ENSO and the anchovy

by phlogiston a.k.a Phil Salmon

If one wishes to gain a “heads-up” as to imminent developments in ENSO and possible beginnings of an el Nino or La Nina event, I would advise turning to the Peruvian anchovy as an important but often overlooked oracle to the oceanography of the anchovy’s home ocean, the Pacific.

The Peruvian anchovy or “anchoveta” is an important fish to the global economy and to the diet of most of us. It is the world’s single largest fishery by landed tonnage, and is a principal component of fishmeal which is a major agricultural feed for farmed fish and animals. One can even order them direct as a pizza ingredient (the “Napoli” pizza for instance). For background, see the Wikipedia.

The anchovy is a filter feeder like a mini-whale, swimming with its mouth agape. This is the key to its huge success in exploiting the massive plankton productivity of the equatorial eastern Pacific off the coast of Peru. It is the archetypal pelagic (free-swimming) filter-feeder.

The anchovy (E. ringens) is a pelagic filter-feeder – there are lots of them off the coast of Peru.

Anchovy – the ENSO fish

The Latin classification of the Peruvian anchoveta is Engraulis ringens (Jenyns, 1842). Like almost no other species on earth (certainly not your average Homo) the anchovy has an astonishing and profound instinctive knowledge of the ebb and flow of the El Niño Southern Oscillation – the ENSO. One could indeed reasonably call the anchovy the “ENSO fish”. The migrations, dispersals and gatherings, and year to year biomass peaks and crashes of the anchovy fishery in the eastern Pacific off Peru are tuned with exquisite sensitivity to ENSO itself. In particular it is the Peruvian upwelling, one side of the Bjerknes feedback (the other being the trade winds) which both couple intermittently to provide the bursts of positive feedback that drive El Niño and La Nina episodes. These two systems are characterised by weakening and strengthening respectively of this upwelling.

The first to know of any developments in the dark deep ocean currents way off the Peruvian coast, signifying portentous shifts in the upwelling stemming from the Humboldt current from Antarctica, is Engraulis the anchovy. Long before any clanking fish-imitating Argo floats, before any TAU or TRITON moored bathyscaphes, or satellite imagery, still longer before any armchair climate punditry, the anchovies respond in real time to upwelling changes with variations in the first-feeding survival and size of their juvenile year classes and their spatial distributions. Thus it was inevitably the Peruvian fishermen, heirs of the ocean abundance provided by E. ringens, who were discoverers of what they called El Niño (“the boy” in Spanish), the periodic anomalous warming of the eastern Pacific surface waters. This event is accompanied by a crash in the anchoveta numbers and catches, and typically occurs in December-January, the time of the celebration by the Christian Church of Christmas, the incarnation of the Christ-child.

El Niño is bad for the Peruvian fishermen since it is bad for the anchovy. Why then, one must speculate, did the Peruvians name this cursed event after the divine infant of their religion? Was there a streak of resentment or protest against their Catholic faith and its priests and offices? Or, perhaps, were so many fisherman heard to shout in frustration “Oh Cristo! Su cálida de nuevo!” (Oh Christ! – it’s warm again!) – like skeptical climate bloggers after every uptick in the global temperature anomaly – that the event became named after the blasphemously invoked member of the Holy Trinity.

The baleful influence of El Niño on the anchoveta is related to the transport of nutrients from deep to surface waters which accompanies upwelling, and which fuels the phytoplankton bloom which in turn provides the primary production which nourishes the vast shoals of anchovy which teem off Peru’s coastline and in fishermen’s nets. This is basic first-year marine biology. Primary production, the photosynthetic algal base of the marine food chain, is nutrient limited and thus one talks of blooms, and also of “bloom-and-bust”, as for example with spring sunshine, in temperate waters, the phytoplankton first grow rapidly but then run out of nutrients and die back abruptly (Paul Ehrlich should have been a marine biologist).

This is why coastal regions are the most biologically productive seas where ocean floor topography causes the upwelling essential to bring nutrient rich cooler bottom water up to fertilise the depleted upper layers. The vast expanses of the oceans by contrast have nutrient limited surface water – therefore the strikingly visible transition from green to blue colour of the sea as you move from fertile coastal water to the barren ocean deeps. The world’s most productive seas are in places such as the south west coast of Africa and, biggest of all, the Peruvian west coast of south America, where cold deep water originating in Antarctica and the Humboldt current wells up to sustain the world’s largest fishery, that of Engraulis ringens the anchovy.

 

Microscope images of phytoplankton single-celled algae, foundation of the marine food pyramid. They are beautifully sculpted microscopic creatures with exotic names like diatoms (upper) and foraminiferans (lower) as well as and radiolarians, dinoflagellates and coccolithophores.

