325

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OBSERVATIONS ON HABITS
AND A METHOD OF TRAPPING
CHANNELED WHELKS NEAR
CHATHAM, MASSACHUSETTS

SPECIAL SCIENTIFIC REPORT-FISHERIES Na 325

u

UNITED STATES DEPtRTMENT OF THE INTERIOI
' fISH AND WILOIIFE SERVICE

United States Department of the Interior, Fred A. Seaton, Secretary

Fish and Wildlife Service, Arnie J. Suomela, Commissioner

Bureau of Commercial Fisheries, Donald L. McKernan, Director

OBSERVATIONS ON HABITS AND A METHOD OF TRAPPING
CHANNELED WHELKS NEAR CHATHAM, MASSACHUSETTS

by

William N. Shaw
Fishery Research Biologist

United States Fish and Wildlife Service
Special Scientific Report — Fisheries No. 325

Washington, D. C.
May 1960

CXDNTENTS

Page

Introduction 1

Study area 1

Food habits of Busycon 1

Estimates of channeled whelk predation 2

Trapping 3

Trap construction 3

Bait 4

Trapping procedure 4

Conclusion 5

Literature cited 6

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FIGURE 1 .--CHANNELED WHELK LAYING EGGS.

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FIGURE 2. --KNOBBED WHELK LAYING EGGS.

IV

OBSERVATIONS ON HABITS AND A METHOD OF TRAPPING
CHANNELED WHELKS NEAR CHATHAM, MASSACHUSETTS

by

William N. Shaw

U. S. Fish and Wildlife Service

Woods Hole, Massachusetts

ABSTRACT

A wooden trap for the purpose of removing the majority of channeled \v4ielks from
oyster beds was designed and successfully tested on Oyster Pond River, Chatham, Massachusetts.
In 1957 and 1948, 2, 174 channeled whelks were trapped from, a 2-acre lease. This paper gives
the design of trap, types of bait, trapping procedure, catch rate, and rate of whelk predation on
oysters. It appears advisable for oyster growers to undertake trapping operations each spring to
minimize oyster losses inflicted by the channeled whelk.

In the spring of 1957 the oyster
growers of Chatham, Mass. reported high
losses of oysters from predation by two
species of large snail, the cheinneled whelk,
Busycon canaliculatum (fig. 1), and the
knobbed whelk, Busycon carica (fig. 2). In
response to their request for help the Woods
Hole Biological Laboratory of the U. S.
Bureau of Commercial Fisheries conducted
studies in 1957 and 1958 on the habits and
possible methods of controlling these pre-
dators. Trapping appeared to be the most
efficient, safest, and cheapest method of
removing the whelks from the oyster grounds.
Since previously devised traps were ineffi-
cient, it was necessary to devise a new
type and test its operation and efficiency
in the field. This paper reports the re-
sults of those studies.

The author is indebted to J. C. Ham-
mond, commercial oyster grower, whose help
in the field made this project possible; and
to Robert K. Brighara of the U. S. Fish and
Wildlife Service for permission to publish
the photographs of the channeled and knobbed
whelk.

STUDY AREA
The study was conducted on Oyster

Pond River, a small indentation of Stage
Harbor, 2 miles west of Chatham, Mass. Depth
of water on the oyster grounds ranges from
2 to 8 feet at mean low water. The average
height of tide is approximately 4 feet.
Water salinity ranges from 29 °/oo to 32
"Ao. The substrate over most of the area
consists of fairly hard-packed sand, but in
deeper water away from shore the bottom is
rather soft owing to a higher percentage of
silt £ind clay.

This locality is near the northern
limits of distribution of the whelks. Ac-
cording to Sumner, Osborn, and Cole (1913)
the range of the channeled whelks extends
from Beverly, Mass. (north of Cape Cod) to
the Gulf of Mexico, and that of the knobbed
from Cape Cod to St. Thomas, West Indies.
Though frequently not distinguished, both
species occur throughout the length of Oys-
ter River, but most of them concentrate on
the commercial oyster beds.

FOOD HABITS OF BUSYCON

The diet or Busycon consists of
several species of pelecypods, annelids,
and occasionally dead fishes and gastro-
pods (Magalhaes 1948). Some of the more
favored species, as observed by Magalhaes

in laboratory experiments, are stout tagelus
(Tagelus gibbus) , cross-barred venus (Chione
cancellata), and quahaugs (Mercenaria (Venus)
mercenaria) . The whelks in Oyster Pond River
appeared to prefer oysters (Crassostrea vir-
ginica) , but were also observed feeding on
quahaugs and blue mussels (Mytilus edulis).

