Forum

 
  Back to OzPolitic.com   Welcome, Guest. Please Login or Register
  Forum Home Album HelpSearch Recent Rules LoginRegister  
 

Pages: 1 2 3 
Send Topic Print
the effect of management regime on yields (Read 5347 times)
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
the effect of management regime on yields
Dec 8th, 2008 at 4:17pm
 
This issue came up in the marine park thread:

http://www.ozpolitic.com/forum/YaBB.pl?num=1192441509/210#210

PJ insisted that current catch rates could not be improved upon. He based this assumption on the fact that people had calculated a maximum sustainable yield (MSY) based on the stock levels as a percentage of unfished (virgin) stock levels. This obviously assumes a certain management regime, but PJ confused that assumption for endorsement of current management regimes. PJ went on to insist that it is therefor not possible to increase both stock levels and catch rates. That is, it is not possible to go above the catch rate corresponding to the current estimate of MSY without causing stocks to collapse - even if you change management regime. This also carries an implicit assumption that the only way to permanently increase stock numbers is to permanently reduce catch rates. Basically it is the old argument - "this is how it has always been done, therefor there is not a better way" - even though current management regimes have only been in place for a few decades.

Take cattle farming as an analogy. Compared to ranching or hunting wild stock, cattle farmers micromanage the land so that it has a far higher stocking rate. They also manage to get a far higher harvest rate than you could get from harvesting wild stock.

Fisheries have only recently come out of the management regime of unregulated harvest of wild stock. The obvious first step was regulated harvest of wild stock. Obviously there are practical issues preventing the sort of micromanagement you can achieve on land. However, the same principle applies - it is not difficult to increase both stocking rates and MSY. The current estimates of MSY assume the management regime is fixed. They are not an endorsement of the current management regime.

Back  to the cattle analogy. The current management regime is similar to harvesting wild, unmanaged stock, but limiting the amount that can be taken in various ways, one of which encourages the harvest of the best (fattest, fastest growing etc) cattle and leaving the runts to breed for next year. Marine parks are analogous to introducing limited protection of the key breeding stocks and providing some areas where stocking rates can reach higher levels. It is similar to having a stocking rate of far less than the natural levels - that is, stocking rate is not limited by the risk of overstocking (as we are familiar with the issue on land), but by the inability of achieving both high stock levels and high harvest rates under the current management regime.

Marine aprks also make the management regime more stable. Imagine that for some reason it was not possible to count the number of cows you had left. You would have to take an extremely conservative approach to harvesting them, as overharvest is difficult to predict and could have serious consequences for future harvests. If you set aside a few paddocks where cattle are not harvested, and from which cattle could leave as their numbers got too high for the paddock, then you could be a lot more secure in your harvests as you would know that there is always a significant number of cattle in the unharvested paddock.

PJ's argument is equivalent to people switching from unregulated harvest to limited regulation, then deciding a few decades later (and in the face of contradictory evidence) that the limited regulation they initially implimented cannot be improved upon. It is an argument based on ignorance, and an assumption that a certain management regime is best, just because it is traditional, even though it's not actually traditional - it has just been accepted already.

Anyway, the analogy obviously breaks down as you get into too much detail. The main point is that maximum sustainable yield (as it is currently estimated) is not a fixed number. It depends on management regime. If you manage the stocks better, you can get higher stock levels, higher yields and a more sustaianble (secure) harvest - one that is less sensitive to your lack of knowledge of the remaining stock levels, and less likely to crash because you kept harvesting while you were unaware that stock levels had plummeted for some reason.

The current estimates of MSY represent the upper limit on what can be taken. In practice, fisheries must harvest well below the MSY due to the risks associated with not knowing with reasoanble accuracy what the remaining stock levels are. Marine parks increase the MSY and allow you to get closer to it in practice, because the management regime introduces an inherent stability. Current management tools make it easy to overharvest in those years where for some reason (eg natural variation) stock levels are unusually low. Marine parks make it much more difficult to overharvest because the breeding stock is far better protected. Under current regimes, only paperwork stands between fishermen and the breeding stock for next year. Fisheries managers are forced to try to limit catches in a scenario where they don't know what the remaining stock levels are and they don't know how many fish a large group of fishermen is taking. They have managed to get it to work, with only a few dramatic failures. While that is commendable, it is no reason to stick with clearly inferior managemen tools.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
pjb05
Gold Member
*****
Offline


OzPolitic

Posts: 1402
Gender: male
Re: the effect of management regime on yields
Reply #1 - Dec 9th, 2008 at 3:07pm
 
Thats pure snake oil by FD. The cattle analogy falls down in that farmers as opposed to ranchers increase the primary productivity by growing special pastures or feeding the cattle grain. This is actually analogous to aquaculture.

