Sunday, May 19, 2019

OPTIMUM YIELD; OR, TRUTH AND LIES ABOUT MSY


There’s an ongoing misunderstanding about fisheries management that often appears in print, when people aver that fisheries are, or legally should be, managed for “maximum sustainable yield.”


The term “maximum sustainable yield” isn’t even defined in the Magnuson-Stevens Fishery Conservation and Management Act, the law that governs all fishing in the federal waters of the United States, although the law does employ that phrase on five occasions (three of those occurring in a single definition).  However, it is defined in related regulations as

“the largest long-term average catch or yield that can be taken from a stock or stock complex under prevailing ecological, environmental conditions and fishery technological characteristics (e.g., gear selectivity), and the distribution of catch among fleets.”
Maximum sustainable yield thus marks the precipice, the point where overfishing begins.  The regulations recognize that fact, and state that

“Overfishing occurs whenever a stock or stock complex is subjected to a level of fishing mortality or total catch that jeopardizes the capacity of a stock or stock complex to produce MSY on a continuing basis.”
Harvesting every last fish possible to achieve maximum sustainable yield is a very risky management approach, as any mistake in calculating either the size of fish stocks or the level of harvest that such stocks can sustain in the long term could easily lead to a population decline.  And there is always enough uncertainty in scientific estimates to assure that, sooner or later, such a mistake will be made.

Thus, Magnuson-Stevens calls for fish stocks to be managed not for maximum sustainable yield, but for optimum yield, which the law defines this way:

“The term “optimum,” with respect to the yield from a fishery, means the amount of fish which—
(A)    will provide the greatest overall benefit to the Nation, particularly with respect to food production and recreational opportunities, and taking into account the protection of marine ecosystems;
(B)    is prescribed as such on the basis of maximum sustainable yield from the fishery, as reduced by any relevant economic, social, or ecological factor; and
(C)    in the case of an overfished fishery, provides for rebuilding to a level consistent with producing the maximum sustainable yield from such fishery.”

“The determination of [optimum yield] is a decisional mechanism for resolving the Magnuson-Stevens Act’s conservation and management objectives, achieving [a fishery management plan’s] objectives, and balancing the various interests that comprise the greatest overall benefit to the Nation.  OY is based on MSY as reduced under paragraphs e(3)(iii)(A) and (B) of this section.  The most important limitation on the specification of OY is that the choice of OY and the conservation and management measures proposed to achieve it must prevent overfishing.  [emphasis added]”
Those definitions open up some interesting possibilities, and dispel some common misconceptions, particularly when linked with other existing regulations.

For example, optimum yield is more than just maximum sustainable yield, possibly reduced to account for a handful of factors.  Optimum yield is, first and foremost, a tool to prevent overfishing.

The regulations don’t say that the most important role of optimum yield is to maximize harvest, or recreational opportunity, or even to enhance marine ecosystems.  First, above any other consideration, optimum yield “must prevent overfishing.” 

That word “must” takes away all discretion.  Overfishing must not occur.

That means that, as a practical matter, optimum yield should be set at a level somewhat lower than MSY.  In theory, if fishery managers’ calculations were absolutely precise, and allowed for no error at all, optimum yield could safely equal maximum sustainable yield.  But in the real world, there is always some level of uncertainty, and that uncertainty means that optimum yield, if properly set, will always be less than MSY.

Earlier, I used the brink of a precipice as a metaphor for MSY; as is the case with any precipice, disaster could easily ensue if one slipped over the edge.  To extend that metaphor just a bit farter, uncertainty is fog, that makes it harder to tell when the brink is drawing close.  

In the case of some fish stocks, that are blessed with good data, managers can come fairly close to the edge—to MSY—with little risk of going beyond; in the case of others, where uncertainties are rife, they’re proceeding in the densest pea soup imaginible, where the slightest haste or lack of care could lead to serious problems.

