TETRAPLATIA VOLITANS 



135 



VERTICAL DISTRIBUTION 



It is well known that Tetraplatia volitans can occur in surface waters in the Mediterranean (Busch, 

 1851) and elsewhere (Komai, 1939; Hand, 1955). The most recent authors to present some details of 

 vertical distribution have been Hand (1955) and Beyer (1955). From a study of horizontal closing- 

 net hauls taken off the Californian coast, Hand concluded that Tetraplatia undergoes vertical migration 

 with centres of population at about 40 m. by night and at about 250 m. or more by day. Hand 

 further concluded from separate open-net hauls that ' in general, the deeper the tow the more specimens 

 were captured '. Concerning this type of fishing (done by the earlier expeditions), we are in agreement 

 with his views that ' little but speculative results can be gleaned from them and no exact information 

 is available on the lower limits of the vertical distribution of Tetraplatia'. 



Beyer (1955) reported two specimens from the 'Brategg' Expedition in a vertical haul from 1000- 

 550 m.,* this being the first indication that Tetraplatia was to be found below 550 m. In an appendix 

 he mentioned briefly other specimens from the closing-net hauls of the Discovery collections. These, 

 together with many additional records (which have subsequently come to light), are discussed here. 



The following table (Table i) summarizes the data on nets, fishing-depth and soundings for catches 

 of Tetraplatia in the closing-net hauls of the Discovery collections. 



Table i . Summary of data on type of net, fishing-depth and 



Expedition Station Type of net Fishing-depth (m.) 



H.M.S. 'Research' 



R.R.S. 'Discovery 11' 



320 



35* 



670 



943 



1773 



1775 



1778 



1913 



2024 



2356 

 2386 

 2496 

 2582 

 2641 

 3230 



3233 

 3234 



3272 

 3273 



TYFB 



N70 V 

 N70V 

 N70V 

 N70V 

 N70B 

 N70V 

 N70 V 



N70V 

 N70V 



N 100 B 



N50V 



N70V 



N70V 



N70V 



N70V 



N70V 



N70V 



TYFB 



N70V 



N70V 



sounding 



Sounding (m.) 

 Over 3657 



2552 

 5202 

 4166 

 3000 

 1628 



4495 

 1980 

 4089 

 3482 



3897 

 4885 



1420-1110 



4817 



2513 

 4848 

 4707 



This table serves to emphasize that Tetraplatia is a pelagic animal frequently occurring far from 

 land and is to be found over very deep water. These results are summarized in Table 2 for the 

 closing-net hauls of 'Discovery H'. 



Only a very small percentage of the Discovery collections have been examined for Tetraplatia, so 

 that we do not propose to discuss the relative numbers of specimens caught at different depths; what 

 does emerge, however, is that Tetraplatia has been taken at all levels from the surface down to the 



* Presumably a closing-net. 