In another slight of hand he ignores that other input reductions are used such as restricting the number of commercial licences, milder forms of area management, gear limits, trip limits and closed seasons. These serve as a buffer to overfishing and avoid the socio-economic problems of outright bans.

Note he also provides no evidence for his musings and is completley silent on the actual evidence (or lack thereof) for NSW marine parks, despite some being in place for 15 years.
Back to top
« Last Edit: Dec 9th, 2008 at 7:47pm by pjb05 »  
 
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #2 - Dec 9th, 2008 at 3:34pm
 
Quote:
Your cattle analogy falls down in that farmers as opposed to ranchers increase the primary productivity by growing special pastures or feeding the cattle grain.


They do that as well. But it doesn't mean they don't manage stocking rates. Obviously the analogy fails in that marine parks will not get you stocking rates above what is natural, but that doesn't mean you can't get both higher stocking rates than current ones and higher catch rates. That is exactly what marine parks do give you. Your assumption that this is somehow impossible is totally baseless.

Quote:
In another slight of hand he ignores that other input reductions are used such as restricting the number of commercial licences


This happened on the GBR, but that just demonstrates that the effects you see in that aprticular case are not down to NTZs alone. This is not usually the case.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
pjb05
Gold Member
*****
Offline


OzPolitic

Posts: 1402
Gender: male
Re: the effect of management regime on yields
Reply #3 - Dec 10th, 2008 at 4:26am
 
I suppose you have some actual evidence for an increased total yield resulting from 20% of grounds being off limits to fishermen?
Back to top
 
 
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #4 - Dec 10th, 2008 at 11:37am
 
That's what the statement of consensus is all about. There is an enourmous body of evidence backing it up.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
pjb05
Gold Member
*****
Offline


OzPolitic

Posts: 1402
Gender: male
Re: the effect of management regime on yields
Reply #5 - Dec 10th, 2008 at 1:29pm
 
freediver wrote on Dec 10th, 2008 at 11:37am:
That's what the statement of consensus is all about. There is an enourmous body of evidence backing it up.


Then it shouldn't be hard to show some should it?
Back to top
 
 
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #6 - Dec 10th, 2008 at 1:36pm
 
Showing some would only make a point if someone was claiming there is none. Rather, the anti-MP lobby prefer to say the evidence that is out there doesn't count because it isn't from Australia, or it isn't from NSW, or it isn't from Sydney, or it isn't from Bondi. That is, they will only accept a specific marine park after it has been proven that it will benefit them, but will not accept any proof that doesn't involve the implementation of the specific marine park.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
pjb05
Gold Member
*****
Offline


OzPolitic

Posts: 1402
Gender: male
Re: the effect of management regime on yields
Reply #7 - Dec 10th, 2008 at 1:58pm
 
freediver wrote on Dec 10th, 2008 at 1:36pm:
Showing some would only make a point if someone was claiming there is none. Rather, the anti-MP lobby prefer to say the evidence that is out there doesn't count because it isn't from Australia, or it isn't from NSW, or it isn't from Sydney, or it isn't from Bondi. That is, they will only accept a specific marine park after it has been proven that it will benefit them, but will not accept any proof that doesn't involve the implementation of the specific marine park.


Why don't you provide some evidence instead of trying to pre-empt my possible argument. You have made some starltling claims about marine parks being the ideal fisheries management tool - even that they will increase the MSY beyond what can be achieved by other methods. Why should we accept this if you can't back them up? 
Back to top
 
 
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #8 - Dec 10th, 2008 at 2:13pm
 
The statement of scientific consensus backs them up. I also posted a reference to a book chapter a while back that was a good introduction to the evidence in favour of marine parks. I'll try to track that down for you.

