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As Justin points out many things can affect a population and therefore when
there is a decline in standing stock of an exploited population it could be
both because of the current fishing level or other factors. This concept is
usually called "productivity regime" nowadays and it is generally accepted
that they occur and can alter change the stock biomass and its
productivity. Fishery allowable yield may be based on assessing the stock in
one productivity regime (i.e. a carrying capacity of K1 and growth rate r1)
giving a maximum sustainable yield Y1. Here assuming that fishing more than
the maximum sustainable yield is the definition of overfishing. Then for
whatever reasons K1 and/or r1 change resulting in a decreased Y1 however
management does not alter Y1 to the new lower yield then "overfishing" is
occuring.
The point I am trying to make is that we can control only fishing and not
nature; therefore, failure to respond to changes in nature can constitute
overfishing under the definitions above. I believe those definitions aren't
too far off from what the USA uses in the Magnusson-Stevenson act.
Daniel
________________________
Daniel E. Duplisea
Fisheries and Oceans/Pêches et Océans Canada
Institut Maurice-Lamontagne
850 route de la Mer
Mont-Joli, QC
Canada G5H 3Z4
-----Original Message-----
From: Justin Johnston [mailto:[log in to unmask]]
Sent: 26 mai 2005 5:55
To: [log in to unmask]
Subject: Re: Is overfishing a scientific or legal term?
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Mike: That is a great article. I realize that there are multiple
definitions of the word. I also realize that "over-fishing" can and does
occur and can influence fish stocks. However, there are a great deal of
other factors that do so as well. I had two main points that I failed to
get across effectively earlier. First, that any declines in stock should be
studied before conclusions are drawn as to the cause be it over-fishing or
anything else. That would go for both definitions that you presented that
are also in the internet article that you cited. Declines that could be
attributed to recruitment over-fishing could also be due to natural
mortality losses during early life stages. A lack of larger fish due to
growth over-fishing could also be due to a decline in condition from a poor
diet (i.e.. The average lake whitefish caught today in Lake Michigan is
smaller than 15 years ago not because of growth overfishing, but because of
a shift in diet from Diporia to dreissenid mussels). The only way to know
is to conduct scientific studies. Secondly, I don't believe that it is
important to qualify a word as 'scientific', 'technical', or 'legal'. What
is important, is that you communicate your thoughts accurately, which can be
done by defining the terms that you use when you use them. If you are using
the term 'over-fishing' you should define it accordingly whether it be
growth over-fishing, recruitment over-fishing, or any of the social and
legal definitions of the term that you are trying to convey. If we really
want to get into semantics, try asking people what the exact definition of
recruitment is and why every article defines it differently. Is it from
birth to when it can be captured using some sort of gear? Is it from age 1
to age 2? Is it from the time it eats one food to another? Is recruitment
from the perspective of a single fish or a population? That is can a single
fish be said to recruit? It is a plastic term, just like over-fishing, and
like over-fishing it must be defined in every work that it is used in.
Cheers!
Justin C Johnston
Biologist
AMEC Earth and Environmental
Professional Building III
11676 Perry Highway, suite 3101
Wexford, PA 15090
[log in to unmask]
office: (724) 940-4200x229
fax: (724) 940-4205
-----Original Message-----
From: Scientific forum on fish and fisheries
[mailto:[log in to unmask]] On Behalf Of Mike Flaherty
Sent: Thursday, May 26, 2005 11:34 AM
To: [log in to unmask]
Subject: Re: Is overfishing a scientific or legal term?
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================================
Donatella wrote:
Justin: overfishing is a common term of course derived from informal
language but the technical definition is easily found in every fishery
science book, you may also distinguish between growth overfishing and
recruitment overfishing (e.g.Sparre, 1987 and many others).
================================
There is a text that I refer to often called...
UNDERSTANDING
FISHERIES
MANAGEMENT:
Manual for understanding the Federal Fisheries Management Process, Including
Analysis of the 1996 Sustainable Fisheries Act
It may be found for free at...
http://nsgl.gso.uri.edu/masgc/masgch00001.pdf
I have included some salient excerpts below on "recruitment overfishing" and
"growth overfishing".
Best,
Mike Flaherty
Wareham, MA
-----------------------------------------------
Assessment Based on a Little Biology (Age at First Spawning)
When little is known about the biology of a fish stock, one of the first
questions asked is, "At what age do the fish spawn?" The second question is,
"What proportion of the fish caught are one year, two-years, and three-years
old?" If some of the fish spawn when they are two-years old, and all spawn
at age three, and most of the fish caught are two-years old, then there is a
danger that too many fish may be caught before they can spawn and replace
themselves. This is called recruitment overfishing.
-----------------------------------------------
-----------------------------------------------
OTHER KINDS OF OVERFISHING
So far we have emphasized overfishing that leads to declining stocks. This
is often referred to as recruitment overfishing. The name indicates that the
mortality rate from fishing is severe enough to affect future recruitment to
the extent that catches are reduced and the stock is jeopardized. Another
type of overfishing is called growth overfishing. Growth overfishing occurs
when the bulk of the harvest is made up of small fish that could have been
significantly larger if they survived to an older age. The concern here is
that the fishery would produce more weight if the fish were harvested at a
larger size. The question biologists, economists, managers, and others must
answer is how much bigger or older should the fish get before they are
harvested.
-----------------------------------------------
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