Year of Publication: 1993
Abstract:
This report, entitled "Biophysical Inventory of Critical Overwintering Areas - Peace River," has been submitted as partial fulfilment of contractual obligations to the Northern River Basins Study. The primary objectives of this study were to locate deep-water areas in that portion of the Peace River upstream of Vermilion Chutes, to select deep-water areas that had potential as critical overwintering habitat for fish communities, and to conduct an intensive biophysical survey of selected areas. This information would then be used to assess the importance of deep-water sites as critical overwintering areas for fish communities in the Peace River. This report presents the findings of studies conducted during October 1992.
Deep-water sites (>7.0 m) are distributed throughout the study area (i.e., Peace River from Vermilion Chutes to the Alberta-B.C. border). The number of deep-water areas in the river ranged from 11 to 21 per 100 km section, with highest densities observed in the lowermost reach of the Peace River. Although abundant, there was a trend towards decreasing depths of deep-water areas from Vermilion Chutes to the Alberta-B.C. border. Mean depth decreased from 9.6 to 8.0 m. This information suggests that deep-water areas are not severely limited in the Peace River. As such, potential overwintering sites are accessible to fish communities in the system.
A reconnaissance survey in three sections of the Peace River (i.e., Many Islands, Notikewin, and Carcajou areas) assessed the suitability of potential deep-water sites for intensive sampling. Qualitative assessments, utilizing echo sounding as the principal method, established the presence of fish in deep-water areas in all three sections. Fish numbers were higher in the deep-water sites than in "normal habitat" in the immediate vicinity. Small to medium sized individuals dominated fish communities at most sites. Fish generally were located in 2.0 to 3.5 m depths along the margins of deep-water zones or were associated with some form of bottom irregularity. The bottom morphology was non uniform at most sites and consisted primarily of large cobble, boulder, or bedrock fractures.
Intensive sampling was conducted in one deep-water area; the Wolverine River Site, which is located near the settlementofCarcajou. Themaximumwaterdepthwas11.3m,andtheportionoftheriverthatexceeded 7.0 m depth was 33 ha, or 20% of the intensive sampling site. This deep-water area extended for approximately 2.95 km. Bottom morphology in the deep-water zone of this site was irregular, indicating the presence of large boulders or bedrock outcroppings. Water velocities in the thalweg of the site were high, ranging from 0.5 to 1.9m/s in the unobstructed watercolumn. High-water velocities such as these would limit the usefulness of open-water locations as holding areas for fish. It is more likely that individuals positioned themselves adjacent to bottom obstructions or along the edge of the thalweg; locations that characteristically exhibit low velocities. Dissolved oxygen and water temperature readings did not vary extensively. approximately 2.5°C, while dissolved oxygen ranged from 13.5 to 15.5 mg/L. This suggests that complete mixing occurred in the water column.
Several sampling techniques were employed in an attempt to capture fish from the intensive sampling site; they included deep-water electrofishing, drift netting, a combination of electrofishing and drift netting, and use of set lines. Prior to employing a particular method, fish concentrations were located with sonar to ensure that sampling effort was directed at a specific location containing fish. During four days of intensive deep-water electrofishing and drift netting, one goldeye was captured and two northern pike were observed. Deep-water sampling with set lines did produce some fish, which included three northern pike, and nine burbot. Captured fish were evenly distributed along the line at depths from 1.0 to 9.0 m. Surface electrofishing utilizing deep water electrodes was conducted to collect fish samples for contaminant analyses. In total, six northern pike, four burbot, and three longnose suckers were collected.Despite an intensive effort to sample the fish community in the Wolverine River Site, very few fish were captured utilizing techniques employed, even though fish concentrations (i.e., as determined by sonar) were present in the sampled area. As such, intensive field sampling of the three remaining deep-water sites was terminated. The study objective pertaining to collection of information on fish communities utilizing deep-water areas, was not achieved. As such, an assessment of the deep-water areas as critical overwintering habitats for fish communities in the Peace River could not be completed.
The results of the study suggest that deep-water areas are not limited in the Peace River, and that fish tend to concentrate at these sites during late fall. However, drift nets and deep-water electrofishing were ineffective as sampling methods used to capture these fish. If future sampling of these sites is to be considered, alternate capture techniques should be utilized. A potential method is combined trawl-electrofishing, which would employ electrical arrays attached directly to the mouth of a trawl net. This type of system would greatly improve the capture efficiency of fish that are immobilized by the electric field. Set lines also may be an alternate technique to intensively sample piscivorous fish species inhabiting deep-water areas; however, there are limitations associated with this method. These include sampling bias (i.e., selection for species such as burbot that rely heavily on olfactory senses to locate food) and high mortality rates of captured fish. If these limitations are acceptable, this method could be utilized to survey fish in deep-water habitats in the Peace River.
