Is fish getting smaller and does it matter?

Asta AudzijonyteDepartment of Environmental Sciences

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Changes in fish size are caused by fishing and climate change

Changes in Atlantic cod size and maturation age

Cause 1: fisheries-induced evolution. We typically catch fastest growing and biggest fish

Cause 2: Increased temperature. Warmer waters hold less dissolved oxygen. Larger individual have smaller surface (obtaining oxygen) to volume (using oxygen) ratio and cannot maintain their respiration capacity

temperature

oxygen

Time

1987

2003

Some cases where reduced body size and earlier maturation has been reported (red dots). In the Baltic Sea: ca 20% reduction in body size of female eastern Baltic Sea cod between 1987 and 2003 (Vainikka et al. 2009)

Who eats whom in marine systems very much depends on size

My earlier results in a different marine ecosystem showed that decreasing length-at-age can greatly increase natural mortality

Audzijonyte et al. Biology Letters, 2013

Gradual but directional changes in size led to positive feedback loops, such as changes in age structure

Year 1 Year 50

Audzijonyte et al. Biology Letters, 2013

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What does it mean for the smaller Baltic Sea cod? Can evolution explain reductions in cod size due as a result of fisheries-induced selection? Stay tuned to find out possible answers to these questions with the evolving Baltic Sea ecosystem model!

THANK YOU