There are two other interesting links here:

http://www.ozpolitic.com/fish/marine-parks-fisheries-management-tool.html#links

http://www.ozpolitic.com/fish/marine-parks-fisheries-management-tool.html#proble...

Size limits also have major problems. Undersize fish frequently die after being returned to the water. More significantly, a minimum size creates selective pressure for fish that grow slower, start breeding younger and put more effort into breeding each year than is optimal. In a natural setting, the most successful breeders tend to be the large fish, and it is the fish that quickly grow large that you want to breed, not the runts. Using minimum sizes is similar to a farmer selecting the runts and small unhealthy cattle each year to be the breeding stock for next year, while selling the prize specimens to the meatworks. This problem is suspected to have contributed to the collapse of many previously productive fisheries, and their inability to recover as quickly as would be expected. Not only are there few fish around, but those fish that remain are runts and pursue breeding strategies that are far from ideal for the quick recovery of stocks. Recent research by Heino and Dieckmann suggests that fish respond quickly to these selective pressures and that only a decade of heavy fishing can introduce serious problems. Unfortunately, the time taken to recover from these problems may be far longer than the time taken to introduce them.

Marine parks overcome all of these problems and provide a 'safety net' to guard against factors that are out of our control. When managing a stock that you cannot see, cannot count and cannot assess on a regular basis such safety nets are essential. Marine parks increase total catches through the 'spillover effect'. This refers to the many ways in which they replenish stocks. Mature fish swim out of the no take zones and get caught. They also provide healthy, fast growing breeding stocks and a consistent supply of larvae.

Note that contrary to popular opinion, it is not true that returned fish always grow bigger and get caught again later. The ocean is a harsh place and most of the returned fish die, even if you ignore 'hooking mortality'. For every kilogram of fish returned for being undersize, far less than 1 kilogram of those same individual fish are caught later in their life. It is the total amount of fish caught that matters and while minimum sizes do help by reducing the total catch, they are far less useful than marine parks as fisheries management tools.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #9 - Dec 10th, 2008 at 2:13pm
 
http://www.ffc.org.au/FFC_files/Sustainable_fishing_edu_files/web_pdfs/2_BOFFFF_web.pdf

Why Should we Sometimes Let the Big Ones Go?

BOFFFF theory – Not just for boffins!

For many years conventional wisdom has told us that
best thing to do to conserve fi sh stocks for the future
is to throw the little ones back and only keep the big
ones. This theory has shaped modern recreational
fi sheries management and lead to minimum size limits
being imposed for most popular species. Scientists are
now beginning to question whether minimum size limits
alone can be effective.

The theory behind minimum size limits and bag
limits is still valid – let as many fi sh as possible reach
maturity before capture (especially for more short
lived species). However this research has opened up
another factor to consider: protecting the BOFFFF.

What does BOFFFF mean?
BOFFFF = Big Old Fat Fecund Female Fish
BOFFFF are the larger, older females which, according
to recent research results, generally produce a lot more
offspring, more times per year, than younger females do.
Additionally, the offspring of larger females are often
healthier and more likely to survive. Older fi sh are more
likely to survive and contribute in the ‘bad years’ when
environmental factors mean reduced recruitment to the fi sh
stocks. For many species, one of the best ways to ensure long
term successful reproduction and replenishment of the fi sh
stocks is to protect the larger, healthy female breeders.

Minimum size limits and evolutionary pressure

There is increasing evidence that fi shing may alter fi sh
evolution. Anecdotal evidence indicates King George
Whiting average size at maturity has actually reduced
over time. This has been linked to the release of smaller
fi sh and the selective fi shing pressure on the larger
individuals. Some fi sh species may actually be getting
smaller on average due to minimum size limit fi shing!

How can we protect the BOFFFF?

There are two major ways to protect the BOFFFF to
help ensure healthy future generations of fish stocks:

1. Return captured large females to the water alive
and healthy.

2. Avoid the capture of some, or all, of the largest
females.

The first option relies on identifying which large fi sh
are female (this is not always possible) and that the
returned fi sh survive and reproduce in a healthy
manner. The stress of capture and release has been
proven to affect reproduction. The level of impact is
dependant on the species being caught and factors
such as the fi shing method, length of time it takes
to land the fi sh, depth of capture and the level of
care taken when releasing the fi sh (see Info Sheet #1
Conserving Your Catch for more info).

