MakoMike
02-09-2011, 04:41 PM
Prof. Ray Hilborn, of the University of Washington, is one of the leading global researchers on adaptive ecosystem management for fisheries. He has consistently argued that the doomsday narrative of continuous global overfishing is not supported by facts; that instead where good fisheries management is applied, fisheries and ecosystems are stable, thriving, and producing huge economic benefits. Given the prominence of the controversies over seafood sustainability, Ray and some of his colleagues have agreed to write a series of occasional comments for Seafoodnews.com when major fisheries papers or ideas about sustainability are published or discussed.
(SEAFOOD.COM NEWS) - Feb 7, 2011 - The following article from Ray Hilborn is in response to NMFS chief scientist Steve Murawski's widely reported comments last month that US overfishing as ended. This is part of a continuing series of occasional articles on fisheries and conservation topics by Ray Hilborn, Professor at the School of Aquatic and Fishery Sciences, University of Washington, prepared for Seafood.com News.
Overfishing has ended in the U. S. said Professor Steve Murawski, former chief fishery scientist for NOAA on January 8th 2011.
Could this possibly be true?
With many fish stocks still at low abundance, subject to rebuilding plans and listed as overfished, how could he argue that overfishing has ended?
To understand the issue we first must begin with the distinction between "overfished" and "overfishing." Overfished is a term used when the abundance of the stock is low enough that its sustainable yield is significantly reduced. Overfishing is when the percentage harvested is higher than required to provide long term maximum sustainable yield. So "overfished" is about abundance and "overfishing" is about the percentage we harvest.
What Murawski said is that the percentage harvested for all U. S. federally managed fish stocks is now within the range that would produce maximum sustainable yield.
We have stopped fishing too hard; but many fish stocks remain at low abundance.
Fishery managers can control fishing pressure, but they have much less control on the abundance of stocks. Even in the absence of fishing stocks go up and down, and we can't control the natural forces that lead to such fluctuations.
The California sardine, icon of fish stock collapses in the 1960s, is now abundant again. Coring of the sea floor shows that it has peaked and crashed repeatedly over the last 1000 years, and the crash in the 1950s was just the most recent. Nothing fishery managers could have done would have prevented the California sardine from a major decline in the 1950's, driven largely by cold ocean temperatures, but fishing pressure made this decline worse, and delayed the rebuilding.
Think of the sardines in the ocean like a bank account, in warm years the account produces a good interest rate, and you can withdraw the interest in the form of harvest and retain your capital. But in cold years there is no interest, and any withdrawals reduce the capital, so that when you get warm years again, you have less interest available because you now have fewer fish in the bank.
When a stock declines because of poor environmental conditions the only thing managers can do is reduce the harvest, which may not stop the decline. Thus Murawski's emphasis on fishing pressure, not the abundance of stocks is appropriate.
The public and Congress are too focused on the abundance of fish as a measure of management success: we should focus primarily on the fishing pressure and get that right. We will likely never have zero stocks overfished: some stocks will always be at low abundance because of environmental conditions. But we can, and have, stopped fishing too hard.
The more we know about fish stocks the more we recognize that their productivity depends more on environmental conditions than the biomass of the stock. Research in my laboratory using a data base of over 300 fish stocks suggests that for 70% of these stocks climate drives productivity much more than stock abundance.
This doesn't mean fishing doesn't affect abundance, but what it does mean is that we should get the harvest rate right, not worry so much about the stock biomass.
For most U. S. fisheries we have set biomass targets, in theory levels that will support maximum sustainable yield, and we have abundance limits, below which we do not want to go. Fishery management plans generally reduce harvest rates rapidly if stocks fall below these limits. Because these limits are hard to estimate for individual stocks we often choose proxy values. For instance the Pacific Fishery Management Council uses 25% of unfished biomass as the definition of what constitutes "overfished" and rebuilding plans and major catch reductions kick in when the stock falls below these levels.
The irony is that for some stocks, at the proxy overfished definition, the stock may produce maximum sustainable yield or very close to it. Thus we are calling some stocks "overfished" that are actually producing optimally.
However, we should also remember that society wants more from the ocean than simply sustainable yield of fish. Economic and environmental objectives will dictate less fishing pressure than would maximize sustainable yield. Some calculations suggest that the total amount of fishing pressure to maximize the economic performance of fisheries may be as low as half of what maximizes sustainable biological yield. Under this reduced fishing pressure average stock abundance would be higher, fish would be larger, catch rates would be higher, and there would be more fish in the ocean.
Stopping overfishing in the U. S. came at the cost of a great deal of social disruption; jobs were lost, fleet sizes were reduced and fishing dependent communities suffered. Some of this was an inevitable consequence of non-sustainable fishing capacity. However, if we were to reduce fishing pressure by half again for economic or environmental reasons, these social impacts would be even greater.
The current debate over rates of rebuilding is another aspect of the difference between overfished and overfishing. If we really want to get stocks out of "overfished" status by rapid rebuilding of abundance, we have to reduce fishing pressure much more than simply stopping overfishing.
The more quickly we insist on rebuilding, the less fishing pressure we allow. Because many stocks are caught in mixed fisheries, reduced fishing on weak stocks means we have to give up more sustainable yield of healthy stocks.
I fear mandates for rapid rebuilding have boxed the Fishery Management Councils into a trap that will force them to keep fishing pressure much less than would produce maximum sustainable yield in order to provide for rapid rebuilding. This will come at a great cost to food production and fishing communities. The additional of annual catch limits on all stocks will aggravate the problem even more as catch limits on more and more rare species will more strongly constrain catches on the abundant species.
