38 BULLETIN OP THE BUREAU OF FISHEBIES 



Food. — The mackerel shark feeds on small fish, especially on mackerel and no 

 doubt also on herring (which are an important article in the diet of its European 

 congener) as well as on such other schooling fishes as shad and menhaden. It is 

 also known to eat hake and squid. We find no record of its eating Crustacea, 

 nor do fishermen report it as doing so. 



Commercial importance. — At the present time the mackerel shark is not of 

 any practical value in the Gulf of Maine. On the contrary it is often a serious 

 nuisance from its habit of rolling itself up in an inextricable snarl of t'nane when 

 it entangles itself in drift or gUl nets. Many years ago shark oil was prized by 

 curriers, and the livers of this species were tried out in considerable quantity, but 

 this was never more than a minor industry, abandoned before the middle of the 

 past century. It is interesting to read, however, that as much as 11 gallons of oil 

 have been obtained from the liver of a single shark 9 feet long, and report has it 

 that the richness of the livers in oU fluctuates over periods of years. 



Fig. 13. — Sharp-nosed mackerel shark (/surus ti^ris) 



12. Sharp-nosed mackerel shark {Isurixs tigris Atwood) 



Jordan and Evermann {Isurus dekayi Gill), 1896-1900, p. 48. 

 Garman, 1913, p. 36. 



Description. — This shark so closely resembles the common mackerel shark that 

 I need merely point out the points of difference. Most obvious of these is that 

 while in the latter the first dorsal originates above the armpit of the pectoral, in 

 I. tigris it stands altogether behind the inner corner of the latter, and the second 

 dorsal originates a short distance in front of the anal. Its snout, likewise, is sharper, 

 its pectorals narrower, and there is a color difference. 



Size. — About the same size as the porbeagle; that is, growing to a maximima 

 length of about 10 feet. 



Color. — Dark bluish-gray or bluish to ashy brown above, white below, and 

 without the black spot on the pectoral fin so characteristic of the common mackerel 

 shark. 



General range. — Gulf of Maine to the West Indies. 



Occurrence in the Gulf of Maine. — As I have pointed out above, there is no know- 

 ing how many of the "mackerel sharks" reported by fishermen in the GuK of Maine 

 may actually belong to this and not to the preceding species. However, not only 

 is it nowhere common so far as known, but its center of abundance seems to be 



