228 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The near-bottom temperatures, which may 

 fairly well reflect the conditions actually pertain- 

 ing during the spawning, were nearly all consider- 

 ably lower than the surface temperatures. Near- 

 bottom temperatures ranged from 4.9° C. off 

 Martha's Vineyard on cruise 1 to about 12.3° C. 

 on cruise 4 at the southern center of distribution 

 of small larvae. Doubtless spawning preceded 

 these observations of temperature by some days, 

 and therefore, at both ends of this range should 

 perhaps be somewhat lower. 



These temperatures give some evidence of con- 

 siderable environmental changes. An invasion of 

 warm water along the edge of the Continental 

 Shelf south of Martha's Vineyard and Long 

 Island occurred on cruise 1 and was strong enough 

 to raise bottom temperatures to 10.9° C. at the 

 edge of the shelf while the surface temperature 

 was only 6.8°. The warming was immediately 

 countered by cold water which persisted until 

 after cruise 6 when at Martha's Vineyard station 

 III the bottom temperature increased from 6.1° to 

 8° C. between cruises 6 and 7. 



Such fluctuating temperature conditions prob- 

 ably occur most frequently along the edge of the 

 Continental Shelf with the alternating invasion 

 and retreat of the warm slope waters. The areas 

 of gross temperature changes are not known to in- 

 clude the 15- to 35-fathom depth zone, which is 

 probably inhabited by the spawning yellowtail, 

 but Ketchum et al. (1951) found that the distri- 

 bution of sea water diluted with river water in 

 the New York bight varied greatly and could be 

 altered suddenly by a storm. Such fluctuations in 

 temperature must be a hazard to the larvae be- 

 cause of the accompanying movement of the 

 water. The surveys show clearly that the larvae 

 are distributed widely over the shelf and that 

 when they descend to the bottom of the ocean they 

 may encounter radically different bottom condi- 

 tions and water temperatures. If yellowtail fry 

 are as delicate as most fish fry, rather small differ- 

 ences in their environment may be fatal. Changes 

 in temperature might even be catastrophic, as in 

 the widespread destruction of the tilefish, which 

 occurred along the edge of the Continental Shelf 

 south of Block Island in March 1882 (Collins 

 1884). This occurrence is believed to have been 

 caused by an invasion of cold water in an area 

 normally warmed by the slope water during 

 winter. 



FAUNAL CHANGES ON THE 

 YELLOWTAIL GROUNDS 



In our studies of the fisheries in the New Eng- 

 land area, we have found two examples of signifi- 

 cant production of other species on yellowtail 

 grounds. The first of these occurred when the 

 landings of haddock from Nantucket Shoals rose 

 to nearly 13 million pounds in 1928 and subse- 

 quently declined (table 46). These are the land- 

 ings credited to the three principal ports in New 

 England in the annual volumes of Fishery Indus- 

 tries in the United States, published by the Bu- 

 reau of Fisheries and subsequently the Fish and 

 Wildlife Service. Most of the haddock appar- 

 ently came from almost exactly the depth range 

 and location subsequently to become a major yel- 

 lowtail producing area. Rounsefell (1948, fig. 6) 

 plotted the areas fished by medium and large 

 otter trawlers seeking haddock from 1928 to 1937. 

 These plots show that the catches credited to the 

 Nantucket Shoals area were centered at about 

 latitude 40°40' N., longitude 69°40' W T ., in a depth 

 of about 25 fathoms, although the spread of the 

 fishing was from approximately 15 to 35 

 fathoms, with some tendency toward fishing 

 shoaler waters from February through May. 

 During most of our studies, the part of this area 

 between 15 and 25 fathoms in depth was the sec- 

 ond most important yellowtail producing ground 

 (fig. 2), with production ranging from 22 million 

 pounds in 1942 to a little over 5 million pounds in 

 1949. 



Table 46. — Landings of haddock and flounders at principal 

 New England ports from the Nantucket Shoals, Lightship 

 Grounds, and No Mans Land areas, 1925-49 



[In thousands of pounds] 



For source see appendix A, p. 237. 



