WIGLEV and BURNS ; DISTRIBUTION AND BIOLOGY OF MYSIDS 



77 m (Tattersall, 1951; Grice and Harf; Hop- 

 kins, 1965). 



Depth range of the NMFS samples is from 

 13 to 179 m. By far the largest number of 

 samples (73rf ), greatest number of specimens 

 (91 "^r ), and highest densities occur between 30 

 and 80 m (Table 4). One collection taken at 

 an unusually deep locality, 179 m, is from the 

 northern edge of Georges Bank. The water 

 circulation in this area and its proximity to 

 shallow waters commonly inhabited by this spe- 

 cies may account for its presence at that rela- 

 tively great depth. 



Table 4. — Bathymetric distribution of Mysidopsis bigel- 

 owi, based on the NMFS collection. 



Water depth 



Somples 



Specimens 



10- 19 

 20- 29 

 30- 39 

 40- 49 

 SO- 59 

 60- 69 

 70- 79 

 80- 89 

 90- 99 

 100-109 

 170-179 



Number 

 4 

 3 

 9 

 8 

 9 

 7 

 6 

 4 

 2 

 I 

 1 



Number 



28 



10 



557 



493 



640 



73 



85 



22 



116 



1 



6 



Total 



54 



2,031 



Spawning 



This species spawns from April to November 

 in the coastal areas of Delaware (Hopkins, 

 1965) . There is no information about spawning 

 habits of the offshore and northern populations, 

 and we did not find a single ovigerous or lar- 

 vigerous specimen in the NMFS collection. We 

 do, however, have immature specimens repre- 

 sented in samples collected in May, August, Sep- 

 tember, November, and December. This is in- 

 dicative of a long spawning season, probably 

 from early summer through fall. 



The large size of immatures, 4.0 to 5.0 mm, 

 in May samples is believed to represent the over- 

 wintering young. The absence of ovigerous fe- 



^ Grice, George D., and Arch D. Hart. 1962. The 

 abundance, seasonal occurrence and distribution of the 

 epizooplankton between New York and Bermuda. Ap- 

 pendix to Ref. 62-4, Woods Hole Oceanogr. Inst. (Un- 

 published manuscript.) 



males in the many large samples collected in 

 December is evidence that spawning most likely 

 has terminated by that time of year. 



Sex Ratio 



The NMFS collection contains 313 males and 

 195 females, a ratio of 1.6 males to 1 female. 



Body Size 



This species is the smallest mysid in the 

 NMFS collection. A summary of body length 

 data by month of capture for males, females, 

 and immatures is given in Table 5. Range in 

 body length among all specimens in the col- 

 lection is 2.4 to 6.6 mm. The average length 

 of immatures is 3.8 mm, males 4.9 mm, and fe- 

 males 5.1 mm. Members of this species were 

 found to mature at 3.5 mm, smaller than any 

 other species in the NMFS collection. 



Table 5. — Means and ranges of body length of Mysi- 

 dopsis bigeloici by months and se.xes. 



Length of Life 



Our samples are inadequate to give an accu- 

 rate estimate of the length of the life cycle. The 

 few available clues, such as the presumably long 

 spawning season and the large size of the over- 

 wintering immatures, are suggestive of a life 

 cycle similar to Neomysis americnna: a short- 

 lived summer generation and a long-lived winter 

 generation. 



Relation to Bottom Sediments 



Many specimens in the NMFS collection were 

 taken with bottom samplers (Smith-Mclntyre, 

 Van Veen, and Campbell grabs) or gear that 



731 



