NOAA Technical Memorandum NMFS NE 155
Food of Northwest Atlantic
Fishes
and Two Common Species
of Squid
by Ray E. Bowman1,2, Charles
E. Stillwell3, William L. Michaels1,
and Marvin D. Grosslein1,4
1Woods
Hole Lab., National Marine Fisheries Serv., 166 Water
St., Woods Hole,
MA 02543
2Current Address: 38
Hilltop Rd., Mashpee, MA 02649
3[Deceased] Narragansett
Lab., National Marine Fisheries Serv., 28 Tarzwell Dr., Narragansett, RI 02882
4Current Address: 23
Fairway Ln., West Falmouth, MA 02540
Print
publication date January 2000;
web version posted October 18, 2001
Citation: Bowman RE, Stillwill CE, Michaels WL, Grosslein MD. 2000. Food of Northwest Atlantic
Fishes and Two Common Species
of Squid. US Dep Commer, NOAA Tech Memo NMFS NE 155; 137 p.
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Abstract
This paper provides a reference document for researchers interested
in the types of prey eaten by fishes and two common species of squids
in continental shelf waters off the northeastern United States. The
stomach contents of 31,567 individuals representing 180 species were
analyzed. Collection of specimens was primarily by bottom trawl
or longline during 1963-84. Most of the smaller-sized fish species
(i.e., <100 cm long) and the two squid species were collected
by bottom trawl during 1977-80. Most of the apex predators, including
the large sharks and tunas, and other large-sized species were collected
by longline.
Dietary data are initially presented as a
summary table which lists for each of 170 predators the relative contribution
of six major functional prey groups (i.e., fish, squid, polychaete,
decapod crustacean, other crustacean, and all other) to its diet. Such
data are subsequently presented as summary tables which list for each
of those six functional prey groups the predators involved and the relative
contribution of seven geographic areas (i.e., Middle Atlantic,
Southern New England, Georges Bank, Gulf of Maine, Scotian Shelf, inshore
north of Cape Hatteras, and south of Cape Hatteras) to each predator’s
consumption of that functional prey group. Also, appendix tables
provide a detailed listing of the overall stomach contents for each predator
species and, for selected species, the stomach contents according to
predator size, or to both predator size and geographic area of collection.
Fifty-nine species fed primarily (i.e., >50% of the stomach contents
by weight or volume) on fish and/or squid. Some of the major piscivores
(not listed in any particular order) were Atlantic cod, silver hake,
almost all of the sharks, winter skate, thorny skate, goosefish, white
hake, bluefish, striped bass, weakfish, Atlantic bonito, little tunny,
sea raven, Atlantic halibut, and summer flounder. Common fish and
squid taken as prey included northern sand lance, hakes, herrings, mackerels,
butterfish, anchovies, scup, flatfishes, sculpins, longfin inshore squid,
and northern shortfin squid.
A variety of prey groups other than fish and squid were important food
for different predators. For example, polychaetes (mostly spionids,
nereids, and nephtyids) were important constituents of the diet of seven
species. Decapod shrimp (e.g., Pandalus spp., Dichelopandalus
leptocerus, and Crangon septemspinosa) and crabs (principally
Cancer spp., Pagurus spp., and Ovalipes spp.) were the main food of 17
species. Crustaceans other than decapod shrimp and crabs made up
a substantial portion of the stomach contents of 32 species, and included
prey such as copepods, amphipods, euphausiids, mysids, and stomatopods. Other
prey groups such as echinoderms, bivalve mollusks, cnidarians, and tunicates
made up most of the food of 37 predators. Eighteen predator species
were diverse feeders and didn’t feed intensively on any one of the above-noted
prey categories.
INTRODUCTION
Trophic
structure of fish assemblages on the continental shelf from New England
to Cape Hatteras, North Carolina, has been examined by the Northeast
Fisheries Science Center (NEFSC) in several large-scale dietary studies. Past
studies have described food-web structure and trophic interactions among
Northwest Atlantic fishes. For the 1969-72 study period, see Maurer
and Bowman (1975) and Langton and Bowman (1980, 1981); for the 1973-76
period, see Edwards and Bowman (1979) and Bowman and Michaels (1984). Also
see Cohen et al. (1982), Sissenwine (1984), and Sherman (1986).
