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Re: Is overfishing a scientific or legal term?


"Trevor J. Kenchington" <[log in to unmask]>


Scientific forum on fish and fisheries <[log in to unmask]>


Fri, 27 May 2005 23:30:49 -0300





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I go away on a 3-day business trip and come home to an e-mail inbox with
multiple copies of an article from the New Bedford "Standard Times" in
which I was quoted, plus a spin-off Fish-Sci thread with upwards of a
dozen messages! I had no idea that so many people cared about a few
words of mine.

Mike Flaherty started the thread with:

> An article titled, "Scallops overfished for past 2 years, official says",
> appeared on the front page of today's New Bedford Standard Times.
> There was one excerpt in it which gave me pause...
> ===============================
> "Overfishing is a legal term, not a scientific term, and is therefore not an
> accurate way to evaluate the health of the scallop fishery, Dr. Kenchington
> said."
> ===============================
> As I roughly understand things, "overfishing" is defined as a point beyond
> which harvest/mortality levels exceed sustainable levels in a fishery. It
> is further my understanding that the thresholds for sustainability are
> arrived at scientifically. If this is true, then isn't overfishing truly a
> scientific term? More importantly, is it a reasonably accurate way to
> evaluate the health of a fishery?

Most members of Fish-Sci will have seen nothing more of the article (a
brief report on one specific meeting, of only limited interest outside
New England), so the context of my comment is missing. Indeed, the
reporter who prepared the article drew that and a couple of other quotes
out of our lengthy conversation (more of a monologue on my part, I'm
afraid), which dipped into some technical issues that very few people
understand, even those who have had far more explanation than I gave
her. If she didn't quite catch the import of all my remarks (as she did
not in this case), it was no fault of hers.

But since Mike has chosen to make an issue of it, I can provide a better
explanation for the very different Fish-Sci audience:

I think we all understand what "fishing" is and "overfishing" clearly
means too much fishing. That is almost "common English" (as Justin
Johnston noted). The problem comes with what we mean by "too much".

On the biological side, there are the usual run of types of
"overfishing": Growth, Recruitment and so forth, as Will Le Quesne
pointed out, though as we move into ecosystem-based management, we will
likely have to coin yet other versions ("Ecological Overfishing"
anyone?). Then there is the bio-economic "Economic Overfishing", which
should perhaps be complemented with "Socio-economic Overfishing", if the
optimum level of fishing which is being exceeded was defined on the
basis of broader considerations than bio-economics alone.

Still technical but not scientific is "Regulatory Overfishing", which
seems to mean running over a set catch limit.

However, in the United States, "overfishing" is specifically defined in
the Magnuson-Stevens Act and thus has a legal meaning -- similar to but
not quite synonymous with some of the technical meanings. The definition
in the Act is considerably expanded and interpretted within the
Guidelines to National Standard One. To oversimplify, they define
"overfishing" as a fishing mortality rate greater than F[MSY] (itself a
very wooly concept). Those Guidelines are required by the Act and were
formally published in the "Federal Register" but they do not have the
status of regulations. Whether or not their version of "overfishing" is
a legal term is a matter of semantics on which I am more than happy to
defer to the judges of the U.S. federal courts.

Also under the Magnuson-Stevens Act, each federally-managed fishery has
its own Fishery Management Plan which is required to provide a specific
definition for F[MSY] for the resources that fall under that FMP. In the
case of the Atlantic Sea Scallop FMP, covering all Placopecten
magellanicus in U.S. waters, F[MSY] is defined to be equal to F[MAX] for
legal/regulatory purposes, while F[MAX] is currently estimated to be
0.24. A fishing mortality rate exceeding that number is "overfishing" in
the legal sense in the United States. Such "Legal Overfishing" (to coin
a phrase) is not allowed under the Act, while various procedures come
into play if F should exceed the set limit.

Scallops, however, are largely sedentary by the time they reach
commercial size. As various authors from Beverton & Holt onwards
(particularly John Caddy) have noted, the yield-per-recruit logic which
leads to estimates of F[MAX] doesn't make much sense with sedentary
resources. To really harvest the theoretical maximum yield-per-recruit,
we would need to apply fishing effort such that each individual scallop
had an annual probability of harvest equal to F[MAX]. At least, we
should set F equal to F[MAX] in each very small local area. Applying a
mortality rate of F[MAX] averaged across the whole resource just won't
do it. It most certainly won't when most scallops are locked up in
closed areas while most fishing effort (i.e. most fishing mortality)
happens in areas where the resource has been thinned by prior fishing --
which is pretty much the current situation in the U.S. scallop fishery.

