Commercial fishing, climate change causing fish to shrink

by CSIRO 
Silver Warehou
.. ©
A new study by Australia's peak scientific body the CSIRO shows that fish around the world are shrinking in size.
Commercial fishing and climate change are believed to be the main culprits behind the decrease, but CSIRO scientists say the shrinking size is also leading to a drop in fish populations, with smaller fish more susceptible to predators.


Marine biologist, Dr Asta Audzijonyte of the CSIRO's Wealth from Oceans Flagship, and colleagues, reported their findings in the journal Royal Society Biology Letters.

Dr Audzijonyte says commercial fishing could be changing the long-term evolution of fish sizes.

She found that even small decreases in the body size of some fish species had a big impact on their population size, because it made fish more vulnerable to predators.

'So basically, if the flathead gets a bit smaller, it's being eaten more heavily by other fishes like barracuda, which is the predator of the flathead,' she explained.
The CSIRO study looked at five Australian fish species: Tiger flatheads, jackass morwong, silver warehou, blue grenadier and pink ling.

'We usually selectively catch the largest and the fastest-growing individuals, leaving the small ones in the ocean. So we only have the small ones left ... But then also, only the small ones get a chance to reproduce, and they are more likely to produce other small and slow-growing fish.

'So in this way, we are getting a long-term evolutionary decline in body size, which is more problematic because the fish will not get bigger quickly, even if we completely stop fishing, because they already became evolutionarily smaller.'

The scientists used a complex modelling system to test how the decreasing fish size affects the interactions between different species.

More at http://www.csiro.au/en/Organisation-Structure/Divisions/Marine--Atmospheric-Research.aspx