ASCLME Research Cruises

The 2009 Seamounts Cruise Blog

noreply@blogger.com (James Stapley) — Thu, 03 Dec 2009 15:05:00 +0000

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

noreply@blogger.com (s.kaehler) — Mon, 02 Nov 2009 16:48:00 +0000

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)

noreply@blogger.com (s.kaehler) — Mon, 02 Nov 2009 15:54:00 +0000

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)

noreply@blogger.com (s.kaehler) — Sat, 31 Oct 2009 20:56:00 +0000

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

noreply@blogger.com (s.kaehler) — Sat, 31 Oct 2009 03:56:00 +0000

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

noreply@blogger.com (s.kaehler) — Tue, 20 Oct 2009 23:44:00 +0000

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?

noreply@blogger.com (s.kaehler) — Mon, 19 Oct 2009 13:05:00 +0000

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 ...

noreply@blogger.com (s.kaehler) — Mon, 19 Oct 2009 11:46:00 +0000

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 ...

noreply@blogger.com (s.kaehler) — Fri, 16 Oct 2009 13:45:00 +0000

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 ...

noreply@blogger.com (s.kaehler) — Wed, 14 Oct 2009 15:51:00 +0000

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)

noreply@blogger.com (s.kaehler) — Wed, 14 Oct 2009 06:21:00 +0000

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

noreply@blogger.com (s.kaehler) — Wed, 14 Oct 2009 05:40:00 +0000

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

noreply@blogger.com (s.kaehler) — Sat, 10 Oct 2009 07:56:00 +0000

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

noreply@blogger.com (s.kaehler) — Fri, 09 Oct 2009 08:15:00 +0000

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 blogg

Author: Kathrine Michalsen (Norwegian Cruise Leader)

Out-Of-Sequence Posts

noreply@blogger.com (James Stapley) — Fri, 02 Oct 2009 15:00:00 +0000

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

noreply@blogger.com (James Stapley) — Fri, 02 Oct 2009 13:08:00 +0000

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

noreply@blogger.com (James Stapley) — Fri, 02 Oct 2009 12:59:00 +0000

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

R/V Dr Fridtjof Nansen docks in Diego Suarez

noreply@blogger.com (Tommy Bornman) — Fri, 02 Oct 2009 12:20:00 +0000

The Research Vessel Dr Fridtjof Nansen docked this morning in Diego Suarez (Antsiranana), Madagascar after succesfully completing the second and last leg of the joint ASCLME, SWIOFP and EAF-Nansen West Madagascar Cruise.

The cruise started on 25 August 2009 in Toliare and surveyed the the southern Madagascar Shelf before following the cruise track shown in the image below. The cruise plan included acoustic transects across the West Madagascar shelf and 11 environmental transects. The first Leg of the cruise ended on 18 September in Mahajanga and the second leg ended today (2 October) in Antsiranana.

SCRATCHING THE SURFACE

noreply@blogger.com (s.kaehler) — Tue, 16 Dec 2008 10:31:00 +0000

What is happening below the surface?

Our first task was to define the eddies using satellite tracked drifters (see previous blog page). The next step was to answer the questions; how can we characterize an eddie when looking downward at its hydrological properties and: how can we investigate its potential impact on the living realm? Our sampling strategy provided a partial but quasi systematic survey of part of the eddy field. The survey consisted of hydrographic stations (black dots on the SLA map below) along a north – south transect. At each station, temperature, salinity, dissolved oxygen and fluorescence were recorded continuously from surface to 1000 m - the nominal maximum depth chosen for this study - focusing in on the biological signature of the eddies (sections plotted to 250 m). Sea water samples were collected at various depths. Analyses (at the laboratory) of nutrients, total chlorophyll, primary production, particulate organic matter, pigments and absorption will produce valuable information to relate the physics to the biology of the ocean.

