Map of the third cruise of Nectalis
It is the end of the Nectalis 3 cruise. The boat arrived just before 9:00 am. Immediately everybody was busy to put everything in order, to disembark the samples that will be stored into the lab, to save the data, store the large pieces of equipment into the dock, and clean the boat so that it is ready for its next cruise in a few days. Everyone contributed: crew and scientific team.
Before everyone flies away, we tried to take a picture of this fantastic team (a few are missing from this picture though).
Since sampling station 19 we steam along the west coast of the Grande Terre in the southward current « Alis » named from the boat we are using and that runs along the coast. We did not observe any upwelling of cold water along the coast which sometimes occur when wind is strong and consistent.
This is our last day of work and we did 2 sampling stations: stations 20 and 21. The last trawl was the 32nd trawl of the Nectalis3 cruise and the 102nd trawl of the series of Nectalis cruises. It was the biggest trawl of this cruise with about 4-5kg of micronekton collected. The lanternfish (Myctophidae) represented the largest biomass with 2.5kg. Many of these fish had external red parasites of a few centimetres long fixed under their skin or in the gills; they are probably copepod parasites.
The trawl also contained large specimens of squids: 2 large Sthenoteuthis oualaniensis measuring about 30 cm and 2 Eucleoteuthis luminosa of smaller size (~20 cm) and recognizable with the long white luminescent stripes on their mantle. There was also a large salp measuring 20 cm and weighting 600 g.
We finished working late at night and we all went to take some rest while the boat was going into the direction of the passage to enter the Caledonian lagoon.
We are getting closer to the Grande Terre and the barrier reef ; two sampling stations left before we arrived at port in Noumea on the 9th of December. We are steaming along the west coast of the Grande Terre, going down south in warm waters.
During the sampling station #19, we conducted the hundredth micronekton trawl of the series of Nectalis cruises. We will celebrate the event for sure. We did two micronekton trawls, at 15 m and 490 m depth. The shallow net contained mainly gelatinous organisms including a species we had never seen before, and salps. The deep trawl contained a large variety of fish, squids and shrimps, each in small quantities.
We are located at the level of the northern part of the Grande Terre. The sea is rough and the boat moves a lot, some scientists are sea sick but it does not prevent us to conduct the work as usual.
The sampling station #18 has been a little bit hectic. We had a problem with the electronic cable that allows to lower down and command the CTD which carries the temperature and salinity probes and the bottles to collect water. It took us 2 hours to check the cable and put everything in order.
The echosounder indicated a dense layer of micronekton and we were hoping for a record catch with the micronekton net. We were a little bit disappointed when we realised the net was full of gelatinous organisms and leptocephalus larvae of eels. However there was also a little fish that resemble an angler fish of the Lophiidae family probably and that was named cow fish, pokemon fish or stone fish by various members of the team.
After a short six-hour break at Chesterfield atoll, we are back in the high seas to progress in our sampling plan. Today we have visited sampling stations 15 and 16. We found large gelatinous organisms in the micronekton net at station 15. The largest one was nearly 30 cm long. We were not that lucky at the following station where there was barely anything in the net.
After sampling station 14 we took the opportunity to enter the Chesterfield atoll lagoon as it was very close. For a few hours we were able to go on land, walk in the sand and take some rest as the wind is still blowing. There is a large population of sea birds living and nesting on the atoll and we were able to observe adult boobies and young covered with their white down.
Picture: Victor Bole
Picture: Annes Lebourges
While working at station 13 last night, a friend paid a visit. A booby came to rest on the rear crane and monitored the work. We conducted the usual list of measurements and samplings including two trawls at 140 and 500 m depth.
The deepest trawl brought us some nice dark red shrimps, a large variety of deep fishes, some gelatinous organisms and some squids including the strawberry squid and the ram’s horn squid. The ram’s horn squid (Spirula spirula) has a white mantel containing an internal chambered coiled shell in the shape of a spiral which is frequently found stranded on beaches.
We are back on our search for the mysterious hatchetfish that we discovered during the previous Nectalis 1 and 2 cruises (check the logbook of these cruises on 8/8/2011, 3/12/2011) by the Chesterfield atoll. During the previous cruises, we detected them on the echosounder as they formed dense schools at depth between 200 and 400 m, a layer where there are usually no organisms. Once again their specific acoustic signature has been observed on the echosounder at 200 m depth while we were heading towards station 14. Unfortunately we could not trawl the school as it was very narrow. We were not able to collect samples but we still think they are the same fish. We now have 3 records for the schools of this species on the eastern side of the Chesterfield atoll.
