19 février 2018 0 Commentaire

Why Do Tuna and Dolphin Swim Together?

Why Do Tuna and Dolphin Swim Together? Image de prévisualisation YouTube



Yellowfin tuna (Thunnus albacares) and spotted dolphins (Stenella attenuata) often swim together in the eastern tropical Pacific (ETP).   This fact has intrigued scientists for decades. A simple synopsis of current thinking  about this issue is detailed below (with figures).

There have been two leading hypotheses about why it happens:

  1. finding lunch (the feeding hypothesis), and
  2. avoiding becoming lunch (the predation hypothesis)

And there have also been many questions:

  • Why is it mostly yellowfin tuna and spotted dolphins who swim together?
  • What are benefits for each species?
  • Is the association necessary for either species?
  • Is the association permanent for either species?
  • Why does it usually happen in the ETP and not other oceans?

A new scientific paper spreads new light on dolphin-tuna associations (see abstract at bottom).  Michael Scott, one of the SDRP co-founders and a senior scientist at the Inter-American Tropical Tuna Commission, along with his co-authors have examined the most prominent hypotheses by tying together three studies:

  1. a simultaneous tracking study of spotted dolphins and yellowfin tuna
  2. a study comparing their prey and daily foraging patterns, and
  3. a study of the oceanographic features correlated with the tuna–dolphin associations.

Study Findings:

The tuna follow the dolphins, but the association is neither permanent nor obligatory.

The benefits of the association are not based on feeding advantages.  The dolphins and tuna tend to feed at different depths, at different times, and often on different prey.

The predation hypothesis was supported. One or both species likely gain protection from predators (such as large sharks) by forming large, mixed-species groups.

The yellowfin tuna also associate with spinner dolphins, although to a lesser degree than spotted dolphins.  The difference is influenced by the different swimming depths of the two dolphin species and the oceanography.

These associations occur under quite specific oceanographic conditions.

How Oceanography Influences the Tuna-Dolphin Association

Ocean Layers by depth, temperature, and dissolved Oxygen

Figure 1. Diagram of ocean layers that differ in depth, temperature, and amount of dissolved oxygen.

In most tropical oceans, there are warm, well-oxygenated waters at the surface called the mixed layer (Figure 1).  Underneath lies a thick layer of colder, oxygen-poor water called the Oxygen Minimum Zone.  Separating these two is the thermocline, a thin layer where the temperature drops rapidly.

What makes the ETP so unusual is that the warm mixed layer and the thermocline are much shallower than in most oceans (10 to 50 meters deep) and the Oxygen Minimum Zone is much thicker and more hypoxic.

eastern tropical Pacific

Figure 2. The eastern tropical Pacific showing the depth of the mixed layer as it deepens from east to west.

As one travels westward in the ETP, the mixed layer and the thermocline deepen (Figure 2).  When these depths reach about 50 meters, the association between the yellowfin tuna and spotted dolphin weakens).

These conditions are not unique to the ETP but  also occur in a few places in other oceans – the nearshore waters of West Africa and the northern Indian Ocean, for example – and yellowfin tuna have been reported to swim with dolphins in these same waters.   The association is most prevalent and consistent in the ETP however where these oceanic conditions are more widespread than in any other ocean.

How Swimming Depths Influence the Dolphin –Tuna Associations

The tuna-dolphin association appears to primarily form during the daytime. The tracking and food habits studies showed that spotted dolphins typically dive deep to feed on fishes and squids at night and travel 15-20 meters below the surface during the day (Figure 3).  The yellowfin tuna swim near the thermocline during the day.

Spotted dolphin and yelowfin tuna by time and depth

Figure 3. Simultaneous diving histories of a spotted dolphin (in orange) and a yellowfin tuna (in yellow). The thermocline depth (blue band) is about 45-50 meters.

The spinner dolphin (Stenella longirostris) is another dolphin species found in the ETP associating with tuna.  This is most likely because spinner dolphins, like the yellowfin tuna, join spotted dolphin herds during the day to reduce the risk of predation (by gaining safety in numbers).  Interestingly, it was the spinner dolphins that helped explain where the tuna-dolphin association can occur.

Spinner dolphins swim near the surface, and there is usually a substantial vertical difference compared with the tuna swimming near the thermocline. In some areas where the thermocline is very shallow, the yellowfin tuna associate with spinner dolphins without any spotted dolphins.