The second option relies on fi shing locations and/or
tackle that exclude the capture of the largest fi sh –
this is a new concept for many fi shers.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #10 - Dec 10th, 2008 at 2:23pm
 
Marine Reserves - A Guide to Science, Design and Use
Jack Sobel and Craig Dahlgren
Island Press
http://www.islandpress.org/books/detail.html?SKU=1-55963-841-9

Chapter 11, Global Review: Lessons from around the world, goes through marine parks from around the world, including New
Zealand and Australia, and outlines the benefits in detail.

Chapter 4, What Marine Reserves Can Accomplish, is also interesting.

I got this book through a university library.

Another paper contains a good reference list to many other scientific papers outlining the improvements to fisheries from marine parks:

The effects of marine reserve protection on the trophic relationships of reef fishes on the Great Barrier Reef, NAJ Graham, RD Evans and GR Russ, Environmental conservation, 30 (2): 200-2008, 2003
www.jcu.edu.au/school/mbiolaq/subjects/mb3310/research/Trophic%20effects%20of%20GBR%20marine%20reserves.p df

There was also a special edition of Ecological Applications 13(1): S3-S7
Plugging the hole in the ocean: the emerging science of marine reserves, J Lubchenco, S palumbi, SD Gaines and S Andelman
palumbi.stanford.edu/manuscripts/Lubchenco%20et%20al%202003.pdf

Also: Jackson, JBC et al Historical overfishing and the recent collapse of coastal ecosystems, Science, 2003, 293, 27 July: 629-638
www.mcbi.org/Advancing/Jackson_et_al_2001.pdf

Another good list of references:
Biophysical operating principles, recommended by the scientific steering committee for the representative areas program
http://www.reefed.edu.au/rap/overview/principles/bops.html

I didn't actually find the list online - will have to folloow the links or ask GBRMPA

Scientific Consensus Statement on Marine Reserves and Marine Protected Areas.

http://www.nceas.ucsb.edu/Consensus/

A paper looking at what level of protection would give the most spillover effect (ie highest catch rates). Answer is probably around 20-40%.

http://assets.panda.org/downloads/benefitsbeyondbound2003.pdf

The limitations of minimum sizes as fisheries management tools:

Minimum legal sizes and minimum net hole size for trawlers are creating selective pressure that is harming fish stocks. By greatly reducing the liklihood of fish spawning when they get larger, they are causing fish to grow slower, spawn younger at a smaller size and put more effort into spawning each year, which further reduces growth rate. This means lower yields from fisheries. Until about ten years ago people thought this selective pressure would take a century or so of heavy fishing to have any effect. But it now appears that just a few generations (10 years) is long enough to see a significant effect. Furthermore it is likely that reversing these changes will take a lot longer than causing them, because the 'natural' selective pressure to get fish to return to a more normal growth and spawning rate is far weaker.

http://www.iiasa.ac.at/~dieckman/reprints/DieckmannHeino2004b.pdf (1.6 MB)
http://www.iiasa.ac.at/~dieckman/reprints/HeinoEtal2000.pdf (0.3 MB)
http://www.iiasa.ac.at/~dieckman/reprints/HeinoDieckmann2003.pdf (0.2 MB)
http://www.iiasa.ac.at/Research/EEP/lectures/UlfDieckmann5.pdf (7.5 MB) - powerpoint presentation
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
easel
Gold Member
*****
Offline



Posts: 3120
Re: the effect of management regime on yields
Reply #11 - Dec 10th, 2008 at 2:32pm
 
Will Aborigines be able to fish in closed zones?
Back to top
 

I am from a foreign government. This is not a joke. I am authorised to investigate state and federal bodies including ASIO.
 
IP Logged
 
freediver
Gold Member
*****
Online


www.ozpolitic.com

Posts: 46879
At my desk.
Re: the effect of management regime on yields
Reply #12 - Dec 10th, 2008 at 2:35pm
 
I don't think there is a general rule about that easel. Usually not.
Back to top
 

I identify as Mail because all I do is SendIT!
WWW  
IP Logged
 
easel
Gold Member
*****
Offline



Posts: 3120
Re: the effect of management regime on yields
Reply #13 - Dec 10th, 2008 at 3:25pm
 
I know they don't need fishing licenses. Or at least last I checked they didn't, or they got them for free, or something?

