Email a Friend
Printer Friendly
Slashdot It!
Submit to Reddit
Add to Facebook

For sardine and anchovy, El Ni'�o events do not always have the same effects

March 01, 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 Ni'�o-La Ni'�a 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 Ni'�o 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 Ni'�o 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 Ni'�a, 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 Ni'�o, 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 Ni'�o 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 Ni'�o to a new cold La Ni'�a 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 Ni'�o episode and to the ability organisms have or have not of taking advantage of such a "loophole". Overall, the El Ni'�o 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 (Se'te, 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 Ni'�o 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.

Institut de Recherche pour le Développement, Paris (IRD)

Science Research Departments

	The Science Book: Everything You Need to Know About the World and How It Works (National Geographic) by National Geographic (Author), Marshall Brain (Foreword) A delight for the casual reader, yet so complete and wide-ranging that science buffs and students will welcome it, The Science Book encapsulates centuries of scientific thought in one richly illustrated volume. Natural phenomena, revolutionary inventions, and the most up-to-date investigations are explained in detailed text, and 2,000 vivid illustrationsincluding 3-D graphics and pictogramsmake the information even more accessible and amazing to discover. The Science Book offers both a general overview of topics for the browsing reader and more specific information for those seeking deeper insight into a particular subject. Six major sections, ranging from the universe and planet Earth to biology, chemistry, physics, and mathematics, encompass everything from microscopic life...
	Scientific Explorer's Mind Blowing Science Kit for Young Scientists by Scientific Explorer Mind blowing experiments to delight and educate young scientists! Erupt a color changing volcano. Mix up magic ooze with a mind of its own. Play with sand that never gets wet. Mix safe chemicals and watch colors change before your eyes. You'll amaze yourself and your friends as you explore the science behind these truly remarkable reactions.
	The Everything Kids' Science Experiments Book: Boil Ice, Float Water, Measure Gravity-Challenge the World Around You! (Everything Kids Series) by Tom Robinson (Author) Science has never been so easy - or so much fun! With The Everything Kids' Science Experiments Book, all you need to do is gather a few household items and you can recreate dozens of mind-blowing, kid-tested science experiments. High school science teach Tom Robinson shows you how to expand your scientific horizons - from biology to chemistry to physics to outer space. You'll discover answers to questions like: Is it possible to blow up a balloon without actually blowing into it? What is inside coins? Can a magnet ever be "turned off"? Do toilets always flush in the same direction? Can a swimming pool be cleaned with just the breath of one person? Get ready to enter the laboratory and learn how to conduct cool experiments, understand scientific terms...
	Science: The Definitive Visual Guide by DK Publishing (Author), Adam Hart-Davis (Editor), John Gribbin (Editor), Douglas Palmer (Editor), Jeremy Cherfas (Editor) This remarkable reference book tells the story of science from earliest times to the present day, taking in everything from ancient Greek geometry to quantum physics, and the wedge to the worldwide web. Exploring science in a thematic, highly approachable manner, each spread takes as its theme a specific event, discovery, invention, experiment, theory, or individual and explains why this subject was so significant in the development of scientific thought and what its impact on history has been. In addition to providing a broad-ranging and comprehensive history of science, the book also explains how science works, employing DK's trademark clarity and visual ingenuity to render tricky scientific subjects easily comprehensible. Science is structured chronologically with five...
	Be Amazing Lab-in-a-Bag Test Tube Wonders by Be Amazing Includes: Bag, test tube rack, giant plastic test tubes with lids, insta-snow powder, magic sand, energy beads, super absorbent crystals, coloring tablets, water gel and instructions.
	The Complete Book of Science, Grades 5-6 by Carson-Dellosa Publishing (Author) The Complete Book of Science for grades 5 to 6 teaches children important science skills! Children complete a variety of exercises that help them develop a number of skills in this 352 page workbook. Including a complete answer key this workbook features a user-friendly format perfect for browsing, research, and review. Over 4 million in print! The best-selling Complete Book series offers a full complement of instruction, activities, and information about a single topic or subject area. Containing over 30 titles and encompassing preschool to grade 8 this series helps children succeed in every subject area! ...
	Scientific Explorer's Disgusting Science - A Kit for Studying the Science of Revolting Things by Scientific Explorer What's grosser than gross' Disgusting Science is the grossest, gooiest, most revolting science kit out there. Grow your own friendly germs and fuzzy molds. Mix up a batch of coagulating fake blood. Even make a stinky intestine model. Learn the science behind sticky and icky bodily functions while doing some truly nasty experiments. Your little scientist will love this disgusting twist on regular science kits. All experiments are safe and kid-friendly.
	Science in Seconds for Kids: Over 100 Experiments You Can Do in Ten Minutes or Less by Jean Potter (Author) Make lightning in your room! Keep paper dry under water! Lose weight by going upstairs! See colors that aren’t there! Experience the magic of science with these quick, easy experiments and activities from Jean Potter. You can complete each activity in ten fun-filled minutes or less. Clear, step-by-step instructions and illustrations help you get it right every time. The projects help you learn about everything from why eggs aren’t round to how submarines surface and submerge. You will find most of the required materials already in your home, backyard, or neighborhood, and you can perform the experiments practically anywhere. The 108 activities in this book cover twelve different subject areas, including air, animals, energy, gravity, magnetism, light, the human body, and much more....
	One Minute Mysteries: 65 Short Mysteries You Solve With Science! by Eric Yoder (Author) Not an ordinary mystery book, One Minute Mysteries makes science fun! Each one-minute mystery (solutions included) exercises critical thinking skills while covering earth, space, life, physical, chemical, and general science. A bonus section includes five mysteries from our upcoming title in the series, One Minute Mysteries: Solve 'em with Math! This entertaining and educational book is great for kids, grown-ups, schools, educators, homeschoolers and anyone who loves good mysteries, good science, or both!
	Scientific Explorer's The Magic Science Wizard's Kit by Scientific Explorer Cast real smoke from your fingertips, make a wizard wand, and whip up color-changing potions in your test tube laboratory. Also included are laminated cards with magic tricks to baffle all your friends, an instruction booklet with 11 activities, lab equipment, and mysterious wizard powders that will mix together to mystify you!