BAY DELTA SCIENCE CONFERENCE: The scientific challenge of establishing appropriate baselines for restoration
Ecosystem restoration generally seeks to reestablish structures and processes in ecosystems that have been degraded by human activities. The success of the project is usually measured by comparing the current conditions to specific targets that were chosen to reflect desired ecosystem states. While such comparisons are convenient for developing restoration strategies and measuring success, they often lead to the assumption that there is a single stable state that the ecosystem should exist in, Dr. Daniel Schindler says. In this presentation from the plenary session of the Bay Delta Science conference held in November of 2016, he discusses how ecosystems are constantly reorganizing themselves and how that presents challenges for establishing appropriate baselines for watershed restoration.
Dr. Daniel Schindler occupies the Harriet Bullitt Endowed Chair in Conservation, School of Aquatic and Fishery Sciences, at the University of Washington.
Dr. Schindler began by positing the question, what are we trying to restore our ecosystems to? What are the conditions and the processes that we’re trying to put back into place in the system? “We often have a view for what that should look like, but it doesn’t necessarily embrace the fact that what it should look like is that the ecosystem should be continuously reorganizing and turning over,” he said. “If we study ecosystems that are doing what ‘should be’, they are a moving target, and this is something that we don’t often embrace when we start thinking about the processes that we should be trying to restore when we think about ecosystem restoration.”
The concept of the shifting baseline syndrome was an idea proposed by Dr. Daniel Pauly 20 years ago. His idea was that through cultural change over the course of decades or centuries, our view of what the ecosystem should look like is slowly eroding through time. Dr. Schindler noted that old pictures show people catching big, monstrous fish, but nowadays, the fish are much smaller. “This is the sort of pattern that we use to think about the way things used to be, and the argument that Pauly makes very powerfully is that through time, we’re slowly eroding what our ecosystems are characterized by simply because we have a short-term viewpoint of how the system should actually look,” he said.
Dr. Schindler said the argument he would be making in his presentation today is that we are thinking of a single state back there in the past, without embracing the fact that it’s actually a moving target. “Ecosystems are continuously reorganizing and what we need to do is think about what are the processes, whether they be physical or biological, that allow this reorganization of the ecosystem,” he said.
He said he would draw on examples from his research in Alaska to demonstrate the fact that ecosystems do turn over a lot and therefore have a lot of variability in them. “The message I’m hoping to get you thinking about today is not to pretend that the rivers you work on down here could ever be restored to the functioning of these systems in Alaska, but I think the processes and the concepts are very important to consider when we think about what are we actually trying to restore in our systems,” he said.
Dr. Schindler presented a slide showing the number of sockeye salmon returning to the rivers in Bristol Bay, which is in southwest Alaska. Bristol Bay produces over half of the world’s sockeye salmon, and the sockeye return to nine major rivers in the region. “The point here is that if we look between the 60s and the mid 70s, most of the returns were associated with a single river system, the Kvichak River which flows out of Iliamna Lake,” he said. “The idea held by managers, by fishermen, and by conservationists is that the jewel of Bristol Bay was this Kvijack River. It was producing as much as 90% of all the fish from this region.”
In the mid-70s, there was a shift in the dominant regime in the ocean, depicted by the changes in color pattern after that point. “The total production of the system has maintained itself or even in fact become more stable and a little bit higher, but you can see that the composition of where the fish are returning to has changed through time,” he said. “So the system has been maintaining function; it has reorganized in terms of what the important rivers are in the system. This amount of reliability that’s produced by reconfiguration of the ecosystem has benefitted people for centuries to millennia.”
A problem with scientists in general is that they never seem to have enough data, not even the 50 or 100 years of data, said Dr. Schindler. A criticism of the last slide is that it is data collected after the system had already been heavily harvested. After the fisheries hammered all the Columbia River stocks in the late 1800s, they all moved north, and then the late 1890s, the they started fishing salmon in Alaska, so the data on the slide was derived well after the fisheries had developed. “One of the concerns is that maybe the dynamics that are being observed in the last few decades are in fact driven by fishing pressure.”
