N.Z. MARINE DEPARTMENT-FISHERIE,S BULLETIN No. .į

end the development of hydro-electric power schemes elsewhere províde opportunities
worth considering.
(2) Traþþittg of elzters as they travel inland each spring. This practice has been
followed for a very long period in the British Isles and in France to obtain supplies
for sale rather than as a control measure. The methocls found effective elsewÈere
rniglrt be suited to some New Zealand streams. This n-rigration takes place
trsually at night, but may be observed by day in some of the opalescent waters of
the Nortl-r Island and may occur more generally by day in waters discoloured by
floods. As upwards of ten years would elapse before any benefit could be expecteã,
the method is best suited to use in conjunction with others.
(3) Traþþing young øels during the secondary migrations which occur eacl-r
summer. The evidence of this movement cornes almost wholly from waters where
obstructions prevent easy upstream movement, but doubtless such movements
occur in rivers generally. There is need of information as to the distance upstream
reached by elvers, the points from which the secondary migration (or migratio¡s,
for a number of year-classes are involved) begin and their extent, the behaviour
of the frsh when travelling, and the duration of their rnovement. The possibilities
are especially worth investigating because, in conjunction with other methocls,
they would enable an attack to be directed against the whole stock.
(4) Caþture of large eels that have reached a size at which they move freely by
night to feecl, principally fron-r october to April. At this stage, fish "r. ,.áa;ti
attracted to baited pots. The possibilities of these fish entering sluggish reaches,
marginal swamps, and stable tributaries of unstable shingle streams to hibernate
and leaving such grounds again in the spring are suggested by rather fragmeptary
evideuce. If such movements were conÊrmed, they would offer additional possibilities
of trapping.
(5) Traþþing wøturing dozvnstream ntigrants. This nTethocl might permit the
capture of the greatest quantities for a moderate expencliture, and might therefore
be useful as a ûIeans of reducing the average cost of capture of eels taken throughout
the season and thereby encouraging commercial utilization. In other respects,
it offers little hope of in-rproving waters for trout, for there is no evidelce of
return of spent eels fronr the sea and no evidence that proger-ry Leturn to the streanr
selected by their parents and, as yet, there is no likelihoocl of control lneasures
being applied to a sufficient nunber of rivers to reduce significanctly the number
of elvers returning from the sea.
(6) Poisoning of noxious fishes in small lakes and strearns has been done in
North An,erica. Fleavy concentrations may be necessary where there is a cleep
ruucl bed. Although the method has been directecl against other. species, its use
against eels in sr-r-rall waters, snbject to proper safeguards, nray be warranted.
After an interval, assisted repopuÈtion of such water with useful fauna coulcl take
place, and, because of the slow growth of eels, a succession of crops of useful
fish might be taken before complete repopulation by eels occurred. Narcotics,
irritant chetlicals, and electric currents have all been used to aicl the clearance
126l
Fisheries bulletin (N.Z. Marine Dept.) no. 9 (1948)
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