Yet management of that fishery faces a whole bunch of extra
complications. For one thing, the scallop fleet is highly mobile, with
some individual boats fishing everywhere from Georges Bank to Virginia
-- while other captains only want to work certain grounds. The primary
control on F, restrictions on the number of Days-at-Sea per boat per
year, is not area-specific and cannot readily be made area-specific
without serious disruptions of the existing socio-economic structures of
the scalloping communities. Even if ways could be found around that, the
available data sets are at least an order of magnitude too limited to
allow management based on spatial units corresponding to the spatial
scales within which adult scallops live. (Their eggs and larvae are, of
course, much more mobile.) Further, if the FMP did separately define a
dozen or so units, each with its own legal "F[MSY]", the manageemnt
system would be overwhelmed by the need to separately assess each unit
and to report the results of each such assessment to the U.S. Congress
(as the Magnuson-Stevens Act requires for each management unit
recognized in an FMP). Add to that lot, a temporal complexity: We
actually want higher F in local areas when the vagaries of recruitment
have supplied a preponderance of older scallops but lower F where there
is an incoming year-class which is still growing quickly. (Such rotation
has the potential to squeeze a few percent more yield from the
resource.) Anybody who relishes trying to explain to the public,
politicans and the courts why, in any given year, some scallop "stocks"
are seeing "overfishing" and others underfishing, and why that is OK, is
more than welcome to the task. What we can't have is a court-ordered,
rigid system in which F in each local area is forced below F[MSY] every
year, on pain of immediate closure of the entire fishery.

A few years back, we tried to come up with an operational definition of
sea scallop "F[MSY]" that would capture all those complexities, while
escaping the serious pitfalls, but the best ideas available within the
time constraints really didn't meet the challenge. So (at my urging as
much as anything), the New England Fishery Management Council opted to
make the legal definition of "F[MSY]", in the scallop FMP, a single
fishery-wide value of F=0.24. That defines sea scallop "overfishing" for
legal purposes, while we get on with the job of actually managing the
fishery so as to harvest optimum yields from the resource, amidst all of
the spatio-temporal complexity (and also while we face up to the
challenge of devising a better definition).

Now: The latest update assessment for this fishery, which was first
announced a couple of weeks ago but again at a meeting on Wednesday of
this week, produced a value of F[2004]=0.34. By the legal or regulatory
definition of sea-scallop "overfishing", and using that term in its
very-definitely legal sense (as it is defined by the Magnuson-Stevens
Act), 0.34 exceeds 0.24 and thus there was "overfishing" in the scallop
fishery last year.

Biologically, nothing is so simple. There are important scallop grounds
on Georges Bank where no scallop harvest has occured in a decade
(because of closures to protect groundfish, which have now morphed into
closures to protect groundfish habitat). Those areas are grossly
underfished for scallops, by any biological definition. However, there
are areas off New Jersey which were fished very hard last year --
certainly at levels which, if sustained, would represent biological
overfishing (though part of those areas is now in a rotational closure
and another part is recently out of such a closure, so the "sustained"
aspect is complex too).

In bio-socio-economics, matters get even more murky (if that is
possible). The emphasis on F[MSY] is a legal issue, while the Act also
implicitly supposes that F[MEY]<F[MSY] (though the U.S. Congress never
got into the technical terminology which might have stated that
inequality directly). For most finfish fisheries, I think those are
sensible starting points for an operational definition of "overfishing".
Scallops, however, (perhaps because they are herbivores that crop
phytoplankton directly) are incredibly robust to fishing pressure. You
can beat them down with heavy fishing, back off a bit, and they will
come bouncing back. So we are not faced with the sort of population
collapses that bedevil management of fisheries for top predators.
Meanwhile, the existing market for scallops wants a small animal (though
that is changing fast as new markets are being developed for the large
"meats" now being produced), which can only be obtained in quantity
through Growth Overfishing, as it is normally understood in the
biological sense. Furthermore, the social objectives of the scalloping
communities would be advanced by having many people working at moderate
catch rates, rather than the current few taking huge catches from very
high biomasses at relatively low F. Hence, if there was no legal
standard requiring something very different, I suspect that the
socio-economic optimum in this one fishery (long-term, not just
short-term) would set F appreciably higher than F[MSY]. (That isn't
legal in the United States and nobody is suggesting that it should be
done. I am just suggesting what "overfishing" might mean in this
specific fishery if the word were free of all legal overtones.)

So, "overfishing" is not purely a legal term, as Becky Evans had me
implying in her article in the "Standard Times" but, in the United
States, it has a legal meaning in addition to its technical and common
meanings. However, the "overfishing" that was announced and emphasized
at the meeting which she reported on was "overfishing" in the legal
sense and was defined as such relative to a rather arbitrary, legal
standard set in the Sea Scallop FMP. Certain parts of the resource
likely are undergoing "overfishing" in biological and other senses.
Certain parts are certainly seeing no scallop harvesting at all. Whether
that all adds up to "overfishing" relative to anything but the legal
standard is a moot point. Hence my explanation to Becky, briefly noted
in her article, that the "overfishing" announced that day was a legal

It has to be ended, of course. Because it is "Legal Overfishing", the
law must and will be obeyed. Interestingly, initial estimates suggest
that it already has been, and without any reduction in boat-days or
hours of dredging: Closure of one rotational area has moved the fishing
effort into areas where scallops are less dense, producing lower F per
boat-day. Which just goes to show the strange and tenuous link in this
fishery between "overfishing" in real-world senses (biological, economic
or whatever) and in the legal sense -- which was the kind of
"overfishing" that stirred things up on Wednesday.

Trevor Kenchington
Consultant scientist to the Fisheries Survival Fund, an organization of
scallop vessel owners

Trevor J. Kenchington PhD [log in to unmask]
Gadus Associates, Office(902) 889-9250
R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251
Nova Scotia B0J 2L0, CANADA Home (902) 889-3555

                     Science Serving the Fisheries

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