For the moment, let’s have a look at what the “physics” say and let’s comment on what the vertical sections tell us. Keep in mind that this transect crossed two cylonic (clockwise) and one anti-cyclonic (anti-clockwise) eddies. Theoretically, a cyclonic eddy is an area of divergence at the surface (basically, due to the earth rotation and the so-called “Coriolis force”), while convergence occurs at the centre of an anticyclone. Surface water missing at the centre of a cyclone has to be replaced from the subsurface layers. This upwelling brings colder water towards the surface, which is clearly shown by the “doming” of the isotherms in the first diagram (see at 150 m depth and 620 km distance). The same signature is also found in the oxygen distribution (water is oxygen depleted relative to the surface at depth) and - interestingly for biology - in the fluorescence distribution. This means that the whole water column (or at least the upper 250 m) upwells toward the surface. This is important in terms of biological productivity. Indeed, deeper water is also richer in nutrients (nutrients are exhausted at the surface due to consumption by the primary production). Upwelling brings nutrients into the upper euphotic zone (i.e. where light is available), so primary production can occur and the whole trophic chain can potentially take benefit from the fertilization! Note that the fluorescence maximum values are higher and shallower in the centre of the two cyclones. Contrary to the above scenario, the convergence at the centre of an anticyclone pushes down the lower layers (downwelling). Again, the temperature, oxygen - and even fluorescence - vertical distribution perfectly illustrate this downward movement (middle of the transect at 400 km). In terms of its biological signature, the anticyclone will tend to suppress productivity, resulting in fewer catches when trawling within a cyclone! Last but not least – at least for an oceanographer – the salinity distribution also illustrates these up and down vertical displacements. Essentially, downwelling in the centre of the anticyclone vertically expands the intermediate layer which is characterized in this part of the Mozambique Channel by a salinity subsurface minimum. In contrast, cyclonic eddy upwelling “compresses” the intermediate layer, which expels the low salinity water around the eddy. Both processes result in a beautiful “bubble” of low salinity water, right in the middle of the anticyclone!written by: Jean-Francois Ternon and Tammy Morris

The post-hunt party

noreply@blogger.com (s.kaehler) — Tue, 16 Dec 2008 09:35:00 +0000

After a successful survey of Mozambique Channel Eddies, work is now drawing to a close and a final social gathering was held before the data analysis starts and before steaming back to South Africa. During our stop-over and braai just off the coast from Vilankulos (Mozambique), our cruise leader Tor turned into a bard and Keshnee Pillay graciously accepted the role of "golden-haired" Santa Lucia and joined the pre-Christmas festivities.

By popular demand Tor's lyrics are provided below (yes … we have all been at sea too long … :)

The Eddie hunt song (by Tor Gammelsrød)

Women on cruises bring favourite pets

For instance did Jenny bring a huge multinet

Keshnee brought chemicals, and got high now and then

Tammy brought drifters, Jackie brought Sven

REF: Nansen Cruise, ocean blue

Fantastic food and an excellent crew

Jackie and Sven they have courage and will

doing production is their favourite skill

always during night, seldom during day

what kind of production they don’t want to say

Nansen cruise…

Jenny loves animals, particularly small

But flirting with her? She’s not interested at all

Says she: if you want fancy me use multi-net

That is the way to get my trousers wet

Nansen cruise…

Both females and males they have sexual drifts

for some a nuisance, for others a gift

For Tammy the pressure got hard, oh my Lord,

she decided to throw her drifts overboard

Nansen cruise…

Bjørn and André they studied Keshnee

Is it possible to get that beauty on my knee?

but she did not want to use them as her pets

She was busy reading books and smoking cigarettes

Nansen cruise…

Trawling for fish for survival is a must

Jean Francois and Doris in acoustics they trust

Records they broke which long stand they will

catch per unit effort was just below nil

Nansen cruise…

The Longliner should help us with catch after all

But she did not meet us. Scandal! said Pascal

This is not only a scandal said furious Michel

It’s a criminal act!; c’est merde!, Quelle bordell

Nansen cruise…

Bevin turned the light in the lab way down low

Avelino and Dino gave a sexy floor show

The lab ended finally up as discotheque

The samples got drunken the filters got leak

Nansen cruise…

The party to night has a scientific aim

so for Bruce the whole cruise should not be in vain

For our patient and dedicated top spectator

finally may study us top predators

Nansen cruise…

Bruce will determine our sex and our age

Sexual maturity, our length and our weight

But I think I will move ashore in a tent

When he starts to sample the stomach content

Nansen cruise…

written by: Sven Kaehler

CHASING EDDIES IN THE MOÇAMBIQUE CHANNEL

noreply@blogger.com (s.kaehler) — Thu, 11 Dec 2008 16:53:00 +0000

As mentioned previously, the aim of Leg 4 of the ASCLME / EAF Nansen research cruise is to survey eddies in the Moçambique Channel. In order to do so, their location needs to be identified first, and near-real time satellite observations help in providing an idea of what is going on in this very chaotic, or even turbulent part of the ocean.

The problem with near-real time satellite observations is just that, they are near-real time. Sea surface height measurements from altimeters are processed by AVISO (www.aviso.oceanobs.com), and in order to provide a map of the currents at any particular day (see figure below), data from a host of satellites needs to be incorporated and interpolated. This takes time, generally the data is made available with a 7 day delay. So, in effect, we have to guess what the eddy is going to do, based on 7 day old information, adjust our sampling strategy accordingly, and hope not much has changed in the last week!!

