anywhere from 1 to 14 arks attached to the
shell of the whelk. The arks were attached to the whelk’s shell
by byssal threads and were approximately the size of a quarter. Attaching
to the shell of a whelk ensured that the baby arks were not washed away
by the constant wave action in the beach surf; however, attaching to
the back of a whelk, one of its main predators, is like trying to ride
on the back of a tiger. If you fall off, you can be eaten.
Dr. Randy Walker
is the Director of the University of Georgia's Marine
Extension Service, and the Shellfish
Research and Aquaculture Laboratory
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Whelk
Studies
By Todd Recicar
During the winter
months when the shrimping season closes in Georgia, some local fishermen
put away their shrimp nets and install heavier duty nets to begin trawling
for whelks. Whelks, which are large-sized marine snails, support a major
fishery in Georgia. There is a large market for whelks in northeastern
U.S. cities where they are sold as seafood in ethnic markets and restaurants.
Italian restaurants use whelks in a dish called scungilli, but whelks
(sometimes sold as the more familiar ‘conch’) can also be
used in snail salads and for fritters. Georgia fishermen trawl for whelks
during the winter months after the close of the shrimping season and
into early spring.
Harvesting
There are four species of whelks in Georgia: the knobbed whelk, Busycon
carica; the lightning whelk, Busycon sinistrum; the channeled whelk,
Busycotypus canaliculatus; and the pear whelk, Busycotypus
spiratus. These whelks are harvested using various methods. Offshore
trawling for the knobbed whelk accounts for the majority of the whelks
caught and sold in Georgia. Whelks are generally found crawling on or
partially buried in the soft sea floor. Trawling for whelk is similar
to shrimping, but the nets are designed a little differently. Whelk
nets have larger holes or meshes than those found in shrimp nets. Whelk
nets also have a heavier chain installed in the front of the net so
that the whelks can be harvested below the sediment. In addition, blue
crab fishermen harvest the channeled whelk as a by-product of their
fishery. The channeled whelk will enter a crab trap in search of the
bait; other local species of whelk usually will not. Finally, oystermen
and clammers will pick up knobbed whelks, lightning whelks, and channeled
whelks from the intertidal zone while gathering oyster and clams. Whelks
will migrate seasonally into the intertidal zone to prey on oysters
and clams in the spring and fall. Whelks tend to migrate off the intertidal
flat during summer and winter months, possibly to avoid extreme high
and low temperatures.
Life History
We know very little about the life history of the various whelk species
inhabiting our coastal waters. Large numbers of knobbed whelks typically
occur in Georgia, with pear whelks occurring rarely. The largest sized
whelk is the lightning whelk, which may reach sixteen inches in length
versus the knobbed whelk which reaches only nine inches in length. The
channeled whelk reaches seven inches, while the pear whelk grows to
only four inches. The Busycon species have a thicker and heavier
shell than the Busycotypus species.
Whelk eggs resemble a telephone cord but actually consist of a number
of separate capsules attached to a “string”. Each capsule
may contain from 0-20 eggs depending on the species of whelk and the
location of the capsule on the string. Frequently the first 5-15 capsules
are empty, with the number of eggs per subsequent capsule increasing
toward the end of the string. Since the beginning of the string is buried
in the substrate as an anchor and the eggs may not be able to survive
under the substrate, the female may be conserving energy by not placing
eggs into these capsules. Energy conservation is very important at this
stage in the female’s life; laying a string of over 100 capsules
may take days to produce! This process can be very strenuous to the
female!
Most marine mollusks have external fertilization of eggs in the water
column, followed by a planktonic larval development phase. However,
when the female whelk deposits egg capsules, the embryos inside are
already fertilized. This is because fertilization is internal in these
species of whelks. This makes them unique compared to most mollusks
in that the young hatch out of these capsules as fully formed juveniles.
Management
Gathering life history information on whelks is very important if we
wish to wisely manage this natural resource. Information on growth rates
of the various species, sex ratios, and reproductive patterns is required
to manage this fishery. For instance, offshore trawling for whelks occurs
in the early spring when whelks deposit their eggs. The large mesh size
of the nets that are used during this process gather the larger-sized
females, while allowing the smaller-sized males to pass through the
net. The danger in this harvesting schedule is that the fishery is removing
the females from the population at a greater rate than the males. In
addition, shrimping in offshore areas during the fall occurs when whelks
are once again depositing their eggs. Therefore, both the whelk and
shrimp nets are dislodging the egg case strings that contain the juvenile
whelks. Once the egg case strings are dislodged, they wash up on the
beach and desiccate. In terms of reproductive biology, females are the
important sex. Thus, when a fishery removes reproductive females from
the population, while at the same time removing the egg cases, the fishery
may be headed for trouble.
Tagging Studies
That is where our tagging studies come in. We want to learn as much
as possible about the life history of whelks in order to protect the
fishery and the whelk populations of Georgia. This may prevent the decline
in both whelk populations and fishermen’s paychecks! We will be
gathering valuable data for three of the species: knobbed, lightning,
and channeled whelks. This data will be used to develop scientific information
needed to wisely regulate the whelk fishery in coastal Georgia. To date
we have tagged nearly 10,000 whelks and released them in the Wassaw
Sound area. Whelks have been released at Cabbage Island, Pa Cooper Creek,
Dead Man Hammock of Wassaw Island, Mud Island, and at the mouth of House
Creek, Little Tybee Island. Prior to their release, each whelk was measured
for its shell length and width, and then tagged with an individual marker
specific to that individual whelk.
Our objective is to find as many of these tagged whelks as possible.
By doing this many times over the next couple of years, we hope to be
able to generate the data required to determine the natural growth rate
of the various whelk species. Furthermore, by determining where the
whelks are at each sample period, we hope to document migrational patterns
for the whelks.
Most of the released whelks were collected by the crew of the R/V GEORGIA
BULLDOG. The crew is presently attempting to design and test a Turtle
Excluder Device (TED) for use by the conch (whelk) industry in Georgia
to prevent the drowning of sea turtles. Whelks gathered by the GEORGIA
BULLDOG were collected from the south shipping channel of St. Simons
Sound.
Todd
Recicar was a research technician with the University of Georgia's Shellfish
Research Laboratory
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