SEASONAL DISTRIBUTION OF SIBLING HAKES, 

 UROPHYCISCHUSS AND U. TENUIS (PISCES, GADIDAE) 



IN NEW ENGLAND 12 



John A. Musick^ 



ABSTRACT 



The seasonal distribution patterns of sibling hakes, Urophycis chuss and U. tenuis, differ from 

 one another in depth and geographic area and within each species by life history stage. 



Urophycis chuss spawns off southern New England in depths of less than 60 fm and probably 

 at temperatures between 5° and 10°C. Two major spawning concentrations occur, one east of Block 

 Island, the other on the southwest part of Georges Bank. Spawning in the Gulf of Maine probably 

 occurs inshore at depths shoaler than 30 fm. After spawning, the adult fish disperse and the larger 

 individuals move offshore into water 60 fm or deeper where the mature fish remain until the 

 following spring. Juvenile U. chuss are inquiline within sea scallops, Placopecten magellanicus , 

 until they outgrow their hosts or until water temperatures, colder than about 4°C, either kill the 

 hake or force them to seek out warmer temperatures in deeper water. Immature U. chuss remain 

 in the vicinity of the scallop beds if water temperatures are compatible until the fish are in their 

 second year of life. During that autumn, the fish migrate inshore to within 30 fm and remain 

 until water temperatures drop to about 4°C, at which time they move to warmer, deeper water 

 along the offshore shelf. The following spring, these fish migrate inshore with the older adult fish 

 during April and by summer are mature and attain the typical seasonal behavior of adults. Im- 

 mature U. tenuis in the Gulf of Maine occur at all depths but tend to remain in shallower water 

 than the adults during the winter. Mature U. tenuis migrate inshore in the northern Gulf of Maine 

 in the summer, disperse in the fall, and move into the deepest area of the Gulf in winter. Along 

 the eastern edge of Georges Bank and west of there, both immature and mature U. tenuis are 

 fish of the continental slope. Both stages occur over the shelf in small numbers, but at all seasons 

 the highest concentrations are found deeper than 100 fm. The distribution patterns of these two 

 sibling species are not coincidental, as assumed in the past. Rather, they are complementary. 

 Urophycis chuss is more abundant in the Mid-Atlantic Bight, whereas U. tenuis is more abundant 

 on the Scotian shelf, in the Gulf of St. Lawrence, and on the Grand Banks. They occur together 

 most often in the Gulf of Maine. But even there, U. chuss is more abundant in the southwest sector 

 and U. tenuis predominates in the northern part and in the Bay of Fundy. 



The geographical ranges and seasonal movements 

 of the red hake, Urophycis chuss (Walbaum), 

 and of the white hake, U. tenuis (Mitchill), have 

 not been defined because previous workers have 

 had difficulty in distinguishing between the two 

 species (Musick, 1973). The purpose of the present 

 paper is to examine the validity of published 

 accounts of the ranges off/, chuss and U. tenuis; 

 to compare the seasonal distribution of the two 

 species with regard to depth, bottom temperature, 

 and substrate in New England waters; and to 

 determine whether the patterns of seasonal dis- 

 tribution vary among juvenile, immature, and 

 adult stages (these stages are defined below). 



' Contribution Number 562 of the Virginia Institute of 

 Marine Science. 



* This paper contains parts of a Ph.D. dissertation submitted 

 to Harvard University. 



' Virginia Institute of Marine Science, Gloucester Point, VA 

 23062. 



Two recent faunal works treat both species 

 together and give the northern limit of distribu- 

 tion of U. chuss and U. tenuis as Labrador 

 (Leim and Scott, 1966) or the Grand Banks of 

 Newfoundland (Bigelow and Schroeder, 1953). 

 However neither documentation nor voucher 

 specimens are available to establish the presence 

 of U. chuss off Labrador or on the Grand Banks 

 (as there are for U. tenuis). Kendall (1909) re- 

 ported U. tenuis from Labrador, and the New- 

 foundland Fisheries Research Commission (1932, 

 1933, 1934) captured U. tenuis along the south- 

 western edge of the Grand Banks during warmer 

 months of the year. Templeman (1966) reported 

 that all Urophycis taken commercially on the 

 Grand Banks have been U. tenuis (1966) and 

 that he had never seen a specimen of U. chuss 

 from Newfoundland waters (pers. comm.). Jordan 

 and Evermann (1898) and Breder (1948) gave the 



Manuscnpt accepted September 1973. 

 FISHERY BULLETIN; VOL. 72. NO. 2. 1974. 



481 



