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The longline experience in the deep

4,5 metres long Greenland shark
A Greenland shark – largest specimen caught. 440 cm and approximately 700 kg
Using 87 500 hooks, fishing to depths ranging from 450 to 4 300 metres, the longline vessel M/S Loran caught 8 800 specimens during their cruise along the Mid Atlantic Ridge. Among the 50 different fish species, the biggest was a 4.5 metres long Greenland shark.

By Jan Erik Dyb and Inge Fossen, Moere Research

The longline vessel M/S Loran was hired to operate alongside the research vessel G. O. Sars during the second leg of the MAR-ECO expedition last summer. The vessel supplemented the sampling directed at demersal fish and other taxa by using passive fishing gear as longlines, gillnet and trap.

During 12 fishing days, a total of 87 500 hooks and numerous gillnet and trap sets were made. The fishing depth ranged from 450 to 4 300 metres, and fishes were caught in the entire depth range. Approximately 8 800 specimens, stretching from 16 to 440 cm in body length and representing at least 50 different species of fishes, were caught. Average fish size in the longline catch was approximately 10 times bigger the average size observed in the trawl catches. The combined effort by both trawl and longline therefore facilitate a description of a broader size group of fish species occurring along the ridge. The longline catches will be particularly useful in describing the larger predatory species.

Collecting and measuring

Onboard whole specimens were collected to the museum, both to complement the museums collection but also to allow for a closer taxonomic examination of the different species caught. Some of them could not readily be identified to species onboard, only to family or genus level. Biological measurements and samples were carried out as soon the fish arrived on deck.

C. armatus
C. armatus, the species caught at 4300 m, the deepest station during last summers exercise 
The samples included tissue samples for genetic studies, stomach and gonad samples together with ear stones or dorsal spines for age determination. Several biological parameters were also recorded such as fish length, total weight, sex and stage of sexual maturation. These data and samples are now being processed and will be used in a number of different studies. The results will in particular help us to understand ecological processes taking place in these deep-sea areas and increase our knowledge of biological parameters among the larger predatory species found along the Mid Atlantic Ridge.

A longliner demands long ropes

Hauling the end
Each pile of rope is approximately 550 m long... Click on the image to see the video Hauling the end".  
The technical success of the cruise was assured through a professional use of the advanced ship and efficient gear handling by a skilled captain and crew. Patience was one of these important skills - which was needed to haule the end of a line at a depth of 3 500 m, as shown in the "Hauling the end"-video.

 


 

Read more

~ See the album with pictures from the cruise on board MS Loran

~ See the cruisereport at the scientific website

~ See the video "Hauling the end"

~ Read Longliner MS Loran chartered (05.05.2004)

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