NEW ZEALAND EELS

Wairarapa Times-Age, 28 December 1940, Page 3

NEW ZEALAND EELS

THEIR FEEDING HABITS STUDY MADE BY SCIENTIST. RELATION TO TROUT CULTURE. A study of eels in New Zealand has been made by Mr D. Cairns, a former member of the staff of the Fisheries Laboratory, but/ the paper he has prepared has not been published yet, and Mr D. F. Hobbs, fisheries research biologist, summarised it for the council of the South Island Acclimatisation Societies, when it met in Christchurch recently (reports the “Press"). The work took two years and involved the collection of material from more than 50 streams and lakes, and the study of the distribution', growth, and feeding habits of eels, and their relationships with trout.

Of the two kinds found in fresh water the female of one kind alone, the long-finned eel, is found widely distributed in inland waters. The males of both species are confined to brackish and tidal waters, and the short-fin-ned female does not venture far from these waters either. The long-finned female is the only one which ever reaches any great size.

“It will be seen that males of both kinds and the -shortfinned females do not commonly venture into waters containing many small trout,” Mr Hobbs said. “Even the biggest of these has a very small mouth.”

Mr Hobbs considered the long-finned female as the only eel big enough to consume trout. Examination of more than 2000 feeding eels between 16 and three inches long showed that about 70 per cent (by nurpber) of their food organisms were mayfly and caddis larvae. Gut contents of trout of similar size showed the same result. The eels taken comprised a general collection from many waters, some containing an abundance of trout, others very few. Eels of more than 30 inches revealed “an enormously heavier consumption of trout.” Of 426 larger eels containing food, 104, or about a quarter of the total, contained trout, and the bigger eels contained much bigger trout than the others. This result was remarkable, Mr Hobbs said, as not all the eels camo from waters containing trout. There was no doubt that trout were more important to eels than all other foods combined. An impression from casual observations on eelless waters was that trout were much more numerous than in similar waters containing eels. “One such abnormally large stock of trout persists in a stream, devoid of eels, in spite of a heavy concentration of shags on the “It is now clear for the first time that any system of bounties for eels killed might have meant a waste ol money and energy on the slaughter ol relatively innocuous eels, and that only the female of one species need cause a serious concern.

Although there is much evidence of the destruction of trout, by shags, it is pertinent to point out that eels are greatly more abundant than shags. About 650 cels to a mile were taken in the Hedgehope stream in Southland, and this stream was not. considered heavily stocked. It is the removal of eels rather than of shags which makes more food available for trout. ’ The report, ended by saying that large stocks of eels were undesirable in trout waters, but it might prove

pacticable to keep stocks within reasonable proportions. Destruction of eels meant the waste of material for which there was unfortunately no commercial use in New Zealand yet, and commercial use was desirable to offset costs of destruction. Data was slowly being gathered to indicate the quantities available and the possibilities of commercial, utilisation.