Mar 27 - A Week at Signy
A Week at Signy
So what has been going on since we last left you?
When we left it last week the mud team had just finished their coring and we had been on a course for Signy in the South Orkneys. The ship was to arrive at the first of it's four stations in the early hours, and the 1500 metre CTD was in the water by 0615. The same mix of tools were continued throughout the day as at previous sites, with the last Agassiz trawl of the day on deck by 2130, and samples being sorted by the scientific staff until towards midnight. The CTD for the 1000 metre station was the first in the water the next day at 0600, with just the 2 shallower stations still to be undertaken, and the last EBS of the day back on the aft deck at 1620.
It was then off to an area outside Borge Bay, where the BAS base, actually closed only a few days previously, is situated. The ship arrived in the evening and was positioned in deep water off Polynesia Point, ready to await weather conditions the next morning. This, though, would be the first time since back in November at Bird Island, when deleterious weather conditions would prevail, hampering ship operations. Over the next day wind speed was averaging between 25 and 40 knot, with conditions unsafe for either diving from the Humbers or deploying the Trammel Nets with the Cargo Tender. Conditions did improve to a point overnight, and after fire and then lifeboat drills, the ship was manoeuvred closer in to shore, so as to assess whether or not operations would be feasible, but it was not to be.
With so many of the dive team having been regulars at Signy in the past, it had been hoped that this would be the easiest and quickest of all the dive sites to obtain samples at, but it was only on the 3rd day that they were actually given the chance to get in the water. By the morning of the 21st, conditions had improved enough to allow the Humbers into the water, and it was decided that diving could be commenced. Two dives were completed in the morning, but the weather was to deteriorate, so that by early afternoon the wind was gusting to 50 knots. The Humbers were thus re-stowed and the ship headed back out into deep water.
The weather was to partly improve overnight, and soon after first light the Humbers were launched, at last allowing the terrestrial party into shore to collect moss samples. It would be by around lunchtime when the shore party had finished all their moss collection and would be ready for transfer back the JCR by Humber. Next it was the turn of the dive team, though the presence of a Leopard Seal close in around the humbers lead to the abandoning of diving for safety reasons. Unfortunately, this was to be the case for the whole day, with the same Leopard Seal continually patrolling that portion of the coastline and seen whenever the Humbers or Cargo Tender were closer into the shore.
At 0915 the Cargo Tender was launched, having several duties over the day. Initially it headed out to deploy the 3 Trammel Nets for the fish team, after which, a small trawl, known as a Raucher Dredge (similar to an Agassiz Trawl, yet MUCH smaller) was used in an attempt to collect brittle stars on the flat seabed of Borge Bay. After several trawls, the tender headed into the jetty at Signy, where those on board would collect inter-tidal limpets samples, keeping out of the way of the many Fur and Elephant Seals that were now happily at home around the empty base.
The next two days would again be in the hands of the octopus and fish teams, with the three Trammel Nets being recovered, emptied, and then re-deployed in deeper water on the morning of the 23rd. The tender was back on board by 1100 and the ship then steamed out to undertake more Otter Trawling until dark. The weather had closed in again overnight, with the decision to leave the Trammels in deeper thus paying off. It would have been unsafe to launch the tender, but due to where they had been deployed the ship was able to recover them directly. All 3 were back on the forecastle deck, ready to be emptied by 1000, allowing another afternoon of Otter Trawling. This was to be the most successful day for the fish team since the start of the cruise and, after an afternoon of trawling, they would be in wet lab, logging the catch until well into the early hours.
The whole week had been fraught with problems due to the weather and local wildlife, but we were now due to leave the South Orkneys. Once the last Otter Trawl was back on deck, the ship continued it's gradual course east, now in the directions of the South Sandwich Islands. The big question is as to whether this next set of work will also be hampered by the wind and swell. With the biggest average wave height of anywhere in the world, we will just have to wait and see if, this time, the team's luck would be in..........You'll all have to wait until next week though.
This weeks science bit with the Fish Team
by Jenny Rock
GENE FLOW IN ANTARCTIC FISHES: THE ROLE OF OCEANOGRAPHY AND LIFE HISTORY*
In addition to researchers studying invertebrate fauna, this cruise also has a team devoted to all things fishy. We use two very different approaches to fishing, (1) a large net which is dragged over the sea floor behind the ship, called a bottom otter trawl, and (2) finer mesh nets called trammel nets which remain stationary in the water and trap fish that swim into them. (When at anchor in sheltered coves, we’ve also been known to cast shipside with a rod and reel, but this is our singularly most unsuccessful fishing technique to date!)
Although we have caught a huge diversity of Antarctic fish so far, our particular interest is in two key species, Champsocephalus gunnari (‘mackerel icefish’) and Notothenia rossii (‘marbled rock cod’), which have been subject to heavy fishing pressures in the past. These two species have very different life histories (e.g. age, reproductive behaviour and distribution of eggs/larvae) and our study examines the influence of both life history variation and oceanography on their dispersal and gene flow (population genetics). This is particularly important because understanding the transport of marine organisms by passive and active processes is fundamental to our understanding of key aspects of marine biology including colonization, speciation and biodiversity.
Using DNA from tissue samples, we employ genetic markers (mtDNA and microsatellites) to identify population structure in these fish at both circumpolar and regional geographic scales. Genetic and life history data is then incorporated with information on ocean circulation patterns generated by several team members who are oceanographers at BAS. These researchers use ocean circulation models to predict the transport speed and direction of planktonic fish eggs and larvae spawned at different locations around Antarctica. Our combined data allows us to compare the actual population biology of the fish with the predictions from the oceanographic model. This will give us greater insight into the nature of biological and environmental constraints on dispersal and gene flow in marine organisms. This approach is important not only because (1) it tests generalised and specific predictions about life history and oceanographic influences on the maintenance of biodiversity, but (2) it identifies the effects of both biological and physical processes on the connectivity (vs. separateness) of populations and survival of exploited fish stocks. Lastly (3), this information on population and habitat connectivity and its relationship to physical and oceanographic variability contributes to the debate on the utilisation of Antarctic ecosystems as sentinel models of global environmental change.
* The source of inspiration and implementation for this project is the result of many years’ gestation and input from multiple investigators. Among the most notable is Dr Helen Wilcock, who tragically passed away this week, and to whom we dedicate all our continued devotions to this work.
Here are some of this Week's Fish
And again finishing with some more of the scientists and crew
And so now on to the South Sandwich Islands........next week.