While monitoring the screens of the micronekton/zooplankton EK 60 echosounder along the cruise track, we were surprised to observe wavelet structures. It is not a problem in the computer or in the echosounder, but real undulations of the micronekton/zooplankton from the surface down to 200 m depth. We believe this behaviour is due to the effect of an oceanic undulation. Probably related to underwater topographic features such as the Lansdowne bank we were approaching, the oceanic undulation induces vertical movements of the water, temperature, salinity and, as observed here on the echosounder, the marine organisms. This phenomenon has been observed elsewhere, for example in Morocco and Senegal.
While on the sampling station 12, we proceeded to the usual set of measures and sampling. We undertook two micronekton net trawls. The first one contained a variety of small shrimps, a transparent lobster larvae, the larvae of a flat fish and among other fishes some lanternfish and some hatchet fish.
The second trawl contained a lot of very tiny specimens: larvae and juveniles of fish, squids and crustaceans, and a larger specimen of pomfret (Bramidae).
Today we are proceeding to the eleventh station out of 22 planned stations; we are midway through our trip. We intended to do another 24 hours station to repeat the 24 hours cycle done during station 1. However we realised that the area was very poor and we chose to postpone this long station to select a more suitable area.
During station 11 we conducted:
- one 600 m CTD profile to collect water and measure temperature, salinity and fluorescence
- one 200 m TAPS profile to measure the zooplankton acoustic signal
- two multinet hydrobios zooplankton net oblique tows between 600 m and the surface
- three horizontal micronekton net tows at 100, 15 and 600 m.
Micronekton trawls brought us interesting samples. In the 100 m depth tow we found a 20 cm gelatinous octopus and a few fish including a strange transparent fish with black stripes and a dorsal fin with long rays. We never saw a fish like that before.
In the second tow conducted close to the surface, at 15 m depth, we collected a beautiful black and yellow sea snake, a Pelamis platurus. The crew hurried to put it back alive in the water before someone gets bitten. It is a pelagic snake living in the open sea contrary to many sea snakes that live close to the shore or to the bottom of the sea. It is a viviparous species that bears several young but do not lay eggs. It is not that surprising to find it that far from any land or reef considering its life cycle. The closest reefs and lands to the sampling station are 100-150 nautical miles.
Collection P. Borsa
The last trawl at 600 m depth brought to the surface a diverse catch of deep fish, Scopelarchidae, Paralepididae, Nomeidae and Myctophidae, cepahlopods, including Taoninae, beautiful shrimps (Oplophorus, Funchalia, Euphausiidae...) and jellyfish.
The weather conditions are still difficult and there are a few damages to the equipment now and then, but the scientific team keeps its good spirit and they are hard-working in the small scientific office where about a dozen of screens allow monitoring the work, recording and analysing the data.
The team has chosen to modify the cruise plan to follow a large eddy and to proceed to physical, chemical and biological measurements to better understand the functioning of this eddy and its impact on the fauna. They are now heading to the North West to reach the reefs and islands of Chesterfield. They are following the direction of the wind facilitating the navigation and allowing the crew to rest. The boat will then go to the south before coming back north-eastward on the western coast of the Grande Terre and arrive in Noumea on the 9th of December.
Instruments keep recording data along the cruise track. The ADCP (Acoustic Doppler Current Profiler) is a current profiler which measures the currents from the surface down to 600 m depth and also allows estimating the relative biomass of micronekton and zooplankton. Mounted on the hull, it records data permanently. Vertical migration of marine organisms is clearly visible on the ADCP vertical profiles. The acoustic signal is stronger (red color) during the night from the surface down to 200 m depth while in this layer, during the day, there is little micronekton/zooplankton (blue color on the ADCP profil).
Another acoustic instrument, the TAPS (Tracor Acoustic Profiling System) is lowered down to 200 m depth at each sampling station. The TAPS frequencies allow detecting the mesozooplankton, zooplankton organisms measuring 0.2-20 mm. At the first station, night and day profiles were conducted showing the vertical migration of the zooplankton with higher quantities in the first 100 m during the night (red) compared to the day (blue). The maximum of zooplankton is located between 70 and 100 m depth both during the day and at night.
