FEATURES OF GENERAL BIOLOGICAL INTEREST 383 



(2) Rough ground with coralUne hydroids and coarse deposits prevails to the south, and in many 

 places along the shelf edge. Finer deposits are found to the northward, with better conditions for 

 trawling. 



(3) The main current affecting the area is the relatively cold Falkland current flowing from south 

 to north, coldest along its offshore margin. The warm Brazil current impinges upon this offshore in 

 the extreme north-east of the area, where the hydrological conditions may be very complex, but this 

 is too far offshore normally to affect conditions on the shelf. On the inshore flank of the Falkland 

 current (which is a movement of sub-Antarctic surface water) the flow is not so strong, so that ' old 

 shelf water ' is warmed and sometimes even flows southwards as a small intermittent counter-current 

 close in to the land. This seems to have an important effect on the distribution and movements of 

 some of the fishes. 



(4) The annual cycle of surface temperatures is centred lower than in corresponding latitudes in the 

 northern hemisphere, with the peak after mid-summer; and the annual range is small. At greater 

 depths, while the range of temperature is of course even smaller, the time lag between sea and air 

 temperatures is even greater, so that bottom temperatures are highest in autumn and lowest in spring 

 or early summer. 



Some preliminary observations on plankton conditions have been discussed, but the large collections 

 obtained will require many years working up by specialists before one could fully consider the inter- 

 actions of this part of the biological environment with the fish fauna. The same must be said of the 

 copious collections of benthos. However, with regard to the plankton conditions, at least, some 

 important features are already fairly clear. While the general facies of the plankton is closely similar 

 to that found in cold temperate waters in other parts of the world, two major differences are already 

 discernible. 



First, with regard to the phytoplankton conditions (the basic element in the life cycles of any sea 

 area) it seems reasonably certain that the onset of the main increase falls later in the year than in 

 corresponding latitudes in the northern hemisphere, especially along the outer edge of the shelf. 

 Production probably begins earliest inshore, owing to more favourable conditions for the establish- 

 ment of a thermocline, but even so the cycle is later than (say) on the hake grounds south of Ireland. 

 Dependent cycles of higher organisms must therefore also be centred later in the year, the whole 

 ' plankton-calendar' (Bogorov, 1941) being later. Even the larger nekton (fish and squids), all of which 

 must be affected directly or indirectly by the plankton conditions, must be expected to show a similar 

 ' lateness ' in their biological seasons. Direct evidence of this is already forthcoming in a few instances, 

 as in the apparent spawning times of some of the fishes. Species apparently corresponding to spring- 

 spawners elsewhere here seem to spawn around mid-summer, and whereas hake may generally be 

 regarded as summer spawners the local species has been found ripe chiefly in early autumn, although 

 some had certainly spawned earlier. 



Secondly, with regard to the zooplankton, although euphausians, Parathemisto, and calanoid cope- 

 pods are prominent among the larger Crustacea, as elsewhere, there is a notable local abundance of 

 ' lobster-krill ', the pelagic post-larvae of two species of Munida. This is paralleled elsewhere only in 

 New Zealand waters (where one of the same species occurs) and on some parts of the Pacific coast of 

 North and South America. Off Patagonia lobster-krill are an important food of whales and seals, birds 

 and fishes, especially the younger individuals of the larger fishes, that later become almost exclusively 

 ichthyophagous, like the hake. (This is equally true of Munida in New Zealand waters, where they 

 are commonly referred to as 'whale-feed'. See Matthews (1932), and Rayner (1935).) 



Proceeding to general consideration of the fish fauna, as a whole : its chief characteristics have been 

 illustrated by comparison and contrast with the faunas of better known fishing-grounds elsewhere. 



