WIGLEY and BURNS: DISTRIBUTION AND BIOLOGY OF MYSIDS 



Length of Life 



An analysis of body length measurements did 

 not disclose trends in growth or separate length- 

 frequency modes that indicated year classes. 

 Immature specimens with an average length of 

 roughly 4.5 mm are present in June, August, 

 September, November, and December. The ma- 

 ture grouijs of both males and females in these 

 same months are mostly between 5 and 7 mm 

 long and do not exhibit the expected increases 

 in size as the seasons progress. Our tentative 

 conclusion is that E. enjfhrojihthalma has a 

 short life span, a rai)id growth rate, and a 

 lengthy spawning season. 



Relation to Bottom Sediments 



Members of this genus are considered to dwell 

 on or near the sea bottom, and our catch records 

 substantiate this view. It is uncommon in plank- 

 ton samples collected in the upper water layers, 

 but is regularly taken in hauls collected near 

 bottom. It occurred most frequently and in 

 greatest abundance on sand sediments (Table 2) . 

 Seventy-seven i^ercent of the samples and over 

 90% of the specimens were taken on, or over, 

 sand sediments. A moderate number of samjjles 

 (lO'^r ) were taken in areas of fine-grained sed- 

 iments. Furthermore, it should be added that 

 most of the sediments along southern Georges 

 Bank, where the majority of sami)les were taken, 

 contain modest amounts of silt, generally be- 

 tween 1 and 10'^. These quantities are insuffi- 

 cient to be incorporated in the bottom type ter- 



Table 2. — Frequency of occurrence of Erythrops ery- 

 throphthalma in variou.s types of bottom sediments, 

 based on the NMFS collection. 



minology (Shepard, 1954) . Although these are 

 small quantitities, the presence of silt on the 

 sediment surface makes it readily available to 

 the mysids. Furthermore, this species is com- 

 mon on the silty sediments in the region south 

 of Martha's Vineyard, Mass. Thus E. erythroph- 

 thalvia appears to inhabit sediments containing 

 a small to moderate amount of silt, in contrast 

 to N. amei-icaiia and M. bir/elmvi, which are 

 more common in sediments having a very low 

 silt content. 



Meterythrops robusta S. L Smith, 1879 



This rather large but uncommon species has 

 a wide distribution in boreal and subarctic wa- 

 ters. In the Atlantic region it has been reported 

 from the Kara Sea, Spitsbergen, Norway, Green- 

 land, Gulf of St. Lawrence, and in the Gulf of 

 Maine as far south as Cape Cod, Mass. In the 

 Pacific it occurs in the area between Alaska and 

 Washington. Moreover, assuming that M. mi- 

 crojihthalma is a synonym for M. robusta (.see 

 Banner. 1951), then its distrilnition also includes 

 the region off the east coasts of Japan and Korea 

 (Tattersall, 1951). 



The NMFS collection contains nine specimens 

 from six stations, all from the ]ieriphery of the 

 Gulf of Maine (Figure (5; Burns and Wigley, 

 Table 7). Four siiecimens were collected at one 

 station in the channel north of Browns Bank; 

 three sjiecimens were from three stations north 

 of Gi-eat South Channel; and two specimens 

 were taken off eastern Mas.sachusetts. 



Bathymetric distribution ranged from 64 to 

 150 m, and all specimens except one were from 

 depths between 110 and 150 m. 



The type of bottom sediments inhabited by 

 this species is distinctive. The bottom sediments 

 contained gravel at five of the six stations where 

 M. rohni<tu occurred. Three of the samjiles were 

 taken on glacial till; one sample was from sandy 

 gravel; one sample was from gravel; and one 

 sample was from silt-clay. All other offshore 

 s])ecies of mysids in the NMFS collection are as- 

 sociated with sand or finer grained sediments. 



All specimens of M. robusta in the NMFS 

 collection were caught in stramin nets or iiatu- 



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