So they asked the question, how variable were salmon returns prior to commercial fishing and do they still show this pattern of reorganization at the landscape scale? They were able to determine this through an approach known as paleolimnology. Dr. Schindler explained that after the sockeye returning from the ocean where they put on most of their growth, they come back to freshwater to spawn; they die and the nutrients from their bodies are released and incorporated into the sediments at the bottom of lakes. The nitrogen brought back by salmon from the ocean is enriched in nitrogen-15, and since the sediments accumulate year after year, if they take a sediment core from the bottom of the lake, they can reconstruct a history of single lakes across this entire region.
He then presented a diagram of the last 500 years of observations from lake sediments. On the y axis is the enrichment of N15 in the sediments, and higher values correlate with higher salmon returns. The resolution is about a decade. “I realize this is a very busy diagram, but the message I want you to take from it is fairly simple,” he said. “About 60% of the world’s sockeye are produced from these lakes, they are all in western Alaska. The question I want you to ask is if you scan across all of these graphs, how many of those patterns are held common among panels? You can pick pairs that look very much like each other, but you get some sites that have a 20-30 year period in them, whereas other sites have 200 year period in them.”
Using a statistical technique called a simple principle components analysis, they can determine if there is a pattern that is held common across this region in terms of the number of salmon produced over the last 5 centuries. He presented a slide showing the results of the four principal components, noting that the only significant one is the first one, shown in blue.
“What you can see is that the big signal captured by the first principle component is this one right here, where you get this distinct decline since 1900,” Dr. Schindler said. “The pattern that’s common to all of these sites is the fact that fisheries developed around 1900, and what we’re looking at here is the depletion of isotopes because all those salmon nitrogen molecules were captured and put in cans; they didn’t escape and release themselves into the lake where they were deposited in the sediments. If we ignore this last decline in the last century – this is not fish decline, it’s just interceptions. But there’s no pattern that’s shared across the landscape. So what this says is even over the last 500 year history of this region, different rivers are doing different things, and as a result they are buffering themselves out. If you have a fishery that integrated across that landscape, it’s going to be much more stable because of the reorganization that’s occurring from site to site.”
That is an example at a broad scale in terms of space and time; Dr. Schindler then drew on an example of a more intermediate spatial scale, looking at the Nushagak River. The Nushagak River is a very remote and very poorly studied; not much is known about it. It supports a very valuable chinook salmon fishery with salmon returns on the order of 150,000-350,000 fish. There are no hatcheries; it’s all wild production. Some of those fish are intercepted.
The question is, is where in the Nushagak watershed were the fish produced? To determine this, they took otoliths out of the fish that were caught in the ocean which contained the strontium isotope signature of individual tributaries across the river district; they could then assign a probability that the fish were produced from different tributaries across the river.
Dr. Schindler then presented a heat map of how many fish were caught in 2011, noting that if they were looking at the map and asking what aspects of the watershed should be protected, they would probably choose to the higher producing tributaries – that would be assuming that the ecosystem is really characterized by a single state.
He then produced the same type map for 2014, and noted how the tributaries that were important in 2011 produced very few fish in 2014. “Most of the fish came out of the tributary that we would have concluded was unimportant or less important at the system scale,” Dr. Schindler noted. “Really the point here is that you have a mosaic of habitat and that mosaic is continuously shifting through time. This is the type of dynamic that characterizes river ecosystems.”
The same thing can be seen at very small spatial scales. He presented a picture of a small river flowing across a floodplain, noting that there’s a lot of habitat heterogeneity in the landscape. “What we’ve learned from studies of places like this over the course of decades is that juvenile fish use different pieces of this habitat at different points of their life cycle,” he said. “What is interesting though, is which habitat they use in any given year changes depending on what the prevailing climate conditions are. In hot dry years, they will use certain pockets of habitat; in wet cold years, they will move and use other pockets of habitat.”
