ASCLME Research Cruises

Where are those drifters?

2010-11-18T17:34:00.000+02:00

It's been some time (about a month) since we deployed the drifters from the Algoa - so let's see how they've been doing out there in the ocean!

NOAA's Physical Oceanography Division (PhOD) has a handy list of drifter ID numbers and their corresponding WMO ID# and the date, location and vessel from which they were deployed. Using this, we find the following:

ID# WMO# Date Lat Long Ship Manufacturer Type Program
70969 17517 2010/10/02 27 13.6S 037 43.4E ALGOA !Technocean SVPBD2 5325
70971 17519 2010/10/23 20 00.0S 054 01.9E ALGOA !Technocean SVPBD2 5325
70972 17681 2010/10/03 26 26.4S 042 11.8E ALGOA !Technocean SVPBD2 5325

(The other two buoys [70970,70973] are not in the system yet).

You can see from the model numbers (SVPBD2) that these have barometers on board - so more data is available from these buoys than just position and sea surface temperature. Very handy for meteorologists, too; these buoys were sent to us from the South African Weather Service.

The WMO ID numbers are used to track the buoys across the world; entering them into the drifter tracking page on the PhOD site, or on NOAA's OSMC site will let us track them. So let's have a look!

Here's 70969/17517, adopted by Indwe Secondary School and Bradley Elementary School, showing the track and SST:

(Try this link to re-generate an image; this will also give you the latest available results from the buoy)
Looks like it got sucked straight into the Agulhas Current - it will be interesting to see what happens to it now - will it spin off into the Atlantic, or travel through the Agulhas Retroflection and then eastwards across the Indian Ocean?

70971/17519 isn't available through the PhOD site yet, so here's a position plot courtesy of the OSMC site:

On the plot, you can see it's gradually heading south, offshore of the east coast of Madagascar. It'll be interesting to see how it travels from here!

Now let's see what happened to the buoy (70972/17681) the younger group of students from George adopted:

The most interesting plot so far! Looks like it's caught in some kind of eddy south west of Madagascar. The temperature plot looks more interesting too! Get the latest version here.

The Algoa will be heading off again in a week or so to deploy the Agulhas Return Current (ARC) mooring in partnership with NOAA - if your school or class would like to Adopt a Drifter, please fill out the adoption forms at NOAA's ADP website as soon as possible!

Jargon Buster! Episode 1 - Satellite Drifters

2010-09-30T17:36:00.000+02:00

All scientists regularly use all sorts of acronyms and jargon in their work and we sometimes assume everyone knows what they mean. Some of the acronyms don't mean all that much when spelt out in full either! I thought it would be a good idea to intersperse this cruise blog with "Jargon Buster" posts, which I hope will explain and illustrate some of these concepts. First up: Satellite Drifters!

Satellite Drifters

We've been talking about satellite drifters for several days now. So what are these things anyway?

Essentially, satellite drifters are oceanographic ("ocean studying") instruments that give us a good idea of how surface currents in the oceans move over long periods of time.To the left, you'll see a diagram of roughly what a drifter looks like, courtesy of NOAA's Adopt a Drifter Program (if you want a closer look, click on it!).

What does it do?
In addition to letting us know how ocean currents move (see the "Where is it now?" section below for information on how that works), all the drifters we deploy carry a sea surface temperature (SST) sensor, which measures the temperature of the water under the surface. Some of the drifters can also measure barometric (air) pressure, wind speed and direction, salinity and even ocean colour.

What's the design all about?

In the diagram above, you will have noticed a tube sticking out of the top of the buoy, then the buoy float itself; this tube is connected up to a barometer that measures air pressure (there was a time I though this was an antenna, but that's inside the main drifter buoy). If you're wondering why they're two-tone, the reddish part is actually anti-fouling paint to try and stop things like barnacles and seaweed from growing on the buoy, which may affect its accuracy (affect its drag), and if it gets bad enough, sink it! On the upper part of the buoy you can often see two stainless steel screws protruding (take a look at the image to the right); I once wondered if they were for checking battery charge, but they're actually submergence sensors that let the system know the drogue is still attached; other models have a strain sensor in the wire rope attachment under the float that performs the same function.

Below the float is a length of plastic-coated wire rope, which connects up the the blue section. The blue section with the holes in it is what we call a "holey sock drogue". The holey sock drogue is there to basically "anchor" the drifter into the water column; if the drifter just consisted of the buoy alone, it would mainly be influenced by the wind or surface wind-driven currents; we're much more interested in knowing what is happening with the water in the upper ocean as a whole, rather than where the wind is blowing! The horizontal lines you see on the drogue are essentially hula-hoops that hold the drogue's cylindrical shape open; the bottom one is weighted to make it sink, and the top one is often slightly buoyant to help the drogue stay upright in the water column. The holes act a bit like the dimples on a golf ball (they affect its drag and how it moves through the water) - essentially, they're there to "disrupt the formation of organised lee vortices". Huh? Picture a rock in a stream (or a bridge piling) and the mini whirlpools that form behind it; those little whirlpools are lee vortices, and in the case of a buoy (which isn't fixed in place like the bridge or rock) affect the drag (how easily the object can move through the water) - and affect the accuracy with which the buoy tracks the actual flow of ocean currents. The middle of this drogue is at about 15m below the surface of the water, so these instruments are pretty long!

New drifters have several biodegradable (I've often noticed that one of the first questions enquiring young minds in South Africa make about deployed oceanographic instruments concerns any pollution they may add to the oceans!) paper fixings that make them easier to handle; bands around the drogue make it easier and neater to deploy from the ship; a cardboard ring stops the wire rope from tangling and a small magnet paper taped on falls off once the buoy is in the water; this magnet activates a relay inside the buoy and is essentially an on/off switch that saves the battery power until the drifter is active.We remove the outer plastic wrap and the bulkier bits of cardboard and dispose of those back on land.

