Video by Pierre Samuel, second commandant during Nectalis 2011
Day 19-16/08/2011: back to port, but the work only begins
We arrived in Noumea port in the afternoon after steaming part of the night and the morning. The last sampling station, the night before, did not go as smoothly as we could have hoped. Despite everybody being well trained with their tasks there are always surprise events. This time it is the micronekton net which gave us some cold sweat. After a successful tow we decided to sample again for the last time during this trip and of course this is when things went wrong. On the very last tow, while setting, one of the trawl doors decided to revolve around the net cables. It took our captain time and expertise to managed to deal with the mess and to bring back to net without damage; at one stage we thought we might lose the net! It was already late at night and despite this event the crew was still ready to work more and we finalized the sampling station with all the other samplings finishing nearly at 4 in the morning.
In this last newsletter we would like to acknowledge the work done by the crew members of the Alis. It has been a very intense trip with a large number of measurements and collections, day and night, and a number of problems which have all been resolved to keep going. During these three weeks we received the full support of the crew members who did a very professional work. They showed endless enthusiasm, a full range of competencies, provided as much help as possible and were always ready for yet another sampling. So to conclude the NECTALIS 1 adventure we would like to thank warmly captain Jean-Francois Barazer and his 11 crew members who made this trip successful, very efficient and extremely enjoyable. We are looking forward to join the crew and the boat again in December for NECTALIS 2.
Result of the next to last tow, a mix of fish, jelly organisms and empty sardine can as well as the label of the legendary Chartrons, the red wine served onboard. We suspect they did not arrive in the net alone…
The NECTALIS 1 team back home!
Day 17-14/08/2011: some preliminary results on the physical oceanography - Nec1016
Last night while steaming between sampling station 15 and 16 we decided to conduct a nighttime trawl. There were nice detection on the sounder and we were hoping for a good collection of micronekton close to the surface around 20m depth. However after half an hour of trawling the result was really disappointing. It has been the same small amount of jelly organisms for all surface trawls we tried and we are wondering if the micronekton net is behaving properly when fishing close to the surface; deep fishing seems more successful; unfortunately we don’t have the probe to monitoring the vertical opening of the net.
Mainly jelly organisms were caught on the micronekton net close to the surface last night
A number of physical oceanographic data have been processed already. Examining surface (0 to 3 m depth) temperature and salinity recorded during our cruise we can clearly see in the north a warmer and fresher water mass while in the south of the area investigated the water mass is colder and more salty. The warm and fresh water mass is characteristic of tropical waters while the colder and saltier waters reflect the northward seasonal migration of subtropical waters. A clear front exists between these water masses. In those 2 regions the S-ADCP backscatter which can be interpreted as a relative biomass of mesozooplankton and micronekton show that in the northern area there are less organisms in the surface water (15 to 40 m depth) than in the southern area which appears richer. Along the ship track, in the surface layer, the flow is clearly not laminar but characterised by a number of eddy-like structures.
Sea surface temperature along the ship’s track. Red indicates warmer temperature.
Sea surface salinity along the ship’s track. Blue indicates fresher waters (note the opposite trend between salinity and temperature)
S-ADCP backscatter anomalies (daytime data minus daytime mean; night-time data minus night time mean to remove the daily cycle) averaged over the top 15-40m depth.
15-40m depth average currents from S-ADCP.
Day 16-13/08/2011: a closer look at zooplankton - Nec1015
During the sampling station of the day we did an extra sampling of water and zooplankton to provide samples to a colleague working on stable isotopes. We collected water at the depth of the maximum of chlorophyll to filter the particulate organic matter (POM) which contains phytoplankton cells but also all the particles in the water. By determining the stable isotope signature of the POM we will obtain the isotope value of the base of the food web. Similarly to heavy metals such as mercury, heavy stable isotopes of nitrogen are accumulating along the food chain by about 3‰ per trophic level. To simplify, if POM has a value of 1‰ then zooplankton grazing on POM will have a value of about 4‰, fish feeding on zooplankton will have an isotope value of 7‰ and tuna feeding on these small fish will have a value of 10‰. Hence isotope has the ability to provide important information on the trophic structure of the ecosystem. To complement the POM analysis, zooplankton were collected and frozen. It will be later sorted by taxonomic groups and stable isotopes will be determined; micronekton samples will also be put aside for these analyses. Considering that we already have isotope values of tuna, we should then obtain a complete picture of the trophic structure of the pelagic ecosystem.