Ending overfishing in the U. S. is a considerable achievement, but it is not the end of struggles over what we are trying to achieve in national ocean policy. With funding and guidance from Congress we could achieve any desired balance between yield, jobs, economic profitability and environmental impacts. But since powerful groups have different views on where that balance should be, expect the struggle to continue over how much fishing pressure to allow.
(SEAFOOD.COM NEWS) - Feb 7, 2011 - The following article from Ray Hilborn is in response to NMFS chief scientist Steve Murawski's widely reported comments last month that US overfishing as ended. This is part of a continuing series of occasional articles on fisheries and conservation topics by Ray Hilborn, Professor at the School of Aquatic and Fishery Sciences, University of Washington, prepared for Seafood.com News.
Overfishing has ended in the U. S. said Professor Steve Murawski, former chief fishery scientist for NOAA on January 8th 2011.
Could this possibly be true?
With many fish stocks still at low abundance, subject to rebuilding plans and listed as overfished, how could he argue that overfishing has ended?
To understand the issue we first must begin with the distinction between "overfished" and "overfishing." Overfished is a term used when the abundance of the stock is low enough that its sustainable yield is significantly reduced. Overfishing is when the percentage harvested is higher than required to provide long term maximum sustainable yield. So "overfished" is about abundance and "overfishing" is about the percentage we harvest.
What Murawski said is that the percentage harvested for all U. S. federally managed fish stocks is now within the range that would produce maximum sustainable yield.
We have stopped fishing too hard; but many fish stocks remain at low abundance.
Fishery managers can control fishing pressure, but they have much less control on the abundance of stocks. Even in the absence of fishing stocks go up and down, and we can't control the natural forces that lead to such fluctuations.
The California sardine, icon of fish stock collapses in the 1960s, is now abundant again. Coring of the sea floor shows that it has peaked and crashed repeatedly over the last 1000 years, and the crash in the 1950s was just the most recent. Nothing fishery managers could have done would have prevented the California sardine from a major decline in the 1950's, driven largely by cold ocean temperatures, but fishing pressure made this decline worse, and delayed the rebuilding.
Think of the sardines in the ocean like a bank account, in warm years the account produces a good interest rate, and you can withdraw the interest in the form of harvest and retain your capital. But in cold years there is no interest, and any withdrawals reduce the capital, so that when you get warm years again, you have less interest available because you now have fewer fish in the bank.
When a stock declines because of poor environmental conditions the only thing managers can do is reduce the harvest, which may not stop the decline. Thus Murawski's emphasis on fishing pressure, not the abundance of stocks is appropriate.
The public and Congress are too focused on the abundance of fish as a measure of management success: we should focus primarily on the fishing pressure and get that right. We will likely never have zero stocks overfished: some stocks will always be at low abundance because of environmental conditions. But we can, and have, stopped fishing too hard.
The more we know about fish stocks the more we recognize that their productivity depends more on environmental conditions than the biomass of the stock. Research in my laboratory using a data base of over 300 fish stocks suggests that for 70% of these stocks climate drives productivity much more than stock abundance.
This doesn't mean fishing doesn't affect abundance, but what it does mean is that we should get the harvest rate right, not worry so much about the stock biomass.
For most U. S. fisheries we have set biomass targets, in theory levels that will support maximum sustainable yield, and we have abundance limits, below which we do not want to go. Fishery management plans generally reduce harvest rates rapidly if stocks fall below these limits. Because these limits are hard to estimate for individual stocks we often choose proxy values. For instance the Pacific Fishery Management Council uses 25% of unfished biomass as the definition of what constitutes "overfished" and rebuilding plans and major catch reductions kick in when the stock falls below these levels.
The irony is that for some stocks, at the proxy overfished definition, the stock may produce maximum sustainable yield or very close to it. Thus we are calling some stocks "overfished" that are actually producing optimally.
However, we should also remember that society wants more from the ocean than simply sustainable yield of fish. Economic and environmental objectives will dictate less fishing pressure than would maximize sustainable yield. Some calculations suggest that the total amount of fishing pressure to maximize the economic performance of fisheries may be as low as half of what maximizes sustainable biological yield. Under this reduced fishing pressure average stock abundance would be higher, fish would be larger, catch rates would be higher, and there would be more fish in the ocean.
Stopping overfishing in the U. S. came at the cost of a great deal of social disruption; jobs were lost, fleet sizes were reduced and fishing dependent communities suffered. Some of this was an inevitable consequence of non-sustainable fishing capacity. However, if we were to reduce fishing pressure by half again for economic or environmental reasons, these social impacts would be even greater.
The current debate over rates of rebuilding is another aspect of the difference between overfished and overfishing. If we really want to get stocks out of "overfished" status by rapid rebuilding of abundance, we have to reduce fishing pressure much more than simply stopping overfishing.
The more quickly we insist on rebuilding, the less fishing pressure we allow. Because many stocks are caught in mixed fisheries, reduced fishing on weak stocks means we have to give up more sustainable yield of healthy stocks.
I fear mandates for rapid rebuilding have boxed the Fishery Management Councils into a trap that will force them to keep fishing pressure much less than would produce maximum sustainable yield in order to provide for rapid rebuilding. This will come at a great cost to food production and fishing communities. The additional of annual catch limits on all stocks will aggravate the problem even more as catch limits on more and more rare species will more strongly constrain catches on the abundant species.
Ending overfishing in the U. S. is a considerable achievement, but it is not the end of struggles over what we are trying to achieve in national ocean policy. With funding and guidance from Congress we could achieve any desired balance between yield, jobs, economic profitability and environmental impacts. But since powerful groups have different views on where that balance should be, expect the struggle to continue over how much fishing pressure to allow.