348 DISCOVERY REPORTS 



cold seems less than that of Merluccius, its tolerance of heat seems similarly restricted, for Thyrsites 

 does not penetrate so far up the east coast of South Africa, into the region of the warm Mozambique 

 current, as does Merluccius capensis. Thus Thyrsites seems limited to cool southern subtropical (rarely 

 sub-Antarctic) waters where the surface temperatures range from about lo to about 20° C. ; whereas 

 species of Merluccius range from areas with surface temperatures below 8° C. to the tropical con- 

 vergences (temperature about 23° C. at the surface). The difference in thermal tolerance may be more 

 precisely expressed by the statement that the optimal range for Merluccius is centred lower than that 

 for Thyrsites, but the total range of Merluccius is the wider. Thyrsites is much more exclusively pelagic 

 in habit than are any of the Merluccius spp., which may be regarded as demersal fishes during the 

 daylight hours, and whose distribution will thus be affected by the cooler subsurface temperatures to 

 a much greater extent. For this reason I believe that Thyrsites will only be found to work southwards 

 into our area close to the mainland coast, in the warmer counter-current of ' old shelf water', or right 

 offshore, where the influence of the warm Brazil current sometimes extends to about 49° S. I do not 

 think that the species would normally cross the colder portions of the Falkland current, and such few 

 stragglers as occasionally reach the Falkland Islands themselves (Norman, 1937, p. 96) have probably 

 come from the north-east. 



T. atun is most excellent eating, with exceptionally firm white flesh of good flavour and (in due 

 season) rather high fat content. In November 1933, when the ' Discovery II ' was outward bound on 

 her third commission, we paid a brief visit to Tristan da Cunha, and there secured a plentiful supply 

 of these fine fish by somewhat novel methods. While lying at anchor in about 7 fm., near the edge of 

 the kelp off the main landing place, the fish were observed ' hovering ' round the gangway lights at 

 night. Fishing for 'five-fingers', etc., had been proceeding all day, and the school of Thyrsites were 

 doubtless (primarily) attracted by some of the resulting offal. A cargo-cluster was lowered over the 

 side (the night being calm) and a few volunteers, fishing with variously improvised jigs (I found an 

 artificial squid very killing), landed close upon three-quarters of a ton of the fish in about 3 hr. The 

 fish were placed in the ship's cold-store as soon as we finished cleaning them next morning, and 

 provided at least one course per day for all who cared for them until we reached New Zealand (and a 

 copious supply of mullet) some z\ months later. It is thus evident that when chilled soon after capture 

 the keeping qualities of Thyrsites are excellent. It is preserved by smoking in Australia, and is both 

 salted and smoked in South Africa. Very large quantities are eaten fresh in both these countries. 



Since Thyrsites is one of the most valuable food fishes in the southern hemisphere, it would certainly 

 merit further attention if any commercial fishery is developed near the area we surveyed, and a 

 discussion of its importance in other regions therefore seems worth while. Any captured incidentally 

 in trawling for more plentiful species would augment the value of the catch, and if the suggestion of 

 an autumnal invasion of the warmer inshore waters should prove a constant feature, it might even be 

 worth while to try trolling for it. 



In South Africa T. atun (locally ' Snoek') is a very important fish. Returns for three years 1929-32 

 (von Bonde, 1934) show it second only to Merluccius capensis (stockfish, hake) in weight of landings 

 and in their value. The quantities landed fluctuate much more violently than those of most of the other 

 important fishes. This is partly explained by the fact that the majority of the snoek are taken by small 

 line-fishing vessels whose activities are much more subject to the vagaries of the weather than are 

 those of the trawlers, which operate from the best harbours, and take the majority of the other fishes. 

 Of the fishes captured by the line-boats Thyrsites is by far the most important. Figures given for two 

 recent years (Director of Fisheries, 1938, 1939) show that Thyrsites yielded 57 and 35% by weight, 

 52 and 46% by value, of the total landings by vessels other than trawlers at the Cape. As these figures 

 include the valuable crawfish landings the importance of the snoek is even greater than it at first 