Because that risk is very real, Congress has established a procedure to help the regional fishery management councils negotiate foggy terrain without falling off the edge of a cliff.  Magnuson-Stevens requires that each regional fishery management council

“develop annual catch limits for all of its managed fisheries that may not exceed the fishing level recommendations of its scientific and statistical committee or the peer review process established [elsewhere in the law].”
Such fishing level recommendations are set in accord with the concept of “acceptable biological catch,” which is defined in the regulations as

“a level of a stock or stock complex’s annual catch, which is based on an ABC control rule that accounts for the scientific uncertainty in the estimates of [the overfishing limit, which is effectively equivalent to MSY], any other scientific uncertainty, and the Council’s risk policy.”
Thus, annual catch limits will almost certainly be set some way below MSY even before the “economic, social, and ecological factors” used to finally establish optimum yield are considered.

When those factors are considered, things begin to get even more interesting, particularly for recreational fishermen.

Fishery managers have long emphasized yield, effectively working to maximize the number of dead fish that can be piled up on the dock.  Some people have argued that is essentially a commercial management measure, and not appropriate for recreational fisheries.



“The benefits of recreational opportunities reflect the quality of both the recreational fishing experience and non-consumptive fishery uses such as ecotourism, fish watching, and recreational diving.”
Leaving a bare minimum number of fish in the water, that is, a biomass equal to Bmsy, isn't likely to provide such benefits.

So when you hear someone say that management is all about yield, and that abundance and similar concepts have no solid foundation in fisheries law, you can feel free to ignore them.  Reducing landings in order to enhance the recreational experience is very much contemplated by the current regulations.

Things become even more interesting when one looks at what may be included under the broad heading of social, economic, or ecological factors relevant to a decision to further separate optimum yield from MSY.


“prudent consideration of the risk of overharvesting when a stock size or reproductive potential is uncertain, satisfaction of consumer and recreational needs,…the decrease in cost per unit of catch afforded by an increase in stock size, [and] the attendant increase in catch per unit of effort…,”
which are all factors that favor managing for building a larger biomass, rather than merely concentrating on landings.

Striped bass are not a federally-managed fish, but given a recent Southwick Associates study, which shows how participation in the striped bass fishery fell off as striped bass became less abundant, it wouldn’t be unreasonable to believe that, at least in the case of species targeted primarily for recreation, higher abundance leads to greater levels of angler participation, which in turn generate greater economic benefits, and thus justify lowering optimum yield for such species on economic considerations alone.

Establishing optimum yield at a lower level for primarily recreational species would also be supported by social considerations, most particularly, as noted in the regulations, the

“enjoyment gained from recreational fishing”
when there are enough fish in the water to provide for frequent hookups, even for relatively unexperienced anglers or anglers who must wait until fish come within range of a pier or of shore before they can catch them.

But setting optimum yield isn’t just about establishing harvest levels that suit participants in a fishery; fishing’s impact on the entire ecosystem needs to be taken into account.  Thus, the regulations inform us,

“…Species interactions that have not explicitly been taken into account when calculating MSY should be considered as relevant factors for setting OY below MSY.  In addition, consideration should be given to managing forage stocks for higher biomass than Bmsy to enhance and protect the marine ecosystem.  Also important are ecological or environmental conditions that stress marine organisms or their habitat, such as natural or manmade changes in wetlands or nursery grounds, and effects of pollutants on habitat and stocks.”
That language makes it clear that, when fishermen wish to escape responsibility, in the form of reduced landings, for a declining stock, and seek to put the blame for decreasing abundance on inshore pollution, wetlands development or the impacts of warming waters, they are unintentionally undercutting their own position, and making a case for reducing optimum yield, and probably increasing catch restrictions, on the basis of relevant ecological factors.

Clearly, the concept of optimum yield is a powerful and far-reaching fishery management tool.

Although regional fishery management councils have not yet realized the full potential that the concept of optimum yield provides, they have already made a slow start in that direction.  While it’s very easy to argue that such councils need to do a lot more to fully and explicitly integrate the concept of optimum yield in their fishery management plans, one thing is already clear.

Managing for optimum yield is very different from managing for MSY.

And it is precisely what federal fisheries law requires.







1 comment:

  1. This is a great post and I read a way while back. It really helped me out.Thank you so much for this great article.



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