Understanding trophic interrelationships among the majority of fish
species within an ecosystem is necessary to define more precisely the
role that predation plays in determining ecosystem structure and the
possible long-term effects of various fisheries exploitation regimes. The
primary purpose of this report is to provide basic diet composition data
on fishes and two species of squids commonly caught in the Northeast
Continental Shelf Ecosystem.
Diet data for some of the species covered in this report are scant or
nonexistent in the published literature. This report’s data expand
on existing diet data for major fish and squid species sampled during
the 1969-72 and 1973-76 study periods, and cover the broader geographic
area from Nova Scotia to Cape Fear, North Carolina, including inshore
areas where bottom depth ranges from 8 to 27 m. Previous studies
only covered the area from Nova Scotia to Cape Hatteras in water depths
of 27-366 m. The majority of data presented here represent the
last of a series of quantitative stomach content collections initiated
in 1973.
Detailed stomach content data, based on percentage composition by weight
or volume, are presented for individual predator species. Also,
we identify six major functional prey groups based on the predators’ stomach
contents.
METHODS
AND MATERIALS
Specimens sampled for stomach content analysis were primarily collected
during NEFSC bottom trawl survey cruises conducted during the spring,
summer, autumn, and winter from 1977 to 1980. Stratified random
sampling was conducted in continental shelf waters from Nova Scotia to
Cape Fear, North Carolina and sampling occurred 24 hr/day. Tows
were 30 min in duration at a vessel speed of 6.5 km/hr, usually in the
direction of the next sampling station. Bottom depths sampled ranged
from 8 to 366 m. The 27-m depth contour (along the coast) delineates
inshore versus offshore sampling areas of the NEFSC. Eight general
areas surveyed by the NEFSC are depicted in Figure
1. They include the six traditional offshore areas --
offshore south of Cape Hatteras, Middle Atlantic, Southern New England,
Georges Bank, Gulf of Maine, and Scotian Shelf -- along with two inshore
areas -- inshore south of Cape Hatteras and inshore north of Cape Hatteras.
Stomach content samples taken during bottom trawl survey cruises were
based on three criteria as follows: 1) offshore species of particular
interest to investigators at the NEFSC for a variety of reasons (e.g.,
species making up the majority of commercial catches or species known
to consume primarily fish), 2) species making up the majority of catches
(by weight) in inshore areas (hitherto not sampled), and 3) species for
which dietary information was scant or nonexistent. Survey technicians
sampled species first for criterion no. 1 if the station was offshore,
or for criterion no. 2 if the station was inshore. Other samples
were taken when time permitted. Samples generally represented the
length frequency of each species caught.
Stomachs of large fish or squid were excised aboard ship, individually
wrapped in gauze with a label denoting vessel, cruise, station, species,
specimen size (i.e., fork length when applicable, otherwise total
length, disk width for rays, or mantle length for squid), sex, and maturity,
and preserved in a 3.7% formaldehyde solution (Formalin and sea water)
by volume. Small fish and squid were preserved whole.
The preserved stomachs were individually opened in the laboratory and
their contents emptied onto a 0.25-mm-mesh-opening screen sieve to permit
washing away the formaldehyde without the loss of any food items. The
stomach contents were sorted, identified, counted, and damp dried on
absorbent paper. Major prey items and commonly occurring but relatively
minor prey, in terms of weight, were identified to species whenever practical. The
wet weight of all stomach content groups was determined to the nearest
0.001 g, and all data recorded. A stomach was considered empty
when no material was found in the stomach, or when the material found
in the stomach both could not be identified and weighed less than 0.001
g.
We also provide information on the food of large pelagic species. These
samples were gathered from various sources during 1963-84. Stomach
content samples of apex predators, including large sharks and tunas,
and other large species (i.e., >100 cm) were mostly collected
from fish caught by rod and reel, or by longline during research vessel
cruises. Some samples were collected from fish caught during fishing
tournaments over the years. The sampling area covered continental
shelf waters from Florida to the Grand Banks (southeast of Newfoundland).