Inside the buoy you'd find some battery packs consisting of "D" cells, a radio transmitter and a some electronics that take care of the sea surface temperature measurements, monitor the submergence or tether strain sensor and translate this information into numeric data and beam this back through the ARGOS network to a data centre along with the drifter's unique ID number. I've often wanted to crack one open and take pictures of the innards, but I can't justify "wasting" a useful piece of scientific equipment like that. Hopefully, one day I'll get hold of an old one to "cross section", or we'll persuade the manufacturers to send us pictures of the innards!

Where is it now?

Whilst some satellite drifters have had a GPS or similar device on board to obtain and transmit their position (and most satellite drifter manufacturers offer it as an option), the satellite drifters we deploy do not use GPS (sincere apologies to everyone I've ever told that this is how it works!). The real method is even more interesting. The satellites transmit their data to a network of satellites known as ARGOS. The position is calculated based on the Doppler shift of the radio signal from the transmitter on the satellite drifter towards the orbiting satellite that receives the signal.

Not using GPS has two benefits; 1) it makes the drifters simpler and therefore cheaper and 2) it takes less battery power so the drifter can be smaller or use less batteries - or last longer for a given battery pack. Depending on the quality of the fix obtained, this non-GPS position finding can be accurate to within about 150m to 1,000m - more than accurate enough to track ocean currents.

If you're not familiar with Doppler shift, think about the last time a police car, fire truck or ambulance drove past you; you may have noticed that the apparent pitch ("tone" or "note") of the sound went up as it came towards you, and then rapidly went down as it went away from you. Even a car's exhaust sound will show this effect (neeeeeeeiiiiiyeeeeeeuuuuurrrr!). This also happens with electromagnetic radiation like light and radio waves; the "red shift" of stars observed by astronomers suggests the universe is expanding (the stars are travelling away from each other and their light "shifts" to a redder [longer wavelength] spectrum; if a star was coming closer to you, its spectrum would shift towards the blue [shorter wavelength]) - and in the case of the drifters, the apparent frequency of the radio signal increases and then decreases as the satellite moves towards the drifter and past it. Coupled with some nifty maths and (well founded) assumptions about the shape of the earth, you can quite accurately work out the transmitter's position; depending on how confident the system is about the quality of the position data, it will be tagged to let the data centre know how reliable the position fix is.

This Doppler Shift-based location calculation is nicely illustrated on their site here. Everything you could possibly want to know about ARGOS is covered in their extensive manual.

How much do they cost?
The basic Surface Velocity Program (SVP) drifter with Sea Surface Temperature probe are about US$1,500 for one. More complex models cost more, depending on what instruments they have on board, up to around US$3,000 or more for extra features.

Why?
Why do we deploy drifters anyway? And why do they measure sea surface temperature (SST)? Great questions!

First the drifters themselves. Being more or less "anchored" in position with the water mass they're tracking by their drogues, the drifters track the movement of ocean water below the surface without being overly influenced by wind. Over time, lots and lots of observed drifter "tracks" let us build up a detailed picture of how the oceans move, and we're beginning to better understand just how complex some of these currents can be (click on the picture of the drifter tracks further up the page for a closer look). And, unlike a research vessel, which can cost tens of thousands of dollars a day to keep at sea, a drifter will send us data for over a year for around $1,500 (more complex drifters are more expensive). Clearly, if we're going to understand much about the oceans at all, we need to understand how the water moves - so knowing the surface currents is an important first step. The global Surface Velocity Program aims to have at least one drifter in every 5ºx5º grid of the ocean - a global network of 1,250 drifters active at any time.

Secondly, SST. Sea Surface Temperature, if you haven't already worked it out, it the temperature of the seawater near the surface of the ocean. The buoy has a small thermistor (a temperature measuring device that works by measuring the [known] change in resistance of an electrical circuit due to temperature fluctuations) poking out from the underside of the float. This device accurately measures SST. We can also measure SST from space using remote sensing (a topic of a later Jargon Buster!), but this data needs calibration, and in situ ("on the ground" / "in place") temperature sensors like the drifters are invaluable for calculating the calibration and correction factors for satellite SST data; this process is sometimes also referred to as "ground truthing". Remote sensing also doesn't work very well when there is cloud cover, so it helps us "fill in the gaps" when there is heavy cloud obscuring our view of the ocean from space. Temperature is one of the most easily measured ocean water parameters, and with enough readings from all over the globe, gives us much useful information about how much and how quickly heat travels around the planet (vital in predicting weather and understanding climate).

If you'd like to see the kind of results you can get by combining a lot of drifter measurements like this, take a look at this illustration over at the Physical Oceanography Division of NOAA's Atlantic Oceanographic and Meteorological Laboratory.

If you're wondering where all the drifters are, here's a picture, again courtesy of NOAA:

Learn more

Visit NOAA's Adopt a Drifter Program to learn how your school or class could adopt a satellite drifter and use the same data that scientists use to learn more about the ocean.
A very comprehensive overview of the global drifter programme is available from here; it will also tell you in detail about the small errors and inaccuracies in the data.
A list of all drifter deployments and model types, and where,when and by what ship they were deployed.

If you'd like to make any comments on any of the blog posts, you can do so with the links below each post, or feel free to contact me through the ASCLME website here.

Some clarifications

2010-09-29T18:56:00.000+02:00

Just in case anyone wants some clarification on some of the points in the previous post that might be a little off (probably more my fault for throwing out far too much information for one day than anything else!):

The ear bones are called "otoliths" and are very useful in determining the age of fishes, particularly in temperate waters; in tropical waters they are often less useful - but the analogy to rings in a tree trunk is pretty apt! Some fishes also deposit growth rings on their scales, but these are generally less reliable. Fishes that live in waters where the temperature varies little throughout the year (like the tropics!) have much less pronounced "rings" on their otoliths that those that live in regions with marked seasonal temperature changes, so interpreting tropical otoliths is much more challenging. Using the right techniques, you can sometimes even see how many days a fish has been alive for. It's important to verify this ageing method; scientists who want to verify the accuracy of this ageing technique in a particular species will often tag a (living) fish for later identification and inject the fish with an antibiotic called tetracycline, which permanently stains the otolith in a ring on the day it is injected. The fish is then released, and when it is recaptured, the otolith is examined under UV light, which causes a prominent glow in the stained ring on the otolith and allows you to verify how regularly bands are deposited.

