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Since size maters in swimming speed for most if not all fish, the trawl fishery can work on their trawling/towing speed for that purpose. Species wimming speed is fundamental in the trawl industry and such an aproach is partialy and sometimes indirectly practiced in bycatch regulations. Settig a maximum size limit has been recomended and practiced in some trap fisheries.
Regards
Hilkka
-----Original Message-----
From: Scientific forum on fish and fisheries [mailto:[log in to unmask]] On Behalf Of Trevor J. Kenchington
Sent: 17. april 2008 13:51
To: [log in to unmask]
Subject: Re: UCSD: Scripps Oceanography News Release: Fishing Throws Targeted Species Off Balance
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Bill,
A lot of trawl fisheries already leave the largest fish uncaught -- and receive a lot of negative publicity for doing so. The "domed partial recruitment" arises (primarily but not exclusively) because many fish species have distributions somewhat segregated by size.
Trawl fisheries tend to concentrate where the highest tonnages can be taken in the least time, which is not in the areas frequented by scarce, large fish. It might well be worth enhancing that trend towards lower fishing mortalities at higher ages but only if enough individuals escape the fishing pressure of the intermediate ages, so that there are big fish to not catch.
As David Kerstetter noted, it should be possible to develop sorting grids that would release larger fish, while retaining mid-sized ones.
However, persuading people that that is the way to go wouldn't be easy. In most fisheries that I encounter, public debates over conservation strategies don't seem able to progress beyond the absurd oversimplification that we just need to let each fish spawn once before it gets caught. There is often strong pressure to push minimum sizes ever higher.
Trevor Kenchington
On 17-Apr-08, at 7:40 AM, Bill Silvert wrote:
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>
> The examples that David gives are mainly from fisheries where the
> catch is handled one by one, as in the recreational fishery or hook
> and line fisheries. I imagine that these are relatively easy to
> control, at least in principle. My concern is more with bulk
> fisheries, especially trawl fisheries, where by the time the fish come
> on board they are either dead or so stressed that they are unlikely to
> survive even if immediately thrown back. Think of the gadoids or small
> pelagics.
>
> Bill Silvert
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