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Subject:

Re: Is overfishing a scientific or legal term?

From:

Donatella Del Piero <[log in to unmask]>

Reply-To:

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

Date:

Fri, 27 May 2005 16:41:18 +0200

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I'd like to remind to everybody the conclusion of the 4th fishery congress in
vancouver last year: a brave said: we lost credibility. Do U remeber?D.Del
Piero
Scrive Daniel Duplisea <[log in to unmask]>:

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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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