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

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Its contributiori to the èatch ir,¿s distinguished by â study of change in abundance
of the year-classes following years in which hatchery fry were released. At the time
of c"plu.e by gill nets, trout were usually of about 1.25 lb. and frve-year-old fish
predominatecl. The stock comprised many year-classes and included a few fish of
up to trllb. The author does not mention the presence of any other species of frsh
¿ it seems unlikely that many predatory fish would have been permitted in a
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small lake carefully farmed for profit. Over the whole period of 14 years a survival
of 18 fish per 1,000 fry released is shown. As in some years poaching may have
reducecl the recorclecl catch, Dahl considers that selected years whicl-r show a '
return of 47 ñ,sh per 1,000 fry give a mofe reliable result. Thus the mortality
probably lay betwãen the limits of 95.3 per cent. and 98.2 per cent. Although
.yrterrl"ii. gill netting each year removed nearly all the large trout, natural repfocluction
still contributed about 50 per cent. of the annual yield.
Paul Lake in British columbia is about 1,000 acres. Mottley (1939) has