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Descartes prize

15. July


Transfer to the next Super station, the Faraday seamount.


Rouleina attrita with an anchor worm.


Despite the fact that Orange roughy are very long-lived, the scientist holding this fish is likely much older still.

Todays Highlights

Date:July 15, 2004
Author:  Sven Klimpel (IFM-GEOMAR, Germany) and David Shale (England)

Today we continued to steam northwards, leaving behind the deep blue but barren waters of our first sampling area. As we approached the Faraday seamount, the indicators of increased productivity appeared. Colder weather (13oC), blue-green waters and an increase in the number of seabirds. Fulmar petrels are dominant with greater shearwaters and giant skuas in attendance.
During the day our smaller ROV "Aglantha" was worked on, 20 metres cut from the cable to try and rectify the faults which have plagued us. We now wait to find out if all the hard work will create success.

The highlight of today was a long tow with the bottom trawl at 800-1500 m to sample the shallower bentho-pelagic fauna close to the seafloor. The deepest layer of the haul yielded a mixture of spectacular fishes. The most conspicuous catch was 14 adult and juvenile specimens of Orange roughy (Hoplostethus atlanticus) in very good condition. These unusual looking fish are brilliantly colored and can live to be quite old (these fish species lives for well over 100 years). Of course the Orange roughy is best known on the tables of many restaurants world wide as a highly regarded food fish.
Other species of the deep layers captured, which are also of commercial value to humans, were the Black scabbard fish (Aphanopus carbo) and two species of grenadier. As in previous tows the Roundnose grenadier (Coryphaenoides rupestris) was very common to the nekton community in the upper layers. Almost as well known is the Onion-eye or Roughhead grenadier (Macrourus berglax). Both of these species get quite large, and are commercially fished. Ironically, although both species are quite good tablefare, another name for this huge and diverse family of fishes is the rattails. Needless to say, you don't see this advertised at fish markets or restaurants. After the big fish trawl, samples were identified, labelled, photographed and stored.

Recently we have analysed the metazoan parasite fauna of different deep-sea fishes. These investigations are very important since parasites are integral parts of all aquatic communities and then important elements of deep-sea biodiversity. In fish biology, parasitological studies have increasing importance, because parasites can help to analyse the diet of fish species, serving as biological indicators of the prey species and their origin. Whereas stomach analyses may provide detailed information on the immediate trophic relationship at the time of sampling, parasitological studies make it possible to infer previous trophic interactions.  Thus integrating short-term variability in the food web to make wider relationships more apparent. Parasitic helminths are particularly useful for such studies, because the different stages in their life cycle are passed through the marine food web until they reach their definitive host. Finally, parasites provide information on habitats and trophic status of the studied fish species within the deep-sea ecosystem.
So far, parasitological studies on deep-sea fish species from the northern mid-Atlantic Ridge are very scarce. One of the main obstacles is the difficult access to deep-sea organisms, which necessitates expensive research expeditions or deep-water fisheries.
For example - the most conspicuous fish parasites in the deep-sea are parasitic crustaceans. Nearly all crustaceans, which parasitize on deep-sea fishes, belong to the copepoda. In contrast to their free-living relatives, they are visible to naked eye due to their relatively large size. They have developed different types of clamp and anchor organs to attach to the host. Recently, we have found many parasitic copepods from the families Sphyriidae and Chondracanthidae, with 3-4 large species. The deep-sea fish Rouleina attrita (softskin smooth-head) is usually parasitized by the anchor worm Lophoura sp. The Lophoura sp. anchors its head into the musculature of the fish. The brown or red body and the yellow or white egg sacs together measure approximately 4-6 cm and at first glance may be mistaken for an artificial tag. After egg release, the parasite dies off and leaves a deep wound behind. Mass development with these copepod infections seem to be one of the most important causes of natural mortality for young fishes in the deep-sea.

 

Weather Conditions

Today the weather was cooler, sunny this afternoon, but by the evening rain and increasing wind.

 

Tomorrows expected highlights

We expect to arrive at Super station 54 and continue our programme with Lander, CTD and trawling.

 

Cruise journal

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July 2004

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August 2004

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