Houssem checking the content of the zooplankton collector
Zooplankton from one of the collectors
Day 15-12/08/2011 - Nec1013 & Nec1014:
Today the first sampling station was off Huon atoll, the last piece of land north of New Caledonia. Huon island is a sandy island where turtles are coming to spawn at summer time. During the station we had to splice the electronic cable which had been twisted, to avoid any future. Some issues appeared again on CTD conductivity and we swapped the 2 probes which seemed to resolve the problem. Other collections of the station went smoothly. Leaving the station we steamed close to the reef and took this opportunity to try and troll. We were lucky to have very skilled fishermen onboard who caught a large wahoo. Fillets were removed for crew consumption but we kept the skeleton and guts for scientific analyses. This sample will be sent to Australia for a colleague conducting a study on wahoo populations in the region.
An important event of the day was Martine’s birthday which we celebrated at diner just before sampling station Nec1014.
Jonathan prepared the Wahoo, flesh for crew consumption and skeleton and guts for science
Francis splicing the electronic cable for the CTD probe and Hydrobios.
Rocks at Huon atoll
Day 13-11/08/2011 - Nec1012:
We had an early start before the sunrise with the hope of finding the satellite tuna tag that has been drifting for nearly 10 days. The chance was with us as the water was flat calm. We have been cruising slowly for 4 hours correcting our trajectory according to the satellite tag position sent to us regularly. The crew was on the deck looking in every direction. However our luck stopped before we could find the tag and we were all disappointed but we had to go back to our plan and steam to the next station Nec1012.
We took the opportunity of the very quiet sea and very small swell to measure the acoustic signal of the noise of the engine and the boat at different speed. These data will be used to correct the acoustic signal later on, but it also helps determining the optimum steaming speed for the acquisition of the best acoustic signal. During this test the best signal was acquired at 6.5-7 knots, however we had to make a compromise at 8 knots not to extend the duration of the transits between stations.
Sampling station Nec1012 went very smoothly with excellent weather condition.
At dawn, looking for a 10 cm long satellite tuna tag lost in the ocean.
Launching the CTD probe and retrieving the zooplankton net on a quiet day.
Day 13-10/08/2011- Nec1011:
We started sampling at station Nec1011 at 14:30. With a very quiet weather the work is really facilitated and we managed to conduct all the sampling without any problem. Just before arriving at the station we saw interesting structures on the echosounder but unfortunately they were not visible anymore at the station. We caught a mahi-mahi (dolphinfish) and looked at the stomach to check what it was feeding on, but the stomach was empty.
The echosounder is a very precious tool for the goal of our cruise as it will allow to establish the vertical distribution of the micronekton and to estimate its relative biomasses. It can also detect large animals and we think we saw some tuna on the sounder. As a matter of fact we observed these probable tuna detection just before arriving at sampling station 4 on Lansdowne bank nearly a week ago. A few hours later we received a message from SPC indicating that a satellite tag inserted on an albacore tuna one year earlier had popped-up at station 4. The bad weather did not allow us to look for it at the time but we are monitoring its drift everyday. Tomorrow is probably our best chance to encounter the tag and we decided to change our route to steam toward the last known position of the tag. We should arrive there is the morning at dawn and all the crew will be outside watching for it. Chances are small however as we do not have the equipment to detect it, just relying on position to find a 10cm tag floating at the surface of the sea is more than challenging.
