Recalculated diet and daily ration ofthe shortfin mako (Isurus oxyrinchus),with a focus on quantifying predationon bluefish (Pomatomus saltatrix)in the northwest Atlantic Ocean

Wood , Anthony D.; Wetherbee, Bradley M.; Juanes, Francis; Kohler, Nancy E.; Wilga, Cheryl

Recalculated diet and daily ration ofthe shortfin mako (Isurus oxyrinchus),with a focus on quantifying predationon bluefish (Pomatomus saltatrix)in the northwest Atlantic Ocean

2009

Wood , Anthony D. | Wetherbee, Bradley M. | Juanes, Francis | Kohler, Nancy E. | Wilga, Cheryl

The diet and daily ration of the shortfin mako (Isurus oxyrinchus) in the northwest Atlantic were re-examined to determine whether fluctuations in prey abundance andavailability are reflected in these two biological variables. During the summers of 2001 and 2002, stomachcontent data were collected from fishing tournaments along the northeast coast of the United States. These data were quantified by using four diet indices and were compared toindex 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, accounting for 92.6% of the current diet by weight and 86.9% of the historical diet by volume. From the 2001– 02diet data, daily ration was estimated and it indicated that shortfin makos must consume roughly 4.6% of their body weight per day to fulfill energetic 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 average 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 shortfin mako predation on bluefish abundance in the region.

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