Coastal Cutthroat Trout as Sentinels of Lower Mainland Watershed ...

78It is widely assumed that most adult cutthroat utilizing the lower Fraser River areanadromous, yet sea-run, river-run and lake-run life history strategies could becommon in the Fraser-Harrison and Lower Fraser tributaries. It is uncertain froma fish culture perspective whether all fish are anadromous stocks or a mixture ofriver, lacustrine and sea-run stocks, the latter risking “hybridization” amongdifferent life history forms that may be from separate breeding populations. Forexample, Voight and Hayden (1997) concluded that large-sized adult cutthroatmonitored by diving in the mainstem of the Smith River, northern California,were a mixture of resident, fluvial and sea-run forms. Life history profiling isrequired with a focus on microchemical analyses of marine rare earth elements(strontium, iridium, strontium: calcium ratios) from existing scale collections orfrom new scale, fin ray or otolith collections. Radio/sonic tracking of adultcutthroat from several tributaries including Wahleach Slough would also bebeneficial. It is possible that molecular genetic can detect differences in some ofthe discrete populations over the geographic range of the Region, but life historyand morphological profiling is more likely to be most effective in the LowerFraser where the current fish culture program is focused.• Quantify wild-hatchery stock interactions associated with the anadromouscutthroat program in the Lower Mainland, particularly in the Lower Fraser andits tributaries.While the collapse of major cutthroat stocks in Oregon was associated with poornear-shore marine conditions and land and water quality impacts, the hatcheryprogram was also considered a factor to the degree that the program wasterminated in Oregon in 1997 (Hooton 1997). Thus in BC, as a pre-emptivemeasure, stock status surveys are required of stocked and unstocked tributaries toexamine the ratio of wild to hatchery adult cutthroat, as well as residual hatcherycutthroat and steelhead. Similarly, the incidence of undesirable hybridization ofcutthroat and steelhead needs to be examined via molecular genetic tools, usingunstocked streams as controls (Waples 1991).Further, an additional workshop review of anadromous cutthroat hatcherypractices is needed to provide guidance on sound measures to minimize oreliminate hatchery-wild interactions. This should be similar to the Ministry’s1990 genetics workshop (Ludwig 1992), which was largely directed at steelheadtrout culture. The workshop needs to examine the full range of hatchery-wildinteractions to provide guidance on:- minimizing cutthroat-steelhead hybridization;- avoiding stock mixtures to minimize genetic homogeneity with loss of uniquestock adaptations including migration and timing of return or maturity;- mating procedures to minimize inbreeding depression and genetic drift;- avoiding recycling of hatchery versus wild brood fish; and- selection of broodstock sources and stocking locations.