NOTES 



AGGREGATION OF THE SIPHONOPHORE 



NANOMIA CARA IN THE GULF OF MAINE: 



OBSERVATIONS FROM A SUBMERSIBLE 



Large concentrations of a physonect siphono- 

 phore, Nanomia cara Agassiz 1865, were present 

 in the Gulf of Maine during fall and winter of 1975. 

 These gelatinous, colonial coelenterates were 

 sufficiently abundant that they clogged trawl ne' s 

 and occasioned considerable losses of time and 

 money to commercial fishermen at several New 

 England ports (Rogers in press). During October 

 and November 1975, scuba divers on the Helgo- 

 land habitat in 30-m shoals off Rockport, Mass. 

 (Figure 1), noted concentrations of N. cara reach- 

 ing 1 colony/m^ throughout the water column (R. 

 A. Cooper and H. W. Pratt unpubl. data). Off 

 Rockport again in late March 1976, divers esti- 

 mated densities of 1 to 2 colonies of A^. cara/m^ in 



CASHES 

 LEDGE 



7-o,o6 ,8r» B-s 



O^-. 00-30 



SUBMERSIBLE DIVES 

 LOCATIONS- JUN. 1976 



 NANOMIA CARA OBSERVED 

 O N CARA NOT OBSERVED 



40 M 

 80 M 



Figure l. — Distribution of siphonophores at dive sites of the 

 submersible Nekton Gamma and the position of the Helgoland 

 habitat (insert). 



water only 9 m deep (H. W. Pratt pers. commun.). 

 In April and again in early May 1976, a series of 

 100-m to surface oblique plankton tows was taken 

 in the Gulf of Maine along a transect from the 

 Wilkinson Basin to Cape Ann, Mass., by AZfta^ross 

 IV, a fisheries research ship of the Northeast 

 Fisheries Center. In these deeper water areas, as 

 well, high densities of N. cara apparently per- 

 sisted through the winter months and were 

 present at each station occupied, although the 

 aggregations were somewhat less numerous and 

 colonies appeared smaller than those encountered 

 during fall 1975 (Rogers in press). 



The difficulties and limitations inherent in 

 using plankton nets to sample quantitatively 

 populations of siphonophores and other fragile 

 gelatinous zooplankton have been reviewed by 

 Hamner et al. (1975), who suggested in situ scuba 

 observations as an alternative method for study- 

 ing gelatinous taxa. In the present study we used 

 the two-man research submersible Nekton 

 Gamma to estimate the size and density of the iV. 

 cara aggregations and to evaluate some of the 

 biotic and abiotic factors which might influence 

 their distribution below depths easily accessible to 

 scuba divers. In June 1976 we made six dives 

 along a transect from Provincetown, Mass., to 

 Cape Ann (Table 1, Figure 1). Dives were of 90 to 

 160 min duration during which we surveyed the 

 water column from surface to bottom. Other ob- 

 servers made 25 additional shorter dives to look 

 for siphonophores at adjacent stations. Observa- 

 tions were narrated and recorded on tape through- 

 out each dive. The submersible pilot relayed in- 

 formation on temperature and depth and this was 

 combined with comments on siphonophore col- 

 onies such as size, density, swimming speed, as- 

 sociated species, and other factors of interest. 

 Photographs were taken with a 35-mm camera 

 and a video tape camera with a sound track was 

 also used to record and verify visual observations 

 and estimates. After each dive information was 

 transcribed from the tapes and videotapes were 

 reviewed and discussed by the observers. 



Observations 



Gulf of Maine surface temperatures in mid-June 

 1976 ranged from 12.5°C in the Wilkinson Basin 



281 



