ABSTRACT
This study was conducted to meet regulatory requirements under the
Fisheries Act in Canada, specifically for a hydroelectric facility on
the Yellowknife River in the Northwest Territories. The research focused
on annual snorkel surveys of adfluvial fish and their spawning habitat
below the facility. Initial observations of egg mortality, potentially
due to overcrowding, prompted the investigation of natural and enhanced
habitat for spawning Lake trout (Salvelinus namaycush ), lake
whitefish (Coregonus clupeaformis ) and cisco (Coregonus
artedi ) from 2016 to 2019. The design and composition of the installed
habitat were based on fish utilization of the natural channel below the
hydro facility and design principles from previous habitat
rehabilitation projects for anadromous fishes. Pre- and post-enhancement
data on egg density and survival were collected using 1
m2 plots on both natural and artificially enhanced
substrates. Three years of post-enhancement monitoring indicated higher
egg densities and a greater proportion of live eggs in the artificially
enhanced habitat compared to the natural habitat, with more pronounced
trends observed for coregonids (lake whitefish and cisco) compared to
lake trout. These findings suggest that habitat enhancement has the
potential to enhance juvenile recruitment for adfluvial fish. A critical
factor in the design was the substrate composition, providing adequate
interstitial spaces for egg development and protection. This study
represents the first documented attempt at habitat improvement in a
regulated sub-Arctic river in Canada. The findings offer valuable
guidance for stakeholders involved in new or existing development
projects that require conservation actions to maintain fisheries
productivity.
INTRODUCTION
Habitat enhancements in freshwater ecosystems have the potential to be a
viable tool for fisheries conservation and management in northern
regions of Canada where effects of climate change, overfishing, and
industrial works have the potential to limit or impair the productivity
of fisheries (McPherson, Cott, Lewis, Swanson, & Poesch, 2023). Habitat
enhancement can also be a legal requirement in many countries, including
Canada, where proponents are responsible to implement project mitigation
or conservation offsets for new developments or existing operating
facilities (DCCEEW, 2012; DFO, 2019; Favaro & Olszynski, 2017; zu
Ermgassen et al., 2019). Indeed, habitat enhancement is a widely
practiced restoration method in many developed regions around the world
where high valued recreational fisheries are in decline, however,
designing and implementing suitable habitat enhancements in northern
(e.g., Arctic and sub-Arctic regions) ecosystems is challenging due to
their remote nature, the difficulty in monitoring the effectiveness of
outcomes, and the paucity of available information and documented
records on past successes or failures in habitat enhancement approaches.
Lake trout (Salvelinus namaycush ), lake whitefish
(Coregonus clupeaformis ), and cisco or lake herring
(Coregonus artedi ) are widely distributed salmonid species found
in the northern regions of North America. They inhabit areas that were
previously glaciated, ranging from the Atlantic watersheds westward
throughout the Canadian provinces to British Columbia. They can also be
found in the Arctic watersheds across the Northwest Territories and
Nunavut (Evans, Reist, & Minns, 2002; Richardson, Reist, & Minns,
2001; Scott & Crossman, 1998). These three species are found in water
bodies of various sizes, ranging from smaller inland lakes (McAughey &
Gunn, 1995) to the largest lakes in North America, including the
Laurentian Great Lakes (Lake Superior, Huron, Michigan, Erie, and
Ontario) and the Mackenzie Great Lakes (Great Bear and Great Slave Lake)
(Evans et al., 2002; MacKenzie, Fortin, & E., 2021). They hold
significant biological, cultural, commercial, and recreational
importance throughout their distribution range (MacKenzie et al., 2021;
Mohr & Nalepa, 2005).
Habitat enhancements in northern ecosystems often focus on general
principles of improving habitat characteristics (Theis, Ruppert, &
Poesch, 2023; Theis, Ruppert, Shirton, & Poesch, 2022), but with a
specific focus on improving spawning substrates habitat (Gatch, Höök,
Roseman, & Koenigbauer, 2020; Selgeby et al., 1995), based on the
assumption that it will improve egg survivorship and ultimately increase
fish abundance. However, the success of enhancing spawning substrate is
heavily dependent on the life history types of the targeted species, and
there is a significant disparity in available research between
lacustrine (lake) and adfluvial (river) spawning life history types. For
example, there is a substantial body of research on the life history,
spawning behavior, and spawning habitat requirements of lacustrine lake
trout (Callaghan, Blanchfield, & Cott, 2016; Fitzsimons, 1995; Gunn,
1995; Richardson et al., 2001). Similarly, extensive literature exists
on the spawning behavior and habitat of lacustrine lake whitefish and
cisco, mainly in relation to fisheries management objectives for
commercial fisheries in the Laurentian Great Lakes (Fischer et al.,
2018; Gatch et al., 2020; George, 2019). Although lake trout, lake
whitefish, and cisco can be found in northern adfluvial systems, our
understanding of the extent to which they use riverine habitats for
spawning is limited. There is a lack of information regarding the
frequency and characteristics of watercourse utilization for spawning,
highlighting the need for further research on the utilization of
riverine areas by these three adfluvial species (Evans et al., 2002;
Jones, Parna, Parna, & Chong, 2018; Richardson et al., 2001).
