FISHERY BULLETIN: VOL. 69. NO. 4 



Bathymetric Distribution 



A'', americana is a shallowwater species most 

 commonly reported from the intertidal zone to 

 depths of 60 m. However, it appears to inhabit 

 somewhat deeper water in the Georges Bank 

 region as indicated by the records of occurrence 

 in Figure 17. Whiteley (1948) reported it from 

 a number of plankton samples taken at stations 

 where the water depth was 75 m, but at very few 

 localities where depths were greater than 100 m. 

 Greatest depth reported for this species is 214 m 

 (Wigley, 1964). 



Depth range for the samples in the NMFS 

 collection is 1 to 232 m. Fretiuency distribution 

 for these samples is listed in Table 8. This spe- 

 cies is common from the intertidal zone out to 

 90 m but is most abundant at dejjths between 

 30 and 60 m. 



Table 8. — Bathymetric distribution of Neomysis ameri- 

 cana, based on tlie NMFS collection. 



A^. amerkanu undertakes I'egular vertical mi- 

 grations between the sea bottom and the upper 

 water layers. Light intensity is the primary 

 controlling element to which the mysids are re- 

 sponding. The.v move to deeper, darker regions 

 during daytime and upward toward the surface 

 at night (Ilurlbut, 1957; Herman, 1963). The 

 NMFS samples jirovide veiy little information 

 on this asjiect other tiian to substantiate i)robable 

 vertical migration in shallow water. At depths 

 of less than 50 m on Georges Bank this si)ecies 

 is more common in bottom samples collected dur- 

 ing the davtime than at night. 



Spawning 



Though spawning of coastal populations of .V. 

 americana takes place throughout the year, it is 

 much more intensive during the warmer months 

 of April through October (Smith, 1879; Fish, 

 1925; Cowles. 1930; Herman, 1963; Hopkins, 

 1965). The Georges Bank population was re- 

 ported by Whiteley (1948) to spawn in the 

 spring. S])ecimeiis in the NMFS collection indi- 

 cate spawning of Georges Bank stocks from 

 March through October and possible spawning in 

 all months of the year. There appear to be two 

 major spawning jieriods, one in the sirring 

 (March through June) and another in the late 

 summer and fall (August through October). 

 Of the ovigerous or largiverous specimens pi-e- 

 pent in samples collected every month from 

 March to October the largest numbers occurred 

 in March through June and August through 

 October. Immature specimens were particularly 

 numerous in August and December. The small 

 number of immature specimens collected in late 

 winter and early spring may indicate occasional 

 small-scale spawning in winter. 



Two distinct size groups (summer generation 

 and overwintering generation) of s]iawning fe- 

 males are discernable; one grouji spawns in the 

 spring, the other in the fall (Figure 18) . Spring 

 spawnei's have an average length of 11 to 12 mm, 

 and ]iroduce a clutch containing about 26 eggs. 

 Fall spawners have an average length of 6 to 

 8 mm, and their clutch contains only about six 

 eggs. Additional information about these two 

 generations is given below. 



Eggs are spherical, 0.38 to 0.42 mm in dia- 

 meter, in both the summer and overwintering 

 generations. 



Size of the larvae varies according to their 

 stage of development. Average lengths in milli- 

 meters for the following stages are: stages I and 

 H— 0.39, stage HI— 0.55, stage IV— 0.85, stage 

 V— 0.96, stage VI— 1.15, and stage VII— 1.34. 



Sex Ratio 



The NI\IFS collection contains 1,574 males 

 and 1,669 females; the ratio is 0.94 male to 1 

 female. 



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