WIGLEY ana BLRNS: DISTRIBUTION AND BIOLOGV OF MYSIDS 



'^ (MMATUflEj' -FmMATURE 



_j I I i_ 



JAN MAR. MAY JULY SEPT. NOV, JAN. MAR MAY JULY SEPT 



MONTHS 



Figure 18. — Schematic diagram of the age-size-maturity 

 composition of Neoriiysis americatia populations from off- 

 shore New England. 



Length of Life 



The Georges Bank population of .V. (uneticdna 

 appears to consist of two generations: (1) a 

 short-lived summer generation and (2) a long- 

 lived overwintering generation (Table 9, Figure 

 18). The summer generation stems from eggs 

 that hatch in late winter to late spring. They 

 grow rajsidly and mature in late summer and 

 autumn. Length of life of this generation is 



Table 9. — Range in body length of the (1) summer and 

 (2) overwintering generations of Neomysis americana, 

 by sexes and periods. 



Ronge in length 



Male 



All 

 specimens 



Ovigerous 



ond 

 lorvigerous 



estimated to be 6 to 10 months. They are the 

 ]irogeny of the overwintering group, the dom- 

 inant groui^ in the offshore New England area. 

 The overwintering generation originates from 

 eggs that hatch during the summer and autumn, 

 and perhaiJS even from late spring eggs. They 

 grow at nearly the same rate as the summer 

 generation but do not reach maturity until the 

 following spring. Thus, they are substantially 

 larger than the summer generation. Adults of 

 the overwintering generation are 10 to 15 mm 

 long, compared with 6 to 10 mm lengths for the 

 summer generation adults. Estimated length of 

 life of this overwintering group is 10 to 14 

 months. 



Relation to Bottom Sediments 



Although A', americana make daily excursions 

 from the sea bottom to upper water levels 

 (see BathiiTnetric Distribution), a substantial 

 amount of their time is spent on bottom, and 

 they appear to be selective in the type of bottom 

 they inhabit. The bottom type with which they 

 are most commonly associated is sand (Table 

 10). Kinds of sands they inhabit, in decreasing 

 order of importance are: fine, medium, and 

 coarse. One explanation for the scarcity of N. 



Table 10. — Frequency of occurrence of Neomysis ameri- 

 cana in various types of bottom sediments, based on the 

 NMFS collection. 



Bottom type 



Somples 



Specimens 



Rock-gravel 



Gravel-sand 



Glacial till 



Shell-sand 



Sond 



Sill-sand 



Silt-clay 



Unclassified 



Totol 



Number 

 5 

 10 

 

 4 

 131 

 7 

 7 



Number 



262 



37 







51 



7,987 



30 



25 



59 



8,451 



' Immotures less than 3 to 4 mm length usually passed through the 

 meshes of the sampling and processing equipment. 



americana in the middle and outer shelf areas 

 south of Rhode Island and New York may be 

 unsuitable sediments. The bottom over much 

 of this area is Ijlanketed with silty sands and 

 sandy silt, whereas on Georges Bank and much 



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