Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

For sardine and anchovy, El Niño events do not always have the same effects

03.03.2005


Near the coasts of Peru and Chile, the Humboldt Current ecosystem is the world’s most productive fishing zone. This cold-current zone, with frequent coastal upwellings (2), occupies less than 1 % of the world’s ocean surface and provides 15 to 20 % of global maritime catches.



Unlike other large regions of upwelling, this ecosystem proves to be more exposed to variations in climate. Its geographical location brings it under the direct influence of disturbances generated by the El Niño-La Niña events which arise every 3 to 7 years.

Other climatic cycles, called El Viejo-La Vieja by reference to the first two, also bear influence, but on a longer time-scale with a period of about 50 years. Large-scale alternation of abundance of sardine and anchovy populations corresponds to these warm (El Viejo) and cold (La Vieja) climatic regimes. At smaller scale, the El Niño events would induce massive die-offs in anchovy, adapted to cold, nutrient-rich coastal waters, whereas the populations of sardine (and of other species like jack mackerel or mackerel), which live in the warmer waters, would experience an upsurge in numbers during or just after these episodes.


A recent study conducted by IRD researchers and their Peruvian partners (1) in this part of the Pacific, has called this traditional theory into question. Indeed, as there is no single type El Niño event, each one different in intensity, length and environmental consequences, pelagic fish would not have one single adaptive response to these events. In order to analyse these adaptive strategies and explain the fluctuations observed in sardine and anchovy populations, the scientists chose an overall approach. This took into account a whole range of available data: climatic, biological and ecological, at different time-scales (3). They put forward a hypothesis, based on the variations in habitat size for each species, to interpret the alternate fluctuations of anchovy and sardine populations at decadal scales, not only on inter-annual periods.

When the environmental conditions are generally cold (La Niña, La Vieja), the upsurge of deep-oceanic cold water, rich in nutrients, is intense. The size of the anchovy habitat increases in these conditions. In parallel, the frontal zone between the colder coastal waters and the warmer oceanic waters, highly suitable for sardine to develop, is pushed back towards the open waters. In the process, conditions become unfavourable for sardine again, especially so in that their larvae are dispersed towards nutrient-poor parts of the ocean.

However, when a warm climatic regime arrives (El Niño, El Viejo), upwelling becomes less effective, primary production diminishes, considerably reducing the habitat favouring anchovy, sometimes as far as making them disappear temporarily. The sardine habitat then extends towards the coast, giving the opportunity for their populations to grow.

The El Niño event of 1997-98 was one of the most powerful episodes of the XXth century, yet it had very little impact on anchovy populations of Peru. The research found that after this episode anchovy was abundant, suggesting the fish were able to adapt and exploit a “loophole” inside the prevailing conditions which were unfavourable to their development. When this episode began in 1997, upwellings persisted in some areas very close to the coast (about 1 km).

The anchovy populations, highly abundant at the time owing to the influence of a cold regime (La Vieja) exerted since the beginning of the 1990s, took refuge and aggregated in these small zones teeming with planktonic production. They are not subjected to any massive predation. The natural predators (sardine, jack mackerel, giant squid, birds, marine mammals) prove to be rare in such zones. Also the latter were protected from industrial-scale anchovy fishing, which was strictly limited by quotas and the obligation to practise beyond 5 nautical miles (about 9 km) from the coast (4).

Adult anchovy have therefore adapted to the changes in the environmental conditions, by extending their period of reproduction and staggering their egg-laying, so that the larvae have more chances to find favourable conditions again. That is what happened for the egg-laying periods of April and June 1998, performed just before the transition, which was exceptionally quick that year, of El Niño to a new cold La Niña period favourable for extending the habitat of anchovy.

The existence of this habitat “loophole” would therefore be the result of a combination of factors, linked in particular to the characteristics of this El Niño episode and to the ability organisms have or have not of taking advantage of such a “loophole”. Overall, the El Niño events would not seem systematically to be unfavourable for anchovy and favourable for sardine.

