76 
Recalculated diet and daily ration of 
the shortfin mako Us urns oxyrinchus ), 
with a focus on quantifying predation 
on bluefish ( Pomatomus saltatrix ) 
in the northwest Atlantic Ocean 
Nancy E. Kohler 4 
Cheryl Wilga 2 
Email address for contact author: awood@gso.un.edu 
1 Graduate School of Oceanography 
University of Rhode Island Bay Campus 
215 South Ferry Rd 
Narragansett, Rhode Island. 02882 
Present address: School for Marine Science and Technology (SMAST) 
200 Mill Road, ATT 211, 
Fairhaven, Massachusetts 02719 
2 University of Rhode Island 
Biological Sciences 
100 Flagg Rd. 
Kingston, Rhode Island 02881 
3 Department of Natural Resources Conservation 
160 Holdworth Way 
University of Massachusetts 
Amherst, Massachusetts 01003 
Abstract — The diet and daily ration 
of the shortfin mako ( Isurus oxyrin- 
chus) in the northwest Atlantic were 
re-examined to determine whether 
fluctuations in prey abundance and 
availability are reflected in these 
two biological variables. During the 
summers of 2001 and 2002, stomach 
content data were collected from fish- 
ing tournaments along the northeast 
coast of the United States. These 
data were quantified by using four 
diet indices and were compared to 
index calculations from historical 
diet data collected from 1972 through 
1983. Bluefish ( Pomatomus saltatrix ) 
were the predominant prey in the 
1972-83 and 2001-02 diets, account- 
ing for 92.6% of the current diet by 
weight and 86.9% of the historical 
diet by volume. From the 2001-02 
diet data, daily ration was estimated 
and it indicated that shortfin makos 
must consume roughly 4.6% of their 
body weight per day to fulfill ener- 
getic demands. The daily energetic 
requirement was broken down by 
using a calculated energy content 
for the current diet of 4909 KJ/kg. 
Based on the proportional energy of 
bluefish in the diet by weight, an aver- 
age shortfin mako consumes roughly 
500 kg of bluefish per year off the 
northeast coast of the United States. 
The results are discussed in relation 
to the potential effect of intense short- 
fin mako predation on bluefish abun- 
dance in the region. 
Manuscript submitted 11 July 2007. 
Manuscript accepted 10 September 2008. 
Fish. Bull. 107:76-88 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National Marine 
Fisheries Service, NOAA. 
Anthony D. Wood (contact author ) 1 
Bradley M. Wetherbee 2 
Francis Juanes 3 
4 National Marine Fisheries Service, NOAA 
Northeast Fisheries Science Center 
Narragansett Laboratory 
28 Tarzwell Drive 
Narragansett, Rhode Island 02882 
A top-down trophic system involves 
consumer control of the community 
structure and the population dynam- 
ics of an ecosystem. In many marine 
ecosystems many species of sharks 
are positioned at the top of the food 
chain, and through predation can 
potentially exert control upon their 
prey communities (van der Elst, 1979; 
Stevens et ah, 2000; Heithaus and 
Dill, 2002). As management decisions 
become increasingly focused on the 
interactions between multiple spe- 
cies, it is important that the effects 
of predation be evaluated (Bax, 1998; 
Overholtz et al., 2000). One of the first 
steps in carrying out such an evalua- 
tion is through the examination of the 
food habits and daily rations of the 
top predators in a system (Wetherbee 
and Cortes, 2004). In the northwest 
Atlantic Ocean ecosystem the shortfin 
mako ( Isurus oxyrinchus) is an abun- 
dant apex predator. We re-examine 
the diet and daily ration of shortfin 
makos in the northwest Atlantic and 
quantify an important predator-prey 
relationship that has existed for 
decades. 
In the northwest Atlantic, the 
shortfin mako ranges from the Ca- 
ribbean Sea and Gulf of Mexico, 
north to Nova Scotia, Canada, and 
the Grand Banks (Compagno, 2001). 
Starting in the early spring (mid to 
late May) shortfin makos appear in 
abundance off the northeast coast of 
the United States. The annual mi- 
gration to this region from the south 
and from offshore locales coincides 
