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

(3) \A/here the deficiency of cover is overcome by increasing depth of water; or
(4) where, with the provision of other cover, measures are also taken to
control eels.
SPAWNING GROUNDS
Spawning grouncls are useful ,xly if accessible. Much attention has been directecl
to this problen-r where dams impecle access of migrating salmon. The question,
however, requires wider consicleration.
Especially on the east and south coasts of the South Islancl, the access of trout
from the sea may be barrecl by shingle barriers in the case of coastal lakes srrch
as Ellesmere and waituna, and also in rive¡s such as the Ashburton, Hinds,
Opihi, and Kakanui. It is possible that trout seeking to enter these waters in
winter, on occasions when access is blockecl, rvoulcl go along the coast to other
streams' Ifowever, it is not known that they usually clo so. Because of tl-re common
excessive rtse of sparvning grotrncls, it is desirable that access shoulcl be give¡
to. as much spawning ground as possible. It is sometimes practicable to achieve
this result for a reasonable cost. fn sorne of these u,aters, anglers sor-netimes cut
an outlet to permit entry of trout from the sea cluring the angling season. It ,¡,oulcl
seem at least equally desirable to ensure entry of fish i'the spawning season.
Access to useful spawning tritrutaries, especially of streams with shifting shilgle
beds, is often impossible because of shallow water at the confluences. Gooã ,po*rring
tributaries at the mouth of the wairau River, in Marlborough, are often
affected in this way. The mouth of Slovens creek, which enters the Broken River
in canterbury, was, in 1933, too shallow for spawning salmon to enter until it
was modified by a fer,v hours' labottr, after which salmon were able to enter freely.
An access problem of a sin-rilar nature occurs at Lake Acland, in tl-re Ashburton
River headwaters. Here the only available spawning ground is an outlet stream
down which trout pass to spar'vn. Hou,ever, intermittently the level of the lake
drops and denies fish access to tlhe sparvning grouncls. Again, the drop may occr.rr
in sutnmer, with loss of young fish in the stream. In such circumstances relief may
be afforded by impounding a reserve of water.
Where natural falls prevent access of sparvning trout to extensive upper reaches
of streams and excessive accumulations of spawners occur below such falls anrl
ûsh released above migrate downstrear¡ while immature, there nay be goocl
grounds for providing access. Especially is this so in such a strearn as the
\Mhitikau-a Tongariro River tributary-which contains no eels. A slight ancl
inexpensive modification of the fall in the Vy'hitikau woulcl give perma¡ent access
to much water which at present becomes available to spawners only when floocls
occur in the spawning season.
Permeable weirs may prevent. dispersar of spawning fish ancl cause them to
concentrate and to become more vulnerable to poaciting. A clam on the Kakanui
River, at Maheno, is of this typr:. Sealing its base would ensure a sufficient florv
r-,ver the top to make it always passable to trout.
Earlier (Hobbs, 1940), attention rvas directed to the significance of spaw¡ing
a¡eas in influencing the distribution and abundance of stocks of trout. Stocki
have developed until they are using most available spawning gronncJs, .usuall1,
to an extent where overlapping of redds and some wastage of eggs occrlrs.
Is the artificial provision of aclditional spawning grounds feasible? Earlier in
Fisheries bulletin (N.Z. Marine Dept.) no. 9 (1948)
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