If they can fish in marine parks, get a few Koori boys together and go have fun catching thumpers!
Back to top
 

I am from a foreign government. This is not a joke. I am authorised to investigate state and federal bodies including ASIO.
 
IP Logged
 
pjb05
Gold Member
*****
Offline


OzPolitic

Posts: 1402
Gender: male
Re: the effect of management regime on yields
Reply #14 - Dec 10th, 2008 at 6:28pm
 
The statement of scientific consensus backs them up. I also posted a reference to a book chapter a while back that was a good introduction to the evidence in favour of marine parks. I'll try to track that down for you.

You can't just harping on about the so called consensus statement. It's akin to asking us to accept these closures on faith alone. 

There are two other interesting links here:

http://www.ozpolitic.com/fish/marine-parks-fisheries-management-tool.html#links

http://www.ozpolitic.com/fish/marine-parks-fisheries-management-tool.html#proble...

Size limits also have major problems. Undersize fish frequently die after being returned to the water. More significantly, a minimum size creates selective pressure for fish that grow slower, start breeding younger and put more effort into breeding each year than is optimal. In a natural setting, the most successful breeders tend to be the large fish, and it is the fish that quickly grow large that you want to breed, not the runts. Using minimum sizes is similar to a farmer selecting the runts and small unhealthy cattle each year to be the breeding stock for next year, while selling the prize specimens to the meatworks.

Once again these are your own unsubstantiated musings.  You counterpoint the merits of catch and release by claiming high mortality. Actual real life studies show high survivial rates (often over 90%). You don't mention that there are slot limits for some species too. Also the largest fish aren't always the best breeders - it depends on the species. The smaller breeders are far larger in no in any case. Its also well known that under fishing pressure fish grow faster and the juvenile classes benifit from less competition for food and predation. In fact fisheries biologists will tell you there is a cost to having lots of large fish - you won't get the same yield. 

This problem is suspected to have contributed to the collapse of many previously productive fisheries, and their inability to recover as quickly as would be expected. Not only are there few fish around, but those fish that remain are runts and pursue breeding strategies that are far from ideal for the quick recovery of stocks. Recent research by Heino and Dieckmann suggests that fish respond quickly to these selective pressures and that only a decade of heavy fishing can introduce serious problems. Unfortunately, the time taken to recover from these problems may be far longer than the time taken to introduce them.

Most fish stocks are have been shown to be able to recover remarkably quickly from overfish. Sometimes as quick as 2 years and usually not longer than 5. Our inshore and estuary fish in NSW are fast growing and appear to have a lot of natural resilence in the face of fishing pressure. In any case if you rely on marine parks you may well end up with depleted fisheries plus a few relatively pristine areas where there is no fishing. The odds are that you really need to tackle problems of overfishing head on. 

Marine parks overcome all of these problems and provide a 'safety net' to guard against factors that are out of our control. When managing a stock that you cannot see, cannot count and cannot assess on a regular basis such safety nets are essential. Marine parks increase total catches through the 'spillover effect'. This refers to the many ways in which they replenish stocks. Mature fish swim out of the no take zones and get caught. They also provide healthy, fast growing breeding stocks and a consistent supply of larvae.

Thats at odds with you assertion that you will get an increased yeild with marine parks in place. A buffer exists only if you are taking less fish out. You don't consider that other types of input reductions will do the same job.

Note that contrary to popular opinion, it is not true that returned fish always grow bigger and get caught again later. The ocean is a harsh place and most of the returned fish die, even if you ignore 'hooking mortality'. For every kilogram of fish returned for being undersize, far less than 1 kilogram of those same individual fish are caught later in their life. It is the total amount of fish caught that matters and while minimum sizes do help by reducing the total catch, they are far less useful than marine parks as fisheries management tools.

Totally at odds with actual studies on catch and release. It's a claim made by anti-fishing activists who no surprise are a big part of the marine park lobby. They need to counterpoint catch and release to justify their fishing bans.   
Back to top
 
 
IP Logged
 
Pages: 1 2 3 
Send Topic Print