The feasibility of using freshwater and first marine year scale patterns to identify component stocks of steelhead trout (Salmo gairdneri) in the Skeena River was investigated. Scale samples and sex and size data were attained from adult steelhead originating from five Skeena River tributaries (Zymoetz, Kispiox, Morice-Bulkley, Babine, Sustut) over a series of different years. Adult scale samples were also collected from the 1984 incidental steelhead catch in the Area 4 commercial salmon fishery for potential stock classification purposes. Significant differences in scale pattern growth, age composition, and sizes at age were found between the five Skeena River steelhead stocks. Linear discriminant function analysis indicated that the five stocks could be classified to correct river of origin with between 45% and 62% average classification accuracy (range Zymoetz 29%-60%, Kispiox 35%-60%, Morice-Bulkley 44%-76%, Babine 54%-64%, Sustut 56%-72%) depending upon the classification model used. Juvenile morphometric analysis for three of the stocks (Kispiox, Morice-Bulkley, Zymoetz) indicated the presence of significant between stock differences in standardized body form. These results support the notion that Skeena River steelhead exist as quantifiably discrete stocks. Classifying the 1984 mixed stock commercial fishery catches to probable stock of origin indicated that distinct peaks of stock abundance and run-timing occur through the fishery. In general, Morice-Bulkley and Sustut River steelhead were predicted to be most abundant with run-timings during the earlier portions of the fishery. Kispiox, Babine, and Zymoetz River steelhead were predicted to be less abundant with later run-timings through the fishery. Potential commercial fishery impacts to steelhead are briefly discussed. These observations suggest that the technique of scale patterns is a feasible method for stock separation in Skeena River steelhead. Further study is required to clarify yearly variance in the technique and to better establish stock specific differences. / Science, Faculty of / Zoology, Department of / Graduate

The composition and distribution of fish assemblages was examined in a floodplain lake system in the Amazon basin. Quantitative samples were collected during the 1992-1993 flooding season at Marchantaria Island, Solimoes River. A total of 25,819 specimens representing 8 orders, 30 families, 101 genera and 139 species of fish were collected. Analysis of species richness distribution among 7 vegetation strata showed that vegetated sites had higher species richness than unvegetated sites. Stands of Paspalum repens had the most diverse fish fauna. Canonical correspondence analysis (CCA) was used to investigate relationship between fish assemblages and 16 environmental variables. CCA revealed that dissolved oxygen, water transparency, water depth and aquatic vegetation structure were significantly related to fish assemblage organization. The results suggest that physiological adaptations to hypoxia and habitat complexity play a major role in the organization of these assemblages. The morphology, ontogenetic development, shape variability and deposition of otolith microincrements are described for floodplain serrasalmin fishes. Serrasalmin otoliths were similar to other ostariophysan, nevertheless their shape was species-specific. Elliptical Fourier analysis showed that Mylossoma aureum lapilli were highly variable in shape when compared to closely related species. PCA and discriminant function analysis indicated that two distinct forms of lapillus can be recognized for M. aureum, and intra-species variation was higher than inter-species variation. Otolith microincrement analysis was tested for these fishes, and microincrement deposition validation showed that Piaractus brachipomus deposits otolith increments on a daily basis. Patterns of spatial distribution, growth and mortality characteristics of larvae and juvenile were examined for M. aureum inhabiting the Marchantaria Island floodplain. Otolith-derived birth date reconstruction showed that M. aureum spawning season extended from late November to March, and peak larvae recruitment to the island occurred in mid-December. Larvae and juveniles had different spatial distributions in relation to habitat usage. Instantaneous growth coefficients (g) varied from 0.0197(d�����) to 0.265(d�����) among cohorts. Early-season cohorts had wider otolith microincrements and higher instantaneous growth coefficients than late-season cohorts. Mortality estimated by the decline of loge (abundance) regressed on age indicated that cohort-specific instantaneous mortality varied significantly among cohorts, ranging from 0.027(d�����) (2.6%/d) to 0.103(d�����) (9.7%/d). / Graduation date: 2001