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A) Overview of recaptures
• Days at liberty between 4-375 days
• Movement of the cod inuenced by season
and release posion (Fig. A)
• Geolocaon needed to reconstruct path
between release & recapture posions
B) Cormorant predaon
• Found by ornithologist on a cormorant
colony half a year aer death
• Captured in shallow, coastal water
(3m depth, Fig. B)
• Inuence on DST performance?
C) Shallow movements
• Scienc survey could miss cod making use of
shallow water habitats in quarter 1 & 4 (Fig.C)
• Upslope or pelagic movements?
• Potenal survey bias if interannual variability
D) Moon phase
• Extent of vercal migraon varies
with moon phase (Fig. D)
• Follow prey organisms in shallow water
at night
• Behaviour only observed with cod released
o the Swedish coast
The Balc cod –
An unexpected journey
Stefanie Haase1*, Kate McQueen1, Monica Mion2, Uwe Krumme1, Michele Casini2, Karin Hüssy3, Annelie Hilvarsson2,
Hans Jakob Olesen3
Conclusion
The DSTs from recaptured cod have already
revealed a surprising diversity in movement
and behaviour patterns of eastern Baltic cod,
both within and between individuals.
Use of shallow water habitats appears to be
more important than previously assumed.
This diversity should be considered when
attempting to understand changes in status
of the stock.
Figure A: Release (le) & recapture (right) posions of the 43 recaptured
DSTs-tagged cod.
Worrying trends such as decreases in stock size
and individual growth rates, and diminished
distribuon range, have been observed in the
eastern Balc cod stock in recent years.
However, the mechanisms underlying these
stock developments are sll poorly understood.
In an eort to beer understand the observed
changes in this stock, 1260 cod in the eastern
Balc Sea were tagged with data storage tags
(DSTs) which record high-resoluon measure-
ments of temperature and pressure. Each of the
43 recaptured tags provides a wealth of valuable
new data, revealing insights into Balc cod
ecology and their individual journeys through
the Balc Sea.
Figure C: Shallowest depth per individual and day between 8 am – 6 pm
(survey operaonal me) The vercal line shows the minimum opera-
onal depth of the scienc survey.
Figure B: Temperature and depth prole of DST-tagged cod which was
eaten by a cormorant. Arrows indicate predaon event.
Feb 15th 2018 Mar 1st 2018 May 1st 2018 May 15th 2018
Figure D: Temperature and depth prole of a DST-tagged cod released
by Sweden.
Nov 16 Dec 16 Jan 17 Feb 17 Mar 17 Apr 17 May 17
North
Sea
North Sea Balc Sea
18°E16°E14°E12°E10°E8°E
57°N
57°N
56°N
56°N
55°N
18
°
E16
°
E14
°
E12
°
E10
°
E8
°
E
55°N
54°N
54°N
0100 20050 Kilometers
Bornholm
*Stefanie Haase, stefanie.haase@thuenen.de
1 Thünen Instute of Balc Sea Fisheries
Alter Hafen Süd 2 18069 Rostock,
2 SLU, Swedish University of Agricultural Sciences, Lysekil
3 DTU, Technical University of Denmark, Lyngby
new moon full moon Temperature [°C]