NOTE Lomond et a I.: Transition from pelagic to benthic prey of group 0-1 Gadus Morhua 
909 
Prey shapes and volume formulae used in 
Table 1 
the study, spl = species length; spw 
= species width; spd = species depth 
Prey type and species 
Shape 
Formula 
Copepoda, Polychaeta, and shrimp and crab zoea cylinder 
V= 3.14 r 2 xspl 
r = spw/ 2 
Amphipoda (straight) and Mysidicae 
cylinder 
V = 3.14 x r 2 x spl 
r = [(spw + spd)/ 2]/2 or 
r = spw/ 2 
Amphipoda (curved) 
1/2 cylinder 
V = 3.14 x r 2 x spw 
r = spl/ 2 
Crab (adult) 
disc 
V = 3.14 x r 2 x spd 
r = [(spl + spw)/ 2]/2 
Crab (megalopa), Isopoda, and Ostracoda 
box 
V = spl x spw x spd 
Crustacean eggs and eyes 
sphere 
V = 4/3 x 3.14 r 3 
r = spl/ 2 
Snail 
circular 
V= 1/3 x 3.14 r 2 x spd 
cone 
r = [(spl + spw)/ 2]/2 
Table 2 
Prey of age group 0-1 cod based on two measurement methods. B = Benthic, P = 
Mean number = number of individuals per stomach; mean volume = microliters 
Pelagic, U = Unknown, Unid. = Unidentified, 
per stomach. 
Method 
Group 0 
Group 1 
Mean number 
Calanoida (P) 
22.7 
Jaera marina (B) 
37.9 
Harpacticoida (B) 
3.6 
Eggs (U) 
17.7 
Unid. Copepoda (U) 
3.2 
Gammarus oceanicus (B) 
3.0 
Jaera marina (B) 
2.7 
Pontogeneia inermis (P) 
3.0 
Pontogeneia inermis (P) 
2.1 
Harpacticoida (B) 
1.2 
Other (U) 
5.7 
Other (U) 
5.8 
Mean volume 
Unid. Gammaridae (B) 
27.4 
Crangon septemspinosa (B) 
297.7 
Gammarus oceanicus (B) 
24.9 
Gammarus oceanicus (B) 
98.4 
Unid. Mysidacea (U) 
12.9 
Jaera marina (B) 
84.0 
Calliopius laeviusculus (P) 
12.3 
Urophycis tenuis (B) 
62.5 
Pontogeneia inermis (P) 
11.2 
Unid. Teleostei (U) 
42.6 
Unid. Copepoda (U) 
10.7 
Unid. Decapoda (U) 
40.9 
Calanoida (P) 
6.5 
Unid. Crustacea (U) 
31.1 
Jaera marina (B) 
6.1 
Unid Polychaeta 
28.9 
Other (U) 
100.0 
Other (U) 
317.1 
(Table 2). Group-0 cod fed predominately on amphi- 
pod taxa ( Pontogeneia inermis, Gammarus oceanicus , 
Calliopius laeviusculus, and unidentified Gammaridae) 
and copepod taxa (Calanoida and Harpacticoida). Pre- 
dominate prey of group- 1 cod were more diverse, in- 
cluding two amphipod taxa, an isopod (Jaera marina), 
invertebrate eggs, a shrimp ( Crangon septemspinosa ), 
white hake (Urophycis tenuis ), and other unidentified 
teleosts, decapods, and polychaete worms. 
Figure 1 indicates a rapid shift from pelagic to 
benthic prey at standard lengths of 60 to 100 mm. 
Four group-0 fish, represented by triangles in Fig- 
ure 1, had <5% pelagic prey. Prey of these fish con- 
sisted of a large volume of unidentified prey and a 
single benthic prey item (e.g. one ostracod or one am- 
phipod head). These fish were omitted in the calcu- 
lation of the mean proportion of pelagic prey for the 
three size groups of cod in Table 3. 
The rapid shift to benthic prey by juvenile Atlan- 
tic cod was related to body size. This change was 
quantified for use in food web computations. The diet 
of cod 40-59.9 mm SL was 98% pelagic prey, that of 