As noted earlier, stomach content data associated with the 1977-80 period
of bottom trawl survey cruises were measured as percentage composition
by wet weight. Data associated with the 1963-66 period were measured
as percentage composition by occurrence. Data associated with the
1969-72 period are based on samples first being grouped according to
fish length, then being measured as percentage composition by wet weight. Stomach
content data presented for apex predators are based on percentage composition
by volume.
No statistical weighting (e.g., length frequency, sample size,
population size, or species distribution) was applied to any stomach
content data. Sources of potential bias or variation in the data
include age/size, sex, maturity stage, and various sampling factors (i.e.,
time of day, season, year, area, and bottom depth and temperature). Accordingly,
dietary listings should be considered only as broad summaries. Some
items listed as stomach contents are parasites (e.g., trematodes,
cestodes, and nematodes), some of which may have been ingested by the
predator when it ate other parasitized organisms. Similarly, some
items identified in the stomachs may have originated from the stomachs
of fish prey and were not directly consumed by a particular predator.
Life history and distribution data for many economically important species
(e.g., Atlantic cod, haddock, silver hake, and Atlantic herring)
may be found in Grosslein and Azarovitz (1982). Details of stomach
content sampling procedures and data processing methods utilized by the
NEFSC are given in Langton et al. (1980). All common and
scientific names of fishes and invertebrates (both predator and prey),
whenever possible, are according to Robins et al. (1991) for fishes
except pleuronectids, Cooper and Chapleau (1998) for pleuronectid fishes,
Turgeon et al. (1988) for mollusks except loliginids, Turgeon et
al. (1998) for loliginid mollusks, Williams et al. (1989)
for decapod crustaceans, Cairns et al. (1991) for cnidarians and
ctenophores, and either Gosner (1971) or Barnes (1987) for other invertebrates.
RESULTS
AND OBSERVATIONS
Detailed
diet data for each predator species are given in tabular form in Appendix A and Appendix B. In
the appendix tables, diet composition is expressed as the percentage
by weight that each stomach content group makes up of the total stomach
contents for each predator species (except in a few cases, which are
noted in the tables, where percentage by volume or occurrence is given
because a different measurement method was utilized during the particular
study from which those data were taken). Percentage subtotals for
phyla and other major taxonomic groups are shown in brackets; subtotals
for minor groups within major groups are in parentheses. The number
sampled, number empty, mean stomach content by weight or volume, and
mean predator length are provided at the bottom of each table.
The stomach contents of 31,567 individual predators, representing 178
species of fish and 2 common species of squid were examined. The
total number of each species examined and the percentage empty are listed
in the earlier-presented taxonomic index. The
area(s) in which samples were collected and the type(s) of data which
are presented for each species are given in the earlier-presented alphabetic
index. All stomachs of 10 species collected were empty; they
are listed at the end of the taxonomic index.
OVERALL PREY
A summary of the stomach content data for the 170 species with food
in their stomachs is provided in Table 1. (Also
refer to Appendices A and B for a detailed listing of prey.) The
functional prey groups (i.e., fish, squid, polychaete, decapod
crustacean, other crustacean, and all other) noted immediately below
and listed in Table 1 collectively made up at least 50% by weight (or
volume) of the stomach contents of the predators indicated.
Fish and/or squid made up the majority of the stomach contents of 59
species. Identified fish prey, for the most part, were northern
sand lance, silver hake, other hakes, herrings, mackerels, butterfish,
anchovies, scup, flatfishes, and sculpins. Squid prey were primarily
longfin inshore and northern shortfin squids. Polychaetes (mostly
spionids, nereids, and nephtyids) were important constituents of the
diet of seven species. Decapod shrimp (mainly Pandalus spp., Dichelopandalus
leptocerus, and Crangon septemspinosa) and crabs (principally Cancer spp., Pagurus spp.,
and Ovalipes spp.) were the principal food of 17 predators. Crustaceans
other than decapods made up a substantial portion of the stomach contents
of 32 species, and included prey such as copepods, amphipods, mysids,
and euphausiids. Note, however, that some of the unidentified crustacean
matter included here may have been decapod remains). The “all other” group
(i.e., stomach contents other than the groups noted above) is
primarily made up of some combination of bivalve mollusks, gastropods,
echinoderms, cnidarians, urochordates, sand, or unidentified material. This
group made up most of the stomach contents of 37 species. Eighteen
predator species were diverse feeders and didn’t feed predominantly on
any one of the above functional prey groups.