The manner in which Busycon attacks
oysters is of interest. According to Colton
(1908), the whelk crawls on top of the oys-
ter; then when the oyster opens, the snail
thrusts the edge of its shell between the
valves and introduces the proboscis. The
oyster is eaten in 40 minutes. According
to Warren (1916), the whelk opens an oyster
by grasping the bivalve in its foot and
chipping away the shell with the edge of its
outer lip. When enough shell is chipped
away, the whelk inserts its proboscis and
consumes the oyster.

We do not know the feeding rate of
channeled and knobbed whelks in nature. In
laboratory experiments conducted by Carriker
(1951) with a mixed group of whelks, each
snail consumed from 0.8 to 2.7 oysters a
week. Fifty percent of the oysters eaten
were less than three-quarters of an inch in
height; all others were larger but did not
exceed 3 inches.

In 1957 studies of the feeding rate
of whelks on oysters were undertaken. As
knobbed whelks were practically never taken
in any trap that had yet been devised, the
study consequently was limited to the chan-
neled whelk. Since most oysters on the
leases in Oyster Pond River are greater than
3 inches in height, the following observa-
tion was made on the rate of feeding of
channeled whelks on large oysters:

A lath box, 24 x 18 x 18 inches, con-
taining 6 large channeled whelks, 12 oysters
(each over 3 inches in height), and 6 large
quahaugs was placed in Oyster Pond River on
June 3, 1957. On July 1, 1957, 8 of the oys-
ters with their shells showing signs of be-
ing chipped by whelks were dead and without
meats. Four oysters and all whelks and qua-
haugs were alive, though 1 quahaug had marks
on the edge of its shell indicating that a
whelk had tried unsuccessfully to open it.

The observed rate of feeding during
this experiment was 0.3 oyster per whelk per
week. This rate probably is lower than that
which occurs under natural conditions be-
cause on several occasions the experimental

box was out of water at low tides and
presumably feeding was interrupted. The
oyster bottoms of this area are never ex-
posed at low water. Reduced circulation
inside the lath box may also have affected
the whelks' feeding rate. Thus it is rea-
sonable to assume that the results of this
experiment yielded a minimum estimate of
the natural feeding rate.

Channeled whelks are known to feed
in temperatures ranging from 60" to 72° F.
This range of temperature in Oyster Pond
River occurs at least during 5 months, June
through October, of each year. It is,
therefore, probable that the feeding of
whelks in the river continues throughout
this period.

ESTIMATES OF CHANNELED WHEIX
PREDATION

Oyster growers estimate their losses
by counting the numbers of dead oysters,
known as clappers or boxes, they find when
culling; but the percentage of these deaths
that result from whelk predation is not
known. By assuming that the consumption of
0.3 oysters per week per whelk is near the
minimum feeding rate, and that 1.8 oysters
per week per whelk (an average of Carriker's
observations) approaches the maximum feeding
rate, the following estimates of probably
whelk damage can be made for Oyster Pond
River .

Since more than 1,000 snails were
trapped annually in both 1957 and 1958 from
a 2-acre lease, we assume in the absence of
any control a minimum of 1,000 snails on
each of the 2-acre leases. At a feeding
rate ranging from 0.3 to 1.8 oysters per
week per whelk, 1,000 snails could consume
from 300 to 1,800 oysters in 1 week, or from
6,000 to 36,000 oysters during the 5-month
period. At approximately 250 oysters to the
bushel, the estimated loss of each oysterman
varied from 24 bushels to 144 bushels. We
may assume that his actual loss is near the
midpoint of the two extremes, i.e., about
80 bushels.

At the present wholesale price of
$11.50 a bushel for Chatham oysters, the
annual losses from channeled whelk predation
can be estimated at $920 for each of the
2-acre leases. This amount may appear in-
significant to large oyster compani,es, but
the loss is considerable to the oyster

side view

FIGURE 3. --TRAP USED TO CATCH THE CHANNELED WHELK.

grower in the Chatham area who markets only
about 2,000 bushels a year.