This suggests that the differences in the swimming depths of the three species, along with the depth of the thermocline  influence where the tuna dolphin association forms.  As the thermocline deepens, the vertical distance between the yellowfin tuna and the dolphins becomes too great to maintain the association.

As shown in Figure 4, when the thermocline is shallow (less than 25 meters), the yellowfin tuna may associate with both dolphin species.

When the thermocline is at a depth of 25m

Figure 4. When the thermocline is at a depth of 25m, the yellowfin tuna (bottom), swimming near the thermocline, associate with primarily with spotted dolphins (left), swimming at depths of 15-20 meters. The surface-swimming spinner dolphins (top) associate with both spotted dolphins and yellowfin tuna.

When the thermocline deepens, the vertical difference in swimming depth between the yellowfin tuna (near the thermocline) and spinner dolphins (near the surface) is too great to maintain the association directly.  At this depth, however, spinner and spotted dolphins still may associate during surfacing to breath, but only the deeper-swimming spotted dolphins associate with yellowfin tuna (Figure 5).

When the thermocline is at a depth of 45m

Figure 5. When the thermocline is at a depth of 45m, the yellowfin tuna (bottom) associate directly only with spotted dolphins (left). The spinner dolphins (top) associate still associate with the spotted dolphins and thus may be indirectly associated with the tuna.



When the thermocline sinks even deeper , the vertical difference in swimming depth between the yellowfin tuna (near the thermocline) and both spotted and spinner dolphins is too great to maintain an association (Figure 6).

When thermocline depth is 60m or greater

Figure 6. When the thermocline depth is 60m or greater, the yellowfin tuna associates with neither dolphin species. The spotted dolphins (left) and spinner dolphins (top) may still associate together. 

This Open Access article may be obtained  from the journal:

Scott, M.D, Chivers, S.J., Olson, R.J., Fiedler, P.C., Holland, K.  2012. Pelagic predator associations: tuna and dolphins in the eastern tropical Pacific Ocean Marine Ecology Progress Series 458:283–302,  or by downloading a pdf.

Questions about the study can be addressed to Michael Scott at mscott@iattc.org


27 décembre 2017 0 Commentaire

Documentaire Incroyable et Rare.

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Je vous le conseil vivement.

15 décembre 2017 0 Commentaire

3 Incredible Inventions That Are Cleaning Our Oceans



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Incroyable article :


Par Madame :


Carla Herreria


The research is clear: Man-made pollution is choking the oceans. From plastics that swirl around the world trashing beaches and killing marine animals, to chemical and oil spills that poison the sea, humans are to blame for much of the oceans’ deteriorating health.

Fortunately for our planet, some people have dedicated themselves to reversing mankind’s mistakes. In honor of World Oceans Day Thursday, HuffPost is highlighting groundbreaking inventions that were designed to take care of the sea.


While these solutions won’t entirely solve the world’s pollution problem ― real change can only happen when humans drastically change their consumption and plastic production habits ― the projects featured below are a good place to start.

1. This genius bucket that sucks trash and oil out of the sea

2. Boyan Slat’s ambitious plan to clean the Great Pacific Garbage Patch.

3. This technology that turns plastic waste into oil


14 décembre 2017 0 Commentaire

Un «trou» grand comme trois fois la Bretagne découvert en Antarctique

Un « trou » au milieu de l’Antarctique qui préoccupe les scientifiques. Une étendue d’eau de 80.000 km², soit trois fois la superficie de la Bretagne, a été découverte le mois dernier en pleine banquise dans la mer de Weddell, une partie de l’océan Austral presque entièrement recouverte de glace.

Un phénomène que les chercheurs peinent à expliquer. « C’est un trou assez remarquable », pour le physicien de l’atmosphère Kent Moore, professeur à l’université de Toronto à Mississauga. « C’est comme si on avait mis un coup de poing dans la glace », explique-t-il au site Motherboard.

 Si on n’avait pas de satellite, on ne saurait pas qu’il existe »

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Ces étendues d’eau entourées de glace sont appelées polynies. Elles peuvent être formées par des remontées d’eau chaude à la surface (notamment à cause des courants marins) ou par des vents, mais on les observe généralement près du littoral, note Kent Moore, alors que le phénomène qui intrigue actuellement les scientifiques est localisé loin dans la banquise. « C’est à des centaines de kilomètres de la lisière. Si on n’avait pas de satellite, on ne saurait pas qu’il existe ». Autre particularité : sa taille. Les polynies peuvent habituellement atteindre quelques centaines de km², très loin de ce « monstre » de 80.000 km².

