Wood et al.: Diet a of Isurus oxyrinchus in the northwest Atlantic Ocean 
77 
Map of the northeast coast of the United States showing the locations (•) of major shark fishing 
tournaments where shortfin mako ( Isurus oxyrinchus) stomachs were collected from May through 
October of 2001 and 2002 to determine the diet of this species. An approximate boundary ( - - - ) 
indicates where fishing took place for these tournaments. 
with the appearance of many teleost prey species. An 
early diet study from this region, during this seasonal 
residence, has indicated that teleosts make up 98% 
of the diet by volume, and that bluefish ( Pomatomus 
saltatrix) account for 77.5% of prey by volume (Still- 
well and Kohler, 1982). Bluefish are undoubtedly the 
most important prey species, but much has changed 
with the bluefish stocks since this initial examina- 
tion of the shortfin mako diet. Throughout the 1980s 
and early 1990s the northwest Atlantic Ocean bluefish 
stock experienced a decline in both young-of-the-year 
abundance and spawning stock biomass (Shepherd and 
Packer, 2006). This decline was likely a result of many 
factors, including natural population fluctuation, envi- 
ronmental and physical stresses, fishing pressure (both 
commercial and recreational), and intense predation by 
shortfin makos and other bluefish predators. 
To examine the current level of bluefish consumption 
by the shortfin mako, and to investigate whether preda- 
tion on bluefish has changed over the past two decades, 
we 1) re-quantified the diet from stomach contents 
data collected from the late May through October of 
2001 and 2002, and compared this current data with 
historical diet data (collected from 1972 to 1983); 2) 
back-calculated bluefish prey size to determine poten- 
tial predator-size-prey-size relationships; 3) calculated 
daily ration from the 2001-02 data with a bioenergetics 
model and the method of Elliot and Persson (1978). We 
attempt to address from our results, focusing on blue- 
fish as the most important prey, whether shifts in prey 
species abundance from historical levels are reflected 
in the shortfin mako diet. In addition, the potential 
regulatory effect of intense shortfin mako predation on 
bluefish in this region is investigated. 
Materials and methods 
Stomach collection 
Stomach contents were examined from shortfin mako 
caught in shark fishing tournaments carried out from 
May to October of 2001 and 2002 along the northeast 
coast of the United States. (Fig. 1). For the purposes of 
comparison with historical inshore data, these samples 
were considered to have been caught <45 nmi from 
shore and at a water depth of <91 m. Historical data 
on shortfin mako diet were provided by the National 
Marine Fisheries Service (NMFS), Apex Predators 
Program, located at the Northeast Fisheries Science 
Center (NEFSC) Narragansett Laboratory, Narra- 
gansett, RI. These data were collected from late May 
through October from 1972 through 1983 by NMFS 
staff and charter boat fishing crews at many of the 
