Reports & papers By category Symposium on Ocean Conditions

Climate, salmon, and preparing for the future

Richard Beamish
Canada Department of Fisheries and Oceans
Pacific Biological Station
Nanaimo, British Columbia

Introduction

Knowledgeable and wise people are impressed with how little we actually know. One only has to stand at the sea shore to be reminded of the complexity of the relationships among plants, animals, and their environment. As fisheries managers we can be overwhelmed by this complexity or we can look for simplifications. In fisheries management science we traditionally simplify the complexities. It is important to remember that we do this because we need to remind ourselves that our assessments are based on uncertainty. The advice that comes from these simplifications is useful but it is only one part of the process required for successful stewardship. It is the process that aggregates all of our information that provides the best stewardship. New information about salmon comes from studies of their relationship with climate and it is the importance of this new information that is considered in this report. It is essential that we learn more about the impacts of climate as the warming of our planet is particularly threatening to salmon in both their freshwater and marine habitats.

What salmon tell us about the impacts of climate

As a species, Pacific salmon are approximately one million years old. This means that they have survived 4 major ice ages, 4 warming periods, the extinction of 35 different genera of mammals including woolly mammoths, camels, lions, and sabertooth cats. Even wild horses became extinct in areas where salmon are found today. We marvel at the salmon's stunning ability to find their way back from the ocean to their place of birth, but we sometimes forget that they have colonized new freshwater habitats in the same manner as less desirable animals and plants have recently moved into our environment. We know that there is approximately 90 to 98% mortality from eggs to entry into salt water. There is also an almost unbelievably high mortality in salt water. In the past few years we have observed ocean mortalities of 99.5% for chinook in the Strait of Georgia and in Puget Sound, 98% for coho throughout their entire southern distributions and about 90% for sockeye from the Fraser River. Despite these high mortalities, stocks of salmon continue to survive. This is not strictly correct because several stocks have been identified as lost, and over a thousand stocks have been classified as at risk of extinction (Slaney et al. 1996; Nehlsen et al. 1991). However, we believe that the loss of these stocks resulted from the added mortalities of fishing or freshwater habitat loss, not from natural causes.

Recently we have become aware of natural fluctuations in the abundance trends of salmon. The abundance trends of salmon are amazingly similar to fluctuations in Pacific sardine abundances off South America, North America, and Asia (Fig. 1) indicating that something of large scale such as climate may be a common cause of the synchrony. We know that sardine catches have fluctuated in abundance for centuries (Baumgartner et al. 1992), leading to the speculation that salmon abundance has also fluctuated naturally (Beamish et al. 1999a). Recently, it has been possible to measure the natural fluctuations of salmon populations using stable isotopes (Finney 1998). When sockeye salmon return to fresh water to spawn, they contain a form of nitrogen that only comes from the ocean. This marine form, or nitrogen 15, is deposited in the lake sediments and provides a way of looking at past fluctuations in abundance. Finney (1998) observed clear trends in the pattern of deposition, which was interpreted as a natural fluctuation in abundance for about 400 years prior to any commercial fishing. Low abundance was noted in the mid-1500s, the early 1700s, the early 1800s, and in the mid- to late 1900s. It is interesting that the salmon returns to the Fraser River were so low in 1827 that there were reports of starvation among natives during the winter. Thus, it is possible that the early 1800s was a period of generally low salmon abundance. Larger abundances were noted in the early 1500s, the late 1500s, the early to mid-1600s, the late 1700s and the mid-1800s to the early 1900s. We also know that the abundance trends in salmon change quickly and in synchrony with large scale climate shifts that we call regimes (Fig. 2, Mantua et al. 1997; Beamish et al. 1999a). Pacific salmon also respond to climate related impacts by changing ocean migratory patterns (McKinnel et al. 1998), changing final body size (Ricker 1995), and changing their horizontal distribution (Welch et al. 1998). It is clear that climate is an important component of the population dynamics of Pacific salmon.