TRAPPING

Oyster Pond River fishermen have
used wooden traps of various designs to
catch whelks. The efficiency of these traps
was unknown, so in the spring of 1957, the
Bureau of Commercial Fisheries began to
test several types. The shapes of the
traps ranged from sides perpendicular to
the base to sides sloping towards the cen-
ter; heights ranged from 6 to 24 inches; and
bases ranged from 18 x 18 inches to 4 x 4
feet. The author considers the one shown
in figure 3 to be the most effective of the
traps tested.

Trap Construction

Over-all dimensions of the trap are
24 inches x 18 inches x 18 inches with sides
perpendicular to the base and ends sloped.
The framing is made of No. 2 grade pine 1
inch X 4 inches and 1 inch x 8 inches, plus
a 2-inch brace across the bottom and two

pieces of No. 16 guage wire across the top.
The frame is covered with 1-inch-mesh
galvanized chicken wire, 18 inches in width.
A piece of 16-gauge wire is woven around
the entrance to prevent the trapper's hand
from being cut on jagged ends of chicken
wire when removing the catch. Four bricks
are used to sink the trap to the bottom. A
buoy is fastened to each trap for the pur-
pose of locating and hauling it.

Traps higher than 8 inches seemed to
discourage snails from crawling up to the
opening in the top. Traps lower than 8
inches decreased the holding capacity; occa-
sionally they became so crowded with snails
that some were unable to enter. The width
of 18 inches was selected because chicken
wire is available in this size and could be
tacked to the frame without trimming. Chick-
en wire 24 inches in width is also available
on the market but was considered impracticcd
because it would require a larger trap jLnd
increase the cost of construction.

The cost of building 12 traps used
in the experiments was $45.38. Materials
and labor costs follow:

18 feet of 1 X 2 inch No. 2 grade pine ($.03/lineal foot) . , , $ 0.54

36 feet of 1 x 4 inch No. 2 grade pine ($.09/lineal foot) . . . 3.24

48 feet of 1 X 8 inch No. 2 grade pine ($.19/lineal foot) ... 9.12

58 feet of 18-inch wide, 1-inch mesh chicken wire

($9. 00/150-foot roll) 3.48

Miscellaneous (rope, bricks, staples, and buoys) 5.00

Total cost of materials $21.38

Total labor (16 hours at $1.50/hour) 24.00

Grand total $45.38

1200
I 100
1000
900
800
700
600
500
400
300
200
100

10

FIGURE 4.

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1 1

1957

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1 — 1 — I — .1 1

20
MAY

10 20
JUNE

29

-CUMULATIVE CURVE OF CHANNELED WHELKS
TRAPPED IN 1957.

Bait

Mussels, quahaugs, cind horseshoe
crabs (Limulus polyphemus) were all tried
as bait. Only horseshoe .crabs with their
shells broken to expose the meat proved
effective in attracting the channeled whelk;
the other baits tested failed to attract
snails. Each trap was baited with one or
two horseshoe crabs. When traps were hauled
old bait was removed and fresh crabs added.

The trapping of whelks correspond
with the period when horseshoe crabs were
migrating from the open ocean to the shallow
water of Oyster Pond River. Since the crabs
visited the river for only a short duration,
less than 2 months, it was necessary to col-
lect a good supply just before trapping was
initiated. A wire pen was installed near the
trapping area to hold the crabs. To prevent
them from escaping, the bottom of the pen

was buried a foot below the surface and the
top bent inward to form an inverted V.

Trapping Procedure

Trapping was conducte
2-acre leases in Oyster Po
May 20 to June 27, 1957, and
June 30, 1958. Initially,
traps with 70 feet between t
on the lease. It was 100 fe
in line with the river flow,
were built, we used 12, whic
the direction of river flow
rows, one row 70 feet offsho
130 feet.

d on one of the
nd River from
from May 12 to
one row of six
raps was placed
et offshore and
As more traps
h were set in
in two parallel
re and the other

The traps were fished and reset on
Monday, Wednesday, and Friday of each week.
Daily catches were less in fouled traps than
in clean ones; therefore, traps heavily
fouled with algae were taken out of water
for a day to be dried and cleaned.

I 100
1000 ■
900 ■
800
700 ■
600 ■
500
400
300
200
100
OL

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1958

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1 1

1

20
MAY

10 20 29
JUNE

FIGURE 5. --CUMULATI VE CURVE OF CHANNELED WHELKS
TRAPPED IN 1958.

