This graph in the ICES advice illustrates vividly how after something like 70 years of incremental increases in fishing mortality (F), the trends after the year 2000 have taken a dramatic dive. This fall in fishing pressure coincides closely with the period during which an array of “cod recovery” measures were applied to EU fleets, although many other factors are undoubtedly involved.
Fishing mortality in the demersal and benthic stocks has been halved since 2000.
The fall in fishing mortality is remarkable in that it applies to all of the three main species groups pelagic (including herring and mackerel), demersal (including cod, haddock and whiting) and benthic (the flatfish including sole and plaice). It also applies right across the whole of the North East Atlantic area, including the North Sea and Baltic and waters around the UK.
Although the development of the pelagic stocks has taken a different course from the benthic and demersal, they are now rapidly catching up.
ICES summarises the situation: Fishing Mortality for benthic stocks gradually increased over time until about year 2000 and have since reduced substantially. For demersal stocks the increase was steeper in the beginning of the time period, peaked around year 2000 and has reduced since. The pelagic stocks have had a very different development over time. F increased significantly in the late 1960s and early 1970s. This resulted in the well known collapse of several important herring and mackerel stocks. Since then, F has been quite low and stable and like for the other two types of stocks, has decreased since year 2000.
In many respects this development will come as no great news to many fishermen who have seen the fishing fleets reduced by decommissioning, consolidation and attrition, to the extent that previously busy fishing grounds are now quite deserted. But it is important to acknowledge the significance of the fact that this trend is now established in scientific opinion and also to consider its implications.
Implications
The clear shift to a lower fishing mortality rate brings with it the need rethink the way we approach both fisheries advice and fisheries management. When the overwhelming concern was to reduce fishing pressure because it was such a dominant factor, there was little need to think too deeply about multi-species interactions – they didn’t really come fully into play. But now that the impact of fishing has been reduced, the need to consider predation patterns and cannibalism becomes much more urgent. ICES' view is that stocks can become so large that they deplete their food sources and eventually eat their own kind. It is necessary therefore to think about the next steps in advice and management: It may be that it will be necessary to increase fishing pressure on some species to achieve an optimum balance. ICES has been working for 30 years on multi-species models. These can now be put to use to inform management decisions.
Another implication lies in the realm of public perceptions. “We all know that fish stocks are collapsing”, has become such an automatic media refrain that it has been difficult for the public to understand that things have changed. But changed they have. North Sea cod, the iconic fish and chips species, is rebuilding steadily to safe biological levels; many stocks are at the management goal of maximum sustainable yield and others are on the way. The recovery of some stocks like North Sea plaice is nothing short of breathtaking, with a biomass beyond anything seen within the historical record.
This is not to say that there aren’t some stocks that have yet to respond in the same way: West of Scotland and Irish Sea Cod are two examples where other factors may be impeding recovery. But the dominant downward trend is too well established, too widespread in geographical terms and across so many diverse fisheries, to be dismissed as a statistical blip.
One telling point in the scientists’s advice puts paid to a number of claims of celebrity chefs and journalists that their own heroic efforts have turned a catastrophic situation around. By the time that Johnny-Come- Latelys such as The End of the Line and Hugh’s Fish Fight turned their attention to fishing the trends discussed above were well established.
Causes
The precise reasons why fishing mortality has dropped so decisively in recent years are not straightforward to discern. Numerous management initiatives have come into play simultaneously and disentangling which worked from which didn’t simply isn’t feasible after the event.
Fleet reductions, tradable quota, increased selectivity, landing controls, effort control, an altered industry mindset, cod avoidance including real time closures have all been in the mix. Some have undoubtedly contributed, others have had perverse effects. ICES points to better control, for example in the Baltic Sea. Norway has been able to check the Russians in the Barents Sea. Other candidates include a move towards long term management plans, setting TACs in relation to maximum sustainable yield and better relations between the fishing industry and fisheries scientists. The answer lies surely in some combination of the above but the weight accorded to each is that science cannot provide.
ICES, however, does not give much credit to the theory that it is nature itself that has created this positive trend in fishing mortality. All species and ecosystems shifting in the same direction simultaneously simply sounds improbable, they conclude.
This article has borrowed freely from both ICES’ 2012 advice and a forthcoming article produced by the Danish Fishermen’s Association and the NNFO.
And here's an excellent resp[onse to the published information from Ray Hilborn
Myths
Fisheries science has been the unfortunate victim of a number of myths that have become widely accepted but are patently untrue. These myths include
we are fishing down food chains all large fish in the oceans are depleted by 90% most of the worlds fisheries are overfished all fish stocks will be collapsed by 2048 the “Ocean Health Index” assertion that France and Spain have the best managed fisheries in the world This page provides some comment on each of these
Fishing Down Food Webs
This myth was started by a paper in 1998 entitled “Fishing down marine food web” authored by Daniel Pauly and several others. The observation was that the mean trophic level of the worlds fish catch was declining as seen in the graph taken from Pauly’s paper. The authors then have gone on to argue that there is a common trend in fisheries, starting to fish at the top of the food chain, once those stocks are depleted, fishing fleets move down the food chain, and the net result is that soon nothing will be left in the ocean but jelly fish. The original paper, published in Science is one of the most commonly cited papers in fisheries and although this myth has been thoroughly debunked it continues to be widely believed, and Pauly and co-authors have an entire web site devoted to defending the idea.
