I'll do my best to finish my presentation in 10 minutes.
Thank you to the committee for inviting me to present.
I apologize for the French version of the document you should have a copy of. The translation's only partial. The labels on the graphs have not been translated. We can get that to you sometime this week. It was a bit of a challenge to get all this stuff done during the course of the week, but everything else is translated.
Today what I'll do is talk to you about the changes that have occurred in the environment and the ecosystem structure on the Newfoundland shelf over the last three, four, or five decades.
If you move to slide number two, this gives you an outline of the things I'm going to be talking about today. It's not an exhaustive list, but they are the key features you have to consider as drivers in responses to the changes that have taken place over time.
If you move to slide number three, here we're going to have a little bit of Biology 101 in terms of giving a sense of what the ecosystem structure is around here.
The timing and extent of ice, the weather, and the fluctuations in these features from year to year are the factors that determine the production of the lower trophic levels. They affect the timing and they affect the magnitude of the overall production of the phytoplankton, which are the microscopic plants on which the food chain depends, and that affects the production of zooplankton.
Both these groups contribute to the growth and production of the forage species, which consist of the young stages of fish, capelin, and shrimp, and all three of these components are important prey for the dominant predators in the system, which consist of a variety of groundfish. The dominant ones are indicated here, but there are a host of others, as well as seabirds, cetaceans, and seals.
One of the things to keep in mind when you're looking at an ecosystem is that it's dependent on its standing stock, but more importantly, it's more dependent on its production. The standing stock currently on the Newfoundland 2J3KL areas is about 1.5 million tonnes if you take all the bits and pieces into consideration, and the total consumption that takes place in that system is in excess of 15 million metric tons per year, so there's a lot more production you're not seeing when you're looking at standing stocks.
If you move to slide number four, one of the things we do around here is spend a lot of time trying to get a sense of what the environment is doing. For that we derive a state-of-the-ocean index, which is a composite of 28 time series that include information on meteorological conditions; the extent, timing, and other features of ice; the temperature of the ocean; the extent of the cold intermediate layer, which is a major oceanographic feature around here; and the salinated water, which reflects the balance in terms of the freshwater input into the system.
The most important feature of this graph is the change we saw from the early 1990s to about 2010, when we went from the coldest period on record to the warmest period on record. This is a dramatic change in terms of the overall conditions in that environment, and although there were periods of warm and cold prior to that, this was a rather dramatic change.
In the last few years we've seen a little bit of a cooling off, and that will have consequences to the dynamics of the species we're looking at, but nevertheless, it's an important feature to keep in mind. However, it is in contrast to what's going on in the Gulf of St. Lawrence, on the Scotian Shelf, and in other parts of the northwest Atlantic, which actually seem to be staying warm and continuing to warm as a result of changes in atmospheric forcing.
If you move to the next slide, which is a little bit more complicated, if you look at the panel on the left-hand side, it shows you the change in the abundance of the different functional feeding groups. By functional feeding groups I mean groups of organisms that feed on the same kinds of things. For instance, piscivores are all feeding on other fish species, and cod is a dominant piscivore in the system, so the changes you see in the blue portion of the graph are actually mostly changes that have occurred in the biomass of cod. The important thing to get out of this, though, is that from the 1980s to about 1994, all the groups collapsed, not just cod. Everything else in that system collapsed. Everything disappeared.
In 1995 we had a gear change, so we've had to adjust the estimates a little bit. At that time, we actually started capturing invertebrates in our nets, and that's why there's a red section there, but what you can see is that from about 1995 until about the mid-2000s, invertebrates increased in abundance, while the other groups weren't doing a whole lot. Starting at about the mid-2000s, the invertebrates started going down, and the groundfish species started to increase in abundance. That's an important thing to keep in mind.
The right-hand panel shows you the acoustic estimates of capelin abundance. Prior to the collapse in 1991, there were about 4 million tonnes of capelin in area 3L, which is just the northern part of the Grand Banks, not the entire area. In 1991, the bottom fell out of it. There were no capelin. They disappeared. They either died or went somewhere else. That was a very dramatic change in the ecosystem. The food base for many of the predators disappeared off the face of the earth—literally—and until the mid-2000s we saw virtually nothing happening. There's been a slight increase, but we're at about a quarter of where we were prior to the collapse.
On the next slide, the top panel shows the trend in abundance, a slightly different index of abundance—the average biomass per tow—of four of the dominant groundfish species: cod, halibut—often referred to as turbot—plaice, and redfish. What you can see is that the most dramatic change has been in cod. It showed a very marked decline, but all the other species declined.
After the period when things settled down, around 1994, the abundance of the other species stayed relatively constant. There was a slight increase in the abundance of turbot, but there wasn't anything else that took over. That's the important thing: there was no filling of the niche that had been occupied by cod.