Une polynie avait déjà été observée dans la même zone de la mer de Weddell dans les années 1970, que les moyens de l’époque n’avaient pas permis d’étudier de près, selon Kent Moore. Après avoir disparu pendant quarante ans, le « trou » est revenu l’an dernier pour quelques semaines. Puis de nouveau cette année.

Parmi les possibles causes de la formation de ce phénomène, l’hypothèse du réchauffement climatique est avancée, mais les chercheurs ne souhaitent pas tirer de conclusions prématurées. Les possibles conséquences sur l’océan Austral et le climat de l’Antarctique ne sont pas non plus connues. A ce stade, « on ne comprend pas vraiment l’impact à long terme qu’auront les polynies », avoue Kent Moore.


1 janvier 2018 0 Commentaire



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We must also learn to support others if we want to move forward

Ashley Cooper  runs https://lnkd.in/gXkumw8 the world’s only climate change photo agency. His book « Images From a Warming Planet » is out now and available from https://lnkd.in/gjvuyyR An art photographic book with foreword by Jonathon Porritt, it contains the best 500 images from the last fourteen years documenting the impacts of climate change on every continent on the planet.


Good Work ! Big Up.


12 novembre 2017 0 Commentaire

Green Chalenge Evenement – Membre du Jury – Casablanca Maroc

Green Chalenge Evenement – Membre du Jury – Casablanca Maroc
Green challenge
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Green challenge 2017, l’événement environnemental par excellence est aussi l’occasion de connaître et rencontrer des personnalités qui œuvrent dans la sensibilisation et l’éducation à l’environnement.

Inviter en tant que membre du jury pour juger les multiples travaux exposer par des bénévole pour l’environnement ( un geste pour l’environnement).

En collaboration avec l’association Vision Verte de Casablanca.


12 janvier 2017 0 Commentaire

Photo depuis ISS

Photo depuis ISS

Une partie de La Grande Barrière de corail photographiée à 400 km, par Thomas Pesquet depuis l’ISS.
Une merveille de la nature qu’il faut protéger.15894734_10154324002025838_6602906159027171878_n




14 décembre 2015 0 Commentaire

Omega Project -NASA- USA

Omega Project -NASA- USA
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The OMEGA photo-bioreactors float in seawater, and are filled with waste water, which is basically freshwater, and means that there is a salt gradient between the waste water inside the OMEGA and the surrounding seawater. We use this gradient to clean the waste water. Here’s how:

There are special water permeable membranes that selectively let water through and keep back almost everything else. This gives them some really interesting uses. For example, if we put one of these membranes between the two sides of a U-shaped tube, and we put salt in one side of the tube to form a concentrated salt solution called brine, the brine, which cannot pass through the membrane, forms a chemical gradient that pulls the water on the left side of the U-tube through the membrane into the brine on the right side of the tube. This process is called forward osmosis (or just osmosis).

Suite à une consultation des services de la NASA, j’ai pu répondre au développement de ce projet qui consiste a dépolluer l’eau de mer à l’aide d’un processus de filtration par les algues, j’étais consulter pour construire l’offshore qui serviras comme support en mer pour la dépollution

nommée ambassadeur de ce projet en nord de l’Afrique par le directeur Johnathan trent.


12 décembre 2015 0 Commentaire

Ateliers sur la plongée et l’exploration sous marine pour Enfants -CAF Francais- Maroc

Ateliers sur la plongée et l’exploration sous marine pour Enfants -CAF Francais- Maroc


Ateliers pour enfants CAF
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Ateliers pour enfants au sein du centre d’amitiés franco-marocain sis Casablanca .

Initiation à la biologie marine, l’exploration des fonds marins, et la plongée sous marine responsable, en protégeant l’environnement marin.

Reconnaissance globale des espèces rencontrés et leurs comportements.

12 février 2014 0 Commentaire

Ateliers Environnemental pour enfants-Institut Français – Maroc

Ateliers Environnemental pour enfants-Institut Français – Maroc
Atelier pour enfants Institut français
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Organisation d’ateliers pour enfants de l’institut Francais d’el Jadida au Maroc, avec la collaboration de la délégation Française dans le but de sensibiliser et répondre aux questions des enfants sur l’environnement, la mer, et le milieu marin.

Reçu d’abord en classe pour une présentation destinée aux enfants, puis organisation d’ateliers de jeux et de dessins pour établir un contact physique avec les enfants, pour les sensibiliser a la nature et a l’environnement marin.


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