Why mackerel must be taken very SERIOUS! Jens Christian Holst Scientific advisor Ecosystembased jens@ecosystembased.com
Living together = competition and predation
Salmon postsmolt migrations first three months at sea
6000+ scientific catches of postsmolt starting 1991
Postsmolt salmon migration first three months at sea
Collapse in postsmolt growth Salsea-Merge 2011
Reduced postsmolt feeding Salsea- Merge 2011
Extreme increase in mackerel stock distribution and stock size
Mackerel distribution 2004 and 2009 Nøttestad 2011
Mackerel distribution 2019
July-august trawl survey 2007 2010 2011 2012 2013 2014 2015 2016 Nøttestad og Utne, Institute of Marine Research, Norway, in Naturen 2016
Three times larger geographic distribution, double density: sixfold increase 2016 2007
Mackerel growth:Total collapse Olavsdottir et al. 2015
Extreme increase in overlap between mackerel and salmon smolts
Mackerel eggs May1992 Mackerel eggs May 2016
Highest mackerel egg densities in 2016
Mackerel also spawning all way up to Northern Norway after 2008
Mackerel fisheries April-June
Mackerel fisheries July -August
Postsmolt life catching aquarium!
Cannibalism in mackerel and the potential for postsmolt predation
30 cm mackerel
30 cm mackerel
30 cm mackerel 12.5 cm smolt
Cannibalism is today common in the starving mackerel
We know exactly where the postsmolts and the mackerel overlap
Camera Trawler Steel-bar Video Camera trawling Triangle of Steel-bars Anticipated picture from underwater camera
VIDEO FRAME
60° 1 1 D C 8 2 2 2 5 2 1 1 6 8 2 5 4 6 1 5 11 2 1 1 1 1 1 3 1 3 3 1 4 2 11 1 1 1 1 2 1 13 1 1 4 2 A 3 1 1 1 1 1 1 1 3 1 RV SCOTIA 2 1 8 1 5 13 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 MAY 2005 58° B 10° 5°
Continuous smolt distribution along trawling track
My experience: Strong resistance against the hypothesis on overgrazing and predation in particular from scientists who are not marine ecologists but river scientists
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