PREY ACCORDING
TO PREDATOR LENGTH
Different diet compositions for fish in different length ranges are
observed for 60 species (Appendix B). Generally,
fish 20 cm long tended to eat some combination of organisms such
as chaetognaths, copepods, amphipods, mysids, polychaetes, and small
decapod shrimp. Fish >20 cm long (e.g., little skate, Atlantic
cod, silver hake, pollock, and white hake) consumed mostly fish, squid,
decapod shrimp, and/or crabs.
Exceptions to this pattern are seen in three groups of predators. The
first group are those species which fed intensively on fish and/or squid
for most of their life. Predators in this group included, in part,
northern shortfin and longfin inshore squids, most of the sharks (e.g.,
dusky shark, sharpnose shark, and spiny dogfish), goosefish, and bluefish.
The second group are those predators which ate primarily planktonic
organisms (e.g., chaetognaths, copepods, pelagic amphipods, mysids,
euphausiids, and/or salps). Most of the herrings, Atlantic argentine,
northern sand lance, Atlantic mackerel, Acadian redfish, and butterfish
are among the fishes included in this group.
The third group of fishes preyed almost totally on some combination
of small benthic crustaceans (mostly amphipods), echinoderms, cnidarians,
and polychaetes. Species such as haddock, Gulf Stream flounder,
witch flounder, American plaice, yellowtail flounder, and winter flounder
are among the predators in this group.
PREY ACCORDING TO
GEOGRAPHIC AREA
A qualitative and quantitative understanding of predation on fish by
fish (i.e., natural mortality, in part) is critically important
for development of multispecies fishery models. The percentage
of fish in the diet of all piscivores sampled from at least two geographic
areas, in sufficient numbers for analysis (about 20 fish per area), during
bottom trawl surveys from 1977 to 1980 are presented in Table
2. Excluding apex predators, the listed species represent the
majority of the demersal fish and squid biomass within the entire study
area.
Spotted hake, which is not listed in Table 2, is a dominant piscivore
in the Middle Atlantic, but too few were sampled during the 1977-80 period
to warrant inclusion. However, during the 1973-76 period in the
Middle Atlantic, 15.9% and 36.9% of their food was fish and squid, respectively
(Bowman and Michaels 1984).
Many large apex predators which fed primarily on fish and/or squid (e.g.,
blue shark, thresher shark, and swordfish) are migratory. They
occur in the survey area only during certain periods of the year. Their
predatory impact on fish and squid populations during these periods should
not be overlooked.
Information on how functional prey groups such as fish, squid, polychaetes,
decapods, other crustaceans, and other organisms are partitioned by predators
within the study area is given in Tables 2-7. (See also Appendix
B.) For each functional prey group, the principal predators
which utilize that group as food are discussed, by area, in the following
sections.
Fish
Overall, northern sand lance was the primary fish prey in almost all
geographic areas during the study period. (See Table
2 and the detailed prey listings in Appendix
B.) In the Middle Atlantic, northern sand lance was an important
food (>10% of all food by weight) of little skate, silver hake, red hake,
summer flounder, and windowpane. Other notable fish prey in the
Middle Atlantic were silver hake (consumed by silver hake, fourspot flounder,
and windowpane), herrings (eaten by spiny dogfish, summer flounder, and
bluefish), and scup (prey of smooth dogfish and black sea bass).