On this EK60 echogram we can see a layer of micronekton between 180 and 200 m depth and just below, around 250 m depth, some isolated signal (in the black circle). This signal can probably be interpreted as a group of at least 2 tuna of about 100cm long
Blue stars indicate the position of the drifting tuna tag. It popped up when we were at station 4 on the 2nd of August and we will try and find it between station 11 and 12 on the 11th of August…
Day 12-09/08/2011: a closer look at the phytoplankton - Nec1009 & Nec1010
After steaming all night, we arrived at the following sampling station in the morning around 10:20. We started with a micronekton net targeting the deep layer around 480m depth as during daylight the organisms dive deeper. It is challenging to trawl at this depth but we managed to collect some good samples with strange looking fish. Again we had some issues with the CTD probe which gives some strange salinity values, some probes were subsequently changed in the hope that it will solve the problem. TAPS, LADCP and zooplankton net went smoothly.
An important part of the work conducted during this cruise is the characterization of the phytoplankton, the microscopic algae which constitute the “grass of the sea” and which is the base of the pelagic food web. In a schematic way, waters rich in nutrients (nitrates…) will allow the development of large quantities of phytoplankton which will be consumed by large quantities of zooplankton which in turn will be eaten by fish. To develop, phytoplankton needs sunlight and nutrients such as nitrate and ammonium. Phytoplankton will capture the light energy using some pigments which are characteristic of each phytoplankton group. Phytoplankton will be quantify in different ways, by measuring at different depth the total quantity of chlorophyll (pigment present in nearly all types of phytoplankton), quantity of chlorophyll for different cell sizes, quantity of phycoerythrin (pigment of cyanobacteria), quantity of other pigments (characterizing other phytoplankton groups), counting the number of cells and determining their size, examining under the microscope the different species of phytoplankton. During our cruise we look at all those characteristics at 8 different depths between the surface and 180 m; light is considered too low below this depth and phytoplankton, like other plants cannot develop without light. For each type of analysis on phytoplankton, water samples have to be filtered on different types of filter which are then preserved frozen for later analysis in the lab on land.
Christophe filtering water for measuring total chlorophyll.
The ingenious system developed by Martine to simultaneously filter for 3 different phytoplankton cell sizes
Result after filtering 4 liters, the small yellow marks on the filter signal the phytoplankton which is poor in this region.
Fluorescence profiles from the CTD fluorescence probe at sampling stations 5 to 8. Fluorescence is a proxy for phytoplankton and results of the probe show a classic vertical structure at station 5 (green curve) with low value at the surface (a lot of light but low nutrients), a maximum around 100m at the level of the thermocline (some light still penetrates and nutrients blocked below the thermocline are diffusing through it and can be assimilated by phytoplankton at this depth), from 180 and below the values are very low. After station 5 the wind started to blow at 25-30 knots for 2 days in a row while we were sheltered in Chesterfield Atoll. When we finally arrived at sampling station 6, the vertical structure was very different (red curve); we hypothesize that the wind had completely mixed the water from the surface down to 120 m depth, light and nutrients becoming available at all depth, the structure is pretty uniform down to 100m before decreasing as the light decreases. With profiles at sampling station 7 and 8 we can see that the stratification is developing again as all the nutrients have been consumed at the surface and are not replaced while deeper, close to the thermocline there is still diffusion of nutrients which are consumed at depth and cannot reach the surface. This interpretation will be confirmed with the discrete pigment and nutrient analyses in the lab.
Day 11-08/08/2011: a good day for fishing - Nec1008
Today we had a sampling station planned at midday, however on our way, when steaming over the eastern slope of the Chesterfield bank, we observed a strong detection on the echosounder around 175m depth and decided to trawl to try and catch the organisms. By the time we were ready to trawl the detection had dive deeper at around 220m depth and the detection was very patchy and did not last for very long. We were not sure the catch would have been successful and the amount caught was poor but very interesting. It was constituted of mainly 2 species, hatchetfish and the crustacean phronimidae which probably inspired the creators of “Alien”; both are common preys of tuna. After this trawl we steamed to the sampling station of the day to proceed to the suite of measurements and collection. There were some issues with the thermosalinographe, the CTD probe and we are not sure what happened to the zooplankton net which did not want to go down; hopefully everything will be resolved soon. We did two trawls and managed to catch the organisms migrating to the surface at dusk and some more organisms closer to the surface at night.