To help us make a more informed guess as to the whereabouts of the eddies, we deployed surface drifters during the first (north-south) transect of our cruise. Surface drifters are essentially buoys attached to a 5 m long sock (for more information go to www.oceanafrica.com/drogues/drogues.html). These drogues drift in the ocean following the currents and transmit their longitude and latitude positions to satellites, which are relayed to our support team in Cape Town and then sent to us. Below right is an image of the near-real time geostophic current velocities derived from sea surface height measurements from altimetry with the successive positions of the surface drifters overlaid. The numbers represent the I.D. of the drifters and the positions where they were thrown overboard. We have lovingly given them nicknames such as “Bob” or “Amper Vergeeten” (in this case as the name states).

Comparing their drift patterns to the week old geostrophic currents (see above), one can see that in some cases these follow the current patter described by the delayed satellite observations, but in many cases they do not. This highlights the difficulty in surveying Moçambique Channel eddies accurately given the tools at our disposal! On one particular day we arrived on station expecting westward currents, but the ship board current meters were showing eastward currents!!

The drifter tracks show that the current system itself is indeed very chaotic and turbulent, with drifter tracks criss-crossing, over-lapping and splitting from each other. Modern thinking tends toward describing the flow dynamics in the Moçambique Channel as “eddy-driven”, and our drifters very neatly show this to be the case.

Written by: Bjorn Backeberg and Tammy Morris

Fishy affairs

noreply@blogger.com (s.kaehler) — Tue, 09 Dec 2008 09:36:00 +0000

Since our departure from Pemba, 10 pelagic trawls have been performed. Four during daytime hours and six during the night when the DSL (deep scattering layer) has finished its ascent. The DSL, is a sound reflecting layer in the water column that can be located with echo-sounders and is caused by aggregations of zooplankton or fish.

At daytime, the surface layer of the water (10m deep) and aggregations present between 200-250m have been trawled. Near the surface, catches consisted almost exclusively of juveniles of coastal coral-reef fish and of tunas. Such fish are often found in the stomach contents of top predators foraging at the surface (some birds and tunas). The deeper water aggregations trawled during the day typically consisted of mono-specific (i.e. single species) schools of mesopelagic fish such as the myctophid (lantern fish) Diaphus richardsoni.

A night, most of the trawls were conducted between 10 to 20m depth. They were charactherized by a high catch of flying squids (Ommastrepidae, essentially Sthenoteuthis oualaniensis) and cigarfish (Nomeidae, Cubiceps pauciradiatus). Myctophids were represented by several species. In deeper trawls (40m depth) the catch of flying squids decreases and the catch of myctophids increases in terms of diversity.

First results

At night, a stratification of the communities is observed, myctophids being deeper in the DSL than the flying squids and the cigarfish.
Coral reef fish larvae and juveniles are observed all over the Mozambique channel even far away from the coasts. This is an interesting observation that suggests that reef-fish populations from the east coast of Africa and the islands of the western Indian Ocean may be connected.
It must be noted than shrimps and euphausids are absent of the trawls.

Cigar fish during night-time surface trawlsOne of the many coastal reef species caught during day-time surface trawls
Red flying squid that are prevalent during night-time trawls
written by: Michel Potier (IRD, France)

Biological Observations

noreply@blogger.com (s.kaehler) — Mon, 08 Dec 2008 05:09:00 +0000

The dominant bird species on the cruise is the Sooty Tern Sterna fuscata. Almost 90 hours of observation have been completed so far producing almost 2000 birds. In the north Common Noddy Anous stolidus, threatened some competition, but this waned as the survey progressed south. Tropical (formerly Audobon’s) Shearwater Puffinus Iherminieri and Parasitic Jeager Stercorarius parasiticus (harassing Sooty Terns) was of interest in the north.

Several feeding aggregations of terns were observed throughout the survey (but not the 6 December), the group size varying from 50 – 480 birds. All the aggregations were associated with feeding activity of small tuna. Some Sooty Terns were seen to grab small slender silver fish. A bird aboard at night regurgitated several small squid, a species taken frequently in trawls conducted to date. Other species were few and far between, but the most productive area for diversity seemed to be on the approaches to Madagascar and northward towards Juan da Nova Island. Of interest in this region was Great Frigatebird Fregata minor, Red-footed Booby Sula sula, White-tailed Tropicbird Phaethon lepturus, Wedge-tailed Shearwater Puffinis pacificus, Jouanin’s Petrel Bulwaria fallax, Black-bellied Storm Petrel Fregetta tropica and Wilson’s Storm Petrel Oceanites oceanicus. The survey moved across to the Mozambican coastline and the steady flow of birds dried up. We await a clearer picture to see where and why the birds numbers improve as the survey progresses. Oddities included Madagascar Squacco Heron and Cattle Egret.