Three papers have shown the errors in both the analysis and also the implications as asserted by the authors. The first paper was published by Tim Essington and co-authors in 2006. Their paper showed that the decline of mean trophic level in most marine ecosystems was not that all the high-trophic level fish were gone, but that in fact catch of high trophic level fish continued to rise. The decline was due to increased yields of lower trophic level fish. So while this paper didn’t challenge the assertion that mean trophic level in the catch was declining, it showed that the assertion that the high trophic level fish were declining in catch was wrong.
In 2010 Trevor Branch and colleagues published a paper in Nature showing that in fact, the mean trophic level in the world’s catch was rising, not falling, and that the decline Pauly had shown was due primarily to two species, the rebuilding of the Peruvian anchovetta stock (low trophic level), and the decline of catches of Atlantic cod. Worldwide the mean trophic level of the catch was rising, not falling. Branch also showed that if you look at the mean trophic level of fish in marine ecosystems, there was no overall decline in mean trophic levels. Branch pointed out that looking at any characteristic of catch, where it is total catch, or trophic level, is not necessarily a good measure of changes in the ecosystem itself since catches are rarely a random sample.
The final paper that nailed the coffin on “fishing down marine food webs” was also published in 2010 in Proceedings of the National Academy of Sciences, by Suresh Sethi, Trevor Branch and several others. Sethi began by asking a basic question — one that should have been asked by the proponents of fishing down a decade earlier. Are high trophic level species more valuable than low trophic level species? Remember the argument in support of fishing down is that fishing fleets begin with high trophic level species because they are more valuable.
What Sethi and co-authors found was that there is no relationship between trophic level and the price or value of fish. Some of the most expensive fish in a marketplace are prawns, crabs, scallops and lobsters, all relatively low trophic level species. Even among higher trophic level fishes there is no correlation between trophic level and value. The mechanism that underlies the theory of fishing down food webs simply isn’t true. Sethi found that fisheries do not begin with high trophic level species, but instead the development of fisheries in different regions of the world is largely independent of trophic level.
Fishing down food web — a Busted Myth.
Pauly, D., V. Christensen, J. Dlasgaard, R. Froese, and F. Torres Jr. 1998. Fishing down marine food webs. Science 279:860-863. Essington, T. E., A. H. Beaudreau, and J. Wiedenmann. 2006. Fishing through marine food webs. Proceedings of the National Academy of Sciences of the United States of America 103:3171-3175. Branch, T. A., R. Watson, E. A. Fulton, S. Jennings, C. R. McGilliard, G. T. Pablico, D. Ricard, and S. R. Tracey. 2010. The trophic fingerprint of marine fisheries. Nature 468:431-435. Sethi, S. A., T. A. Branch, and R. Watson. 2010. Global fishery development patterns are driven by profit but not trophic level. Proceedings of the National Academy of Sciences of the United States of America 107:12163-12167. ______________________________________________________________________________ All large fish in the oceans are depleted by 90% This myth began with a 2003 paper in Nature entitled “Rapid worldwide depletion of predatory fish communities” in which the authors, Ransom Myers and Boris Worm, used a large body of Japanese tuna fleet longline records to show that the catch per hook declined very rapidly when the fishery began across a range of species, and that by 1980 catch per hook around the world was roughly only 10% of what it had been in the 1950s when the fishery began. This was taken as evidence of depletion of the oceans of tunas and relatives, and is the basis for repeated statements that 90% of the fish of the ocean are gone.
This paper caused an enormous controversy because this decline in longline CPUE had been known for a long time by scientists working on tunas and it was widely recognized NOT to reflect changes in abundance. Rebuttals were rapid and rather vehement, Carl Walters entitled his rebuttal “Folly and fantasy in the analysis of spatial catch rate data.” In 2006 John Sibert and colleagues published a paper in Science showing that abundance of large tunas and other species in the Pacific had not declined by anything like 90% by 2000, and had hardly declined at all by 1980. Further they showed that for these species in the Pacific the stocks were generally at or above the management target levels that produce maximum sustainable yield To some extent the last word on this issue was a paper published in 2010 in PNAS by Juan-Jorda and colleagues. They showed that globally tuna stocks by 2010 were at 40-50% of their unfished abundance, still generally at or above target levels, and that in 1980, when Myers and Worm had argued tuna had declined by 90%, in fact tuna stocks had been depleted only slightly and were at 80% of their unfished abundance.
The myth that fish stocks have been depleted to only 10 or 20% of the original abundance based on the tuna and bilfish of the high seas is another BUSTED MYTH.
Myers, R. A. and B. Worm. 2003. Rapid worldwide depletion of predatory fish communities. Nature 423:280-283. Walters, C. J. 2003. Folly and fantasy in the analysis of spatial catch rate data. Canadian Journal of Fisheries and Aquatic Sciences 60:1433-1436. Sibert, J., J. Hampton, P. Kleiber, and M. Maunder. 2006. Biomass, Size, and Trophic Status of Top Predators in the Pacific Ocean. Science 314:1773-1776. Juan-Jorda, M. S., I. Mosqueira, A. B. Cooper, J. Freire, and N. K. Dulvy. 2011. Global population trajectories of tunas and their relatives. Proceedings of the National Academy of Sciences of the United States of America 108:20650-20655.
