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Optimising Fishing and Economic Policy

March 13, 2012
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Editor’s Note: This is another blog from guest writer Dr. Sidney Holt.  Here he continues his exploration of how we might best diverge from MSY to achieve rational and sustainable targets, while offering recommendations to the Green Group in the European Parliament. 

In my last post on this site – Rescuing Maximum Sustainable Yield – I presented some little calculations of maximum economic yield assuming that fishing became unprofitable (cost of catching exceeding market value of sustainable catch) around a point of msy. That was simply an illustrative example. I also emphasized that there is no single msy catch or stock ‘level’, but an infinity of them, depending on the selectivity of the fishery by size and age of fish liable to be captured by the gear and operational pattern employed (The Grand MSY – absolute – is unavailable because it requires an impossibly intense fishing effort to obtain it).

Since I wrote that I have had the opportunity to complete a wider examination of that process, with results that surprised and pleased me. The opportunity came with the request that I offer to the Green Group in the European Parliament arguments supporting their policy of pressing for fisheries regulation to allow stock abundance to be greater than that purportedly providing msy – so requiring reduced fishing effort – and, getting down to brass tacks, just how far should such reduction go? One reference point for that is mey, which I prefer to call msey – maximum sustainable economic yield is not a unique target but certainly provides a better guide to a desirable regulated fishery than does any msy; I’ll come back to that later.

Where and in what circumstances Michael Graham’s Great Law of Fishing – Fisheries that are unlimited become inefficient and unprofitable – comes into play depends, of course on many factors, especially on the dynamics of the exploited population, the cost of causing a certain fishing mortality rate, the price of fish, the ratio between those two quantities and possible changes in that ratio resulting from increasing technical efficiency and the elasticities of price and demand, and the availability of subsidies. And what we would normally see is a pattern of the at first rising, then sharply falling, profitability of not sustainable fishing, but fish-mining.  But in discussing policy options we have to concentrate on – hopefully – sustainable situations. And I have demonstrated that sustainability by no means guarantees profitability

Lack of overall profit can come even before fishing intensity reaches what would become. eventually,  if stabilized, a situation of maximum sustainable yield. But a state of loss or zero profit is certain to arrive later, after the msy-fishing mortality rate has been passed.  In that region of ‘parameter space’ the decline in the catch rate accelerates and the total catch itself steadily declines, ultimately precipitately as reproduction of the stock is impacted.

So this time around I assumed that ground zero’ would be reached when, for example the fishing rate (for a given selectivity-situation) was well below the fmsy-level (two-thirds) or well above it: 50% more, or double). Remember, f is the ratio of the instantaneous fishing mortality rate to the natural mortality rat, F/M).  The msey fishing levels turn out always to be much lower than I had found from a few earlier, exploratory, calculations – mostly around one -third of the effort needed to take msy. They depended hardly at all on the range of biological parameters in the mathematical model used and yet always assured a reasonably large total sustainable catch as measured against the theoretical msy, within the range 70 to 90% of msy.  Where msey is and how big it is come from the basic geometry of age-structured population models and specifically on the steepness of the left-hand (‘under-fishing’) limbs of the curves of sustainable yield against fishing mortality rate, i.e. fishing effort.

This is a summary of the results:

  1. The fishing rate is always somewhere between one half and double the natural mortality rate of the fish in question (f between 0.5 and 2.0);
  2. fmsey is always between 25% and 35% of the fishing intensity required to sustain msy – that is fmsy;
  3. msey is always between 78% and 93% of the msy.  If price elasticity is such as to change the cost-price ratio then the result, if correctly acted upon, will be beneficial, causing fmsey to be a bit lower;
  4. The rate of profit, assuming the ratio of cost to price is the same as it would have been under msy-conditions, would be in the range 100%-200%

Whether it is worthwhile for any vessel, fleet or company to take a share of the msey depends, of course, on the rate of catch it offers – the expected catch-per-unit-effort (cpue). Most economists would say the expected rate of profit rate has to be comparable with, if not greater, than would be obtained by investing resources in something else. We cannot say, ex cathedra, where that could be and, specifically, be obtainable from a total effort greater than fmsey or would have to be from an effort less than fmsey, with correspondingly higher cpue. And in setting policy limits to fishing effort society may have to decide whether  it wants to have a few fishermen making a very good living, or more of them making an adequate living.

My advice to the Green Group, therefore, is that it is in all our interests to limit fishing effort to a sustainable level somewhere in the region of that required to provide us with maximum net economic yields, which would be around one quarter of one third of that expected to provide maximum sustainable physical yield by weight or by gross value.

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