These systems are relatively stable in terms of the number of fish they produce, and they are stable because the system still has options on the table, said Dr. Schindler. “When we restore ecosystems, when we protect ecosystems, what we should be asking is, where are the options for the animals that we’re caring about here?”
In the case of the Nushagak River, the Pebble Mine has been proposed for one of those major tributaries, and the assessment of how that mine may impact that river system critically depends what timeframe or even what year the functioning of the ecosystem is assessed.
He presented a shot from Alaska’s Chena river near of Fairbanks, noting that it’s a large floodplain that has a road cut through it. “What you’re looking at is the legacy of where that river used to be,” he said. “All of this is important habitat for fish, and when it’s used, it’s probably going to depend on what year and under what climate conditions where prevailing. The options are still on the table – until you a road along it. And what the road is doing here is taking away a bunch of options from the aquatic life that’s trying to make a go of it in that river.”
Dr. Schindler then had one last example, asking how do human communities respond to this reshuffling in the environment? Are there goals that we can try to shoot for, that will enable sustainable communities? This example is from the coastal fisheries of Alaska. The fisheries are all now managed under a limited entry system and for the last 30 years, every permit that has been fished in Alaska has been tracked in terms of the amount of revenue that is generated from it and the amount of catch and of what composition each person caught.
The series of pictures on the slide are from scientific surveys in the Gulf of Alaska between the late 70s and the 80s. “You can see that among those three pictures, there’s no resemblance of the conditions that were seen in the 80s compared to the conditions seen in the 70s,” said Dr. Schindler. “Some people would argue that this is a result of overfishing, and chances are fishing did have a role to play here, but we also know that climate and other environmental conditions resulted in these massive shifts and reorganization of the ecosystem.”
The graph Alaska catches of Pacific herring with different colors for the different regions. “These are the type of data that would go into a graph showing the number of collapses globally; all of these would show up as collapses in an analysis such as that,” he said. “What you’re seeing here is that different regions are producing herring in this case at different times. Fishing may have something to do with these rapid declines, but chances are a lot of this is simply environmental variability and population responses to it.”
A paper by Nate Mantua and Steve Herr from a few years ago analyzed one of these regime shifts that occurred in 1989. The study looked at what is the correlation between recruitment dynamics of commercially important species for which there is data and environmental changes. “What they saw was that there was a distinct shift that occurred in 1989; during this time period, many of the fisheries in Alaska so-called collapsed,” he said.
Dr. Schindler said we often hear how ‘ecosystems collapse’, but that’s the wrong metaphor. “Ecosystems don’t necessarily collapse; ecosystems reshuffle, and the challenge is for human communities, is how do you adapt to that?,” he said. He then discussed a study that was undertaken to look at how Alaskan communities responded to that change in the regime. “What we found was that if the communities have no diverse fishing opportunities, if they have few options on the table, they can’t turn over, and in this case, they lost about half of their fishing revenue. Communities that had a high diversity of fishing revenue generally held their own in terms of maintaining the revenue streaming into their communities; this is important for Alaska simply because most of their tax revenue is generated from tax on fishing, but then there’s these few communities that both have turnover and high diversity; they actually made a profit from that regime shift. So we can think about ways that the social science has to offer in terms of what policies might we help implement to help communities diversify and basically roll with the punches.”
Dr. Schindler than gave his concluding thoughts. “We really need to think more carefully about this conflict. When we restore ecosystems, are we putting things back to where they used to be? And what they used to be suffers from the shifting baseline syndrome, but even aside for that, we often think of a single condition that we’re trying to restore to. The reality is that ecosystems are continuously changing and reorganizing, and when we talk about resilience of systems, a resilient system is one that can take an external shock, for instance from climate change or from an environmental regime, and maintain function. The way ecosystems maintain function is through these reorganization processes.”
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