The crew members Steve and Felix making sure the micronekton net is properly rolled
Valerie and Houssem sorting the micronekton catch of the day
Sternoptychidae or hatchet fish, silvery little fish which were caught around 200 m depth on the slope of the Chesterfield bank.
Crustacean Phronima, beside its salp which it uses as a shelter and where it spawns its eggs. Eggs and larvae of Phronima were observed in the salps.
Day 10-07/08/2011: on the road again - Nec1006 & Nec1007
As planned we left Chesterfield Atoll yesterday afternoon and we went back to the previous sampling station that had been cancelled. It had been a busy and early day with 2 sampling stations at midnight and 1:30pm. All the collections went very smoothly with a good catch in the micronekton net at 1:30am this morning. The catch was not so good in the afternoon but with interesting specimens. Some ropes had to be replaced on the zooplankton net in prevision of the next sampling station. In the evening while steaming towards sampling station 8 we came across a very step seamount which summit reaches 40 m depth, a very impressive sight on the echosounder.
Echogram of the seamount encountered rising from more than 2000m depth and which summit reached 40 m depth. There are large echo (in green) around 80-100 m depth indicating dense patches of organisms on each side of the seamount, however the density is higher on the right on this picture.
Martine and Christophe collecting sample water from different depths for ammonium analyses.
Day 9-06/082011: another day waiting for improving weather
The wind is not decreasing quickly but forecasts are better and we left our shelter around 4pm today; we should arrive to the sixth sampling station at midnight. During this day we polished our new cruise plan and processed some of the data; correcting anomalies in the fishing echosounder records and calculating current direction.
Down below are some first results extracted from the onboard S-ADCP which records continuously the echo from particles using a 150kHz sounder. The echo reflected by organisms in the water column is normally used to deduce current direction. But a new application of this instrument is to try and quantify the amount of organism in the water column; it is considered that organisms detected are between 1 mm and several centimeters (zooplankton and micronekton) depending on the sensibility of the apparatus and the density of organisms.
S-ADCP results showing the East-West currents along our route with an alternation of Westward (blue) and Eastward (red) currents. Importantly this graph shows that the currents in the water column are very homogeneous from the surface down to 150 m depth.
S-ADCP data integrated for the surface layer (0-150m) show the south-east “Alis current” along the coast of New Caledonia and more chaotic current structure towards the West of the area
We can also interpret the S-ADCP echos as density of organisms. In this graph we can see that in the 0 to 150 m depth layer the density of organisms is higher close to the surface during the night (around the date label which indicates midnight) and lower during the day. This structure is expected as zooplankton and micronekton migrate vertically at dusk to stay close to the surface at night and they migrate in the deeper water at dawn.
Jacques, our cook, preparing the catch of the day
Day 8 - 05/08/2011: sheltered from rough weather in Chesterfield Atoll
No improvement of the weather so far and the wind is still oscillating between 25 and 30 knots. We anchored in Chesterfield atoll, and there are also 3 sailing boats around waiting for better conditions which are not expected before tomorrow during the day. We took the opportunity of this quiet day to work on the data accumulated so far and to revise our cruise plan. Indeed, with sampling stations taking more time than originally planned and what look like 2 days anchored, we were getting really late. We had to drastically cut into the number of sampling stations from 29 to 18 as we still want to conduct all the experiments at each station. The crew members also had some work to do on the micronekton net particularly. No sampling but still a busy day
Chesterfield atoll where many birds are nesting and feeding apparently
Captain J.F. Barazer and his crew, fixing the cables of the micronekton net
Lieutenant J. Boudet working on some net
Plan B for Nectalis with less sampling stations.