Cetaceans were scarce, but when seen exhibited a reluctance to be remotely close to the vessel, which severely inhibited their identification. This behaviour may result from the acoustic equipment used for fish location. However, despite this Sperm Whale Physeter macrocephalus, Minke Whale Balaenoptera acutororostrata, Cuvier’s Beaked Whale Ziphius cavirostris, Short-finned Pilot Whale Globicephala macrorhynchus, False Killer Whale Pseudorca crassidens, Bottle-nosed Dolphin Tursiops truncatus, Common Dolphin Delphinus delphis and Spinner Dolphin Stenella longirostris, have been positively identified. I might add that only the Minke Whale sightings have been relatively close to the vessel.

False Killer Whales
Sooty Tern

written by Bruce Dyer – MCM, Top Predator observer (photos: S Kaehler)

THE NAMING OF THE GUNGE

noreply@blogger.com (s.kaehler) — Sat, 06 Dec 2008 12:34:00 +0000

Finally we have a name for the brown gunge that has been visible in broad streaks at the ocean surface since entering the first cyclonic eddy, and which has been clogging our plankton nets and slowing down the filtering of our numerous water samples - Trichodesmium. In our samples it appears as masses of loose fibres and fuzzy clumps. It occurs in nutrient poor tropical and subtropical ocean waters, and is an important marine nitrogen-fixing bacterium that is being studied extensively for its role in nutrient cycling in the ocean. It forms blooms and provides a substrate for many small oceanic organisms, such as other bacteria, diatoms, dinoflagellates, protozoa, and copepods. The species Trichodesmium erythraeum is endemic to the Indian Ocean.

Trichodesmium is commonly called "sea saw-dust" because its colonies and large brown blooms have been mistaken as sandbars by ships in the ocean (including Captain Cook who wrote the first documentation of Trichodesmium over 200 years ago). These photosynthetic cyanobacteria can be found as filaments (trichomae) comprised of 10's-100's of cells or in colonies 1-10 mm in length. The fact that these colonies can be seen by the naked eye is what gave Trichodesmium its name - the Greek word "trichoma" for hair and "desmus" for bonded = "bonded-hair," which is how Trichodesmium colonies look to the human eye. The colonies can be yellowish-brown to deep red in color due to their primary light harvesting pigment, phycoerythrin. They are buoyant and able to regulate their position in the water column due to large gas-filled vacuoles or vesicles in each individual cell. Trichodesmium blooms are surface aggregations that can be 10-1000's of km wide. They occur during periods of low wind stress and warm temperatures. Some of these blooms are so vast that they are visible from space. However, the bacteria on the surface do not generally survive for extended periods of time for various reasons, including UV damage. [Source: Wikipedia]

Figures: (a) Streaks of Trichodesmium seen from the Nansen; (b) a Trichodesmium bloom visible from space (from AIMS Research.); (c) thick Trichodesmium “gunge” from the bongo net haul; (d) Trichodesmium sp. as seen under a microscope.

Written by: Jenny Huggett (DEAT: Marine & Coastal Management, South Africa)

Strong Currents near Pemba, northern Mozambique

noreply@blogger.com (s.kaehler) — Sat, 06 Dec 2008 12:08:00 +0000

Ocean currents typically range between 10 – 50 cm/s. Outside Pemba, however, vessels have experienced strong south-flowing currents when trying to enter the port. These could not be explained as tidal currents, because the bottom depth is more than 1000m and therefore tidal currents are weak.

Experimental oil drilling at 1000m depth is planned in the area, which is another reason to learn about the local ocean currents. So a team of scientists from the Instituto de Investigacao Pesqueira, Moçambique and the Universitetet i Bergen, Norway deployed a current meter mooring at about 1000m depth (photo: preparing and deploying the mooring).

This instrument has an internal data recorder, so we have to pick the mooring up again next year to get access to the data.

During the deployment we recorded current speeds using the ship mounted current meter (ADCP) of almost 2 m/s (= 4 knots, almost the speed of a fishing vessel)! If this turns out to be a typical current speed this is bad news for the oil companies, because the currents would cause too high a load on both the drilling platforms and the 1000m long pipes from the surface to the bottom, for present technology to cope with. We will know next year.

Written by Tor Gammelsrød (photos: Tammy Morris)