With regards to the bioluminescent bacteria in anglerfishes, the anglerfish supply nutrients to the symbiotic bacteria that live in their "lures", and the bacteria use this to grow, reproduce and - of course - produce light. The luminescent chemicals are all contained within the bacteria; they are similar to the luciferin and luciferase system you may be familiar with from fireflies (and those "snap" glow sticks).
Many dinoflagellate algae produce bioluminescence too - not to attract prey as in the anglerfishes, but instead to attract predators to eat would-be dinoflagellate predators, or perhaps to confuse potential dinoflagellate predators with a burst of light.

Chlorophyll a is one of the most important photosynthetic pigments in plants. In a device called a "fluorometer", commonly attached to a CTD, pulses of UV light excite chlorophyll a in marine algae within the water column; during the time the light is off, a sensor measures the amount of red light given off by the chlorophyll as it returns from its "excited" state to its "resting" state. This gives a measure of the amount of chlorophyll a in the water, and a measure for the productivity of that water (how much plant matter - and therefore food - is available to the ecosystem in that area). You can find some simple experiments (and pictures) with extracting chlorophyll and seeing this effect at this link. Keep the mixtures as cold as you can, and in the dark if you're not using them, as the chlorophyll quickly degrades otherwise. If you don't have a centrifuge (who does at home!?) you can pour the mashed up residue through a filter paper (a paper coffee filter works nicely). A little bit of sand helps to macerate the tissue when you're grinding it up.

Our young researcher slightly exaggerated the numbers of fish species in the sea; the Census of Marine Life estimates that there may be as many as 20,000 species of marine fishes (over 15,000 are currently described), and around 160 species of fish are described (identified and given a scientific ["latin"] name) every year. Including freshwater fish species, there are well over 30,000 species in the world.

The deepest part of the ocean is Challenger Deep in the Marianas Trench, which is around 11,000m deep; on average, the oceans are about 2,000m deep. Humans have been to the bottom once, in 1960 in a vessel called the Trieste. No manned vehicle currently exists that can make it to that depth safely. The highest mountain on earth, Everest, is currently measured at 8,848m above sea level.

He's quite correct about the "Mozambique Current" not existing as a strong western boundary current as it is still represented in school textbooks (and old oceanography ones too!). Since around about 2002/2003, more and more evidence has been mounting that the current flow in the Mozambique Channel actually consists of a series of anticyclonic eddies, which give the illusion of a strong southward-flowing current along the Mozambique coastline. At some stage, these eddies merge with the Agulhas Current, which flows down South Africa's east coast. It appears that when these eddies join the Agulhas Current, they cause events known as Agulhas Pulses and may also be responsible for the shedding of Aghulas Rings, which take warm, salty water up as far as the North Atlantic, and may influence climate and weather globally. In addition to remotely sensed data of sea surface temperature, mesoscale satellite altimetry and ocean colour, a series of moorings, known as LOCO, have been extremely important in learning more about these eddies and the flow in the channel. Satellite drifters (see picture to left) have also been instrumental in providing very obvious data on just how circuitous the flow in the channel can be. One of Algoa's objectives on this cruise, together with partners from the Royal Netherlands Institute for Sea Research (NIOZ) in the Netherlands, is to service this array and extend it out from the south east corner of Madagascar. If you're interested in the region's oceanography, Professor Lutjeharms wrote us a very comprehensive overview of it for the ASCLME website when the Project began. We're learning more and more about this surprisingly dynamic part of the world's oceans, and its vital role in the global weather and climate is increasing the amount of interest (and important international research partnerships) in the region.

Coelacanths are indeed found near Sodwana Bay near the South Africa's border with Mozambique. This discovery by a group of SCUBA divers spurred the creation of Phase I of the African Coelacanth Ecosystem Programme (ACEP) and then Phase II of the Programme, who are important partners of the ASCLME Project.

Life on the Algoa - according to a student.

2010-09-29T18:29:00.000+02:00

One of the young students from George asked me for some paper to write down some of what he had learnt during his day on the Algoa - bearing in mind he'd been awake since early that morning and was writing this quite late at night, I was very impressed with what he remembered. You can click on the picture to the left to read it yourself; I've transcribed it below for easier reading. I think I would also like to have my job title officially changed to the one he gave me in the first sentence! I've tried to retain the formatting and spelling as is:

Life on the Algoa, 25 September 2010

When we got on the ship there was a warm welcoming by James the expert of the ocean. First there was a tour of the ship and after that we had some breakfast after that we went ot the front deck where James explained to us more about the ocean and different things that exists these are some of the questions and answers that went out:
How do you tell the age of a fish?
Inside the ear of the fish if you open it up you will see that there are rings similar to those produced by trees each ring represents a year of life

How do anglerfish provide energy for the light on theire heads?
The anglerfish do not produce the energy it's actually bacteria that mixes with chemicals in the water and when they react to each other it produces light

Some children got sea sick and had to leave for theire cabbins while the rest of us whent to see everything in the bridge
first of all there is everything and more that you whould expect to see like radars, charts, radios etc.
We learned about the chlorofil of plants in the sea and we also learend about the eye and how light travels through the eye.
There is also a trawler on the ship with huge nets that they use to catch fish with and sort them out to do some research on the species and to varify the population and sex of the fish. There are over 3 million fish species in the world and only about 150,000 are descovered each year and we know so few of the ocean and did you know that the deepest depth of the ocean is about 2 kilometres straight down to earth
The famous Mozambique current does not exist and the reason people think that there is a current is because of the eddy's which turn in an anti-clockwise mosion and spirals down the coasts making the elusion of of a current
The part I did not mention was that the chlorofil in the ocean plants can redirect the uv-light say for instance you take a uv-flashlight and shine it at the plant ant take it away it would glow
Our current speed is ten nots which is basically 18 klilomitres an hour earlier we spotted some humpback whales and the were just slapping the water like crazy and splashing and playing in the water we watches a slide show on some of the previos research toures where the whent to Sodwana bay and actually found sealacamps the fish that every one thought was extinct

I was impressed with how much of the overwhelming amount of information he remembered during a very long day - with a bout of seasickness to overcome too!

