eight fish circling each school. The numbers of fish 

 that could be seen at this time were in the thou- 

 sands. During the day the dogfish retreated to 

 depths of 3 to 5 fathoms. Several hundred were 

 handlined from this depth for tagging and for 

 examining the embryos in the pregnant females. 

 In the lat« afternoon, occasional fish were again 

 observed at the surface. South of Cape Cod, the 

 dogfish were taken again a few fathoms below the 

 surface. They appeared whenever the otter tra wl 

 was hauled in and unwanted fish were discarded. 



Edwards, Livingstone, and Hamer (1962) 

 studied the distribution of fishes across the Con- 

 tinental Shelf from Nantucket Shoals to Cape 

 Hatteras. Their results indicate that male spiny 

 dogfish are usually found in cooler water than 

 the females. 



Little is known of the salinity preferences of the 

 spiny dogfish. Bigelow and Schroeder (1948), 

 however, note a record of a spiny dogfish that en- 

 tered a river in Denmark. In their opinion the 

 water was undoubtedly brackish at least near the 

 bottom, rather than fresh, since both cod and 

 Merhwc'tuH were also present in the river at the 

 same time. Spiny dogfish captured off British Co- 

 lumbia and studied in the laboratory, were able to 

 live for more than 1 hour in distilled water and 

 for nearly 2 hours in tap water (Quigley, 1928a). 

 The author concludes, "Since the dogfish continued 

 to breathe for an average of 113 minutes in tap 

 water and remained active during most of this 

 time, they probably could escape from a freshwater 

 stream even if they were to swim into it above 

 tide water level." 



TAGGING STUDIES 



Spiny dogfish have been tagged over most of 

 their range by biologists interested in making pre- 

 cise determinations of the migration routes of this 

 fish, and also in learning something of the nature 

 of the dogfish populations. Tag returns from 

 most of the experiments have been at a lower rate 

 than for tagging experiments with commercially 

 valuable fishes; in most fisheries the dogfish is 

 either a nuisance to he avoided or, at best, is re- 

 tained as a very minor pari of the catch. Al- 

 though many tagged dogfish are undoubtedly re- 

 captured, most are discarded at sea without having 

 their tags noticed; consequently, few tags are re- 

 covered. Tagging returns suggest thai t lie dog- 



fish is long lived, for several fish were at liberty 

 for 10 years. Some individual fish migrated long 

 distances. 



In a British experiment in November and De- 

 cember 1957, 75 spiny dogfish were tagged with a 

 yellow plastic tab attached with a braided nylon 

 loop (Beverton, Gulland, and Margetts, 1959). 

 The fish were tagged incidentally during a whit- 

 ing tagging experiment in the northwest part of 

 the Irish Sea. At the time of the report, after 7 

 months at liberty, only two tagged dogfish were re- 

 turned despite the fact that originally the dogfish 

 appeared particularly robust and little affected by 

 capture or tagging. No information was given as 

 to the place of recapture of the tagged fish. 



One thousand spiny dogfish were tagged near 

 the Shetland Islands, north of Scotland, in Nov- 

 ember 1958 (Aasen, 1960). The mark used was a 

 yellow slip of polyethylene film with printed text 

 rolled up as a cylinder and attached to the fish 

 with a stainless steel bridle in front of the first 

 dorsal fin. After 2i/o months at liberty, 12 tagged 

 fish (1.2 percent) were recaptured, most of them 

 near the west coast of Norway. After 2 years at 

 liberty, 10.8 percent of the dogfish had been re- 

 captured. The returns from this experiment, 

 combined with returns from nearly 3,000 dogfish 

 tagged in later experiments, yielded a combined 

 return rate of 6 percent. Aasen (1962) con- 

 cluded, "It is obvious that most of the fish migrate 

 towards the Norwegian coast in winter and return 

 to the grounds northwest of the British Isles in' 

 summer." 



Holden (1962) tagged 278 dogfish in the Irish 

 Sea during 1957-59, and 15 (5.4 percent) were re- 

 captured. Most of the winter recaptures came 

 from the southern part of the Irish Sea, while the 

 summer and autumn recaptures came from Scot- 

 land, as far north as the Shetland Islands. Pre- 

 sumably the dogfish wintered in the Irish Sea and 

 migrated to mingle with the Norwegian dogfish 

 north of Scotland in the summer. 



Nearly 10,000 dogfish were tagged in the waters 

 off British Columbia and Washington in the 1940's, 

 and 655 (6.7 percent) were recovered (Holland, 

 1957). In general, the tag returns demonstrated 

 a southward, coastal migration in the autumn and 

 winter and a northward migration in the spring 

 and summer. Several long-distance recaptures 

 were reported from the coastal migrations but the 



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U.S. FISH AND WILDLIFE SERVICE 



