THE LOWER FISHES 



151 



Fig. 58. Thresher shark. 



THRESHER SHARK (fOX SHARk) : AlofiaS VulfeS 



Size: Matures at 14 feet. Rarely to 20 feet. 



Weight: Matures at 500 pounds. Rarely to 1,000 pounds. 



Distribution: Cosmopolitan in all warm seas. North to the state of Washington 

 and to New England in summer. 



Identification: Blackish to slate and brown, sometimes with a metallic luster. 

 The teeth are rather small. 



Habits: This is a pelagic species of ferocious appearance, but it is quite harm- 

 less and is almost exclusively a fish-eater. It provides one of the very few examples 

 of cooperative feeding among fishes, another being found among the puffers. 

 Several sharks herd moderate-sized, schooling fishes such as mackerel, herring, 

 or bonito into tight groups with the aid of their tails. Attack is thus made easier. 

 They may also use the tail to stun prey. The thresher is swift and voracious. 

 One was found off Scodand containing a bushel of fish in its stomach. Contrary 

 to rumor, threshers do not attack whales. It is a good food fish. 



SMOOTH DOGFISHES: Family Triakidae 



The first dorsal is large and just behind the pectoral fin. The second dorsal 

 is reduced in size, but it is not as reduced as in the similar requiem sharks, 

 Carcharinidae, so is noticeably larger than the anal fin. The lower lobe of the 

 tail fin is poorly developed. The last two gill slits are over the pectoral, and the 

 body is slender and tapering. These fish are very much like the requiem sharks 

 and are characteristic of shallow, warm temperate, and some tropical waters 

 the world over. However, thev tend to small size and are considered harmless. 

 There are both ovoviviparous and truly viviparous species. The flesh of most 

 species is good as food. 



SMOOTH dogfish: Miistehis canis 



Size: Averages 2V2 to 3V2 feet. Up to 5 feet. 



Distribution: Winters from Cape Hatteras to Chesapeake Bay. Arrives in 

 New England from May to June when the bottom water warms to about 45° 

 Fahrenheit. Rare in tropics, but known to Brazil. 



Identification: Plain gray to brown. Can change shade from dark gray to pale, 

 pearly white when over a light bottom. The change takes two days for maximum 

 effect. This is one of the few sharks able to change color. 



Habits: This, like all smooth dogfishes, is a shallow water fish rarely straying 

 beyond the 10-fathom limit except in the southern part of its range. It is most 

 common in bays and may enter brackish and fresh water. The teeth are arranged 