Pacific salmon evolved from a freshwater existence to an anadromous life history (Neave 1958). The retention of the freshwater stage over the past million years indicates that there is value in returning to fresh water to reproduce. The production of a large number of juveniles in fresh water and the exceptionally large marine mortality is an indication that the marine habitat is harsh for salmon. Beamish and Mahnken (1998; 1999) proposed that salmon reproduce in fresh water as a safe refuge for their young. This ensures that there is a diversity of genetic traits and life history types available for the salmon population when it enters the harsh ocean habitat. There is an abundance of food in the ocean, but the large ocean mortalities spotlight the costs of moving into this habitat. We may not be able to control the marine habitat, but we can recognize its influence on the biology of salmon. The occurrence of natural trends in abundance is clear evidence that the carrying capacity in the ocean changes. The variation in abundance of returns that we see today is a result of ocean habitat changes as well as from the impacts of fishing. The natural fluctuations prior to commercial fishing indicate that salmon have an evolved ability to survive extreme changes in their environment. The fact that some fish from each stock, always come back despite the large amount of marine mortality, tells us that a mechanism exists that "buffers" salmon from the randomness of death at sea. In some way, Pacific salmon have evolved not only to survive the uncertainties of the ocean habitat, but also to ensure that a few representatives of each stock always return.

Evidence of a linkage between salmon productivity and climate

Understanding the process that ensures the return of salmon is essential for our stewardship of salmon. It is essential because we intervene in the evolved, precisely tuned mechanisms that allow salmon to compete successfully with other organisms. It is also our responsibility because we have been trusted to spend the earnings of many people in our efforts to protect salmon and salmon fisheries. It was the desire to do the right thing and our lack of understanding of climate impacts that convinced us that hatcheries were a solution to management problems. Hatcheries made sense because we believed that the reduced abundances of salmon resulted from human impacts. We overfished or we prevented successful spawning. We believed that this error could be corrected by avoiding the high freshwater mortality, which we viewed as wastage, rather than having any evolutionary value. Furthermore, because we believed that the ocean carrying capacity was much larger than currently being "used" by salmon, we thought that we could produce more fish for harvest if we "planted more seeds" in this vast ocean pasture. Now that we know that the productivity of this pasture changes, we need to be more careful with the seeds we sow. Hatcheries have a role in management and our experiments with hatcheries provide us with an excellent way of studying marine impacts on salmon (Coronado and Hilborn 1998), but we need to reconsider the role of hatcheries in times when reduced ocean survival is limiting total returns.

The marine survival of coho in the Strait of Georgia, Puget Sound, and of Oregon follows a pattern that corresponds to large scale changes in climate. After 1989, the ocean survival of the aggregate of stocks in these three areas all declined dramatically (Beamish et al. 1999b). The other change occurred in 1977, a well-known period of climate change (Ebbesmeyer et al. 1991; Mantua et al. 1997; Minobe 1997; Beamish et al. 1999a).

Although there was a change in the trends of survival in the three areas after 1977, the change was not the same as it was after 1989. The reasons for the different responses are not known, but the differences emphasize the importance of looking for specific responses within any given ecosystem when regimes shift. The climate change associated with these shifts can be illustrated using the Aleutian Low Pressure Index (ALPI) (Beamish et al. 1999a). The ALPI is a measure of the intensity of winter winds in the Subarctic Pacific. The intensity of winds, in turn has been linked to changes in production (Brodeur and Ware 1992; Sugimoto and Tadokora 1997; Lagerloef 1995; Polovina et al. 1995). The Aleutian Low Pressure Index shows virtually the same fluctuating trends as other indices such as the Pacific Decadal Oscillation (Fig. 2). The Pacific Decadal Oscillation (Mantua et al. 1997) is a measure of sea surface temperature change, but it also represents changes such as annual flows from large rivers. The Pacific Circulation Index (PCI) (King et al. 1998) is an index of the general Pacific atmospheric circulation in the winter (December-March). The index was developed by categorizing the atmospheric processes over the North Pacific into zonal (west), meridional (northwest) and easterly (southwest) wind patterns. The positive trend in the PCI indicates a period of below average meridional and above average zonal or easterly processes. The changes in circulation trends in the PCI are similar to the trends in the other climate/ocean indices in Figure 2 and therefore are linked to both ocean changes and salmon abundance trends. It is important that there is such a close relationship between the wind related indices, the sea surface temperature dominated Pacific Decadal Oscillation and salmon production as it demonstrates the linkage between atmospheric circulation, ocean processes and biological responses. Other indices of climate change in the Arctic (Thompson and Wallace 1998) and in the North Atlantic have some similar trends to the Pacific indices. Hurrell (1996) has shown that there is a linkage between the trends in the atmospheric pressure based North Atlantic Oscillation Index and the surface air temperatures in Europe. The relevance is that we are learning that there are long-term trends in climate that are related to the measures that we use to characterize fish production.