As we were saying goodbye at the harbour in Port Elizabeth, the same young scholar told me as he came running past "You must keep studying the oceans, it's too interesting and important!" - motivation indeed!

In the next post, I'll clarify some of these points for your interest.

Satellite drifters

2010-09-26T20:56:00.000+02:00

We sailed into Mossel Bay this morning around 8am, and quickly swapped the students from Indwe Secondary School with a group of younger students from several schools around George.

We're currently about to sail past the Knysna Heads here.

After breakfast this morning, most of the Indwe Secondary School students were feeling a little better, so I took a drifter (70969) out of storage and very quickly explained how it works - time was pressed as they had to get off shortly thereafter. The students applied the NOAA stickers they had earlier signed, together with one from Bradley Elementary School in the USA.

We had thought about actually deploying the drifter on this leg, but we stayed fairly close inshore on our leg to Mossel Bay, never much more than 15 Nautical Miles from land; the Captain and the scientists I spoke to thoughtt the drifter was most likely to wash up ashore within a few days that close to land, which wouldn't be a very exciting deployment for the students to follow! My colleague, Tommy Bornman, will ensure that the 5 drifters we put aboard are deployed in the Mozambique Channel as they cross towards Madagascar, or along the southern coast of Madagascar. The drifter may end up entrained in one of the Mozambique Channel eddies, and that will certainly be interesting to follow!

The new group of students and I spent most of the morning on the foredeck in glorious sunshine, with the students and teachers asking me questions about all sorts of aspects of ocean science and life in the sea and on board boats, ranging from how does a boat float, to what happens to the oil in a ship if it sinks or catches fire, the effects of the Horizon Deep oil spill and we even covered some genetics, life history strategies (including a brief foray into the world of intra-uterine cannibalism, as seen in a fairly common shark species (the ragged tooth or sandtiger shark) and evolutionary biology!

In a short while, we'll see who feels up to touring the bridge; we're promised some rough weather a bit later, with a 30 knot wind, which will definitely give us a bit of a wild ride until we reach the shelter of Algoa Bay, which will be around 3am this morning; we'll start docking procedures into Port Elizabeth around 7am.

(This post was written several hours ago - I've been waiting for a cellphone signal before being able to post it!).

Underway - and some pictures

2010-09-25T14:44:00.000+02:00

FRS Algoa in Cape Town Harbour

We're currently sailing along here, just outside False Bay, having passed Cape Point a little while ago.


Cape Point

Students from Indwe Secondary School, Mossel Bay.

If I can inspire this much excitement for marine science, I'll be doing well! It looks like the Soccer World Cup in South Africa really made an impression. Here the students have spotted the impressive Green Point soccer stadium.

Setting Sail

2010-09-25T10:53:00.000+02:00

After some difficulties persuading the gate guard to let our little group into the harbour, we finally got everyone on board at around 8:45, before setting sail at 9.

After a brief talk in the mess (dining room), and watching the Algoa depart Cape Town harbour, it was time for a quick life jacket drill so everyone knows where their lifejackets are and which life rafts they are assigned to, along with some basic safety on board. Unfortunately, by this time, many of our young colleagues were feeling the gentle heaving of the ship and were looking a little under the weather.

As I type this, the rest of Algoa's guests are in their cabins, waiting for some seasickness medication to have a chance to act, so I thought I'd take the time out to update the blog.

After lunch, we'll tour the bridge, so the students can see how the ship is controlled and navigated.

At around 3PM, we'll be deploying a satellite drifter, so the students can see first hand how we deploy these very useful pieces of scientific equipment. We'll be launching another one between Mossel Bay and Port Elizabeth, and have another 3 that will be deployed later on as the vessel crosses the Mozambique Channel.

If the students are up to it later, I'll introduce them to you! Once I find my camera data cable, I'll add some pictures too.

2010 Mooring Cruise

2010-09-24T21:30:00.000+02:00

I'm sitting on the FRS Algoa in Cape Town Harbour, having enjoyed a braai on the trawl deck during Heritage Day! Tomorrow morning at around 9am, the ship will leave the harbour and make its way towards Mossel Bay.

On board will be several high school students from the Mossel Bay and several teachers, who will experience first hand a little of what life is like aboard a research vessel, and learn why we go to sea aboard in the first place. In Mossel Bay, we'll give some more students and teachers from George a chance to do the same thing, before the ship docks in Port Elizabeth.

From Port Elizabeth, the Algoa will travel northwards towards Toamasina in Madagascar. To the North of there lie a series of moorings which the ASCLME Project deployed in partnership with NOAA in 2008. These ATLAS mooring buoys need regular maintenance. Unfortunately, they lie in the "High Risk" Piracy zone of the Indian Ocean, so the Algoa will be escorted by a Seychelles Coast Guard vessel during that leg. If we can make updates whilst up that way, please note we won't be giving detailed activity notes as it represents a security risk to do so!

On the way to Toamasina, in partnership with Dutch researchers, we deploying some LOCO moorings, which measure ocean currents and have already helped us to understand the complex flow patterns in the Mozambique Channel; we'll be extending this array of moorings off southeastern Madagascar.

The students and teachers on board are taking part in NOAA's "Adopt a Drifter" Program, which pairs students from a school in the USA and a school overseas (South Africa in this case), who jointly "adopt" a satellite drifter, and use this as an opportunity to learn more about the oceans and how they function - using the same data scientists use, following their drifting buoy in near-real time as it journeys across the ocean. I'll be on hand to explain what the ship is used for, some of the instrumentation on board and why it's important to do this kind of research.

It looks like we'll be in for some rough weather...

I'll post another update tomorrow.