Southern New England piscivores which ate northern sand lance include,
in part, smooth dogfish, winter skate, silver hake, Atlantic cod, summer
flounder, windowpane, and yellowtail flounder. In this area, silver
hake were prey of fourspot flounder, silver hake, and goosefish. Atlantic
cod were identified as prey of Atlantic cod and fourspot flounder. Unidentified
gadids were found in the stomachs of spiny dogfish, white hake, red hake,
and Gulf Stream flounder. Herrings were the prey of spiny dogfish
and summer flounder. One of the few instances of predation on spiny
dogfish (i.e., by Atlantic cod) was observed in this area.
Georges Bank predators fed on a wide assortment of fish prey. Major
fish prey were northern sand lance (eaten by winter skate, thorny skate,
Atlantic cod, pollock, red hake, summer flounder, winter flounder, windowpane,
bluefish, and longhorn sculpin), herrings (consumed by spiny dogfish,
thorny skate, silver hake, and bluefish), various gadids (found in the
stomachs of spiny dogfish, white hake, red hake, Atlantic halibut, bluefish,
sea raven, and goosefish, with Atlantic cod and haddock specifically
being identified as food of Atlantic halibut and goosefish, respectively),
and longhorn sculpin (prey of little skate, Atlantic halibut, bluefish,
and goosefish).
Gulf of Maine predators ate primarily northern sand lance (food of spiny
dogfish, winter skate, silver hake, haddock, red hake, and Atlantic halibut),
silver hake (prey of silver hake, Atlantic cod, white hake, red hake,
Atlantic halibut, Acadian redfish, sea raven, and goosefish), and herrings
(found in the stomachs of thorny skate, silver hake, Atlantic cod, Atlantic
halibut, and goosefish). Haddock was preyed on by goosefish.
Scotian Shelf fishes ate northern sand lance (prey of red hake), mackerel
(eaten by spiny dogfish and silver hake), herrings (food of silver hake),
silver hake (preyed upon by silver hake, white hake, and red hake), haddock
(identified in the stomachs of red hake and goosefish), unidentified
gadids (a portion of the diet of Atlantic halibut and goosefish), and
longhorn sculpin (found in the stomachs of goosefish).
Inshore north of Cape Hatteras (i.e., Cape Hatteras to Nova Scotia),
fish prey were northern sand lance (>10% of the food of winter skate,
silver hake, Atlantic cod, pollock, summer flounder, black sea bass,
and scup), herrings (consumed by Atlantic sharpnose shark, spiny dogfish,
thorny skate, Atlantic cod, Atlantic halibut, summer flounder, bluefish,
weakfish, and goosefish), mackerel (eaten by dusky shark), silver hake
(a food of silver hake, red hake, Atlantic halibut, and windowpane),
butterfish (prey of smooth dogfish and bluefish), and anchovies (preyed
upon by Atlantic sharpnose shark, black sea bass, weakfish, northern
kingfish, and windowpane).
South of Cape Hatteras (including inshore and offshore areas from Cape
Hatteras to Cape Fear), fish prey were almost exclusively anchovies (food
of Atlantic sharpnose shark, dusky shark, summer flounder, bluefish,
black sea bass, weakfish, southern kingfish, northern kingfish, and spot)
and herrings (consumed by Atlantic sharpnose shark, bluefish, black sea
bass, and weakfish).
Squid
Longfin inshore and northern shortfin squids were the principal squid
species identified as prey within all areas sampled except the Middle
Atlantic (Appendix B). In the Middle
Atlantic, only longfin inshore squid was found to be a major squid prey,
although it didn’t make up >50% of the stomach contents of a single species.
Table 3 shows that several species fed intensively
on squid (i.e., the stomachs of all predators noted immediately
below contained on average >50% squid by weight). For example,
the diet of summer flounder and bluefish sampled in Southern New England
was mostly squid. On Georges Bank, squid was an important prey
of bluefish and fourspot flounder. In Scotian Shelf waters, predation
on squid was noted by pollock and northern shortfin squid. Goosefish
was identified as having >50% squid in the diet for the inshore area
north of Cape Hatteras. No predators were observed with >50% squid
in their diet for the area south of Cape Hatteras.
Polychaetes
Polychaetes were an important food source (i.e., >50% of stomach
contents by weight) for relatively few species, but they were taken as
prey in all areas sampled (Table 4 and Appendix
B). Taxonomic groups making up the majority of the polychaete
prey were nephtyids, nereids, lumbrinerids, flabelligerids, spionids,
and ampharetids.
