216 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 39. — Number of mature and immature yellowtail, by length, sex, and age, from the southern New England stock, 



May 1943 



50-percent point as s 2 = 0.946. From this it fol- 

 lows that the standard error s = 0.973 and the 95- 

 percent fiducial limits are 30.03 and 33.93 cm. 



Spawning Season 



Only scattered information on the spawning 

 season of yellowtail has been available. Bigelow 

 and Welsh (1925 : p. 499) observed that spawning 

 commences near Gloucester, Mass., by the middle 

 of March and seemingly lasts all summer. They 

 also found young larvae off Sandy Hook, N. J., 

 on August 1, 1913. Perlmutter (1939) found 

 pelagic larvae off Long Island, N. Y., in the vicin- 

 ity of Montauk Point, Jones Inlet, and Fire 

 Island Inlet, between May 16 and June 17, 1938 ; 

 and between June 8 and June 17 he found bottom- 

 living postlarval stages near Moriches Inlet, 

 Jones Inlet, and Fire Island Inlet. The larvae 

 observed off New York and New Jersey belonged 

 to the southern New England stock of yellowtail 

 flounder, but they were considerably removed 

 from the location of the fishery during the spawn- 

 ing season, which was centered off No Mans Land 

 and Block Island during our study. 



During the spring of 1943 the catch from these 

 areas, which was being landed at New Bedford, 

 was sampled periodically and the number of each 

 sex and the stage of maturity of the females re- 



corded (table 40). All females were dissected 

 and the ovaries were easily classified into the 

 three categories of immature, mature, and spent. 

 The inside of the immature ovary appears reddish 

 and somewhat gelatinous to the unassisted eye, 

 whereas the developing ova cause the mature 

 ovary to have a granular appearance several 

 months before spawning. After the fish spawns, 

 the ovarian contents are watery for several weeks, 

 usually include some unspawned eggs, and often 

 exhibit blood clots. Table 40 records the date on 

 which the vessel landed ; the fish were captured 1 

 to 4 days earlier. This lag could introduce error 

 if the ripe fish have the spawn squeezed out of 

 them by pressure in the fish hold and so be classi- 

 fied as spent. However observations indicated 

 that pressure affected only a small proportion of 

 the fish and no correction in the date was 

 warranted. 



Estimates of the peak and duration of the 

 spawning period were obtained by transforming 

 the data to probits (calculations are given in ap- 

 pendix F, p. 266) , and by fitting a line as indicated 

 in figure 24 which resulted in the formula 

 y = 8.281 + 0.04348,/-, in which y equals the esti- 

 mated probit and x equals the day of the year less 

 100. From this formula the following points were 



