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Fishery Bulletin 96(3), 1998 
of teleosts; lower mandibles (“beaks”) from cephalo- 
pods; tooth cusp plates (“combs”) from agnathans; 
and exoskeletons and eyes from crustaceans. Prey 
items were identified with the aid of a laboratory 
reference collection and published guides, including 
those of Bigelow and Schroeder (1953), Clarke ( 1986), 
Harkonen (1986), and Scott and Scott (1988). 
Prey importance 
Relative food importance in the autumn diet of the 
harbor porpoise was determined by 1) frequency of 
occurrence, 2) proportion of numerical abundance, 
and 3) proportion of total ingested mass. Frequency 
of occurrence is the percentage of porpoise stomachs 
containing a particular food type. Proportion of nu- 
merical abundance is the number of individuals of a 
prey species recovered from all stomachs, divided by 
the total number of all prey from all stomachs. The 
number of individuals from each fish species in each 
stomach was determined by summing the number of 
intact fish and half the number of free otoliths. The 
number of either upper or lower beaks (whichever 
were more abundant) from each species was used to 
determine the number of squid present. 
Proportion of prey mass is the percentage of total 
prey mass in the stomach at the time of death that 
was represented by a particular species. Reconsti- 
tuted mass, or the mass of prey prior to ingestion, 
rather than the existing mass of partially digested 
prey, was used in this calculation. Reconstituted prey 
masses were estimated from body lengths of intact 
prey and the lengths of otoliths or cephalopod beaks 
(Table 1). If a stomach contained more than 25 
otoliths from the same species, all otoliths from that 
species were counted, and a subsample of 25 was 
randomly selected and measured. Otoliths were 
scored on a scale from 0 (undamaged otoliths re- 
Table 1 
Equations used to estimate length and mass of harbor porpoise prey. ML = mantle length; H = 
length; OL = otolith length; LRL = lower rostral length; and SL = standard length. Length is in 
hood length; M = mass; FL = fork 
millimeters and mass is in grams. 
Prey species 
Equations 
Source 
Bathypolypus arcticus 
ML = 15.4 + 12.28 H 
Clarke, 1986 
(North Atlantic octopus) 
In M= 1.06 + 2.55 In H 
Clarke, 1986 
Clupea harengus 
FL = 69.23 OL - 27.48 
Recchia and Read, 1989 
(Atlantic herring) 
log M = 3.12 logFL - 5.41 
Recchia and Read, 1989 
Gadus morhua 
ln(FL/10) = 3.3138 + 1.6235 ln(OL/10) 
Hunt, 1992 
(Atlantic cod) 
M= 0.0124 (FL/10) 2 93 
Bowen and Harrison, 1994 
Illex illecebrosus 
(Northern short-fin squid) 
lnM= 1.773 + 2.4 1 nLRL 
Clarke, 1962 
Loligo pealei 
log ML = 1.767 + 1.4 log LRL 
Gannon et al., 1997b 
(Long-fin inshore squid) 
M = 0.25662 (ML/10) 2 1582 
Lange and Johnson, 1981 
Maurolicus weitzmani 1 
FL = 9.82 + 28.75 OL 
Harkonen, 1986 
(Weitzman’s pearlsides) 
M = 0.3737 OL 2 503 
Harkonen, 1986 
Merluccius bilinearis 
FL = 20.9 L- 0.41 
Recchia and Read, 1989 
(Silver hake) 
logM = -2.26 + 3.08 log(FL/10) 
Kohler et al., 1970 
Peprilus triacanthus 2 
SL= -9.15919 + 25.01871 OL 
Present study (r 2 =0.983) 
(Butterfish) 
log M = -0.67576 + 3.222 logOL 
Present study (r 2 =0.924) 
Pollachius virens 
ln(FL/10) = 3.251 + 1.6251 ln(OL/10) 
Harkonen, 1986 
(Pollock) 
M = 0.0134 (FL/10) 294 
Bowen and Harrison, 1994 
Scomber scombrus 
FL/ 10 = 7.33 OL + 0.37 
Recchia and Read, 1989 
(Atlantic mackerel) 
M = 0.00756 (FL/10) 3 082 
Kulka and Stobo, 1981 
Sebastes spp. 3 
FL = 16.165 L 1 224 
Harkonen, 1986 
(Rockfish) 
M = 0.0741 OL 3 295 
Harkonen, 1986 
Urophycis spp. 4 
FL/10 = 1.525 OL 1 1456 
Clay and Clay, 1991 
(Red and white hake) 
M = 0.003998 (FL/10) 3 1718 
Clay and Clay, 1991 
1 Taxonomy of the genus Maurolicus has been revised recently (Parin and Kobylansky, 1996). The equations used to estimate M. weitzmani size 
are those given by Harkonen (1986) for M. muelleri. 
2 Standard length range: 49-153 mm; weight range: 3-104 g; n = 44. 
3 Equations given by Harkonen (1986) for S. marinus. 
4 Equations given by Clay and Clay (1991) for U. tenuis. 