Species in the Middle Atlantic whose main prey was polychaetes are winter
flounder, Gulf Stream flounder, and scup. In Southern New England,
polychaetes didn’t make up >50% of the stomach contents of any predator
examined. However, the stomachs of haddock, winter flounder, and
Gulf Stream flounder all contained >40%. On Georges Bank, yellowtail
and witch flounders were identified as two species which fed intensively
(i.e., >50%) on polychaetes. Of all species examined from
the Gulf of Maine and Scotian Shelf, only witch flounder stomachs contained >50%
polychaetes (in both areas). The inshore area north of Cape Hatteras
yielded the most predator species (i.e., 10) with >10% by weight
of polychaetes in their stomachs, but the stomachs of only two species,
witch flounder and spot, contained >50%. Not a single species examined
from waters south of Cape Hatteras had stomachs containing >50% polychaetes,
and only scup stomachs contained >10%.
Decapod Crustaceans
Relatively few species made up the majority of decapod crustacean prey
throughout the entire survey area, but those species were an important
food source for many predators (Table 5 and Appendix
B). For example, decapods accounted for >50% of the stomach
contents of dusky shark, smooth dogfish, and blackbelly rosefish in the
Middle Atlantic, and for >50% of the stomach contents of smooth dogfish,
windowpane, northern kingfish, and southern kingfish in waters south
of Cape Hatteras.
In the Middle Atlantic and in waters south of Cape Hatteras, Crangon
septemspinosa, portunids (e.g., Ovalipes ocellatus), Cancer
irroratus, and Munida spp. were important decapod prey.
Four predators examined from the Southern New England area (i.e.,
smooth dogfish, black sea bass, longhorn sculpin, and sea raven) fed
intensively on decapods. In this area, for all predators which
ate decapods, the most important prey were C. irroratus, C.
borealis, Crangon septemspinosa, and Dichelopandalus leptocerus.
On Georges Bank, the same species of prey as noted for Southern New
England were also principal food, along with Hyas spp. and Pagurus spp. Only
the stomachs of longhorn sculpin and sea raven sampled on Georges Bank
contained >50% decapods.
The largest portion of the decapods consumed in the Gulf of Maine was
made up of a combination of Cancer borealis, Hyas spp., Pandalus
borealis, and D. leptocerus. Predators in this area
with >50% decapod prey were blackbelly rosefish and longhorn sculpin.
In Scotian Shelf waters, decapods such as C. irroratus, Pasiphaea spp., Crangon
septemspinosa, and D. leptocerus were the most important
prey. The stomach contents of both sea raven and longhorn sculpin
contained >50% decapods. Also worthy of mention is Atlantic halibut
with 49.6% decapods.
Fish from the inshore area north of Cape Hatteras fed principally on Cancer
irroratus, O. ocellatus, Crangon septemspinosa, and D.
leptocerus. Predators in the inshore area with >50% decapod
prey were smooth dogfish and black sea bass.
Crustaceans Other
than Decapods
Five taxonomic groups accounted for the majority of crustacean prey
other than decapods. Three of these (i.e., copepods, amphipods,
and euphausiids) were an important food in all geographic areas sampled
(i.e., either individually or in some combination they made up >50%
of the diet by weight of several predators). The other two groups,
mysids and stomatopods, were important prey in only four of the seven
areas sampled (Table 6 and Appendix
B). Mysids were important as a food source in the Middle Atlantic,
Southern New England, inshore north of Cape Hatteras, and on Georges
Bank. Stomatopods were major prey of several predators in the Middle
Atlantic, Southern New England, inshore north of Cape Hatteras, and south
of Cape Hatteras.