The 2009 Seamounts Cruise Blog

2009-12-03T17:05:00.000+02:00

The IUCN-led Seamounts Project, funded by the GEF, is also undertaking cruises aboard the Dr. Fridtjof Nansen. Rather have our readers go to two places for information on this joint ASCLME/Seamounts Project Cruise, we've decided to redirect you to out partner's blog - so, for more information on this exciting expedition, please visit the 2009 Seamounts Cruise Blog. This blog is also being syndicated by BBC News on their Earth News section.

Reception and Good-Bye Comoros

2009-11-02T18:48:00.000+02:00

After a successful completion of the cruise, we have arrived back in the Comoros, this time at Anjouan Island (Nzwani). The day has been busy with a reception of local and national heads of government, local heads of commerce, UNDP and ASCLME delegates as well as the press. After the welcomes, meetings and speeches on the island, the group joined the Research vessel for a tour of the ship and a closer inspection of the equipment, work and samples that have kept the scientists busy for the past month. As a big surprise to everyone, the president of the Union of the Comoros, his excellency Mr Ahmed Abdallah M. Sambialso also graced us with his presence. The atmosphere was congenial and many discussions were held.

Now, the time has come to conclude this cruise. Most of us will leave the vessel tomorrow morning and scatter back to our places of origin to work up and start analysing the miriad of collected samples. After that the Dr Fridjof Nansen will continue on to La Reunion ... to start a new collaborative cruise (with the IUCN) on seamounts.

Zooplankton distribution (some results)

2009-11-02T17:54:00.000+02:00

Preliminary results suggest that mesozooplankton biomass was highly variable throughout the survey and ranged from 11 to 94 mg /m^3. Total zooplankton wetmass was highest south-east of the Comoros and lowest south west of the islands (see below). Spatially this pattern coincided closely with the position of a cyclonic and anti-cyclonic eddie in the vicinity of the Comoros.

As in previous cruises in the region, the horizontal (geographical) distribution of zooplankton suggests that warm-core eddies contain overall very little zooplankton when compared to cold-core eddies and frontal boundary regions. While this result needs to be reinvestigated once updated altimetry data is available, current data suggest that zooplankton biomass increases drastically outside of the warm-core eddies.

The predominant taxa in the smaller size fractions from most stations were:

280μm – 500μm: copepods (also some gastropods, ostracods and amphipods)
500μm – 1mm: copepods (also some amphipods, ostracods and euphausiid nauplii)
1mm – 2mm: small euphausiids and chaetognaths (also some large copepods, amphipods, decapods)

The larger size fractions were more variable in composition, with euphausids, decapods, fish larvae and gelatinous zooplankton making up the bulk of the biomass. These larger size fractions of the zooplankton tended to make up a large proportion of the total biomass only during night-time stations.

Further and more detailed analysis of the multinet samples and the 180um Bongo samples is still outstanding and cannot yet be commented on.

Juvenile stages of coastal fish (some results)

2009-10-31T22:56:00.000+02:00

With all the surface trawls having been completed, we have had a preliminary look at some of our data on juvenile fish stages. During a total of 19 trawls, some 151 taxa were distinguished, photographed and prepared for bar-coding and identification. The taxa ranged from species with potential commercial importance such as scombrids (2 or 3 tuna species), anchovies and carangids (10 kingfish species) to coral reef inhabitants such as parrot fish, rock cods and surgeon fishes. To get an idea of the variety of forms and colours, click on the image below. Any guessed on the species in question? Some are easier to associate to their families than others. If you get it right, we will let you know once identification has been completed.

In terms of juvenile species richness (number of species), distribution and abundance the current cruise data must be interpreted with great care. The number of trawls was relatively low and no attempts have yet been made to link our sample compositions to the physical environment. In order to strengthen the data, samples from previous ASCLME cruises as well as upcoming regional cruises need to be added to the analysis. Nonetheless some patterns do seem to emerge (but for now, need to be treated with a pinch or salt).
The number of species caught in each trawl did not vary dramatically between locations (see below). On average 21 species were distinguished per trawl. The fact that this is only a tiny fraction of the total number of species identified, suggests that we have either seriously under sampled (likely) or that different species are found in different localities (apparently true in some cases). Only a more complete analysis of all data sets will allow for a less subjective interpretation.
While the number of taxa collected show little variation between locations, the number of individuals per unit water volume vary more dramatically (see below). The highest densities of juveniles were generally caught along the Madagasi shelf, with fewer being observed in the Comoros region and the lowest overall abundances along the Mozambique coast. Again, additional samples need to be added to this analysis to see whether this pattern stands up to scrutiny.
The juveniles caught during this cruise will add to a regional juvenile identification guide, will allow us to better understand larval and juvenile origins and dispersal (with the help of genetics) and should eventually allow for more informed regional management strategies (pertaining to commercial fisheries as well as coastal ecosystem health).

Cruise Progress: 30 October 2009

2009-10-31T05:56:00.000+02:00

We are now on our last transect off the Mozambique Coast and are slowly making our way back to the Comoros. The past ten days have kept everyone on board occupied with continuous physical, chemical and biological sampling. Since the beginning of the cruise, some 136 CTD and 46 full biological stations have been completed. In addition, one demersal, three mesopelagic and 16 surface trawls were undertaken (see map for CTD stations).

As we are slowly coming towards the end of this cruise, data is being transcribed, the first analyses are being conducted and reports are being prepared. We hope to be able to present at least some preliminary findings before we leave the ship next week.

Cruise progress: 19 October 2009

2009-10-21T01:44:00.000+02:00

As of yesterday 19th October, transects 10, 3 and 2 have been completed (see also map, blog entry 9-Oct-2009)! Due to some delays with national research permits, more time that anticipated was initially spent in the close vicinity of the Comoros islands. Nonetheless, since then, the first three transects have been completed and we are now on our way back to the islands while undertaking stations on transect 3. To date, physical, chemical and chlorophyll measurements have been obtained at some 39 stations and full environmental stations (incl. zooplankton and phytoplankton collection) at 19 locations. Additionally, one demersal trawl was carried out south of Grande Comore and a total of 12 surface and meso-pelagic trawls.
With the exception of some rough weather and swell after rounding the northern tip of Madagascar, conditions for sampling have so far been favourable. During the latter transect, multi-net deployments were deemed too risky.

