48 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



white spots on each side from the pectoral fin to 

 abreast of the anal fin, and with a few other 

 white spots in front of the first dorsal and behind 

 it, also in front of the second dorsal fin. These 

 spots are most conspicuous on small fish up to 12 

 or 14 inches long and they fade with growth until 

 they disappear altogether in some specimens. 

 The margins of the first and second dorsals, and of 

 the caudal are more or less dusky at birth, but 

 soon fade. The lower surface ranges from pale 

 gray to pure white. 



Size. — The majority are between 8% and 13 

 inches long when born. Most of the adult males 

 are from about 2 feet to a little less than 3 feet 

 long; adult females are from a little less than 2% 

 feet to almost 3% feet; maximum length about 

 four feet. Mature females average 7 to 10 pounds, 

 a few reach 15 pounds if very fat, and 20 pounds 

 has been reported. 



Habits. — Much has been written of the habits 

 of the spiny dogfish, but nothing to recommend 

 it from the standpoint either of the fishermen or 

 of its fellow creatures in the sea. It is one of the 

 more gregarious of our fishes, swimming in schools 

 or packs. Swedish fishermen assert that young 

 dogs school separately from their parents, and it 

 is certain that fish of a size continue to associate 

 together as they grow, the result being that any 

 given school runs very even, consisting as a rule 

 either of the very large mature females, or of 

 medium-sized fish (either mature males or im- 

 mature females) , or of small immature fish of both 

 sexes in about equal numbers. 



Apart from their general seasonal migratory 

 movements, dogfish are governed by the move- 

 ments of the fishes on which they prey. And re- 

 cent marking experiments have shown that some 

 of them cover long distances in their wanderings, 

 for two tagged near St. Johns, Newfoundland, in 

 mid-July 1942 were recaught off Cape Ann, 23 

 one on November 23, 1943, the other on Decem- 

 ber 4 of that year, 24 while others from the same 

 tagging experiment were caught within the Gulf 

 of St. Lawrence. 25 Fortunately they seldom stay 

 long in one place, but there is seldom, if ever, a 

 time during the summer when they are not com- 

 mon on some part of the Gulf of Maine coast. 

 So erratic are their appearances and disappearances 



23 About 14 miles offshore. 



24 On Middle Ground about 25 miles off Cape Ann. 



" Templeman, Fish. Res. Bull., Newfoundland Dept. Nat. Res., No. 15, 

 1944, pp. 67-69. 



that where one has good fishing today he may 

 catch only dogfish tomorrow and nothing at all 

 the day after, the better fish having fled these sea 

 wolves and the latter departing in pursuit. 



The dogfish use their back spines for defense, 

 curling around in a bow and striking, which makes 

 them hard to handle on the hook. It is probable, 

 too, that the spines are slightly poisonous, general 

 report to this effect being corroborated by the 

 fact that the concave surfaces are lined with a 

 glandular tissue resembling the poison glands of 

 the venomous "weever" (Trachinus draco) 26 of 

 Europe. 



Voracious almost beyond belief, the dogfish 

 entirely deserves its bad reputation. Not only 

 does it harry and drive off mackerel, herring, and 

 even fish as large as cod and haddock, but it 

 destroys vast numbers of them. Again and again 

 fishermen have described packs of dogs dashing 

 among schools of mackerel, and even attacking 

 them within the seines, biting through the net, 

 and releasing such of the catch as escapes them. 

 At one time or another they prey on practically all 

 species of Gulf of Maine fish smaller than them- 

 selves, and squid are also a regular article of diet 

 whenever they are found. Dogfish are also known 

 to take worms, shrimps, and crabs. And when 

 they first arrive at Woods Hole in May they 

 are often found full of Ctenophores, being one 

 of the few fish that eat these watery organisms. 

 Often, too, they bite groundfish from the hooks 

 of long lines, or take the baits and make it futile 

 to fish with hook and line where they abound. 



Fishermen are familiar with the fact that the 

 female spiny dog bears "living" young (this has 

 been known since the days of Aristotle). The 

 eggs are large, well stored with yolk, and during 

 early stages those in each oviduct (so-called 

 "uterus") are contained in a horny capsule that 

 breaks down later, leaving the embryos free in the 

 "uterus," to which they have no placental attach- 

 ment. The number in a litter is commonly 4 to 6; 

 sometimes as many as 8 to 11, or as few as 2. 



According to recent studies, the females carry 

 their young for 18 to 22 months. Accordingly, the 

 adult females caught in our Gulf contain either 

 very early embryos, averaging only about three- 

 fourths of an inch in length by September, or 



* Evans (Pbilos. Trans. Royal Soc., London, Ser. B, vol. 212, 1923, pp. 8, 

 27) describes the spines and gives clinical records of the effects of wounds 

 inflicted by them. 



