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Fishery Bulletin 96(3), 1998 
and hypurals (Trippel and Beamish, 1987), and 
cleithra and dentaries (Hansel et al., 1988). Measure- 
ments of the dimensions of diagnostic bones have 
often then been used to estimate original prey size 
(Trippel and Beamish, 1987; Hansel et al., 1988; 
Carss and Elston, 1996). Previous studies on the food 
habits of piscivores have used fish otoliths as an aid 
in prey identification and original prey size estima- 
tion ( Jobling and Breiby, 1986). However, acidic pre- 
servatives, such as formaldehyde, can dissolve 
otoliths, resulting in unreliable otolith length and 
fish length relationships (McMahon and Tash, 1979). 
In addition to bones, external morphological mea- 
surements, such as eye diameter and caudal peduncle 
depth, have been used successfully to reconstruct 
prey body size for recently consumed prey fishes 
(Crane et al., 1987; Scharf et al., 1997). However, 
the majority of fish feeding studies employing such 
techniques have been directed at freshwater 
piscivores, whereas researchers examining the diets 
of marine fishes have utilized these techniques much 
less frequently (Crane et al., 1987; Scharf et al., 
1997). Moreover, no such techniques are currently 
available to enhance diet analyses and more com- 
pletely define the role of piscivorous fishes in struc- 
turing fish communities in the Northwest Atlantic. 1 
Here, we generate a series of predictive regression 
equations to estimate prey fish total length, fork 
length, and weight for ten fish species. Original fish 
size is estimated from four external morphometric 
measurements including maximum body depth, eye 
diameter, caudal peduncle depth, and pectoral-fin 
length, as well as from length measurements of three 
diagnostic bones: the opercle, the cleithrum, and the 
1 Rountree, R. A. 1997. Food Chain Dynamics Investigation 
(FCDI). Northeast Fisheries Science Center (NEFSC), National 
Marine Fisheries Service (NMFS), 166 Water St., Woods. Hole, 
MA 02543. Personal commun. 
dentary. The prey species used here include several 
of commercial and recreational importance and com- 
monly occur in the diets of marine piscivores in the 
Northwest Atlantic, representing approximately 52% 
of the total fish prey consumed by piscivorous fishes 
during 1973-90 (Grosslein et al., 1980; Langton and 
Bowman, 1981). 2 We also identify and describe the 
unique characteristics of the three diagnostic bones 
for each fish species and assess their potential value 
as tools for field identification of prey fishes recov- 
ered from predator stomachs. 
Materials and methods 
Over 700 fish representing ten species in five fami- 
lies ranging in size from 52 to 340 millimeters (mm) 
total length (TL) were measured and dissected (Table 
1). Fish were collected as part of Food Chain Dynam- 
ics Investigation (FCDI) (NEFSC, NMFS) research 
cruises conducted on Georges Bank during June and 
August of 1995 and 1996. FCDI research cruises were 
sponsored through the National Oceanic and Atmo- 
spheric Administration Coastal Ocean Program- 
Georges Bank Predation Study. Fish were also col- 
lected from waters off the Northeast U.S. coast dur- 
ing September and October of 1996 as part of the 
NEFSC Fall bottom trawl surveys. Additional fish 
were collected by personnel from the Massachusetts 
Division of Marine Fisheries as part of a coastal 
trawling survey conducted in May and September of 
1996. All fish were immediately frozen until they 
could be returned to the laboratory. In the labora- 
tory, fish were thawed and weighed wet to the near- 
2 Food Chain Dynamics Investigation (FCDI). Northeast Fisher- 
ies Science Center, NMFS, 166 Water St., Woods Hole, MA 
02543. Unpublished data. 
Family, species, number ( 
n ), and size range (total length 
Table I 
in millimeters) of prey fishes used to construct predictive equations. 
Family 
Species 
Common name 
n 
Size range 
Clupeidae 
Alosa pseudoharengus 
Alewife 
137 
73-282 
Alosa aestivalis 
Blueback herring 
38 
83-134 
Clupea harengus 
Atlantic herring 
84 
97-269 
Scombridae 
Scomber scombrus 
Atlantic mackerel 
56 
158-330 
Stromateidae 
Peprilus triacanthus 
Butterfish 
108 
54-193 
Ammodytidae 
Ammodytes dubius 
Sand lance 
75 
109-209 
Gadidae 
Urophycis chuss 
Red hake 
45 
108-340 
Merluccius bilinearis 
Silver hake 
95 
75-300 
Melanogrammus aeglefinus 
Haddock 
47 
79-202 
Gadus morhua 
Atlantic cod 
31 
52-140 