The sound of (sound) waves: What is fisheries acoustics?

2009-10-19T15:05:00.000+02:00

Fisheries acoustics rely on the physics of sound travelling through water to quantify the distribution of biota in the water column. By sending a signal of a given frequency through the water column and recording the time of travel and the strength of the reflected signal, it is possible to determine the size and location of fish and estimate biomass from the acoustic backscatter. The intensity of the returning echo is a measure of the target strength of a given individual at a particular sound frequency. As a fisheries assessment tool, fisheries acoustics technology is an efficient, non-intrusive method of mapping the water column at a very fine spatial and temporal resolution. It provides a practical alternative to bottom and mid-water trawls. However, validation of fish targets is an essential part of interpreting the acoustic signal for any given location. Output from acoustic surveys can be mapped in relation to bottom habitat type, bathymetry, temperature, time of day etc. The ability to census aquatic organisms are more difficult in deep water as many fish species here lack a swimbladder – the major acoustic reflector in most shelf species.
In its most direct form, we could say that fisheries acoustic produces relative information on size distribution of targets, numbers of organisms in the water column, and estimates of biomass, based on the physical properties of sound traveling through water. However, there are many factors that limit the confidence with which this information can be interpreted into accurate measures of absolute numbers of fish, fish lengths and total biomass.

Acoustic surveys onboard Dr Fridtjof Nansen
Dr Fridtjof Nansen uses ER-60 echo sounders (with ER-60 software) and LSSS (“Large scale survey system”, also called “El-triple-S”) for scrutinizing of echoes. The acoustic transducer is attached to an adjustable keel that can be lowered in rough weather to avoid the damping effect of bubbles. Echo intensities per nautical mile are integrated continuously, and mean values per 1 nautical mile are recorded for mapping and further calculations. The echograms, with their corresponding sA-values, are scrutinized every day. Contributions from the seabed, false echoes, and noise are deleted.
The acoustic survey has been carried out by zigzagging between 50 and 500 meters bottom depth around the Islands, as well as along all the transects (north-south, west-east and oblique transects). Four frequencies are being used (18, 38, 120 and 200 kHz). The survey will target firstly plankton, mesopelagic fish and pelagic fish aggregates. Secondly, the dynamics of the migrating scattering layer and the pelagic layer communities will also be studied in more detail using fisheries acoustic and multinet trawling.
The corrected values for integrated echo intensity are allocated to species according to the trace pattern of the echograms and the composition of the trawl catches. Data from pelagic trawl hauls and bottom trawl hauls considered representative for the pelagic component of the stocks, which is measured acoustically, will be included in the stock abundance calculations.
The echo sounders are watched continuously, and trawl hauls in addition to the predetermined hauls are carried out whenever the recordings change their characteristics and/or the need for biological data makes it necessary. Trawling is thus carried out both for identification purposes and to obtain biological observations, i.e., length, weight, maturity stage, stomach data, and age.

So far the R/V Dr Fridtjof Nansen has undertaken acoustics transects around the 3 Island of the Comoros and Mayotte to determine the distribution and abundance of small pelagic fish shoals. Mid-water trawls have been used on fish aggregations to determine species and size composition. However, very few pelagic shoals have been recorded. Schools of fish have been observed in the surface a couple of times, and we have tried to catch them by rod fishing, but so far with little success. These fish aggregations have not been recorded acoustically either. The reason for this could either be that they are too close to the surface (the echo-sounder can only record fish deeper than 6 m depth, or that the fish swim fast and/or actively avoid the research vessel. Strong scatters of mesopelagic fish have been recorded, but no schools which resemble commercially important species.
The conclusion is that there are very few fish in this area. We keep an eye on the echo-sounder all the time and we will conduct pelagic trawling whenever we see any acoustic signals that are strong enough to suggest higher fish abundance.

author: Katherine Michalsen (Norwegian cruise leader); image: Pascal Cotel.
We also made a post about Acoustic Surveys last year with some other details - take a look at this post on acoustic surveys.

Trainees and participants continued ...

2009-10-19T13:46:00.000+02:00

Soifa Ahamed Soilihi, I am a former student of the University of Tuléar, Madagascar. After my Master's degree I became Conservationist Agent in the non-governmental organization A.I.D.E (Association of Intervention for the Development and the Environment) in the Comoros. I am the national focal point for Coral reef monitoring. After training in the taxonomy of Holothuridae in the Royal Museum of Central Africa (MRAC) in Belgium, I am now in charge of the research unit for Holothuridae, at the mini laboratory of marine biology of INRAPE with the cooperation of the conservatory of the CNDRS museum in the Comoros.
During this ASCLME cruise, I have gotten a big passion for the marine environment, its biodiversity and the importance of every category: the phytoplankton, zooplankton, fishes and finally the big marine mammals. The necessity of having many researchers in the marine environment is a priority for every country and much more for us the island countries.
My passion, led me to resume my studies and to move towards scientific research of marine environments. I followed two Oceanographic training courses, at MARE (Cape Town) organized by the ASCLME project and at ORI (Durban) organized by the SWIOFP project. Now, I would like to proceed with longer term research projects.

Life onboard the Nansen provides comfort and a productive work environment within a well established and respected program. Every day, the work becomes more familiar and routine. We are working with a focused enthusiasm which one rarely encounters on land. I hope that the ASCLME project will continue to be a key to open opportunities for research on the marine environment for all the countries in this region.

Nicolas Rascle completed his PhD in Brest, France, on the drift of materials at the ocean surface. He then moved to the University of Cape Town 10 months ago to undertake a postdoctoral research on general ocean circulation and its link to the earth’s climate. His research interests include all the physical properties of the ocean near the surface: the temperature, the salinity, the turbulence, the waves… Passionate about diving and spear-fishing, this cruise is also an opportunity for him to gain experience in biological oceanography and fisheries related research. And, as soon as the captain authorizes it, to put on the snorkel and look at what is going on down there.