The development of habitat enhancements to improve spawning substrate
based on life history characteristics of multiple adfluvial species
provides the potential to help prioritize conservation measures for the
benefit of multiple species. To do this, we require an understanding of
life history types and similarities and differences of these advluvial
species, their habitat use, and spawning characteristics, based on
empirical information. Lake trout, lake whitefish, and cisco have unique
life histories and spawning behaviors, but they also share certain
similarities, which may allow for some synergism in developing habitat
enhancements. For example, all three species are members of the
Salmonidae family with lake trout belonging to the Salmoninae sub-family
and lake whitefish and cisco belonging to the Coregoninae sub-family
(Evans et al., 2002; Richardson et al., 2001; Roberge, Hume, Minns, &
Slaney, 2002). Secondly, all three species are fall-spawning,
lithophilic broadcast spawners, meaning they deposit their eggs in
granular substrates (Roberge et al., 2002; Scott & Crossman, 1998;
Stewart, 1997). Thirdly, while their lacustrine and/or anadromous
populations have been extensively studied, the adfluvial populations of
these species, which migrate to rivers for spawning, have received less
research attention regarding their life history, spawning behavior, and
habitat requirements (Evans et al., 2002; Richardson et al., 2001).
Finally, all three species play significant roles in commercial,
Indigenous subsistence, and recreational sport fisheries in Canada
(MacKenzie et al., 2021; Mohr & Nalepa, 2005), which make them highly
suitable candidates for habitat enhancements measures and offsetting in
general.
The availability of suitable spawning habitat plays a crucial role in
the recruitment of spawning salmonid populations. Numerous studies have
highlighted the significance of spawning habitat availability for
freshwater fishes and its impact on year class strength and population
variability (Fitzsimons, 1995; Gunn, 1995; Milner et al., 2003).
Unfortunately, anthropogenic activities have significantly impacted the
spawning habitat of anadromous salmonids (McPherson et al., 2023;
Poesch, Chavarie, Chu, Pandit, & Tonn, 2016), resulting in degradation
and fragmentation. Factors such as habitat degradation, hydroelectric
dams, and overfishing have contributed to these impacts (Cowx &
Welcomme, 1998; Whiteway, Biron, Zimmermann, Venter, & Grant, 2010;
Zeug et al., 2014). To address these challenges and restore or enhance
fisheries production, government agencies and non-profit organizations
have dedicated substantial resources to the restoration of degraded
spawning habitat. Efforts have included the installation or creation of
artificial spawning habitat and the evaluation of different designs and
approaches for rehabilitating anadromous salmonid populations (Murchie
et al., 2008; Pulg, Vollset, & Lennox, 2019; Roni, Hanson, & Beechie,
2008). Various rivers and waterways along the Pacific coast of North
America, as well as the Atlantic coast of North America and Europe, have
seen the construction and assessment of artificial spawning habitat for
anadromous salmonid species, including chinook salmon, steelhead trout,
Atlantic salmon, and brown trout (Barlaup, Gabrielsen, Skoglund, &
Wiers, 2008; Pedersen, Kristensen, Kronvang, & Thodsen, 2009; Whiteway
et al., 2010). Overall, these efforts highlight the importance of
addressing the impacts on spawning habitat and the implementation of
restoration measures to support the sustainability of salmonid
populations.
The Great Slave Lake fishery is home to adfluvial species such as lake
trout, lake whitefish, and cisco. It heavily relies on the major
tributaries surrounding the lake for essential flows, nutrients, and
energy for food webs. These tributaries also serve as critical spawning
and egg incubation locations for fall-spawning adfluvial salmonids
(MacKenzie et al., 2021; Rawson, 1951; Stewart, 1997). Located at the
outlet of Bluefish Lake on the Yellowknife River, approximately 18 km
upstream from where the Yellowknife River meets Great Slave Lake, is the
Bluefish Hydroelectric Facility (hereafter ‘Bluefish’) (KCB, 2017). In
2011, the Northwest Territories Power Corporation (NTPC) received a
Fisheries Act Authorization (FAA) from Fisheries and Oceans Canada (DFO)
for the construction of a new primary impoundment dam and spillway for
the facility (Golder, 2019). The FAA mandated monitoring, including
confirming the spawning of fall-spawning salmonid species (lake trout
and coregonids), in the lower spillway of the historical Yellowknife
River channel and downstream of Bluefish. Observations of spawning
adults and fertilized eggs in the area provided direct evidence of
adfluvial lake trout, lake whitefish, and cisco spawning in the
Yellowknife River below Bluefish (Golder, 2019) (Figure 1).