In the 2 years of trapping, 2,174
channeled whelks were caught, 1,122 in 1957
and 1,052 in 1958. The cumulative curves
for total numbers of channeled whelks caught
in 1957 and in 1958 (figs. 4 and 5) indicate
that after 50 percent of the total catch
was taken, the rate of trapping gradually
declined. In 1957, more than 80 percent of
the total catch was attained during the
first 2 weeks of trapping; in 1958 a month
passed before the same percentage was
reached.

Because almost equal numbers of
snails were caught in 1957 and in 1958 from
the same oyster bed, it appeared that whelks
were moving to the oyster bed from other
localities. When trapping was terminated in
1957, the rate of capture was less than 2
snails per trap per day (fig. 6), yet during
the first 10 days of trapping in 1958, the
rate was as high as 6 snails per trap per
day (fig. 7). It is probable the high ini-
tial rate in 1958 was due to an influx of
snails from other localities. When trapping
was terminated in 1957, very few channeled
whelks were observed on the study area.
This suggests that the success in trapping
in 1958 is related to snail movement; there-
fore, it is advisable for oyster growers to
undertake trapping operations each spring
to minimize whelk predation.

FIGURE 6. --THE NUMBER OF CHANNELED WHELKS CAUGHT
PER DAY PER TRAP IN 1957. {SURFACE TEMPERA-
TURE WAS TAKEN WHEN TRAPS WERE FISH.)

JUNE

FIGURE 7. --THE NUMBER OF CHANNELED WHELKS CAUGHT
PER DAr PES TRAP I:J 1358. (SURFACE TEMPERA-
TURE WAS TAKEN WHEN TRAPS WERE FISHED.)

Trapping was initiated when the
rising water temperature reached a 50° F.
level. There is some indication that as
the temperature rises the number of whelks
per day per trap decline (figs. 6 and 7).
Generally, the greatest number of whelks
were caught when the traps were first placed
on the beds, after which a slow decline oc-
curred. Although temperature may have some
effect on the behavior of snails, a more
logical explanation is that the decline in
catch rate resulted from a decrease in the
abundance of snails. Trapping was termi-
nated for the year when the rate fell below

1 snail per trap per day or when the rate
was below 2 snails per trap per day for more
than 2 consecutive weeks.

During the 2 years of trapping only

2 knobbed whelks were caught, although from
visual observations the beds were heavily
populated with this species. Hence there
is no known method for trapping knobbed
whelks, they must be controlled by mechani-
cal methods, such as dredging and tonging,
or be picked up by skin divers.

CONCLUSION

The damage caused by whelk predation
is often overlooked by many oyster growers.
When drills and starfish are present on
oyster beds, little concern is given to the
whelk as a serious predator. From labora-
tory and field observations it is apparent

that whelks can do a considerable amount of
damage; and if they are present on the oys-
ter beds, trapping should be conducted each
spring to keep them under control.

By using the method of trapping de-
scribed in this report most channeled whelks
can be removed from an oyster bed. Because
each oyster lease varies in size and shape,
the oyster grower can determine by trial the
number of traps to be used on his grounds
and their most effective arrangement.

COLTON, H,
1908.

How Pulgur £ind Sycotypus eat oys-
ters, mussels, and clams. Pro-
ceedings of the Academy of Natural
Sciences of Philadelphia, vol. 60,
pp. 3-10.

MAGALHAES, HULDA.

1948. An ecological study of snails of
the genus Busycon at Beaufort ,
North Carolina. Ecological Mono-
graphs, vol. 18, pp. 377-409.

LITERATURE CITED

CARRIICER, MELBOURNE ROMAINE.

1951. Observations on the penetration
of tightly closing bivalves by
Busycon and other predators.
Ecology, vol. 32, No. 1, pp. 73-
83.

SUMNER, F.
L.
1913.

WARREN, S.
1916.

B., R. C. OSBURN, AND
J. COLE.

A biological survey of the waters
of Woods Hole and vicinity. Bul-
letin of the Bureau of Fisheries,
vol. 31, (part I), (1911), 544 pp.

Feeding habits of Busycon .
Nautilus, vol. 30, pp. 66-68.

MS #913

INT.DUP..D.C,60- 752m

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