The ALPI changed in 1977 and 1989 (Fig. 2). The change in 1989 was from a period of extreme low pressures (stormier winters) to a period of average pressures. It is important to remember that ALPI is an index of change and the actual changes in a particular ecosystem and their impacts on a particular species would need to be determined. The relevance of the reduced marine survival of coho after 1989 is that the marine habitat for coho changed and that the ocean could not support as many coho as it did previously. We do not believe that this is simply a percentage change in survival. Thus, adding more coho would not be expected to improve future adult returns. However, proving that adding more coho would not lead to production of larger adult returns is a difficult scientific problem without doing the experiment, which is also complicated. When the ocean carrying capacity is reduced, it is also possible that adding more coho from hatcheries may reduce wild coho abundance (Sweeting et al. 1999; Solazzi et al. 1990).

Beamish et al. (1997) showed that the rate of increase of the total Pacific catch of three species of Pacific salmon from the mid-1970s through to the mid-1990s was similar. However, the catch of chum salmon was estimated to be 84% hatchery fish, pink was 23% hatchery fish, and sockeye was approximately 5% hatchery fish. Thus, the addition of hatchery fish did not appear to alter the rate of increase during the favourable ocean regime in the 1980s (Fig. 3).

The linkage between changes in climate/ocean environment and the natural regulation of abundance has been proposed to be through the amount of growth during the summer (Beamish and Mahnken 1998; 1999). They considered that the abundance of salmon is regulated naturally in the ocean in two principal stages. There is a large mortality shortly after salmon enter the ocean. This early marine mortality is predation based and may be related to size. During the summer, the young salmon compete for food with other individuals of the same species and with other species. Climate impacts may alter the total amount of food produced and the abundance of competing individuals. According to the hypothesis of Beamish and Mahnken, Pacific salmon and coho salmon in particular must grow to a minimum size by the late fall in order to survive the severe conditions during the winter. If they do not reach a critical size, they are not physiologically able to survive. In some cases, juveniles revert back to a parr like appearance that ultimately ends in death (Mahnken et al. 1982). This second mortality is a physiologically based death. Because the amount of total mortality is related to competition, it is expected that some fish will always grow to the critical size by the critical time of the year. In this way, some individuals of each stock will always return. In the future, Pacific salmon abundances would be expected to continue to fluctuate over 10 to 30 year periods in response to natural changes in climate. These persistent trends in abundance would change abruptly in response to shifts in climate as they have in the past. Beamish et al. (1999a) recently speculated that a common event is responsible for these long-term shifts and that the common event is associated with large scale energy redistributions within the Earth and its atmosphere. Such a fundamental mechanism would be important as its discovery would provide a basis to forecast changes in the trends in the dynamics of local marine ecosystems.

A Russian index of the general circulation of the atmosphere in the Northern Hemisphere is called the Atmospheric Circulation Index ACI (Beamish et al. 1999a) and is the European equivalent of the PCI. The ACI, like the PCI, is an attempt to simplify the dominant direction of the westerly winds on an annual time scale. When the ACI is compared to the measured change in the daily rotation of the solid part of the Earth or length of day (LOD) expressed as an average annual change, there is an amazing, inverse relationship (Fig. 4a). The PCI also has a close inverse relationship with the length of day (Fig. 4b). It may take time to sort through the possible explanations for the linkages between Earth rotation and ecosystem productivity, but it is a relationship that may show that the complexities of ecosystems are linked through a common factor.

There have been some important changes in the trend of the Aleutian Low in the 1990s. After the period of intense lows from 1977 to 1989, there was a period of average lows from 1989 until 1998. It is the period of average lows that has been associated with the synchronous decline in the marine survival of coho. In the last two years, the Aleutian Low has been intense and average. We suspect that this is the beginning of another change in trend that we speculate may be to more extreme fluctuations. An obvious question is how marine survival of coho will be affected. Our answer, unfortunately, is that we do not know. We do know that fishing impacts will remain important, but they no longer should be considered in isolation of the effects of the ocean environment.

