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

LOSSES IN ARTIFICIAL PROPAGATION
Earlier it was shown what quantity of eggs was rrandled in a usual operational
year, whence these eggs came ancl whither they went, the number of streams in
rvhich they were collectecl ancl the number into which resultant fish went, the
¡>r-oportiou retained where collectecl ancl the number clispatched elsewhere, and
the extent o[ the return macle to streams of origin. It was shown that the total
'umber
of eggs stated to have been plantecl anã of young fish releasecl was 11
per cent' less than the number of eggs collectecl. Howãver,-as only some societies
urade a deduction for losses, the total loss rnust have æxceeded 11 per cent. Norv
it is proposed to inquire further into the cluestion of the usual extent of losses
in lrlew Zealand hatcheries. The of;ñcial reports, which migl-rt have proviclecl clata
for this Ptlrpose, are a tlixture of those wherein no allowance is macle for loss,
those where it would appear that a nominal allowance has beer-r nrade, ancl-much
less cot¡rnonly-those in which something approaching a carelul attempt has bee'
made to ascertain the truth.
Factors which may have rnilitated against the publication of true losses in
hatcheries are, in part, probably those inherent in commercial enterprises ancl i¡
organizations where governing bodies neecl to satisfy the electors and where staffs
iu turn need to satisfy such boclies. So long as competitive selling of ova encouragecl
ver-rdors to shorv that their offeri'gs were of irigh cluality ancl so long as a
popular demancl existed for ever-increasing releases of nrn, .o long did ltrong
motives exist for suppressing data on heavy losses. Failure to ascertain and publist
clata on losses cannot be ascribecl to these caLlses alone. fn part it would ãppear
to be attributable to the feeling that, as even with the best of care some loss is
inevitable, there is no point in paracling the fact. The shortcomings of records to
which reference has been macle are equally eviclent in the official reports of
hatchery operations publishecl by both acclimatization soçieties and by State
Departments.
Where, in what follows, reference is made to heavy losses at particular l.ratcheries
ilo criticism is intended. Although losses will be shown to vaiy from hatcl-rery to
hatchery, the aim is not to contrast operations carriecl out in face of different
difficulties, but to assemble data which rvill indicate the extent of losses in the
t1'pical Ne"v Zealand hatchery.
As later the relative efficiencies of natural and of artificial propagation will be
considered, it is proper that all losses incidental to trapping should be taken into
accottnt. Relevant losses are all which occur from the time the upstrearn Íìovetnent
of natural sPawners is interfered with until the fish hatched fiom their eggs
have been released.
Losses Incidental to Trapping and Stripping
LOSSES OF MATURE TROUT
In 1941, at the Selwyn River in canterbury, onry 35 fish of over 12,000
spawners which entered the trap are known to have clied or suffe¡ecl serious
injury through becoming gilled or entanglecl in the netting. At Inchbonnie in
westlancl, in 7934, 6 per cent. of a spaw'ing run of trout, mostly of 13 to 16
inches, were lost in this manner, These latter fish were much below tLe size usually
s8l
Fisheries bulletin (N.Z. Marine Dept.) no. 9 (1948)
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