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The Fraser River system consists of five white sturgeon ( Acipenser transmontanus) management units, two of which are listed as endangered populations under Canada's Species at Risk Act. The delineation of these management units was based primarily on population genetic analysis with samples parsed by collection location. We used polysomic microsatellite markers to examine population structure in the Fraser River system with samples parsed by collection location and with a genetic clustering algorithm. Strong levels of genetic divergence were revealed above and below Hells Gate, a narrowing of the Fraser canyon further obstructed by a rockslide in 1913. Additional analyses revealed population substructure on the Fraser River above Hells Gate. The Middle Fraser River (SG-3) and Nechako River were found to be distinct populations, while the Upper Fraser River, although currently listed as an endangered population, represented a mixing area for white sturgeon originating from SG-3 and Nechako. Differences between these results and previous genetic investigations may be attributed to the detection of population mixing when genetic clustering is used to infer population structure. [ABSTRACT FROM AUTHOR]

This paper extends a state–space Bayesian mark–recapture framework to multiple-recapture data to estimate fishery-specific capture and mortality rates and seasonal movement rates for fish in different length classes. The methodology is applied to tag recapture data for white sturgeon (Acipenser transmontanus) collected in the recreational fishery and the Canadian Department of Fisheries and Ocean’s test fishery at Albion in the lower Fraser River. Significant differences were found between some estimated movement rates by season and length class, supporting the notion of there being marked differences in seasonal movement patterns between different life history stages of A. transmontanus in the lower Fraser River. Uncertainty in the tag reporting rate parameter, quantified using a recreational creel sampling program, is summarized by a prior distribution. The utility of recreational fishing effort as a model covariate in accounting for seasonal and spatial variation in recapture rates is addressed using Bayesian model evaluation criteria. The data provide strong support in favour of models that include fishing effort as a covariate. The appropriate level of stratification for the recreational catchability parameter q is assessed using Bayesian model evaluation criteria; models in which q is estimated by season and length class have the highest posterior probabilities. [ABSTRACT FROM AUTHOR]

Brackish marshes of the Fraser River delta provide important habitats for such high-profile animals as White Sturgeon (Acipenser transmonranus) , Pacific Eulachon (Thaleichthys pacificus), Pacific salmon (Oncorhynchus spp.), Western Sandpiper (Calidris mauri), and Lesser Snow Goose (Chen caerulescens caerulescens), the latter comprising the "Fraser-Skagit" segment of the Wrangel Island (Russia) population. This study assessed whether the current numbers of Snow Geese are exceeding the carrying capacity of brackish marshes in the Fraser River delta. Simulation modelling predicts that those marshes are presently capable of supporting ∼17 500 Snow Geese-a value that is greatly exceeded by the numbers of geese that have overwintered there in recent years (∼80 000 in 2004-2005). The Pacific Flyway Council's target 3-y average population and segment sizes of 120 000 and 50 000 - 70 000, respectively, were set without considering the carrying capacity of natural wintering habitats, the potential impacts of too many geese on upland agriculture, or implications for hazards to civilian aircraft at Vancouver International Airport. The modelled results of the present study suggest that the Fraser River delta can sustain the current numbers of Snow Geese that stage or winter there only if those birds also forage in agricultural and refuge fields-a relatively recent phenomenon that likely bolstered the Snow Goose population. Over-use by Snow Geese can degrade the productivity and habitat quality of marshes. There is documented evidence that some key plant species (e.g., Scirpus americanus) of the brackish marshes of the Fraser River delta are well below their biomass potential (∼15%), primarily because of grubbing by Snow Geese. Other species that depend on this brackish environment as well as human interests in the Fraser River delta may be adversely affected by an overabundance of Snow Geese. The future effectiveness of hunting as a primary means of population regulation is questioned. [ABSTRACT FROM AUTHOR]

The primary objective of this study was to identify and characterize juvenile white sturgeon ( Acipenser transmontanus) habitat in the Lower Fraser River downstream of Hope, BC, Canada. A secondary objective was to estimate the juvenile white sturgeon population in the Lower Fraser River. A total of 1867 white sturgeon was captured with gill nets at 26 sites in the Lower Fraser River. The greatest numbers of sturgeon were caught in three sloughs; all but three sturgeon were captured in the June to August period. These three sloughs all had water deeper than 5 m and current that was multidirectional. Turbidity ranged greatly from 1.5 NTU (Nephelometric Units) to 67.0 NTU and the substrate of most sites was fine sediments, fine sand, silt and clay. Stomach contents were mysid shrimp ( Mysidacea), midge larvae ( Chironomidae) and peamouth chub ( Mylocheilus caurinus). We identified three of 26 sites with appreciable numbers of juvenile sturgeon, identified water quality parameters of these sites, identified any incidental species that might be prey and also determined that between 1985 and 1993 the juvenile white sturgeon population had declined. [ABSTRACT FROM AUTHOR]