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

CHA}{GE I}f SIZE OF TROUT-SOUTH ISLAND
Atteltio¡ is directecl firstly to the period 1880-1900, for rvhich data are given
in Tables II and III for six rivers-the Oreti, rrly'aipahi, Shag, Temuka, Rangitata,
ancl Ashburton. In four of these, all represented by substantial sanrples-namely,
the Oreti, Waipahi, Temuka, and Ashburton-significant falls iu average size are
sholvn. I-ittle change is shorvn in the Shag. Where there is goorl eviclence, it is of
clepreciation rather than of a lvell-maintainecl average size.
Fron 1890 on1r,arcls, the Oreti alone provides evidence of long-continuing
clepreciation; in this case it extended into the 1920's. The Pomahaka shorvs a
fali in size, which in the case of its tributary, the Waipahi, was arrested before
1910. In tl-ie Shag also there rvas a drop in size at about the turn of the century.
Although clepressecl periods are sometimes shown later, there is no clear eviclence
of progressive depreciation after 1890 in the Aparirla, Otapiri, Opihi, Temuka, or
Ashburton. Data from the Wynclham, Nfimihau, and Sehvyn are available only
from 1910 onwards. No dorvnward trencl is sholvn in these cases.
A ferv rnore fragmentafy recofds may be added to the foregoing. An early
recorcl from the Mirnihau is of the captufe, with fly, in 1896, of 71 trout weighing
130 1b. This is the aggregate of tl-rree selected bags, but whether they were chosen
because of the number or the size of the fish comprising them is not stated. The
nnrrbers are ¡ot outstanding by more recent staudards; the size is. The Lyttelton
Tintes of 20lh December, 1882, records aû "extraordinary take of 10 fish of a
total weight of 40{ 1b." in the Selwyn. Such a catch would not be ren-ralkable
to-day. In the Lee, where Arthur (1883) gave 1.25 lb. as the average rveight
frorn 1875 to 1B78 ancl 7.521b. for the years from l87B to 1883, a stnall sarnple
of 36 ñsh i¡ thc 1930's averaged 1.04 lb. The Waiu'cra yiclclecl 33 fish aver':rgitrq
2.01 11t. in the scasons 1879-83. ßetlr'een 1935 ancl 19+5, 143 trottt averagecl otrlv
I.24Ib. Frolr the OnarzLura, first stocked in 1875, Arthur (1883) recorcls the
capture of 19 fish, fout 1,'ears after, of 2.111b. itl average rveight- This srnall
str-eam in 1940 yielclecl 16 fish averaging 2.57Ib. The Waitaki is a major river,.
of wl-rich the Ornarar.na is a triltutar-f. It rvas first sti¡ckecl in 18ó9. Spackmar.r
(1892) recorcls that l0 ye:rrs iater 22 trout taken there averagecl 1.06 lb.; the
heaviest inclivichral was 5.75 lb. In 1890-91, 169 trout averagecl 6'64 lb' ; the
heaviest u,as 14lb. One hunclrecl trout takeu about 1940, probabll' farther rrpstfealn,
averagecl 3.38 lb. arlcl incluclecl one of 16 lb. The u'eight o{ sea-run trout
at tire ruouth of the \\,'aital