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SOME POPULATIONS OF THE AUSTRALIAN "SALMON", Arripis trutta by the Late W. S. air bridge* ABSTRACT Australian salmon occur in large shoals, usually A preliminary account is glvell of the lnvesti atioll close inshore. They have the habit of coming close of thc Australun Salmon (Arripis truth) p~?cipaf ly as into the beach while in these shoals, especially in an examination of the distribution (m a1 hfephases) certain localities, and it is then that the fishermen of different stocks of the species along the Australian catch them. coast, and the taxononnc status of thesc stocks. ,Mor- bolo iml and othcr evidence 1s presented to support an This is usually regarded as an onshore species. EyptLis that the stocks constitute distinct ncs with Shoals are not commonly sighted beyond the conti- separate breeding grounds. nental shelf; but there are reports, apparently reliable, The Australian salmon is a percomorph, and of salmon shoals being sighted, and specimens caught, not in any way related to the Salmonidae. The well out in the Tasman Sea, popular name was presumably given to it by the Figure 1 shows the general world distribution early settlers in this country, on the strength of some of the species. In Australia it extends up the east superficial resemblances to the true salmons and and west coasts to about latitude 30°S, though trouts. occasionally it is taken very much further north. The present paper is only a progress report. The There is a large* alld apparently quite untapped, results are not yet fully tested and definite, but it population of in New It Occurs was thought that delegates might be interested as also in the waters around Norfolk Island and Lord much in the lines along which the work is progress- HOwe Island. ing as in the final results. The story which is When the present investigation was started in emerging is, as a matter of fact, somewhat un- 1947 it was believed-for want of contrary evidence expected; and it is of considerable interest to workers --that the dmon of south-east Australia were prob- in Australia. ably all of one stock, probably distinct from the The subject is that of raciation. salmon of south-west Australia. It was believed that the Western Australian fish were in some way In the so-called Australian "Sdmon" we have different from those of the south-east because of a common, 'pecies, of which there are geographical separation, and because the salmon of several very full taxonomic descriptions. Yet when the south-west are very much larger, and the scales we come to investigate it, we find that an apparently indicate a very faster growth-rate. homogeneous and continuous stock is divisible into two distinct subspecies; and one of those subspecies Thc first and most important discovery of the is further divisible into two separate popu- present investigation was that the salmon from south- lations. ~h~ morphologic differences which we have west Australia have fewer gillrakers than the sal- found between the populations are of standard taxo- mon New South The Western nomic characters, which however the early taxom salmon have 25 to 30 gillrakers, and the New South nomists apparently overlooked. Wales salmon have 33 to 3 8. Each group shows a spread of about 5 gillrakers, but there is no overlap An idea of the appearance of the fish can be and, in fact, there is a sizeable gap between the two got from Plate 2 (upper). groups. In general the species is used for canning. It This shows that there is indeed a definite dif- is not greatly fancied as fresh fish. ference between the salmon of the west and of the There are two main fishing centres-namely in east. the south-east and the south-west corners of Austra- Following quickly on this discovery it was La. The fishery in the south-east is capable of pro- found that some of the iuvenile salmon from Tasma- ducing about 4 million pounds a year. The fishery nian and F'ictorian waters also belonged to the group on the south-west is of quite recent development, with the low count. In other words, they were and last Year the production was 5 $5 million lb. distinct from the salmon of New South Wales. * Late Blologat. C.S.I.11.0. Division of FFllerles, Australia, (Hereafter, these groups will be referred to as the The next step in this work was to obtain sam- western and eastern subspecies-the western sub- ples of salmon from New Zealand and from Lord species has 25 to 30 gillrakers, and the eastern bas Howe Island. It had been effectively established by jj to 3 8. These juveniles of the western subspecies the work on the gillrakers that there was no appre- which arc found in the south-east of the continent, ciable interchange between the stocks supporting the were fish of from 6 cm. length (mere fingerlings) fisheries of the south-east and of the south-west, but up to 30 or 40 cm. in length (at which size they it was possible that there was interchange between are severaI years old). It was found that in Tasma- New Zealand and New South Wales waters. nian and Victorian waters, and in Bass Strait gener- Two good samples of New Zealand salmon ally, the two subspecies often occurred mixed in the (about $0 fish) were obtained; and a small sample one shoal. Such shoals might be preponderantly of was obtained frim Lord Howe Island (about 10 fish). one or the other subspecies. Unfortunately it has so far been impossible to get In Figure 1, the distribution of the eastern sub- any fish from Norfolk Island. The samples obtained species is distinguished from that of the western were compared with New South Wales specimens subspecies by hatching, and the area where the mixed by means of 18 proportional measurements, ahd by shoals occurs is shown similarly. There is no inform- counting scales, fin-rays, vertebrae and so on. ation yet from the west coast of Tasmania. Though Though there were so few in the sample from it is known that there are salmon there, it is not Lord Howe Island, it was apparent that one had to known to which subspecies they belong. The zone do here with a very different looking fish. The head of mixing of the two subspecies in Victorian waters- was shorter than in the others, and the body was between Wilson's Promontory and the south-east much stouter; in addition, the flesh was extremely oily. corner of the continent-is of some interest. It hap- Oil is very low in Australian salmon at all times of pens 'to be the approximate division between two the year, and was low in both of the New Zealand previously well-established zoogeographical areas. samples. All these characteristics of the Lord Howe Island fish point to good feeding and fast The South Australian specimens came from the and that conclusion is confirmed by the scales. Of "Gulf" area. It was found that they agreed very more importance, it was found that the gillrakers closely with the samples from Western Australia in were substantially different in number in comparison everything but the girth scale count-and that ap- with the finding for the eastern subspecies of Austra- parent difference may prove not to be significant lia: they varied between 36 and 41, and this feature when larger samples are obtained. seems to distinguish the Lord Howe Island salmon Even more significant perhaps, was the growth- from all others. rate of the South Australian salmon, as shown by The New Zealand salmon were much less distinct their scales. The faster growth and larger size of the from the New South Wales stock than were the West Australian salmon, compared with the New Lord Howe Island salmon. However it is almost South Wales salmon, has been previously mentioned. certain that they are distinct from the New South Though the South Australian fish were young- Wales salmon, because there was a difference of about mostly 2 and 3 year 014s-their scales showed a 1 scale in the girth and about 0.34 in the dorsal ray powth-rate that agrecd very well with the West counts. The material is not yet full enough to Australian salmon. eliminate any chance that sex and year-group may We may now examine the tables of gillraker be affecting these meristic counts; but the data do counts, girth scales and dorsal rays. These figures show that if either variable has an effect, it is not do not embrace all the material available, but have of such magnitude as to invalidate the differences in been drawn up simply for the purpose of illustration. the girth scale count. It must be emphasized that the work is to be regarded The proportional measurements have not yet as very incomplete as yet. been tested statistically, but there appears to be The samples in this. table have been divided up absolutely no difference between the New Zealand into tht possible or suspected discrete populations. and the New South Wales salmon. The two are undoubtedly very closely allied. There are consider- It will be seen that, as far as gillrakers are able differences, as stated above, between the New concerned, there is no doubt about the break be- South Wales and the Lord Howe Island salmon, tween the eastern and western subspecies. There is mainly involving the short head and the great girth probably no significant difference between New Zea- of the Lord Nowe Island fish.

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