Day 7 - 04/08/2011: sampling station Nec1006 and Nec1007
The weather is getting worst and worst and with 25 to 30 knots of wind the captain decided it was too dangerous for the crew and the equipment. After skipping station Nec1006 we steamed towards station Nec1007 hoping for better weather however it is not improving and forecasts are not very optimistic for the coming days. We decided to change the plan and to steam toward the Chesterfield atoll to shelter the boat in the hope that it does not last too long. We are all in standby the boat moving a lot waiting for a better weather to start working again
25 to 30 knots of wind…
Day 6 - 03/08/2011: sampling station Nec1005
The weather is not improving and it is difficult to enjoy the blue sky when the wind is more than 20 knots and the boat is moving a lot. It does not facilitate the work on the deck for the crew members to launch the different measuring instruments and the work in the lab is also difficult. However after 5 stations the routine is pretty much implemented and everybody has found his role. The station of the day went pretty smoothly. We decided to lower the current profiler LADCP even deeper, at 800m depth and the zooplankton sampler down to 600m. We hope to capture what is happening below 500m which seems to be a transitional level. It was daytime when we did the sampling station Nec1005 so we did not hope much from the micronekton sampling. We targeted the 20m depth layer as there was some acoustic signal; next signal was deeper than 500m, out of reach of our net. As expected the net came back with few specimens but interesting ones, of the type consumed by tunas: some reef fish larvae as illustrated below. The sampling station being located between Lansdowne Bank and Chesterfield reef, it is not surprising to find this type of fish.
Reef fish larvae found in the micronekton net, fished at 20 m depth between Chesterfield and Lansdowne Bank
M. Rodier and C.Menkes collecting water samples from the CTD Rosette and F.Gallois with crew members getting ready to launch the LADCP
Day 5 - 02/08/2011: sampling station Nec1003 and Nec1004
We started sampling at station NEC1003 late at night with the CTD, LADCP and TAPS profilers but when came the turn of the Hydrobios zooplankton net the cable suddenly get caught into the pulley. Fortunately the Hydrobios was still onboard when it happened; the cable had to be cut and was under repair when we decided to put the micronekton net in the water. It was really bad luck because when the net was lowering at the chosen depth for fishing, another cable again get caught in the net pulley. It was the middle of the night and the boat was moving a lot as the weather had changed. The conditions were really hectic, but the captain and his crew did an exceptional work managing to repair everything and bringing back the micronekton net. Everybody was exhausted and had a deserved rest while steaming towards the sampling station Nec1004 which we reached at midday and which is located East of the Lansdowne bank rising at 40 m depth when the surrounding waters are more than 2000m depth. All went smoothly during this sampling station.
Captain J.-F. Barazer and his crew replacing some cable on the micronekton net.
Crew members gathering around V. Allain looking at the catch of the day, poor but very high quality.
Some transparent lobster larvae found in the net at station Nec1004.
Day 4 - 01/08/2011: sampling station Nec1002
After station Nec1001, we had to fix a number of problems and we were lucky to have an efficient team and the help of the crew to deal with all the minor troubles. The major issue was to repair the LADCP which provides current profiles. Our electronician F.Gallois tested all the connections and cables and arrived at the conclusion that he had to open the case to look for any problem inside the apparatus; and sure enough he found the problem, a tiny component was broken. He applied his magic and, with brio, managed to repair the LADCP. We were very happy to see it working during the following sampling station Nec1002. This second station went much more smoothly than the first one and we conducted 2 micronekton nets at 120m and 15m depth (among small fish, squids and shrimps we caught a small cookie-cutter shark which feeds by biting pieces of muscle off tuna and other large pelagics), one LADCP profile at 500m, one TAPS profile at 200m, zooplankton sampling, CTD profile and water sampling for chemical analyses.
A ready-to-go but non-working LADCP (in yellow).
F. Gallois with the dismantled LADCP which he managed to repair after a long day working on the problem.
CTD profile of station Nec1001 showing a very homogeneous water mass (mixed layer) in temperature, salinity, oxygen and fluorescence (proxy for phytoplankton biomass)down to 125 m depth where there is a very weak thermocline. From 125m oxygen and phytoplankton decrease.This profile is remarkable by the absence of maximum of phytoplankton which show homogeneous low values.
