Dear Zakia,
You have asked about some very different things. M and K are biological properties of the fish. For many teleost species, the M/K ratio is set at about 1.5 -- M/K=1.5 is one of the "Beverton-Holt Invariants". However, those are not truly invariant. Species with atypical life histories can have very different M/K.
B0 is also a property of the fish -- but be careful not to confuse B0 with Bv, as most people do! B0 is the result of back-calculating to zero fishing mortality, using a model of an exploited resource. Bv is the biomass before fishing begins. They can be very different. BMSY is perhaps another property of the fish, though one that involves human activity and policy goals.
However, F and B are variables and their values could represent current (or past) reality, policy goals or something else. Is your interest in the ratios (F/K, B/B0, B/BMSY) as reference points for fisheries management? If so, the first general rule of management (though certainly not optimal for every fishery!) is that the goal should be F=M, so F/K = M/K, which for many species is about 1.5. That is a start but it would be badly wrong for some fisheries and it makes no allowance for the massive uncertainties in estimating F and K.
I don't know why anyone would suggest that B/BMSY>0.4 represents "good" status. There are fisheries where human employment in fishing is more important than the value of the catch but, in general, we should be aiming for the "safe" side of MSY, with B above BMSY and F below FMSY. So, unless someone has a very good rationale for depressing a resource more deeply, I would say that "good" requires B>BMSY. [Please understand that I am here using "MSY" as useful shorthand for far more complex ideas. MSY itself, in the sense that Graham and Schaffer meant it, was an over-simplification and should have been discarded decades ago. Unfortunately, it continues to be perpetuated.]
BMSY/B0 depends on the population dynamics of the fish but is often around 0.3 to 0.5. So B>0.4B0 might be a rough definition of "good" for many fisheries. But remember that 0.4B0 is not the same as 0.4Bv.
Y/R is different again. Although a ratio, it is more like F or B -- a variable that could describe a present condition or a policy goal. Like F or B, the biologically-possible values vary widely and I don't think that anyone could set a general guideline.
Having said all of that, I would recommend returning to Cornelia's last comment:
Population-dynamic analyses of fishery resources are satisfying for biologists. Sometimes they will persuade fishermen and governments to act, regardless of whether the numbers are accurate or not. But you can spend many thousands of hours working and end up with conclusions so uncertain as to be scientifically useless. (And a great many fisheries scientists spend their time doing just that.) What is important for many (not all) Mediterranean fisheries is to reduce fishing effort and reduce it by a very large fraction -- though even moderate reductions would help. If estimating F and B relative to reference points helps convince decision-makers that effort reduction would benefit fishermen, then the calculations are worth doing, but only a means to and end. Perhaps you can get estimates for your Phycis and Boops resources that are reliable enough for you to judge whether your fisheries are among the few that do not need effort reduction. If so, that would be worthwhile too.
However, the important task is very likely to be finding a way to get fishing effort down. You should not be deflected from that by playing with the equations of population dynamics -- even though that is much more satisfying for a scientist!
Trevor
Dear Zakia,
such parameters are being assessed for diff. stocks and regions for diff. time periods. A recently developed method (CMSY) has allowed an international team of scientists to assess 397 stocks in European waters. The method was taught successfully during a workshop in India and elsewhere. Perhaps it might help you to look up these materials and possible contact the researchers involved directly: https://www.q-quatics.org/cmsybsm-workshop-india/
Hi Zakia,
As Cornelia indicated, these are assessed for different stocks by region and their value can change as stock assessments are updated. If you can identify the species by country that you are interested in, we might be of more help. Here are a couple of sources that might be helpful to you; I work on the RAM Legacy Stock Assessment Database that is shown in the second link: http://www.fao.org/docrep/003/v8400e/V8400E02.htm;
https://sustainablefisheries-uw.org/databases/
Dear Charmane
Thank you for sharing links and answering to my question. As i sad Iam interested in Mediterranean fisheries and actually work on commercial fisheries from Algeria (Phycis blennoides and Boops boops).