Trainees and participants continued ...

2009-10-16T15:45:00.000+02:00

Jaffar Mouhiddine has a MSc in oceanography, is a teacher and research scientist at the Ministry of Education of Anjouan, Comoros. He is also a member of the national center for scientific documentation and research (CNDRS) of Anjouan. In 2004, he was part of his first cruise, conducting research on the Coelacanth. He attended the ASCLME and SWIOFP training course in South Africa in June / July 2009 because he wants to undertake a PhD thesis on Comoran fisheries. This cruise will give him a lot of experience on the fishes and on the general food web of Comoran waters. He also hopes to be part of the identification and treatment of the samples taken during this cruise, which could help him with his research. Presently, the Comoros are lacking knowledge on fish identification and on fisheries management. He would thus like to gain experience among experienced scientist in South Africa and transfer knowledge back to the young university of the Comoros. E-mail address: jaffar_mouhhidine@yahoo.fr

Kate Munnik is a MSc student at the University of Cape Town, South Africa. Her MSc project is focusing on the movement of inshore line fisheries on the west coast of Southern Africa from the Northern Benguela to the Southern Benguela region. Kate’s research interests include physical oceanography, ichthyology and marine biology. This is her first research cruise and she is very excited to learn about all the different sampling procedures across the disciplines. Personally, she enjoys running in the mountains, sushi, rowing, reading and hockey (in no particular order).

Trainees and participants continued ...

2009-10-14T17:51:00.000+02:00

Soafia Binty Ali is based at the Institut Haleutique et des Sciences Marines (IH-SM), University of Toliara, Madagascar. She completed her DEA (Masters) on identification and distribution (through space and time) of zooplankton that exist in the Toliara Bay. For the preparation of her PhD, she is concentrating on zooplankton biomass in the Toliara Bay. This is the first time that she will be participating in a research cruise therefore it is very important for her because she has the opportunity to see different materials that is not available in her institute. In addition, she is gaining experience in different methodologies. This cruise will help her collect data and will assist her in the comparison of zooplankton between Madagascar and Comoros. She would like to participate in the analysis of the zooplankton samples collected during this cruise. In her free time she enjoys reading, watching movies and playing handball.

Caren George is an intern based at SAEON Egagasini node (offshore) and is awaiting her final results from her MSc. Her project centered on the physical, chemical and biological interactions along the STC to the south of Africa. Her research interests include physical oceanography, biological oceanography and fisheries management. She is in the process of developing a PhD topic which she hopes to start next year. She is very excited to join this cruise and gain experience in fisheries related sampling and participating in an international and multi-cultural research cruise. In her spare time, Caren enjoys relaxing at the beach, rock climbing and yoga.

A demersal trawl south of Grande Comore (Ngazidja)

2009-10-14T08:21:00.000+02:00

Part of the cruise strategy is to assess the bottom (demersal) fauna and biodiversity of shallow shelf areas. This is typically done by demersal trawls in areas that are neither too steep and rough nor covered in vulnerable species such as corals. To date, around the Comoros, such habitat has only been found once as the volcanic origin of the islands have resulted in very steep and uneven slopes. To visualise the extreme of the slopes, imagine the ship anchored outside the port of Moroni. While the bow (front) anchor was in 35m of water, the stern (back) of the ship was floating 300m above the bottom.
Our first demersal trawl at 90m depth therefore caused much excitement. Highlights of this trawl were the capture of what appear to be six species of Unicorn fish (Naso sp). While some species such as the humpback unicornfish were easy to identify, others did not agree with all characteristics as provided by species keys. Are there more species in this genus than currently accepted? Only a closer examination of the specimen back at the museum will tell! Below are shown some examples.

Introduction to trainees and participants

2009-10-14T07:40:00.000+02:00

Over the next few days, the different research participants and ASCLME/SWIOFP trainees will be given a chance to introduce themselves. Here are the first two:

Charine Collins is a PhD student at the University of Cape Town, South Africa. Her PhD project is focusing on the dynamics of the Comoros Gyre and how it may impact on coral reef biodiversity in the region. Her research interests include physical oceanography, marine biology and ocean modeling amongst others. She would like to gain experience in onboard sampling procedures as well as contribute to the collection of data of which some will be used in her research. On a more personal note, Charine enjoys reading books.

Youssouf Ben Ali abdallâh is a native of the Comoros; he has obtained his diploma in Engineering in Oceanography at the University of Sciences and Technology houari Boumediene of Algiers, Algeria. Youssouf’s main research interests are marine seaweeds. His participation on this cruise is his first experience of this kind. It allows him to familiarize himself with different sampling techniques as well as sampling instrumentation, notably the CTD. This is also a big opportunity for him to discover another universe of marine research as carried out by the famous research vessel, the R/V DR FRIDTJOF NANSEN. He is part of the team lead by Dr Sven Kaehler and it is very important to him to be part of this scientific adventure.

Identifying fish larvae and juveniles

2009-10-10T09:56:00.000+02:00

The management of exploited Western Indian Ocean (WIO) fisheries and reefs is dependent on the reliable identification of juvenile fishes, both to understand their potential dispersal, recruitment and recovery, but also to help understand their importance as a food source to many higher order predators (through gut content analysis).

Typically, juvenile/larval identification is difficult as regional keys and guides are scarce the world over and juveniles and adults often show little resemblance to each other. The ultimate aim of this project is, therefore, to develop an illustrated identification key/database of common juvenile and larval fishes, to facilitate their reliable routine identification in the field.
The Fish Barcode of Life initiative (FISH-BOL) aims to facilitate reliable fish species diagnostics using mitochondrial DNA cytochrome oxidase I (COI) sequences that are kept on a centralised database. By comparing COI sequences from juveniles to those already available from adults, species can be matched and identified. The correctly identified juveniles may then be described and illustrated in a field guide.

