The Dolly Varden Story
Anadromous Dolly Varden preparing to spawn in Fish Hole Creek, Northwest Territories
Neil Mochnacz is a Fisheries Research Biologist working out of Fisheries and Oceans Canada's (DFO's) Central and Arctic Region. His primary area of study relates to sensitive fish and their habitats north of 60 degrees latitude.
One such fish is the Dolly Varden charr. They are considered to be sensitive fish because they typically mature late compared to other species, are particularly vulnerable to habitat change, and don't bounce back to stress as readily as other species. As such it is a species of concern to DFO Fisheries Managers and researchers.
Two years ago the department was tasked with gathering and summarizing all the information it had on northern Dolly Varden populations so that the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) could assess the species and determine what category they might now fall under – "sensitive", "threatened", or "endangered".
"One of the major unknowns," notes Mr. Mochnacz, "with respect to the Dolly Varden is: how do changes to habitat affect populations? Our stock assessment research section focuses on population size and structure, whereas I study the habitat that fish use. You can have all the fish in the world, but if you don't have enough habitat, it doesn't matter."
What makes them unique and more susceptible than other species is that because they live so far north, the opportunities for them to overwinter are few and far between. The amount of habitat available to them is limited because most of the rivers freeze completely to the bottom.
Underground springs, which are groundwater sources, create key habitat for this species because it allows sections of these freshwater rivers to be ice-free or at least not freeze completely to the bottom during winter.
Mr. Mochnacz points out that, "The carrying capacity - the amount of available habitat - appears to be lowest during the winter. If winter habitat were taken away, or reduced substantially, it could severely impact populations."
Although general spawning areas are known for most Dolly Varden populations in the north, what scientists didn't know was where exactly the high discharging groundwater locations were, and where discrete overwintering habitat was.
Conducting Dolly Varden Habitat Research
Mr. Mochnacz: "When I first started the project, one of my primary objectives was to identify and characterize groundwater sources so we could precisely determine where they were and how fish use these habitats. Using an infrared camera, we looked for temperature differences between surface water and groundwater. Obviously, in the winter, the springs will be warmer than the ambient air temperature. What's most important, and we did this last fall, is to see where these spots are in relation to where the fish are spawning. Last year we were quite fortunate. We could see where adults had excavated their redds and laid their eggs and we were able to document that key information."
The end result of such work is that scientists are able to establish baseline conditions in three important areas: overwintering, spawning and rearing, with all three typically overlapping. As they identify, delineate and quantify habitat they are able to provide this information to COSEWIC for their assessment, particularly surrounding critical habitats.
Mr. Mochnacz: "The questions that always are at the top of my mind are these: "Have their habitats changed, and if they have, is it through natural occurring change, change attributable to climate change, or some other kind of other human intervention?"
One comment that Mr. Mochnacz received from local communities was that rivers used to be deeper and there aren't as many pools as there were 20 years ago.
He notes, "Here again, the only way to really figure that out is to establish some type of baseline. Once you've established a baseline, then you can monitor it over time. For example, are there actually fewer pools in some of the rivers now? Is the river shallower and has the river morphology changed? Based on our research we know that pools are important habitat, however, if in the future there are fewer pools in northern rivers, will that affect the population?
What we also have done is establish 'reference sites' in a couple of these rivers. Last year we surveyed known spawning habitat in one of the rivers. Once our survey was complete, we developed a two-dimensional hydrodynamic fish habitat model for this study reach. The computer model will allow us to estimate how much habitat will be available for Dolly Varden at various times of the year based on different water levels.
First and foremost of concern is winter habitat. We hypothesize that at some point in the fall the primary base flows are almost 100% from groundwater as opposed to surface water (i.e., precipitation) and groundwater in the spring and summer. So let's say we go through a really low water year where we get very little contribution from surface water. There could be some years where the spawning and overwintering areas are actually fragmented or disconnected from downstream habitat. This would be a worst case scenario for annual recruitment.
The second scenario would be that water is low and the actual amount of winter and spawning habitat available to fish is decreased substantially. If you think of it as a fishbowl, if the fishbowl is completely full, you can fit five fish in there. If the fishbowl becomes half full, then you're reducing it by 50%, with disastrous results for those five fish.
So that's the thinking that we're following: how the system functions in terms of carrying capacity for fish at critical periods from a habitat perspective."
This research is important because DFO and allied agencies along with various co-management boards and community groups are all looking for new tools to manage better, using an ecosystem perspective. It is critical that all stakeholders start to understand that stock assessment issues are inextricably connected to habitat conditions. This is especially important in areas where development may occur, but also in areas where the habitat may change naturally and which could affect fish abundance over time.
Fisheries and Oceans Canada has traditionally recommended annual fishing quotas based on estimates of population size and/or structure. Now, with the focus on an ecosystem approach to species management, the understanding of fish habitat will remain front and centre in scientists' investigative concerns.
For Dolly Varden, if COSEWIC lists the species as "threatened" or "endangered", the next phase will be to develop recovery plans and do the necessary research to support those plans.
The research and monitoring is an ongoing process. It is a process that Mr. Mochnacz remains enthusiastic about. He says, "In my opinion, I have the best job in the world. I get to do some really amazing things in some wonderful places. It's essentially my passion, and what I feel like I was meant to do."
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