Dear Cornelia thank you for your response and for sharing the documentation. As froese et al. 2019 suggested in their paper of the LBB method used for poor data assessment , that B/Bmsy0.4 a good status. Iam trying to find other biological standards or ranging which help to characterize a stock. Then I can think about a management program. Actually I am working on commercial fisheries fish from Algeria (Phycis blennoides and Boops boops).
Dear Zakia,
if you go to FishBase you can check the resilience indicators for Phycis blennoides and Boops boops as additional hints about vulnerability. If you have length frequency data from non-selective gears you may be able to estimate growth parameters for comparison. Watch the prevailing temperature regime as this affects growth. If data are scarce in general a conservative approach to management is an insurance against ecological and economic waste through overfishing. As many Med. stocks are in particularly poor state, such a prudent approach may even hold hope for recovery. Froese suggested at a Fisheries Committee meeting of the European Parliament that even 20% of reduction in fishing effort would allow rebuilding stocks and therefore safeguarding, even increasing catches that can be taken safely. The big problem is that so many stocks have biomasses too low to produce MSY. That's a big waste, ecologically and economically.
Dear Zakia,
You have asked about some very different things. M and K are biological properties of the fish. For many teleost species, the M/K ratio is set at about 1.5 -- M/K=1.5 is one of the "Beverton-Holt Invariants". However, those are not truly invariant. Species with atypical life histories can have very different M/K.
B0 is also a property of the fish -- but be careful not to confuse B0 with Bv, as most people do! B0 is the result of back-calculating to zero fishing mortality, using a model of an exploited resource. Bv is the biomass before fishing begins. They can be very different. BMSY is perhaps another property of the fish, though one that involves human activity and policy goals.
However, F and B are variables and their values could represent current (or past) reality, policy goals or something else. Is your interest in the ratios (F/K, B/B0, B/BMSY) as reference points for fisheries management? If so, the first general rule of management (though certainly not optimal for every fishery!) is that the goal should be F=M, so F/K = M/K, which for many species is about 1.5. That is a start but it would be badly wrong for some fisheries and it makes no allowance for the massive uncertainties in estimating F and K.
I don't know why anyone would suggest that B/BMSY>0.4 represents "good" status. There are fisheries where human employment in fishing is more important than the value of the catch but, in general, we should be aiming for the "safe" side of MSY, with B above BMSY and F below FMSY. So, unless someone has a very good rationale for depressing a resource more deeply, I would say that "good" requires B>BMSY. [Please understand that I am here using "MSY" as useful shorthand for far more complex ideas. MSY itself, in the sense that Graham and Schaffer meant it, was an over-simplification and should have been discarded decades ago. Unfortunately, it continues to be perpetuated.]
BMSY/B0 depends on the population dynamics of the fish but is often around 0.3 to 0.5. So B>0.4B0 might be a rough definition of "good" for many fisheries. But remember that 0.4B0 is not the same as 0.4Bv.
Y/R is different again. Although a ratio, it is more like F or B -- a variable that could describe a present condition or a policy goal. Like F or B, the biologically-possible values vary widely and I don't think that anyone could set a general guideline.
Having said all of that, I would recommend returning to Cornelia's last comment:
Population-dynamic analyses of fishery resources are satisfying for biologists. Sometimes they will persuade fishermen and governments to act, regardless of whether the numbers are accurate or not. But you can spend many thousands of hours working and end up with conclusions so uncertain as to be scientifically useless. (And a great many fisheries scientists spend their time doing just that.) What is important for many (not all) Mediterranean fisheries is to reduce fishing effort and reduce it by a very large fraction -- though even moderate reductions would help. If estimating F and B relative to reference points helps convince decision-makers that effort reduction would benefit fishermen, then the calculations are worth doing, but only a means to and end. Perhaps you can get estimates for your Phycis and Boops resources that are reliable enough for you to judge whether your fisheries are among the few that do not need effort reduction. If so, that would be worthwhile too.
However, the important task is very likely to be finding a way to get fishing effort down. You should not be deflected from that by playing with the equations of population dynamics -- even though that is much more satisfying for a scientist!
Trevor
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