The main goal of this study was to provide a comprehensive summary of
the collected data on spawning activity at Bluefish and contribute to
the limited existing research on adfluvial lake trout, lake whitefish,
and cisco spawning behavior and habitat requirements, both for natural
and artificially enhanced substrates in northern freshwater ecosystems.
STUDY AREA
The study area is located on the Yellowknife River, situated downstream
of Bluefish Lake and upstream of Prosperous Lake, in the northern region
of Yellowknife, Northwest Territories (refer to Figure 1). The
Yellowknife River drainage area, just downstream of the study area at
the entrance to Prosperous Lake, spans approximately 11,300
km2 (ECCC, 2020). Further downstream, at the outlet
where the Yellowknife River meets Great Slave Lake, the total drainage
area expands to around 16,000 km2 (Spence, 2001). The
Yellowknife River basin falls within the sub-Arctic Canadian Shield
physiographic region, specifically within the Taiga Shield Ecozone. This
basin is characterized by shallow and exposed Precambrian bedrock, an
open black spruce forest, and a multitude of lakes, with surface water
covering approximately 25% of the basin area (Spence, 2001).
The study area encompasses the lower portion of the historic Yellowknife
River channel, situated downstream of the Bluefish Lake Dam, which
serves as a natural spillway for Bluefish. The construction of the
Bluefish Lake Dam took place in 1940 at the Yellowknife River’s outlet,
primarily to facilitate storage for the G1 generating plant (KCB, 2017).
Subsequently, in 1994, a second generating plant (G2) was constructed
approximately 20 meters west of the G1 plant. In 2012, a new dam and
spillway were built around 400 meters downstream from the original dam
(KCB, 2017). The discharge of flow from the G1 and G2 plants occurs into
the main Yellowknife River channel, situated 80 meters east of the
spillway outlet, within a section known as the Tailrace Area (Golder,
2019). The Tailrace Area spans approximately 110 meters in width and
exhibits depths reaching around 4 meters.
The spillway, which carries water not utilized by the generating plants,
incorporates the historic Yellowknife River channel (Golder, 2019).
Within this channel, the Instream Flow Gate was installed in 2012 to
ensure minimum flows for fall-spawning fish, with a regulated minimum
flow of 0.75 m^3/s. Prior to the installation of the gate, flow in
the spillway was maintained through leakage from the old dam, spanning
from 1942 to 2010 (Golder, 2019). The downstream section of the
spillway, providing habitat for fall-spawning salmonids, is referred to
as Reach 1. It is characterized by a natural waterfall at the upstream
end and extends to the confluence with the Tailrace Area, where the flow
enters the main Yellowknife River channel at the downstream end. Reach 1
measures 178 meters in length and exhibits water depths of up to 1.5
meters. The substrate composition is predominantly boulders and cobbles,
with exposed bedrock areas interspersed (Golder, 2019). Adfluvial
fall-spawning fish species, such as lake trout, lake whitefish, and
cisco, migrate annually from either Prosperous Lake or Great Slave Lake
to spawn in Reach 1 and the Tailrace Area (Golder, 2019; MacKenzie et
al., 2021; Stewart, 1997).
METHODS
The
study was conducted over a 4-year period, including Pre-Habitat
Enhancement Construction Monitoring (2016), Habitat Enhancement
Construction (2017 & 2018) and Post-Habitat Enhancement Construction
(2017-2019) during the months of September through October. Annual
monitoring of spawning fish abundance and distribution was conducted in
the Yellowknife River below Bluefish as part of the regulatory
requirements for Bluefish operations under the FAA for the new
impoundment dam since 2013 (Golder, 2019). Spawning fish counts were
made during six to eight snorkel surveys conducted from September to
early November, timed to coincide with suitable temperatures for the
spawning of lake trout, lake whitefish, and cisco (Scott & Crossman,
1998). During the surveys, one observer was in the water enumerating
spawning, while a recorder on the shore documented the observations. It
is important to note that surveys in 2019 began in early October,
missing the peak arrival of lake trout, and therefore, the snorkel data
for lake trout in that year are not included in the analysis.
To assist with the interpretation of trends across study years, we
summarized supporting environmental data on daily water temperature and
river flow discharge, from the Water Survey of Canada (WSC) hydrometric
gauges in the Yellowknife River (ECCC, 2020). Daily discharge data were
obtained from station no. 07SB003, located below the Tailrace Area
(Figure 1), while daily water temperature data were obtained from
station no. 07SB015 in Bluefish Lake, upstream of the dam. Historical
”baselines” were defined on data collected from 1991 to 2020.