The situation is different at station Nec1002 where the maximum of phytoplankton is clearly located around 70m depth in the mixed layer just above the thermocline. Thermocline is still weak but shallower than in station Nec1002 at 100m depth.
Day 3 - 31/07/2011: sampling station Nec1001
Third day of the cruise which is getting into full swing. It was our first trial of the serie of collections we have to undertake at every station and as expected unfortunately it did not go as smoothly as we wanted. All the sampling gear, lab and electronic equipment had been tested earlier before departing and it was all working perfectly, but it was another story when the real work was supposed to start. The order of the experiments had to be changed to leave some members of the team to fix several incidents. The CTD took a while to warm up but worked well and we did two consecutive profiles collecting some water samples for chemistry and phytoplankton on the second profile. The Acoustic sounders EK 60 was working perfectly as well as the TAPS, another acoustic gear with which we did a 200m profile. With the zooplankton sampler we realized at the end of the set that 3 out of 5 flowmeters were not working properly and they were replaced for the next sampling. The micronekton net was set at 500 m which is really deep; we were targeting a small detection on the acoustic sounder, unfortunately it dove to 530m out of reach of the net which came back quite empty but with interesting specimens nonetheless. Our LADCP profiler did not want to work and is still under repair and we have hopes that we can use it for the next sampling station. It has been a very intense day for the crew and the scientists, full of excitement and the procedures are now in place which should allow us to be very efficient for the next sampling.
Captain J.F. Barazer and his crew members recovering the CTD after it established a temperature, salinite, fluorimetry, transmissometry, oxygen profile down to 500m depth and collected water samples between 200 m depth and the surface.
H. Smati pick up the 5 collectors of the zooplankton net which allow to sample 5 depth range in one vertical tow between 500 m depth and the surface
The crew members deploying the large micronekton net.
A sample of the organisms collected at 500 m depth. We can see in this tray some small shrimps, a squid, lanternfish and bright silver hatchet fish. Specimens were all less than 5 cm length.
Day 2 - 30/07/2011: acoustic calibration
Second day of the cruise, we departed from Noumea port at 8:30. It took less than one hour of steaming before we anchor in 13m depth in the sheltered Ste Marie bay. The main purpose of this day was to calibrate the acoustic sounder SIMRAD EK60 which will be used during the cruise to detect micronekton schools composed of small fish and squids and constituting the main preys of the tuna. Acoustic will allow estimating micronekton biomass and their vertical movements; the acoustic signal will be recorded 24hours a day. This sounder also has the capability of detecting tuna schools. While E. Josse and J.-Y. Panche were conducting the calibration, the other members of the team organized the lab, attaching all the equipment in prevision of rough seas, calibrating the lab apparatus, preparing all the sampling gears to be ready for the first sampling early the following day.
Tungsten and copper balls are placed under the boat to proceed to the calibration of the 4 frequencies (38, 70, 120 and 200 KHz) of the EK60 acoustic sounder
E. Josse and J.-Y. Panche in front of the acoustic sounder screen, proceeding to the calibration
Day 1 - 29/07/2011: loading the equipment
First day of the cruise, but the boat is still at “Scientists quay” in Noumea port. This first day saw the team loading the different pieces of heavy and light equipment, chemicals and electronics, organizing the lab and fixing everything to get ready. Departure is planned on Saturday 30 July 2011 at 8:00 to spend probably the full day in a sheltered bay to calibrate the EK60, the acoustic sounder that will be use to detect fish schools and micronekton.
J.-Y. Panche on the deck of the N/O Alis, finishing to prepare the CTD (temperature-salinity depth profiler), LADCP (current profiler) and the bottles to collect water at different depths. The “rosette” carrying all this equipement will be dropped down to 500m depth to establish oceanographic vertical profiles.
M. Rodier in the wet lab, preparing the system to filter sea water to collect phytoplankton for chlorophyll and other pigment measurements