The current sampling strategy provides for 10 to 16 surface trawls during this cruise, in coastal and off-shore areas close to the Comoros, Mayotte, Madagascar, Mozambique and Tanzania. To date, two surface trawls have been completed and have yielded some 42 species of juvenile/larval fishes. Once back in the laboratory, barcoding will identify these by linking their DNA sequences to those of existing sequences from a database of adult fishes.

The current study is a part of a regional (WIO) research effort that has previously been collecting samples from throughout the Mozambique Channel. Examples of identified juveniles and their corresponding adult stages are shown in the figure below.

Authors: S. Kaehler & M. Mwale

R/V Dr Fridtjof Nansen off to study the Comoros Basin

2009-10-09T10:15:00.000+02:00

Once again the R/V Dr Fridtjof Nansen has left port (Moroni, Comoros), this time for a joint ASCLME / SWIOFP research cruise with excited scientists from 6 nations onboard. The aim of this cruise is to establish for the very first time the physical, chemical and biological characteristics of the Comoros Gyre. The Gyre is an anti-cyclonic eddy that is generally located from 10°S to 15°S and between the north-east coast of Mozambique and the north-west coast of Madagascar. The location of the Gyre is not constant necessitating long transects of about 500 km to either side of the Comoros (see map). A number of recent exploratory cruises, satellite tracking and remote sensing studies have shown the northern Mozambique Channel to be a generally oligotrophic environment that nonetheless supports a large number of fisheries, a high biodiversity and high densities of ecologically important top predators. To date, the processes that sustain the biomass and diversity of this ecosystem are not well understood. It has been acknowledged, however, that the region at a global scale, is physically unusually dynamic and it has been suggested that the observed spatial and temporal variability of the physical environment may well play an important role in enhancing both pelagic and coastal production and the distribution of fish, zoo & phytoplankton and coral larvae.

Since the 6th October, the R/V Dr Fridtjof Nansen has completed acoustic surveys around two of the Comoros islands to determine the distribution and abundance of small pelagic fish shoals. Mid-water trawls have been used on fish aggregations to determine species and size composition and surface trawls to collect juvenile fish stages. Biological sampling to determine the length, weight, sex, and reproductive condition of random samples of selected species was also undertaken at each biological station. But more of this later!
Another important part of this cruise is capacity building of trainees & young scientists. In the next few days you will hear more from them about their experience during the cruise. This is a unique survey that will provide important information for the region, so keep following our blog

Author: Kathrine Michalsen (Norwegian Cruise Leader)

Out-Of-Sequence Posts

2009-10-02T17:00:00.002+02:00

Apologies for the out-of-sequence posts below. There seems to be a glitch in the blogger software and dates. We'll restore order as soon as we can!

Situation report from D.F. Nansen 12.08.2009

2009-10-02T15:08:00.000+02:00

Dear all,

POSITION AND PROGRESS
The R/V Dr.Fritjof Nansen is at 15 08S, 40 57E on station 5 on the second environmental line from the north (line 5 in the Cruise orders). We spent most the daylight hours of 11.08.2009 surveying Nacala bay. Today the wind has subsided and the sea is calmer even in deeper (>500m water).

JUVENILE FISH SAMPLES
Both Domingos and Sven have pointed out the utility of samples of the juvenile fish. We therefore did a "blind" haul in Nacala bay, with a small catch of juveniles.

ACOUSTIC REGISTRATIONS
In Nacala bay some few small schools at about 200m depth were observed during daylight hours. The ships crew considered them too small and far apart to have a chance of catching them using the trawl during daylight. Therefore we have no biological samples of the schooling fish, but we have allocated them to the PEL 2 group in the acoustic analysis.

It will be interesting to see if we continue to observed such schools close to shore further south. Hopefully the aggregations will increase so that trawl sampling can be carried out.

MARI NE MAMMALS, BIRDS AND OTHER OBSERVATIONS
In Nacala bay we again observed seabirds (a species of tern), although in smaller numbers than in Bai de Memba. We observed some birds feeding at the surface, but no fast schools of fish at the surface. Humpback whales were also observed, but in smaller numbers than in Bai de Memba. These observations are very qualitative in nature as we have no dedicated observer effort for whale s or birds onboard. There are neither any protocols for conducting such investigations. Therefore it will be impossible to make any kind of quantitative assessment of their numbers. We're only able to detect major changes (ie. No birds or birds present), or new species of marine mammals. However, for future surveys including marine mammal and seabirds observers might considered.

Best Regards

Erik Olsen

Mozambican Scientists on the R/V Dr. Fridtjof Nansen. (L-R): Mauricio Lipassula, Pedro Pires, Isaias Tembe, Martinho Padera

Situation Report, 13 August 2009

2009-10-02T14:59:00.000+02:00

SITUATION
R/V Dr.Fritjof Nansen is currently at 15 51S and 40 49E on station 6 on environmental line 4 (number 3 from the north). The weather is very good, it is now almost no wind and the sea is very calm. Our work is proceeding according to plan and we seem to have enough time to cover all our predefined tasks. Whether or not we have time to service the mooring off Pemba will be decided upon when we have finished the pelagic survey and head towards Pemba.

FISH SAMPLING AND ACOUSTIC REGISTRATIONS
Yesterday we reinterpreted all the acoustic data based on methods and thresholding levels specified by Pascal Cotel who has analyzed the 2008 acoustic data. His input has been very helpful and we are now more confident about the acoustic interpretation, although the differentiation between the PEL 1 (clupeoid) and PEL 2 (scombridae, carangidae) is still difficult as there are few schools observed and the trawl only catch these groups during nighttime. The highest densities are observed close to shore and in bays. Last night (23:00) we had a haul in the bay off Mocambique where we caught various species of scad, anchovies, barracudas and others.

We're also continuing with daytime surface hauls to sample the juveniles.

MARINE MAMMALS AND BIRDS
The last day few whales and no birds have been observed because the vessel has been far offshore in deep waters during daylight hours. To improve bird and whale observations we plan to set our course from the end of the pelagic survey to Pemba close to shore and make a more determined observing effort from the bridge and deck.

- Dr. Erik Olsen