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NEWSLETTER ISSUE 1/09 February 2009

Greenland Halibut - Tag, Study, Manage!

After Jesper Boje, Senior Scientist at the Danish National Institute of Aquatic Research, DTU Aqua*.

Over the recent decades, Greenland Institute of Natural Resources (GINR) has studied Greenland halibut (Reinhardtius hippoglossoides) in Greenland waters. The studies have produced much needed information on the Greenland halibut stock structure for fisheries use. Today the emphasis in research is focused on improving biological knowledge as basis for a sustainable fisheries management.

Greenland halibut stock structure and migratory behavior has been poorly determined in the past which has resulted in inadequate stock and fisheries management. Since the mid 1980s conventional tagging with T-bar tags has improved the overall perception of large scale migration. Tagging projects and other methods in genetics and meristics have given us a better picture of the Greenland halibut stock structure.

Since 2001 The GINR has used Star-Oddi DSTs (with temperature and depth sensors) in tagging projects on the Greenland halibut. Tagging has been done in some fjords in western Greenland, where commercial fishing is high ensuring a recapture rate of approximately 10%. Acquired depth measurements have been compared to the depth contours in the area increasing the knowledge on the seasonal migration of Greenland halibut.

In September 2008 the GINR tagged 43 Greenland halibut with DST comp-tilt loggers (sensors for tilt in three dimensions, relative compass heading, temperature and depth) and 50 halibut with DST centi tags (temperature and depth). Scientists hope to recover new information on the halibut's spawning behavior - which still remains a mystery - with the new compass and tilt tags. The tagged Greenland halibuts were released in Denmark Strait (deep sea area between Iceland and Greenland), where the halibut is expected to migrate long distances as part of feeding and spawning migrations. Relative compass readings will hopefully shine light on the migratory routes over longer period of time. Further more information on important retention areas where fish spend more time spawning and feeding could be recovered.

So far only a few tags have been recovered from this study (the area where tagged halibuts were released is vast and thus expected recapture rate low). Denmark Strait is one of the most important international fishing areas for Greenland halibut in the Northwest Atlantic, and the GINR will continue the research in this area in order to further improve the fisheries management.

*DTU Aqua has a close cooperation with the Greenland Institute of Natural Resources


DST comp-tilt and NEW DST Magnetic

 

Star-Oddi manufactures now two compass loggers, DST compass and DST comp-tilt. The third compass logger DST magnetic will be launched this April. All Star-Oddi compass loggers are centi size (15mm x 46mm). Star-Oddi loggers with compass heading sensor are unique in the world market.

DST comp-tilt measures temperature, depth (pressure), tilt in three directions and compass heading with reference to magnetic north. Basically DST comp-tilt is a combination of Star-Oddi DST tilt and DST compass loggers. The compass measurements have limited tilt compensation, which means that increase in tilt still has some influence on the compass accuracy. The magnetic field is measured in two directions and the third axis is calculated in the SeaStar software.

DST comp-tilt loggers have been used in studies e.g. on migratory routes and spawning behaviour of some fish species. The DST comp-tilt has a memory size of 20000 measurements, for both of the parameter pairs, compass-tilt and temperature-depth. With this memory capacity you can record 111 measurements every day for six months.

The DST magnetic measures apart from temperature and depth, tilt in three directions and compass heading with reference to the magnetic north. The magnetic field is measured in three directions providing a relative reading of the magnetic field strength at each point.

Compass heading measurements are compensated with the tilt measurements. This enables good tilt compensation on compass heading and thus more accurate heading readings. DST magnetic also provides an absolute value of magnetic field inclination for each reading. The memory capacity on DST magnetic is 17000 measurements for both of the parameter pairs, 94 measurements a day for six months.

Data Storage Tags - DSTs

Star-Oddi DSTs are small data loggers available in three different sizes. DSTs vary also in sensors, memory size and battery life. All DSTs have a biocompatible ceramic housing. DSTs are used in various industries and in scientific research for environmental monitoring.

DST sizes: centi, milli and micro


Star-Oddi compass and tilt recorders


-DST Pitch & Roll measuring temperature, depth and pitch&roll movements of the DST in two directions, in reference to the earth gravity

-DST Tilt (3-D) measuring temperature, depth and tilt in three directions. Better resolution! More accuracy!

-DST Compass measuring temperature, depth and compass heading with reference to the magnetic north in two directions.

-DST Comp-Tilt (3-D) measuring temperature, depth, tilt in three directions and compass heading with reference to the magnetic north. Better Resolution! More accuracy!

 

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Did you know that...?
 
In 1783-1784 Laki or Lakagígar (Craters of Laki) volcano and the adjoining Grímsvötn volcano erupted, pouring out an estimated 14 km3 of basalt lava. Clouds of poisonous fluorine and sulfur-dioxide compounds killed over 50% of Iceland's livestock, leading to famine.

The meteorological impact of Laki resonated on contributing significantly to several years of extreme weather in Europe.

In France a sequence of extremes included a poor harvest in 1785 that caused poverty for rural workers, accompanied by droughts and bad winters and summers, that destroyed crops. This in turn had a major effect on the build up of poverty and famine that triggered the French Revolution in 1789.

Laki nowdays, quite peaceful..
 

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