What we were able to do from these data was identify areas that were dominated by cod, shown as the red symbol in the middle panel on the left-hand side. Redfish is the purple one, halibut is blue, and plaice is green. When you look at the spatial distribution shown in the lower panel of the six panels grouped in five-year chunks, what you can see is that prior to the collapse, most of the Newfoundland shelf was dominated by areas that were dominated by cod.
During the collapse, there was a fragmentation of the environment. The distribution of the communities became very fragmented. Areas where there had been cod disappeared and were basically literally fished out. Following that, there were several years before we actually saw any kind of rebuilding of the cod. What happened is that the community got dominated largely by the halibut and redfish communities, as well as by the expansion of some of the coastal species, which are less abundant in total biomass.
What we saw in mid-2000 to about 2013 was a reappearance of cod-dominated areas, but on the southern portion of the range where we had normally seen the cod. Although this has not been updated to 2015, what's happened is that the area in the northern part, which used to be dominated by cod, still has not recovered.
You saw this next slide last week during a presentation by Dr. Brattey. This is the estimate of cod. What you can see is that although there's been a resurgence in the last 10 years or so, we're nowhere near where the stock used to be.
The next slide shows another thing that changed during the collapse of the cod, which is the shift in the diet. The only things you really have to concentrate on in this panel are the red and the yellow sections. The yellow section represents the relative proportion of capelin in the diet of cod.
You can see that prior to the collapse, the diet of cod was dominated by capelin. During the collapse, there was a shift towards shrimp, because there was virtually no capelin available. In the mid-2000s or so we saw that most of the diet consisted of shrimp, as that was basically the prey that was available.
Since then, we've seen a resurgence in capelin and a decrease in the overall abundance of shrimp in the diet of cod, and not only for cod but for other species of major predators in that system as well. There has been a bit of a shift towards other species as well, which we don't quite understand yet.
Slide 9 shows that we investigated the dynamics of cod during the pre- and post-collapse periods. That was modelled using three key drivers: the capelin abundance, the fishery catches, and the seal predation. All these were estimated based on information, not guesswork. What ended up happening is that both capelin abundance and the fishery were statistically significant drivers of the changes in cod biomass in the region, but seal predation was not, no matter what combination of variables we actually included in the model.
If you look at the panel on the left-hand side, the blue dots are the abundance of cod from the research vessel survey estimates and the yellow dots are the abundance of capelin. You can see that the two track rather well.
If you turn to slide number 10, these are the dynamics of shrimp. We did not have good, reliable estimates of shrimp prior to 1995. You can see that the abundance of shrimp increased significantly—this is SFA 4, so it's areas 2J and 3K, basically. The abundance of shrimp increased until about the mid-2000s. It has been in decline ever since.
If you look at the middle and left-hand panels in the graphs here, they're a little bit complicated. I'll try to walk you through them.
The red line indicates the annual production, normalized or standardized so that we can put everything on the same scale. The red line represents the production of shrimp, and you can see that it fluctuates a fair bit from year to year, but the general trend from 1995 to 2015 has been a decline. When we started, we had high production in that system, and that's the increase in the biomass as well as the fishery catches relative to the previous year. That's generally been in decline.
In the middle panel you can see the composite index of environmental condition, which has been flipped so it makes the figure a little bit less noisy. Warm is down, towards the bottom, and cold is up, towards the top of the graph. You can see that it tracks fairly well with the changes in production from year to year. It's also reflected in the timing of spring phytoplankton booms. The dynamics of that whole ecosystem, from lower trophic levels to upper trophic levels, is reflected in this graph.
However, at the same time, if you look at the right-hand panel, the blue line or the black line shows the abundance of predators, and the green line shows the estimate of consumption. Again, they've been standardized to put them on the same graph. You can see that during the period when there was a decline in the production of shrimp, there was an increase in the number of predators and the overall consumption by predators. The most recent decline that we see in the graph, on the right-hand side in the green line, is basically because there's been a shift from shrimp to capelin in the diet of the major predators.
The next slide shows you the time series of capelin, which we discussed earlier. I'll walk you through the bottom graph. It basically shows the relationship between the production of the capelin stock and the timing of the ice retreat in the spring, just to give you a sense of how important the environment is to the dynamics of this stock. There are two lines on this: one is the pre-collapse and one is the post-collapse relationship with the timing of ice. It basically reflects that there's been a regime shift in the system that we don't really quite understand at this time.
The final panel here shows you the time series of catch per unit effort for crab in relation to the availability of cold water during the first year of life. You can see that in all situations there's fairly good tracking between the availability of cold conditions and the production of the crab stock.
On the final slide, to summarize, the biomass of Atlantic cod and other groundfish species as well as capelin has increased since the mid-2000s. The abundance of northern shrimp and crab have declined as a result of warming ocean conditions. The recent cooling trend may be beneficial to shrimp and snow crab, but the impact on groundfish and capelin is still uncertain.
We're going to continue to monitor the environmental conditions and investigate species interaction. We're currently conducting research to better understand and forecast the effects of changes in ecosystem structure on these key species.
Thank you.