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

If man is to improve the fertility of inland waters, his efiorts are tnost likely to
be fruitful if clirected (1) to watefs which have basic deficiencies, (2) to those
of the'r where nutrients w-ill be usecl ancl not carried to sea, and (3) to those
where nutrients aclclecl will, becattse of favourable physical conditions, be most
likely to have an appreciable effect-that is to say, to sl.rallow rather than deep
lakes.
In waters where sparvnilrg facilities are usecl to capacity, fertilization car-rnot be
expectecl to change the r-rumerical abunclance of trout. It can lle expected to chaflge
thå rate of srowtir of trout only if growth is at present inl-ribited through insufÊ-
ciency of foãã rather than temperature or otirer conditions which rnay affect the
Again, i^rprovecl gror'r'tlt of trout, at the top of the foocl chai'' will not
"pp.iit".
result if there is a non-chernical limitation at some intermecliate point in the food
chain. For instance, the adclition of inorganic compounds to lake waters may
stimulate the procluction of minute plant organisms ancl thereby increase tire
¿rrnount of zooplankton. There, for all practical purposes, the process may stop
unless there exist small frshes capable of usirlg the increasecl plankton an