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Dr. Craig Purchase

A Q&A with fish expert and national committee volunteer

Campus and Community

By Mandy Cook

Spawning season is a busy time in Dr. Craig Purchase’s world.

But despite a near around-the-clock schedule ferrying salmon gametes from the lab to the river, the evolutionary ecologist sat down with the Gazette recently to share some insight into another one of his roles: volunteer for a national organization dedicated to the scientifically sound classification of wildlife species at risk.

Dr. Craig Purchase
Dr. Craig Purchase
Photo: Chris Hammond

Dr. Purchase, an associate professor of biology and ocean sciences, explains below how his work as an evolutionary ecologist relates to his work on a sub-committee of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) — an organization about to mark its 40th year.

MC: Tell me a little bit about how your work at Memorial relates to your voluntary work with COSEWIC.

CP: One of the reasons why I remain interested in my role on COSEWIC’s Species Specialist Sub-Committee for Marine Fishes and continue to volunteer my time is that the endangered species designation process is split into two.

There’s the science process which is the COSEWIC part, which makes the recommendation for a species to be listed as endangered or threatened, and then there’s the political part of it and whether COSEWIC’s recommendations are then listed under the federal Species at Risk Act or not.

MC: What’s the purpose of the split?

CP: The split removes political input from the recommendation process. COSEWIC recommends based on biology; the government then weighs outcomes to decide whether to list or not. In the science process when a species is evaluated, most of the time one of the things related to the evaluation is whether the species should be broken up into smaller units of biodiversity.

“For many marine fishes, even though they declined rapidly, it may or may not be that obvious that they are quickly on their way out.”

The federal Species at Risk Act allows for the protection of biodiversity at a finer resolution than is the species. Most people can think of sub-species, but that’s not exactly how it works. The language we use to refer to the concept is designatable units.

Each, then, of those designatable units can be evaluated on its status and whether it’s in trouble or not. How you decide if a species has one designatable unit, or two, or 100 I find fascinating, and that’s how it relates most closely to my work.

MC: How does that process function, in terms of how potentially threatened species are assessed?

CP: I do a lot of work related to local adaptation, and whether we take a species and “split” it into designatable units or not depends on a couple things.

The default is a species equals a single designatable unit. If you have no data to suggest otherwise — which doesn’t mean it shouldn’t be split, there’s just no evidence, having no evidence is not the same as having evidence against — you have to go with one designatable unit. A lot of things that COSEWIC has dealt with across all taxa is that a species equals one designatable unit.

“Many of the East Coast ground fish populations loss more than 99 per cent of their individuals a few decades ago, but there were still millions of animals left.”

But in more well-studied species, often there is evidence to be considered about splitting the species up. One way of thinking about it are the regions a species occupies, like salmon in different rivers. The different regions a species occupies have to be distinct (since they’re not interbreeding with each other), but they also have to be significantly different.

Within a species, sometimes it’s one designatable unit, sometimes one or two populations of that species make up one designatable unit, but there could be hundreds of populations that make up one unit.

So, we have to decide on the designatable unit structure, then we have to evaluate population trends through time and how this relates to criteria for whether you recommend something is not at risk or endangered or threatened or these types of things. The SARA process enables protection of each of these units.

MC: Can you provide some detail about the fish-related aspect of your COSEWIC work?

CP: I’m on the Marine Fishes Species Specialist Sub-Committee. In my eight years we have evaluated dozens of species, even more designatable units.

For example, we are evaluating sockeye salmon now and there may be hundreds of designatable units for that species. Atlantic salmon, there were 16, I think in our last assessment, but that might change in the future as we get more data.

The marine and freshwater fishes groups split the workload — anything that spawns in fresh water and migrates to the sea, like salmon, the marine fishes group does them. We do all the sharks, cod, plaice, lump fish . . . there’s dozens of species that have been through the evaluation process.

MC: Can you give a little bit of specific information about a particular species? Salmon, for example, which seems to be under stress for some time now?

CP: For many marine fishes, even though they declined rapidly, it may or may not be that obvious that they are quickly on their way out.

Many of the East Coast ground fish populations loss more than 99 per cent of their individuals a few decades ago, but there were still millions of animals left. However, it is not always that way. For example, you have Anticosti Island in the Gulf of St. Lawrence. It’s believed there are only a few hundred individual adult Atlantic salmon in that designatable unit.

In the Maritimes, the inner Bay of Fundy, that designatable unit of Atlantic salmon is critically endangered. The Lake Ontario designatable unit of Atlantic salmon is extinct. There was a unique form of Atlantic salmon in Lake Ontario; they’ve been extinct for a long time.

The Marine Fishes Species Specialist Sub-Committee has put a lot of effort on the East Coast ground fisheries after the collapse in the ’90s, but we’re moving on now with the Pacific salmon and when you think of sockeye salmon, are they endangered, well, sockeye salmon as a whole are not in danger of extinction.

But there are likely hundreds of designatable units for sockeye salmon. We know some of them have already gone extinct. And there are likely dozens that are critically endangered.

The way the designatable unit concept works is that if they are lost, they can’t be replaced. There’s something unique about those populations that other members of the species can’t fill their void.


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