nation of the two — is not clearly understood. 

 Part of the problem is the mystery of where the 

 dogfish spends it winters. Bigelow and Welsh 

 (1925) stated, "The winter home of the Gulf of 

 Maine dogfish is still to be learned." They ex- 

 amined the evidence, including the presence of the 

 adults in deep water in Long Island Sound in mid- 

 summer, the almost simultaneous appearance of 

 the fish all along the coast north of North Carolina 

 in the spring, and the capture of dogfish by the 

 Albatross, February 1920, in 164 to 365 m. along 

 the continental edge off Chmcoteague, Va., and 

 off Delaware Bay, and concluded that this ". . . 

 argues for an on-and-off rather than a long-shore 

 migration, with the deep water off the continental 

 slope as their winter home." 



More recent evidence of the presence of dogfish 

 in deep water during the winter has been accumu- 

 lated from observations of dogfish off the Middle 

 Atlantic and New England States (Bigelow and 

 Schroeder, 1936, 1948, 1953). In January 1961, 

 spiny dogfish were taken in an otter trawl by the 

 Bureau of Commercial Fisheries research vessel 

 Delaware in 158 to 183 m. along the edge of the 

 Continental Shelf 80 miles south of Martha's 

 Vineyard. 



At times, however, dogfish may come into shal- 

 low water in the winter. Collins (1883) quotes 

 an item in the newspaper "Cape Ann Advertiser" 

 dated February 10, 1882 : "Immense, schools of 

 dogfish, extending as far as the eye can reach, have 

 appeared off Portsmouth, an unusual sight in 

 winter." 



The accumulated wealth of evidence suggests 

 that temperature governs the seasonal movements 

 of the spiny dogfish. Bigelow . and Schroeder 

 (1948) note that dogfish do not appear along the 

 east coast until the water warms to 6° C. and dis- 

 appear when the water temperature rises to about 

 15° C. The preferred range of temperature on 

 the offshore wintering grounds seems to be 6° 

 to 11° C. 



Survey data (table 1) collected during 1949-59 

 by the Bureau of Commercial Fisheries Biological 

 Laboratory at Woods Hole indicate dogfish in the 

 Northwest Atlantic prefer bottom water tempera- 

 tures between 7.2° and 12.8° C. (average, 9.8°). 

 The average temperature at which 100 or more 

 dogfish per haul were caught during the period 



January-June was 8.3° C. ; for the period July- 

 December, 11.4° C. 



The survey data also tend to support Bigelow 

 and Schroeder's statement that this species winters 

 in relatively deep water, moving into shoaler water 

 in summer and fall. The average depth at which 

 100 or more dogfish were caught during the period 

 January-June is found to be significantly differ- 

 ent from the corresponding depth for the period 

 July-December (134 and 85 m., respectively). 



In Alaska waters incidental catches of spiny 

 dogfish are reported by Hanavan and Tanonaka 

 (1959) during experimental gill netting for sal- 

 mon. The dogfish were caught in the Bering 

 Sea and in the Gulf of Alaska during July and 

 August when the surface water temperatures 

 ranged from 7° to 13.3° C. 



In waters off Japan, Sato (1935) reports an in- 

 teresting diurnal migration of spiny dogfish. He 

 recorded the body temperatures of dogfish caught 

 in the daytime and at night, on a fishing ground 

 in depths of 110 to 128 m. Thirty dogfish caught 

 at night in a surface drift gill net had body tem- 

 peratures of from 9.5° to 11.2° C. The surface 

 water temperature at the time was quite similar, 

 from 9° to 12.2° C. In contrast, 28 dogfish caught 

 during the day on a longline on the bottom had 

 body temperatures of from 3.5° to 5.8° C. Unfor- 

 tunately Sato does not report the water tempera- 

 ture on the bottom. It seems reasonable to assume, 

 however, that the bottom water temperature was 

 within the range of the body temperature of the 

 fish caught on the bottom and that the dogfish were 

 rising to or near the surface at night and descend- 

 ing to the bottom during the day. 



In early August 1961, during a cruise of the 

 Bureau of Commercial Fisheries research vessel 

 Delaware, dogfish were frequently observed at or 

 near the surface on many of the inshore Gulf of 

 Maine fishing grounds (Robert L. Edwards, per- 

 sonal communication ) . The water temperatures at 

 the surface were normal for the season (around 

 15.6° C), but at the bottom they were abnormally 

 cold (2.8° to 3.9° C. at 73 m.). Few dogfish were 

 taken in the otter trawl at this time. 



Edwards (personal communication) observed 

 the dogfish appeared at the surface itself late at 

 night and early in the morning. One morning in 

 Ipswich Bay they were observed to be harrying 

 small schools of euphausiids — as many as six to 



LIFE HISTORY OF SPINY DOGFISH 



531 