The next crisis

Another important climate change is global warming. There is no dispute about the warming of the planet (Fig. 5). There is ample documentation of warming trends and there is no serious debate among credible scientists about the warming trend. There is debate about the cause of the warming. It is intriguing that the Northern Hemisphere surface temperature trend looks more like the trend in the climate indices than the build up of CO₂, which is the main contributor to global warming. This suggests that the warming is a result of both natural trends and CO₂ increases. There is a tendency to try to separate natural climate change from the global warming impacts before we consider the consequences. It is a serious mistake for fisheries managers to become mired in the debate about the reasons for the current warming. We need to go no farther than the certainty that the planet is warming. It is not that the debate is unimportant, but rather it is that we need to act immediately to address management issues related to the warming. The impacts will be in fresh water and the ocean and the impacts will relate to temperature effects and ecosystem effects. One common sense response to the impacts of global warming is to respect the ability of wild salmon to adapt to extreme environmental change. The evolved ability of salmon to survive the extremes of one million years of ocean habitat change is stored in the genetic make-up of salmon. If we believe in evolution, we believe that surviving extreme changes in the environment is the reason different species exist. In other words, the genetic traits of wild salmon are the most effective adaptation to the inevitable extreme changes in climate. Thus, when conditions in the ocean are less favourable as indicated by the recent low marine survival, we need to ensure that wild stocks are protected. It may be our preservation of the naturally evolved genetic ability to survive extreme environmental events that enables salmon to remain in their more southern habitats.

In periods of low marine survival or low carrying capacity, we need to modify our expectations of having high abundances. If we accept lower abundances as a reality, we can address the issue of the importance of wild salmon. We need to change our objective of sustaining historic high abundances of salmon to protecting the evolved ability of wild salmon.

Change is part of the make up of all living things. We are in a period of very profound and obvious change in our climate. We have a responsibility to recognize this change and adapt our thinking and our management of salmon (Bisbal and McConnaha 1998). The desire to do the right thing for salmon has always been embedded in the culture of Pacific Rim peoples. The difficulty is that as we learn more about the factors that affect salmon such as climate, we also realize how much more there is to learn. Recognising that we will always be learning, I recommend we do the following to prepare for the future. I hope that it makes sense to you:

1. Protect freshwater habitat as a safe refuge for spawning and for baby salmon to grow.
2. Respect the marine habitat of salmon because most salmon do not survive the complexity of factors that can cause their death.
3. Recognize that the life histories of the various species of wild salmon have evolved to adapt to a wide range of natural conditions which means that if salmon were left alone they could solve their own survival problems.
4. Be concerned that we have not left salmon alone.
5. Be even more concerned that we have intervened in the natural regulation process while understanding very little about the natural mechanisms that affected survival.
6. Fishing should not prevent a stock from replenishing itself, but knowing what the safe level of fishing should be will always be a challenge.
7. Be careful of advice that tells you that you can rebuild salmon with computers.
8. Accept that climate affects the survival trends in salmon.
9. Believe that the planet is warming and the climate is changing, but do not delay responding while experts debate if the cause is from our production of greenhouse gas or natural trends as it is probably from both.
10. Recognize our uncertainties and speak openly about what you know and don't know as expectations will become more realistic and people will like fisheries biologists better.
11. Remember that everyone cares for salmon, it is the interpretation of our ignorance that creates conflicts.
12. Expect the unexpected, prepare for change as do all animals, and believe that the future survival of salmon is a measure of our ability as a species to live in balance with other species.

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Figure 1. Catch of sardines (1000 tonnes) from the three major stocks in the Pacific Ocean (updated from Kawasaki and Omori, 1988). Note the synchrony in catch trends.

Figure 2. The relationship among three indicators of climate over the North Pacific and the total, all nation catch of pink, chum and sockeye salmon (approx. 90% of catch of all species of salmon). The salmon catch is unsmoothed and the Aleutian Low Pressure Index (ALPI), the Pacific Decadal Oscillation Index (PDO), and the Pacific Circulation Index (PCI) are in the CuSum form (Beamish et al. 1999a). The vertical dashed lines represent regime shifts: 1925, 1947, 1977, 1989 and possibly around 1998.

Figure 3. A comparison of the total all nation catch of chum salmon and pink salmon to sockeye salmon.

Figure 4 a, b. The relationship between the index of atmospheric circulation (a) ACI (solid line) and (b) PCI (dashed line) to the measured average annual change in the rotation of the solid Earth or length of day (LOD, milliseconds, dotted line). The relationship shows that the change in the index of the dominant, annual direction of the westerly winds is inversely related to the average annual rotational velocity of the solid part of the Earth. The implication is that the relationship may represent patterns of energy transfers between the solid earth and the atmosphere.

Figure 5. The 1000 year estimated average Northern Hemisphere surface temperature anomalies from Mann et al. (1999), with the predicted temperature for the year 2050 from global climate change models. Instrument data begins in 1902. Data from 1000 to 1902 reconstructed from tree ring measurements and a smoothed 40- year average.

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