*Microsatellite diversity assessment of steelhead (/Oncorhynchus mykiss/) population structure before and after hatchery operation in the Kitimat River, Skeena Region, British Columbia*
Jan Heggenes1,3 , Mark Beere2 , Patrick Tamkee3 & Eric B. Taylor3
^
^1 Laboratory of Freshwater Ecology, University of Oslo, PO Box 1172 Blindern, 0318 Oslo, Norway,
^2 Fisheries – Skeena region, Ministry of Water, Land and Air Protection, Bag 5000, Smithers, B.C. V0J 2N0
^3 Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, B.C. V6T
. The objective was to investigate the genetic structure of natural steelhead populations in the Kitimat River before hatchery stocking started in 1984 (baseline samples 1976-1977, 1983-1984, n=145), and to assess potential genetic impact of in-river interbreeding of returning cultured adult fish with wild spawners over almost 20 years of large-scale hatchery operation (1987-2003, n=188).
Because of relatively long histories of considerable stocking through the use of wild, native brood stock, a number of watersheds in British Columbia can be regarded as long-term genetic field experiments. In the Kitimat River of the Skeena region, British Columbia, hatchery steelhead of known numbers and origin, have been released annually since 1984 (mean 50 297 ±SD 8109, Table I). Scales have been collected in various years from hatchery brood stock parents (Table I). Fortunately, steelhead scales were also collected from wild fish in 1976-1984, i.e. before hatchery stocking (Table I). Dried, preserved fish scales provide sufficient tissue for the extraction of DNA in order to look at the genetic structure of each individual fish. Thus the material collected represented a rare opportunity to test whether the natural genetic variation in the wild populations was maintained in the presence of hatchery operation. Therefore, the objectives of this study were to use DNA obtained from archived adult fish scales to:
1) identify the genetic structure of natural steelhead populations in the Kitimat River before hatchery operation was initiated, and
2) assess the potential genetic impact on genetic structure and molecular variation, if present, of almost 20 years of large-scale hatchery operation.
*STUDY AREA*
The Kitimat River is located at the head of Douglas Channel on the north coast of British Columbia and flows into the Pacific Ocean approximately 230 km southeast of Prince Rupert (Figure 1, 2). The Kitimat River watershed drainage area is approximately 217 000 hectares and lies within a wide glaciated valley that has been extensively logged; almost all of the mature conifer forests have been removed. Water discharge ranges from 19.4 to 1 670.7 m3 s-1 and the mean annual discharge is 148.8 m3 s-1 . Due to the removal of much of the flow stabilising riparian vegetation within the watershed and the fact that most of the valley’s soil is loose glacial till, discharge can vary dramatically over a short period of time. The climate of the Kitimat area is moderated by the Pacific Ocean; precipitation can be considerable with heavy snowfalls in winter and wet and warm summers.
The only previous studies we are aware of which directly investigated the questions relevant to the Kitimat River results were undertaken on the Hood River, Washington, USA. Based on DNA studies, Blouin (2003) reported that traditional ‘old’ domesticated hatchery stocks (multiple generations in the hatchery, out-of-basin origin) of steelhead had shown much lower total fitness than wild fish, while ‘new’ conservation based hatchery stocks (i.e. only wild brood stock were used each year as for the Kitimat River, had fitness similar to that of wild fish. This contrasts with results in Kostow (2004), where juvenile local hatchery steelhead exhibited poorer survival than wild fish, probably for environmental reasons. This will, however, lead to modified selection and potential genetic changes. Based on results in Blouin (2003), an ongoing project in the Hood River is currently testing the prediction that using wild brood stock for hatchery production will not have negative genetic effects on the wild population. The results from the Kitimat River, where ‘new’ conservation based hatchery stocks have always been practiced, since its start in 1984, appear to confirm this prediction.
In conclusion, the results from the Kitimat River indicate little genetic differentiation among the studied year classes, or between pre and post hatchery populations. Likewise, pairwise testing did not indicate any significant trends or changes. Compared to other relevant studies, there is little indication to date that hatchery stocking of steelhead trout in the Kitimat River until now has had any substantial genetic effects, at least as assayed using microsatellite DNA variation.
Author
Topic: Steelhead Hatcherys in B.C. are GOOD and no changes to DNA. (Read 1630 times)