In the Middle Atlantic, crustaceans other than decapods made up >50%
of the diet of alewife, haddock (only one fish was examined), and northern
sand lance. Southern New England fishes which fed intensively on
one or more of the nondecapod crustacean groups noted earlier in this
section are alewife, yellowtail flounder, Atlantic mackerel, northern
sand lance, and ocean pout. Predators identified for Georges Bank
were alewife, Atlantic mackerel, black sea bass, Acadian redfish, and
northern sand lance. In the Gulf of Maine, seven predators fed
for the most part only on nondecapod crustaceans: Atlantic herring,
alewife, Atlantic mackerel, summer flounder, Acadian redfish, northern
sand lance, and longfin inshore squid). Within the Scotian Shelf
area, the stomachs of Atlantic herring, alewife, Atlantic mackerel, Acadian
redfish, and ocean pout all contained >90% by weight of crustaceans other
than decapods. Predation on these crustaceans inshore north of
Cape Hatteras was most important to species such as alewife, Atlantic
mackerel, northern sand lance, fawn cusk-eel, and windowpane. None
of the species examined from waters south of Cape Hatteras had stomachs
containing >50% nondecapod crustaceans.
Other Prey
Major stomach content categories such as echinoderms, gastropods, bivalve
mollusks, chaetognaths, cnidarians, nemerteans (i.e., rhynchocoels),
tunicates, animal remains, and sand made up the majority (either individually
or in some combination) of what is found in the stomachs of 32 predators
(Table 7). Of these categories, only
those which individually made up >50% of the stomach contents by weight
of a predator within a particular area are noted in the remainder of
this section (excluding animal remains and sand).
None of these prey categories totaled >50% of the stomach contents of
any predator in the Middle Atlantic or Southern New England. On
Georges Bank, Atlantic herring fed intensively on chaetognaths, American
plaice ate (for the most part) only echinoderms (92.3%), and Atlantic
wolf-fish consumed bivalve mollusks. In the Gulf of Maine, echinoderms
were an important food of haddock and ocean pout. Only one predator
each within the Scotian Shelf, inshore area north of Cape Hatteras, and
area south of Cape Hatteras fed primarily on any prey category considered
here (i.e., winter flounder eating cnidarians, ocean pout consuming
echinoderms, and butterfish preying on tunicates, respectively).
OBSERVATIONS
Scientists at the NEFSC’s Woods Hole Laboratory have conducted broadscale
dietary studies of fishes sampled during bottom trawl surveys since 1963. Dietary
data presented here, which are largely based on samples from the 1977-80
portion of the survey series, corroborate earlier reports that relatively
few species account for a substantial portion of the food of Northwest
Atlantic continental shelf fishes and squids [Edwards and Bowman (1979),
Bowman and Michaels (1984), Bowman et al. (1984), Maurer and Bowman
(1985)]. The abundances of some species identified as critical
prey are known to fluctuate among seasons and years based on indices
generated by these surveys. During 1977-80 (i.e., this study’s
period, in part), when the survey indices rose for northern sand lance,
we simultaneously found sand lance to be a major prey item.
This report summarizes much dietary information into various predator/prey
groups, but that information does not take into account predator/prey
population sizes, or spatial/temporal aspects, of predation (i.e.,
overlap of predator and prey populations). Before the impact of
predation on a population can be determined, these factors must be considered.
A complete list of all stomach contents for all predator species in
this report can be obtained from the Food
Chain Dynamics Investigation at the NEFSC.
ACKNOWLEDGMENTS
Personnel
of the NEFSC’s Food Chain Dynamics Investigation contributing to the
compilation of this report, listed alphabetically, were: John Hauser,
Brian Hayden, Richard Langton, Lisa Lierheimer, Donald Mack, Ronald Mack,
Scott McNamara, Thomas Morris, Jacqueline Murray, James Myette, Stephen
Spina, Andrea Swiecicki, and Lynn Whiteley. Eleanore Beale, Elke
Bergholz-Nelson, Edward Brown-Ledger, Caroline Karp, Lisa Urry, and numerous
summer students and survey technicians helped to collect and analyze
stomach contents. Members of the NEFSC’s Apex Predators Ecology
Investigation deserving special thanks for processing stomach contents
and providing data summaries are John Casey, Nancy Kohler, and Robert
Medved. Jon Gibson, Michael Fogarty, and Russell Brown provided
useful suggestions on the organization and content of the manuscript.
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