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Copyright of Canadian Journal of Fisheries & Aquatic Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The southern Gulf of St. Lawrence (sGSL) White Hake Designatable Unit (DU) has been assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). This DU consists primarily of White Hake occurring in the Northwest Atlantic Fishery Organization (NAFO) Division 4T. The Recovery Potential Assessment for this stock found that extremely high natural mortality was preventing the recovery of this stock, while fishing mortality with a bycatch limit of 30 t has a negligible effect on the population trajectory. However, if fishing effort is increased as proposed with the expansion of the Redfish fishery, the impacts of bycatch fisheries on this population may no longer be considered negligible. This report aimed to examine existing information from surveys and fisheries to evaluate whether increased catch levels of Redfish would result in increased bycatch of White Hake. Significant overlap in the spatial distribution of White Hake and Redfish was noted in along the deep waters of the Laurentian Channel. This is partly the result of diet interdependencies among these species and the shift of White Hake to deeper waters to avoid predation. Bycatch of White Hake associated with Redfish was lower at depths greater than 380 m, whereas bycatch was much greater in the months of June, July, and December. Bycatch did not differ significantly based on gear type, however bycatch was overall greater in the southern region of the Laurentian Channel. Overall, the mean value of bycatch was 10.5% in the Redfish fishery. Even in the absence of fishery removals, the sGSL White Hake stock is expected to decline due to extremely high natural mortality. The sGSL White Hake population was projected forward 25 years assuming that productivity would remain at recent levels. SSB was estimated to decline by 38.7% with no catch and 39.3% with annual bycatch of 20 t, the recent level. With annual bycatch of 150 t to 350 t, SSB was estimated to decline by 43% to 48%. With bycatch of 500 t to 1,500 t, SSB declined by 53% to 70%. At present, the White Hake stock is sustained by unusually high recruitment rates which depend largely on a single cohort each year (age 4). The extinction risk for this stock (below 2,000 t) is 22 to 26% with no bycatch up to 150 t, and increases to 30% and 49% at bycatch levels of 350 t to 1,500 t respectively. If recruitment rates were to decline even slightly to the levels seen in the 2000s, the extinction risk for this stock would increase. At the present 30 t bycatch limit for White Hake, White Hake will become a choke species for the future Redfish fishery. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Zoology is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Community attributes result from processes operating at various spatial scales. The hierarchic organisation of rivers and the prevailing hypotheses about the variables that affect fish communities make lotic ecosystems particularly suitable to study processes taking place across spatial scales. The general goal of this study was to investigate how river flow regime and local habitat properties explain and predict fish community attributes in unregulated and regulated rivers. Our objectives were: (1) to identify the hydrological indices that best describe the flow regimes of river segments subjected to different regulation types (unregulated, run-of-the-river, storage, and peaking), and; (2) to estimate the relative importance of hydrological indices (river scale), and water depth, water velocity, and substrate composition (local scale) in explaining and predicting local fish community attributes (species richness, total density, and total biomass). We surveyed 880 sites (~300 m) in 25 rivers (14 unregulated and 11 regulated) located in six physiographic regions of Canada. Based on a discriminant function analysis, nine hydrological indices were selected to represent river flow regime. Models of fish community attributes were developed using linear mixed-models (LMM) by nesting sites within rivers and regions. A few hydrological indices along with habitat properties predicted fish community attributes at the site scale (0.43< cross-validation $$R_{CV}^{2} < 0. 6 6$$ ). Specific hydrological indices and local habitat properties can be managed to preserve fish community attributes in regulated rivers. Combining variables associated with different scales in a LMM was a powerful and efficient way to model fish community attributes and produced reliable predictive models. [ABSTRACT FROM AUTHOR]

Studies attempting to describe fish community structure in shallow riverine environments typically rely on electrofishing and/or visual (snorkelling) surveys, but few have addressed the relative efficiencies of these two methods at estimating fish density and biomass across wide ranges of geography, taxonomy and life history stages. Multiple paired electrofishing and visual surveys were conducted in 18 temperate Canadian rivers in order to obtain community-wide density and biomass estimates from both methods. Partial canonical multivariate analyses were applied to the paired fish community matrices comparing the results of both surveying methods at the taxonomic levels of family, genus and species, as well as size classes within families and species, to assess the particular effectiveness of each sampling method. Although electrofishing estimates of family and species richness were generally greater, snorkelling surveys tended to generate higher density and biomass estimates for different size classes of many salmonid and cyprinid species. Moreover, mean river biomass estimates derived from visual surveying matched those obtained from our best mean river biomass estimates arising from the two methods combined. This study provides empirical evidence that electrofishing and visual survey methods generate different types of information when assessing fish community structure at the family level or by size classes. Our results provide ample background information for determining the most accurate sampling method for a particular fish community assemblage, which is fundamental to fisheries management and research. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]