In the presence of this upwelling, the east equatorial Pacific is cooler than surface waters further west, setting up a temperature and pressure gradient that drives the prevailing pattern of trade winds, the east to west (“easterly”) winds that for millennia have carried intrepid human seafarers from the Americas to populate the Pacific islands. As well as being impelled by this sea surface temperature difference, the trade winds further amplify the eastern Pacific upwelling by dragging the surface water westward, and this reinforcing positive feedback – the Bjerknes feedback – lies at the heart of the El Niño southern oscillation (ENSO).

However, this positive feedback can cut both ways. From time to time, initiated by no-one knows quite what (although hypotheses abound and swarm like the anchovies themselves) Kelvin waves of warm water surge eastward, interrupting the Peruvian upwelling. This warms the east Pacific surface water, reducing the temperature gradient on which the trade winds depend and thus choking them off, resulting in the dreaded “doldrums” – no wind and reduced upwelling off Peru. This slackening part of the Bjerknes feedback is the El Niño event. And in turn, the reduced upwelling is bad news for the anchovy as he has to stay deeper to access life-giving nutrients, and the Peruvian fishermen once more cry “O Cristo – El Niño!”.

El Niño now? What does the anchovy have to say?

So what significance does all this have to the current conditions in the Pacific? For more than a year now, ENSO-watchers have been on the edge of their seats waiting expectantly for El Niño to arrive (I call this “waiting for el Ninot”, theatrically adapted from Waiting for Godot.

But El Niño has stubbornly resisted all entreaties to manifest itself like in the good old days of 1998 and even 2010. Now, again, the Nina3.4 index is rising into what on paper is El Niño territory so that those who feel the need, can proclaim that El Niño is here. But something is missing.

The problem is that the anchovy, the ENSO fish, does not seem to agree that El Niño is here. The latest on the Peruvian anchovy fishery can be found in the following article from the website “Undercurrent News” which gives up to the minute news on fisheries and fish markets around the world [link].

Last year, the abortive El Niño conditions pushed the Peruvian fishery authorities to suspend anchovy fishing due to fears that a developing El Niño could cause a decline in anchovy numbers that would make the fishery susceptible to over-fishing. The Peruvian anchovy fishery is closely managed, in the wake of the famous and spectacular crashes of the fishery in the 1970’s and especially in 1982-83 caused by a combination of a strong El Niño event and poorly managed massive seine-net over-fishing. Despite strengthened fishery management following those crashes, the record-breaking El Niño in 1997-1998 again hit the fishery hard with significant societal impacts for Peru.[link].

So early this year, in the month of January-February when an annually phase-locked El Niño by rights ought to occur, Peruvian fishery ministry survey boats tentatively checked out the anchovy fishery – how many shoals of anchovy were out there, and where? What they found was that in spite of all the feverish talk of El Niño, the anchovy fishery was in surprising rude health. This caused them to cancel a previously considered suspension of the whole fishing season (a relatively frequent occurrence for the anchovy fishermen of Peru) and allow a full quota season to proceed.

 Seine-net industral fishing for anchovy off Peru.

The news as of April 24 was that the fishing fleet was proceeding quite rapidly toward catching the entire season quota of anchoveta. However what is also interesting is what the fish meal market is doing. As mentioned in the introduction, the Peruvian anchovy dominates the global supply of prime fish meal and, as might be expected, China dominates the demand. When there is a discrepancy between what a commodity is expected to do and what it actually does, markets sometimes pause to take stock and see what will happen. Right now, contrary to predictions of the fishery being hit by the long-expected El Niño, the fishery is strong and sustaining high catch volumes. Since this will cause the price to decline, the market is anticipating this and holding back on prime fishmeal orders. In the words of a Peruvian exporter:

“We don’t want to take risks and close at a price now, as we don’t know the development of the fishing season. We hope to finish the fishing season in May, a month earlier than it is supposed to end, as catches are good so far.”

Of course, there is still the expectation of renewed surges of Kelvin waves and the final, long awaited epiphany of El Niño. This is causing uncertainty among those with an interest in the fishery since on the one hand, it is currently in robust health, but on the other, there is this ongoing expectation of el Niño crashing in to spoil the party.

Latest developments in ENSO and the anchovy fishery

This tension or contradiction continues into May between, on one hand, oceanographic conditions of warming in the East Pacific increasingly pointing to el Niño inception, and on the other, continued strong catches of anchovy off Peru indicating that the anchovy shoals are still being sustained by continued upwelling.

This is an interesting scenario since both of these cannot continue – either the building el Niño will choke off the Peruvian upwelling and anchovy numbers – or the upwelling will choke off the el Niño.

