Evidence of meeting #22 for Fisheries and Oceans in the 42nd Parliament, 1st session. (The original version is on Parliament’s site, as are the minutes.) The winning word was year.
A recording is available from Parliament.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
Okay. What are the factors that determine year class strength in cod?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
It's very difficult to pin them all down. Clearly, one of the most important is the size of the spawning biomass. If you don't have a lot of spawning biomass, you're not going to get a lot of recruitment. There are other things like productivity at the low end of the ecosystem, primary productivity that produces plankton and small copepods, which are food for young cod. These are very important in predicting what year class strength might be, and then we have to see good survival from the very young ages through to ages two and three. Much of that happens when the fish are feeding on small plankton, so these are critical as well.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
What's the natural mortality rate of cod, outside of fishing?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
For many years it was assumed to be around 0.2. In historical assessment models, for lack of better information, an assumed value of 0.2 was used, so this means that roughly 20% of the fish died from natural causes every year and just disappeared from the population, due to predation and disease and things like that.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
Did that figure of 0.2 go down as the commercial exploitation increased?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
No, it didn't.
Conservative
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
The most recent assessment suggests that this 0.2 value is a bit low. The most recent assessment, which we have with this new model, is able to estimate what the level of natural mortality is. This is a new feature, and it's a very important one. It suggests that natural mortality is quite variable annually, so it takes this into account. We think that natural mortality may be a little bit higher, and it's also much higher in younger fish than it is in older ones.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
That makes sense.
I'm going to dredge up my memories of my population ecology class. Would cod be an r-selected species or a K-selected species? Obviously, if they're K-selected, it makes it a little more difficult for them to recover. What are they?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
They're not so much K, where it's boom and bust. They're more r-selected.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
Okay. An r-selected species would be one that can handle a bit more, so it would recover.
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
Yes, capelin and small, fast-reproducing short-life-history species are what we call K-selected.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
Why has the recovery been so slow? There was a moratorium on walleye fishing in Lake Winnipeg in the mid-1970s. Within three years the population had come back significantly, almost to the same level it was. Why is it so slow? We're talking decades here.
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
I don't believe science has a good explanation, but I think the fundamental reason is that the natural mortality level stayed very high. For more than a decade we would go out to do our surveys. We'd see young fish produced each year but in fairly small numbers. The next year, when they were one year old, there would be a lot fewer; at two years old, there would be a lot fewer. They didn't survive beyond age six. The level of mortality for more than a decade was so high that it was simply eliminating very quickly what was produced each year. None of them was surviving much beyond age six or seven.
Conservative
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
It is.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
In an unfished population of cod, what would the maximum age be?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
It would easily be 25 years.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
Okay.
Does every female spawn annually, or do they skip a year or two?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
They can skip a year when feeding conditions are not good, but if the feeding conditions are good, they can spawn every year.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
Okay. Are you seeing older fish now in the population?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
We are. I referred to the biomass plot going up 12.5 times, much higher than the abundance. The reason the weights are going up is that we have bigger, older fish, and the oldest fish we see of any abundance are extending by one year each year.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
So you're seeing a dampening in the fluctuations, then, of your class strength? Things are kind of becoming a little bit more stable?
Research Scientist, Newfoundland and Labrador Region, Department of Fisheries and Oceans
Certainly we're seeing a broader age structure in the population, and that's a good thing.
Conservative
Robert Sopuck Conservative Dauphin—Swan River—Neepawa, MB
It sure is.
I think my time is up. Thank you very much.