190 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The average rate of movement of the S group larvae during the period from May 4 

 to June 6, while they were dependent for transport on wind-impelled drift, was 6 

 nautical miles per day. As nearly as may be estimated from data recorded on the 

 Beaufort Scale, the net wind movement in the direction of the resultant (neglecting 

 forces under Beaufort 3), was about 60 nautical miles per day. The movement of the 

 center of post-larval abundance between June 6 and July 1, accomplished in part by 

 swimming, averaged 3% nautical miles per day. If the movement of post-larvae 

 between June 27 and July 24 may be taken as from off Shinnecock to off Chatham, the 

 average rate during this period was 6 nautical miles per day. 



The movements of the R and T groups of larvae can be traced in the same manner 

 as were those of the S group. The R group, beginning with cruise I, as 3 to 5 mm. 

 larvae, moved southward from the Winterquarter section to the Chesapeake section. 

 Like the S group, they remained at this southern extremity of the range through 

 cruise III and also probably through cruise IV, though during the latter cruise there 

 were not sufficient stations occupied in this area to prove this. On cruise V, however, 

 they were found to have moved northward to Cape May, and on cruise VII were 

 discovered off Shinnecock. At the beginning of this northerly movement, they were 

 already 8 to 10 mm. long, and thus capable of swimming. With favoring winds 

 during all but the last portion of this northerly trip, their movement was rapid, 

 averaging 1 1 nautical miles per day. 



The T group could not be so readily followed, but in general its movements 

 were with the wind in the larval stage and indifferent to the wind in post-larval stages. 

 Between cruises III and VI, when the winds were from the southwest, it shifted 

 in an easterly direction from the Shinnecock section to the Martha's Vineyard section. 

 The correspondence between wind direction and this movement was not as perfect 

 as that of the S group, formerly described. From cruise III to cruise IV, there 

 appeared to be a spread in both easterly and westerly directions, and between IV 

 and V, there was a contraction toward the center of the group off Montauk Point. 

 These changes in distribution may be indicative of spurts of spawning rather than 

 movements of the egg population, for they occurred during periods of egg develop- 

 ment, and the stages chosen may not have been exactly the continuation of the original 

 stage A eggs of cruise III. It probably suffices to note that when first seen as stage 

 A, they were off Shinnecock, and by attainment of lengths of 4 to 5 mm. at cruise VI, 

 they were off Martha's Vineyard. Then between cruises VI and VTI, with only 

 a slight wind movement from the west, the zone of densest larval population remained 

 at Martha's Vineyard, though fair numbers were as far west as Shinnecock. Between 

 cruises VII and VIII, while the winds were from the southwest, the members of this 

 group spread over the waters abreast of Long Island, extending from the New York 

 to the Shinnecock section. During this interval they had grown into the post-larval 

 stage, 10 to 12 mm., when swimming activity made their movements fairly independent 

 of the wind. 



It may be concluded therefore, that the movement of eggs and larvae (up to 10 

 mm. in length) in the southern spawning area between Cape Cod and Cape Hatteras 

 was governed by the drift of surface wateis, and this, in turn, by the direction of the 

 stronger winds during the 40 days while the mackerel were passing through these 

 phases of development and growth. These drifts may be as fast as 6 nautical miles 

 per day and may convey the mackerel several hundred miles. After reaching the 

 post-larval stage (10 mm. and upward) the movements are less dependent on drift, 

 and probably are considerably aided by the tiny fishes' own swimming efforts. The 



