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.

05.04.2005


The warm El Niño episodes are generally accepted to be harmful to the development of cold-water anchovy populations, but favourable for abundant populations of sardine, adapted to warmer waters. IRD researchers and their Peruvian partners (1) have been studying fluctuations in pelagic fish populations in the world’s richest oceanic ecosystems for fish, the Peru-Humboldt Current system, off Peru. They showed that the traditional explanation does not always hold true. During the 1997-98 El Niño event, one of the strongest of the XXth century, anchovy in fact adapted and reproduced by taking advantage of refuge habitat ‘loopholes’ located very close to the coast. The existence of these areas, with specifically different climatic conditions, appear to have favoured the survival of these populations in spite of generally unfavourable climatic conditions.



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.

Hélène Deval | EurekAlert!
Further information:
http://www.ird.fr

More articles from Ecology, The Environment and Conservation:

nachricht International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht World Water Day 2017: It doesn’t Always Have to Be Drinking Water – Using Wastewater as a Resource
17.03.2017 | ISOE - Institut für sozial-ökologische Forschung

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: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>