CONTENTS Taxonomic Index (PDF) Alphabetic Index (PDF) Introduction Methods and Materials Results and Observations Acknowledgments References Cited
NOAA Technical Memorandum NMFS-NE-155
Food of Northwest Atlantic Fishes and Two Common Species of SquidRay E. Bowman1,2, Charles E. Stillwell3, William L. Michaels1, and Marvin D. Grosslein1,4
1 Woods Hole Lab., National Marine Fisheries Serv., 166 Water St., Woods Hole, MA 02543
2 Current Address: 38 Hilltop Rd., Mashpee, MA 02649
3 [Deceased] Narragansett Lab., National Marine Fisheries Serv., 28 Tarzwell Dr., Narragansett, RI 02882
4 Current Address: 23 Fairway Ln., West Falmouth, MA 02540
Web version posted October 18, 2001Citation: 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.
Information Quality Act Compliance: In accordance with section 515 of Public Law 106-554, the Northeast Fisheries Science Center completed both technical and policy reviews for this report. These predissemination reviews are on file at the NEFSC Editorial Office.
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.
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.
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.
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).
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 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%.
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.
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).
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.
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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