The latest ENSO conditions can be seen [here]. Without re-posting the individual figures from this page here (you can see them yourself at the above link) I would summarize the situation as follows:

• SST map shows warming equatorial east Pacific temperatures suggestive of el Niño development [link]
• However trade winds are for now holding up except in the far west Pacific where the winds are reversing to westerly [link]
• The equatorial upper-ocean heat anomaly for 180-100W seems to have peaked already and to be in decline [link]
• The Hovmoller diagrams of surface and subsurface temperature mapped against longitude in the x axis and date in the y axis, show that while at the surface the currently breaking Kelvin wave is at its high temperature peak, at depths of 55-155m the peak is past and temperatures are cooling again [link]
• The BoM Subsurface Pacific Ocean Equatorial Average Temperature and Anomalies at 150 meters, while red-hot in the mid equatorial Pacific, are still mixed at the Peruvian coast [link]
• Finally, the animated “Equatorial Pacific Sea Surface Temperature – 30 Days Including 7 Day Forecast” shows that cold temperatures are building seasonally up the west coast of southern South America, reflecting approaching winter in Antarctica.[link]

The point of this article is not a full analysis of current ENSO conditions. However one can speculate that the normal phase-locking of el Niño to Christmas or just after might be due to coincidence with the Antarctic high summer and a relaxation in the Peruvian upwelling driven by the Humbolt current from the south. Now it is already May and this Antarctic driven upwelling may be strengthening, implying that el Niño has “missed the boat” and will be cut short by this upwelling.

Turning to the anchovy fishery there have been two important recent news articles in Undercurrent News; first from May 6 [link]. This shows, as in April, continuing strong catch volumes of Peruvian anchovy so that the season’s fishery is still on course to land its full quota one month ahead of schedule. Indeed such is the strength of the anchovy landings that the article speculates on long term growth of the fishery as a whole. This is hardly what one expects in el Niño conditions.

Secondly from May 8 [link]. The ambiguous market response to this robust anchovy fishery, also continues. Clearly the big buyers of anchovy in China and elsewhere are being pulled by conflicting signals. On one hand the predictions of anchovy-busting el Niño become more and more shrill. But on the other the landed volumes continue as strong as ever. So for now the buyers are holding back, although there are signs that China could start buying this week.

Note BTW that the latest news of today, May 11: [link] looks downbeat but really refers to events of 2014, especially the cancellation of one entire anchovy season, due to weak el Nino like conditions last year. The fishery by contrast appears to have strengthened in early 2015.

In my view, the current continued strength of the anchovy fishery indicates that upwelling is still strong and yet to be fully interrupted by Kelvin waves and a nascent el Niño. The inception of a proper, full-on el Niño requires not just meteorological conditions or other surface factors, but a simultaneous development in the ocean currents and mixing, linked to the thermohaline ocean circulation, to entrain the Bjerknes feedback to trigger a pause in the upwelling. This could still be balanced between happening or not happening.

So who will win? El Niño, or the anchovy (representing Peruvian upwelling)? The next few weeks should tell us. Right now it seems too close to call.

Conclusion

My conclusion is just this – if we are interested in the ENSO status of the Pacific and what might lie ahead, where better to turn than the wise and all-knowing Engraulis ringens? It’s well worth checking out what’s happening with the Peruvian anchovy fishery before making pronouncements on the current or future status of ENSO.

JC note: The seasonal forecast models are once again very bullish for a strong El Nino by summer.  The Nino 1+2 (off the coast of South America) has been a bit slow to catch up with Nino 3+4, but the temperature anomalies are now warm in all of the tropical Pacific Nino regions [link].  While atmospheric westerly winds currently dominate only in the far west Pacific, over the past month westerlies have been more evident across the equatorial Pacific [link].

The forecast for a strong El Nino in summer 2014 went bust (see my El Nino post last year on April 14); what is different this year? Last year at this time, SST warm anomalies were enhanced throughout the whole north Pacific (preventing the Walker circulation from changing). SST anomalies this time around [link]  have trended to the canonical pattern (the blob in the North Pacific is diminishing).

From the looks of it, the Pacific seems overall less unusual this year and some sort of El Nino seems likely (although in a month I expect all this will be less ambiguous, and higher confidence in the forecasts initialized June 1).  If the El Nino forecast does go bust this year, it will be interesting to assess the wisdom of the anchovies.

Weird things have been going on the Pacific for the past almost two years, so I personally don’t have a lot of confidence in the seasonal forecast models right now particularly on the tail end of the spring predictability barrier.  Will be interesting to see how this plays out.

As with all guest posts, please keep your comments relevant and civil.