A main concern in fisheries science has been to identify an accurate index of fish abundance. An underlying paradigm in the science has been that the amount of effort (calculated in hours and standardized for boat size) spent fishing was the best variable to be used to account for the variation in catches. The use of the ratio, catch per unit of effort (cpue), assumes that variations in fish abundance are due to human-controlled processes above the ocean's surface. It does not account for variation due to oceanographic processes that affect fish behaviour and movement patterns below the ocean's surface. This study investigated the possibility that oceanographic factors such as temperature, salinity and depth could have effects on the variations observed in the apparent abundance of a demersal rockfish, Pacific Ocean Perch (Sebastes alutus. Gilbert). Simultaneous monitoring of physical variables and fish abundance estimation was achieved by attaching oceanographic equipment to the fishing gear of commercial vessels, monitoring the acoustic equipment and sampling the fish catch. It was found that Perch prefer a temperature range from 6.7 °C, down to at least 4.8 °C and that their movement patterns are linked to the movement of these temperatures by coastal wind patterns. Perch prefer areas with steep bathymetry, characterized by frontal activity due to interactions between the local bathymetry and tidal currents. Concerns that sampling only from highly successful commercial vessels may have biased abundance estimates, prompted the analysis of historical records of fish catch and government research surveys. Analyses between different boat sizes, different areas and different seasons from the original historical data base and a corrected subset revealed that it was mainly differences between areas that was responsible for the biasing of estimates. Deeper areas predictably produced more fish for all sizes of boats, but were fished more often by the larger boats used in the study. Therefore the field abundance estimates are likely to be biased towards areas of larger perch concentrations. / Science, Faculty of / Zoology, Department of / Graduate

Pacific ocean perch (Sebastes alutus) is a slow growing species of demersal rockfish, which inhabits the continental slope of the west coast of North America. This species represents a highly commercial fishery and an important part of the groundfish fishery of British Columbia. A variety of biological factors are known to influence the concentrations of trace metals in fish, including, age, body size and diet; all of which vary in this species. Little is known of the concentrations of total mercury and total arsenic in Sebastes alutus from British Columbia, a Canadian province where marine groundfish have previously been found with elevated concentrations of mercury. The spatial variability of trace elements across different fishing regions within British Columbia is also unknown. Substantial variability in concentrations of both mercury and arsenic has been reported in marine fish from around the globe. In the case of arsenic, associations between concentrations in muscle tissue and a variety of biological variables are not frequently reported. This contrasts with mercury, which is known to be intrinsically linked to the biology of fish. Consequently, biological variability in fish has the potential to confound studies of mercury and possibly arsenic in fish. This thesis examines the influence of biological variables and fishing region on total mercury and total arsenic in Sebastes alutus from British Columbia. It also assesses the concentrations found in muscle tissue from a food safety perspective. Samples were obtained from a commercial fish processing plant on Vancouver Island and had been caught by a commercial fishing vessel in Hecate Strait, Queen Charlotte Sound and the west coast of Vancouver Island. A multivariate outlier determination method was used to quantify the natural background variability across all three fishing regions. Significant differences in concentrations between regions were identified. This spatial variability of total arsenic did not appear to be related to age, body or body size. However, the spatial variability of mercury concentrations appear to be associated with the size and age of the fish sampled. The outlier determination procedure also identified the presence of elevated concentrations of both mercury and arsenic in specimens that were determined to be outliers. Outliers originated predominantly from the west coast of Vancouver Island and exceeded regulatory limits for both mercury and arsenic. In addition to the outliers, estimated quantities of MeHg frequently exceeded Provisional Tolerable Intakes for children and pregnant women. Generalized Additive Models were produced to examine the effect of age, body size (length and mass) and diet (δ13C and δ15N) on concentrations of total mercury and total arsenic in Sebastes alutus within each fishing region. These identified significant nonlinear, qualitative patterns between mercury and body size in two out of three fishing regions. A significant nonlinear effect of age on arsenic concentrations was found. Model results also suggest an effect on arsenic concentrations of organic carbon sources; i.e., fish with stronger links to continental slope or inshore food webs (with relatively enriched δ13C signatures) had greater arsenic concentrations. / Graduate

This study examines the reproductive and population biology of a long-lived (80-y life span) fish, Sebastes alutus (Gilbert). The objectives of the study were (i) to establish whether groups of adult S. alutus delineated by exploitation histories could be objectively identified as separate sub-populations; (ii) to identify the effects of density-independent mortality caused by exploitation, and relate them to predictions of life history theory (iii) to examine the long-term implications of this mortality pressure on the dynamics of the species; and (iv) to determine the contribution of these results to the development of management programs for this species. A lernaepodid copepod gill parasite (Neobrachiella robusta (Wilson 1912)) was used for the first time as a biological tag to delineate separate sub-populations (stocks) of a commercial fish. Intensity of infection and mean characteristics of the parasite population per fish achieved complete separation between stocks indistinguishable with morphological features. Discriminant analysis showed the parasite also functioned moderately well (34-76% correct classification) as a stock discriminator of individual fish. Use of auxilliary information on the stock identity of hosts improved the classification power of the discriminant function. The density-independent mortality of the commercial fishery on S. alutus has severely truncated the age spectrum of some stocks. Some compensatory growth changes for fish in the stocks under the strongest selection are evident. Examination of the variance structure of female length at age suggests an inverse relation of mortality and growth rate giving rise to smaller, older fish. Smaller, older fish can be accounted for using the same growth function as for the larger fish seen at younger ages, and these similar growth forms can give an aggregate appearance of quadratic growth. Growth changes do not yield significant differences in size at maturity, although age at maturity changes, implying developmental or environmental constraints on maturation. Fecundity estimation methodology was evaluated and the volumetric method previously used for this species found to be inferior to a gravimetric method. Significant differences in fecundity as a function of body variables were found among exploitation groups. Significant differences in oocyte characteristics among stocks were found, with size and age shown to have separable effects. Lightly exploited stocks had significantly higher oocyte quality (as expressed in oocyte weight), effected through differences in the oocyte diameter-oocyte weight relationship. Histological examination details the developmental sequence of oocytes and establishes the maturation period of oocytes and fish. Northern stocks were shown to have significantly larger oocytes. Follicular atresia is suggested as an alternative energy source to the embryo death which has been presented as the source for matrotrophy in this genus. Complete atresia of a ripe oocyte complement was identified in this genus for the first time. No evidence of reproductive senescence was found. The hypothesis of increasing reproductive effort with age, including the independence of age and size effects, was confirmed. No evidence of reproductive cost could be found. The hypothesis of increased reproductive effort earlier in life as a mechanism to offset increased adult mortality was supported. However, the potential of this increase, achieved by growth rate increases, is much less than is needed to compensate for the reduction in lifetime reproductive effort caused by high fishing mortality. The effects of changing mortality rates on several reproductive value indices was examined with deterministic and stochastic simulation models. Cohort reproductive value is the most sensitive of the indices examined and may be the most robust to measurement error. Reproductive value is a more sensitive index of population state than other indices in use and may play a role in determination and evaluation of optimal harvest policies. However, an experimental approach to its use will be required. / Science, Faculty of / Zoology, Department of / Graduate