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 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: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Tiny microenvironments in the ocean hold clues to global nitrogen cycle

23.04.2018 | Earth Sciences

Joining metals without welding

23.04.2018 | Trade Fair News

Researchers illuminate the path to a new era of microelectronics

23.04.2018 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>