Once More into the Breach

Welcome to the webblog for the Dutch contribution to the International Blue Whiting Spawning Stock Survey 2016, an international collaboration between Norway, the Faroese Islands and several EU countries. Unfortunately, Russia is not participating in this year's survey. 
 
We are aboard the RV Tridens, which departed from Galway in the early hours on Monday 21st of March. You can track the vessel here:

https://www.vesselfinder.com/vessels/TRIDENS-IMO-8821852-MMSI-244033000

The seas were remarkably calm throughout Monday. We reached our first station (GPS position at which we begin our transect or take measurements), near the continental shelf edge at the Porcupine Bank, at about 7 p.m. and began the acoustic transect work. Here is an example of an echogram we recorded.



Acoustics is a scientific means of detecting and measuring the changes of density in a medium (in this case sea water) using sound. Since fish are more dense than water, they are readily distinguished in the water column. It makes for a powerful, non-invasive method to estimate stock abundance and biomass of large schools of fish. To verify the acoustic readings, we will be doing fishery analysis via trawl net. 

In the meantime, we had a look at the local birds. They were predominantly gannets, black-headed gulls, fulmars and a few blackbacked gulls.  



The sea is a little rougher today with an area of low pressure coming towards us. 

 









We are currently about three quarters into our second transect, no sight of large whiting schools yet, hopefully this evening. Lots of sea to cover.  

The Journey Home

Tuesday 7th April

We luckily managed to fit a last haul, haul number ten, along our remaining transect. We targeted a few small schools of blue whiting which were shown on the echo sounders. Usually we wouldn’t consider targeting such small schools but given that our time was nearly up, we decided to fish. The haul contained fewer blue whiting than past hauls but this wasn’t a big surprise due to the echograms. We also landed a few mesopelagic specimens in the haul.

From the last waypoint of our final transect we headed straight for Scheveningen harbor at around 18:00 Tuesday night. Flat seas allowed fast progress on our journey home (averaging around 12 to 14 knots) which meant we arrived at Scheveningen about 12 hours earlier than expected: 17:30 Thursday evening. The conditions on the way back would have been perfect for some marine mammal observation, or just to enjoy the view, however this was made impossible due to a thick fog that remained with us most of the time. Instead we finished processing and recording remaining data, and reading the last of the blue whiting otoliths. 

Flat seas!

Into the fog.

Blue whiting otolith through the microscope.

Eric keeping us on the straight and narrow with one of his legendary lectures.

In summary we did 9 blue whiting hauls in total landing around 10 – 15 tonnes of blue whiting; one deep sea haul observing around 50 different species; 30 CTD stations; covered 2200 nautical miles; with a bonus wet and windy weekend on the Isle of Lewis!

Land in sight.

Arriving at Scheveningen

 Until next year!

Hauls 7 (deep sea), 8 and 9

We had a very busy Easter Sunday with three hauls taking place in one day. First was a deep water haul, over 1000 meters deep which was landed on board at around 2am. From this we sorted the blue whiting from the haul and measured and weighed the less abundant, larger species. We then caught a few hours’ sleep before meeting at 9am to resume identifying, measuring and weighing the smaller, more numerous species. Identification can be quite a difficult task due to the similarity of some species who display only very subtle differences as their determining feature. 

Deciding who's who.

Sorting the species...

... and finally some organisation.

This haul contained more interesting species compared to last year’s deep haul due to an increased towing time. Included among the 30+ deep sea species were two deepwater spiny dogfish “Centrophorus squamosus” (one juvenile and one adult female), five black scabbard fish “Aphanopus carbo”, a few snipe eels “Nemichthys scolopaceus” and many lantern fish species from the myctophid family.

Think we need a bigger board...

“Centrophorus squamosus” profile.

Black scabbard fish “Aphanopus carbo”.

Snipe eel "Nemichthys scolopaceus”.

Myctophidae 'lantern fish' species.

A tray full of horror - "Chauliodus sloani".

"Lampadena speculigera"

"Stomias boa"

A "Pseudoscopelus altipinnis" smile.

Many of these species contain light producing organs called photophores, these are used for communication in the darkness of the deep sea and come in an array of attractive colours!

Blue on myctophidae species.

Pink on pearlside (Maurolicus muelleri).

Even on squid!

Multicolour on unknown squid species.

Haul 8 was fairly standard mostly containing medium sized blue whiting. During haul 9 we targeted a single dense school of blue whiting at around 550 m deep. Unfortunately we just missed the main mark as little was seen entering the net on the netsonde. Instead we used the time to trawl on a scattering layer at around 200 m which turned out to be mostly pearlside (Maurolicus muelleri). Despite the near miss, haul 9 did contain a monster blue whiting of 42cm – not the biggest on record, but not far from it! The large female deepwater spiny dogfish also made an appearance in haul 9 but only as she had been stuck in the net all day, vouched by a crew member who saw her while shooting the net earlier that day.

Monster blue whiting.

Part of processing the blue whiting samples is to determine what sex they are, this is important to understand stock health and productivity. In case you were wondering what they look like, here you are!

The females..

..and the males.

We are now steaming towards the start of our last transect before heading back to the Netherlands - hopefully we will be able to have our last and final haul during this time.