Marie Guillaume – DIC
Translation : Nicholas Flay

(1) This research work was carried out in a joint effort between the research unit UR ACTIVE, the IRD Centre de recherche halieutique méditerranéenne et tropicale (Sète, France) and the Instituto del Mar del Peru (IMARPE, La Punta Callao).

(2) upwelling: the transfer of cold deep-ocean waters, rich in nutrients, towards the ocean surface.

(3) These are: climatic fluctuations of the El Viejo-La Vieja type, of the intensity and duration of El Niño events, the state of fish populations before the event, of the natural and anthropogenic predation pressure (fishing), reproduction characteristics and the presence of local upwellings.

(4) Consequently, the anchovy have not been captured, nor integrated into fisheries statistics. The fishing effort has therefore been refocused on sardine. The abundance of anchovy has also been underestimated in assessments by acoustic methods, as the standard oceanographic research vessel cannot operate in the “loophole” habitat zones, situated too near the coast.

Marie Guillaume | alfa
Further information:
http://www.ird.fr/us/actualites/fiches/2005/fiche217.htm

More articles from Ecology, The Environment and Conservation:

nachricht Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel

nachricht Removing fossil fuel subsidies will not reduce CO2 emissions as much as hoped
08.02.2018 | International Institute for Applied Systems Analysis (IIASA)

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Attoseconds break into atomic interior

A newly developed laser technology has enabled physicists in the Laboratory for Attosecond Physics (jointly run by LMU Munich and the Max Planck Institute of Quantum Optics) to generate attosecond bursts of high-energy photons of unprecedented intensity. This has made it possible to observe the interaction of multiple photons in a single such pulse with electrons in the inner orbital shell of an atom.

In order to observe the ultrafast electron motion in the inner shells of atoms with short light pulses, the pulses must not only be ultrashort, but very...

Im Focus: Good vibrations feel the force

A group of researchers led by Andrea Cavalleri at the Max Planck Institute for Structure and Dynamics of Matter (MPSD) in Hamburg has demonstrated a new method enabling precise measurements of the interatomic forces that hold crystalline solids together. The paper Probing the Interatomic Potential of Solids by Strong-Field Nonlinear Phononics, published online in Nature, explains how a terahertz-frequency laser pulse can drive very large deformations of the crystal.

By measuring the highly unusual atomic trajectories under extreme electromagnetic transients, the MPSD group could reconstruct how rigid the atomic bonds are...

Im Focus: Developing reliable quantum computers

International research team makes important step on the path to solving certification problems

Quantum computers may one day solve algorithmic problems which even the biggest supercomputers today can’t manage. But how do you test a quantum computer to...

Im Focus: In best circles: First integrated circuit from self-assembled polymer

For the first time, a team of researchers at the Max-Planck Institute (MPI) for Polymer Research in Mainz, Germany, has succeeded in making an integrated circuit (IC) from just a monolayer of a semiconducting polymer via a bottom-up, self-assembly approach.

In the self-assembly process, the semiconducting polymer arranges itself into an ordered monolayer in a transistor. The transistors are binary switches used...

Im Focus: Demonstration of a single molecule piezoelectric effect

Breakthrough provides a new concept of the design of molecular motors, sensors and electricity generators at nanoscale

Researchers from the Institute of Organic Chemistry and Biochemistry of the CAS (IOCB Prague), Institute of Physics of the CAS (IP CAS) and Palacký University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on High Temperature Shape Memory Alloys (HTSMAs)

15.02.2018 | Event News

Aachen DC Grid Summit 2018

13.02.2018 | Event News

How Global Climate Policy Can Learn from the Energy Transition

12.02.2018 | Event News

 
Latest News

Basque researchers turn light upside down

23.02.2018 | Physics and Astronomy

Finnish research group discovers a new immune system regulator

23.02.2018 | Health and Medicine

Attoseconds break into atomic interior

23.02.2018 | Physics and Astronomy

VideoLinks
Science & Research
Overview of more VideoLinks >>>