The Nectalis 3 team has been at sea for one week now. As usual for a cruise at sea, some unpredictable events occurred. We left port with 24 hours of delay, on the 21st of November instead of the 20th. When we were about to depart we realised that the freezers were not working properly. We store the micronekton and some of the zooplankton samples in the freezer, so we had to repair them before leaving.
Once the freezers were repaired, the boat left in the eastern direction to reach station 1. On our way we stopped in the Woodin Chanel to calibrate the EK60 echosounder. When data analysis time comes, the calibration will allow us to transform the acoustic signal into biomass estimates of micronekton and zooplankton.
We stayed for 24 hours at the first station. The objective was to record the vertical movements of the zooplankton and micronekton during a 24 hours cycle. Most of those small organisms undertake a vertical migration every day, coming at the surface at night to feed and diving often deeper than 400 m depth during the day to seek protection from the predators.
With the 24 hours delay at departure, we decided to modify the sampling plan and we did not go the easternmost station, but instead the boat headed south.
During each station we collect water from the surface down to 500 m depth to determine its chemical composition and to analyse phytoplankton. We also collect zooplankton with a net towed in oblique from 600 m depth to the surface. The zooplankton net is equipped with 5 nets which opening and closing depth can be chosen. To estimate the quantity of zooplankton we also use the TAPS which is an acoustic sounder lowered down to 200 m depth. At last, le micronekton trawl allows us to collect small fish, squids, shrimps and gelatinous organisms.
Along with those chemical and biological collections, a number of probes onboard are recording information on physical parameters such as strength and direction of currents, temperature, and salinity. The first results show that the first 2 stations were located in warm waters with low salinity while the following stations were in colder waters with higher salinity. Currents also indicate that we are crossing eddies with currents changing from one direction to the other.
Weather has been rough so far with trade winds blowing. The boat moves a lot and does not make the work easy, hopefully conditions will improve.
Nectalis 3: a new exploratory cruise to better understand the tuna ecosystem
A better understanding of the high seas ecosystem that sustains the tuna production is still a priority if we want to continue savouring tuna. It is necessary to acquire a good knowledge of the climate and fishing impacts on tuna resource for scientists to provide the best information to decision-makers for a sustainable management of tuna fisheries in the Pacific.
The Nectalis 3 cruise contributes to this objective by exploring the southern area of the exclusive economic zone (EEZ) of New Caledonia in the south-west Pacific to collect data and samples on the pelagic ecosystem where tuna swim, particularly albacore tuna.
Cruise plan for Nectalis 3
A team of 6 scientists from SPC and IRD (French Institute of Research for the Development) has embarked onboard the IRD research vessel R/V Alis based in Noumea, New Caledonia. They will collect oceanographic data on physical (currents, temperature, salinity...), chemical (oxygen, nitrates, phosphates...) and biological (phytoplankton, zooplankton and micronekton, the tuna food) parameters to characterise and better understand the tuna ecosystem.
The boat already has a lot of equipment but the team has also embarked some specific gears to collect marine organisms: a zooplankton net and a micronekton trawl. With those 2 nets we hope to collect as many organisms as possible.
Zooplankton is composed mainly of crustaceans measuring between 0.2mm and 2cm. Micronekton, which forms the food of tuna, is constituted of larger organisms: fish, shrimps or squids measuring between 2 and 20cm. We are likely to discover new species as micronekton is poorly known because it is seldom studied and difficult to sample.
We will also estimate the quantities of zooplankton and micronekton and we will try and understand their spatial distribution in the ocean in relation to hydrology (currents, temperature...) and biology (phytoplankton), to better understand the spatial distribution of tuna in constant search for food. To this end we will use several acoustic instruments (EK60, ADCP, TAPS) to estimate the quantities of marine organisms present between the surface and 600m depth along the track of the cruise.
Nectalis 3 cruise is a follow up of Nectalis 1 and 2 conducted on the same topic in 2011 in the northern part of the New Caledonia EEZ. A fourth cruise, Nectalis 4, will be undertaken in 2015 to assess the impact of the cold season on the distribution of the marine organisms.
The Nectalis 3 cruise will depart on the 22th of November 2014 and our scientific team will be at sea for 3 weeks of hard work. We wish them all the best for this adventure and we are looking forward to hear about their fascinating discoveries.
The Nectalis 3 cruise received the financial support of IRD, SPC and AAMP (French Marine Protected Areas).
Sea Surface Temperature