Clownfish decline due to aquarium collecting

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A recent study has shown that collection for the aquarium trade has negatively impacted wild clownfish populations.

The study by Alison Jones and coauthors involved visual surveys for clownfishes on two areas of the Great Barrier Reef with contrasting histories of disturbance.

The authors found that anemone and clownfish numbers were adversely affected by the amount of bleached coral present, with both anemones and clownfishes being absent in bleached and unprotected reefs.

It is thought that leaching causes the anemones to lose their symbionts after which they may shrink and eventually die due to the temporary loss of photosynthesis.

The shrinkage, weakening or disappearance of the host anemone can limit the population, the size of the female fishes and the potential for new recruits.

Additionally, loss of fishes can then affect the survival and growth rate of the anemone.

This negative cycle of shrinkage as a result of bleaching and subsequent loss of protection followed by further shrinkage may have led to serious declines in the anemone habitat available for new fish recruits and this may have depressed the reproductive success of the remaining fishes.

The authors also discovered that sites that were closed to fishing and aquarium collecting had more anemones and clownfishes, with the clownfish density being as much as 25 times higher than in sites that were more disturbed and where fishing and aquarium collecting were permitted.

The authors assert that the collection of clownfish for the aquarium trade has had a negative impact on populations: ...the assumption of commercial collectors that removing breeding adult increases survivorship and growth of young recruits is contentious

Removing breeding adults or even sub-adults could cause the anemone to shrink, thereby reducing the amount of space for new recruits, and it may be up to 6 months before the fishes begin to breed again

For more information, see the paper: Jones, AM, S Gardner and W Sinclair (2008) - Losing ~Nemo : bleaching and collection appear to reduce inshore populations of anemonefishes. Journal of Fish Biology 73, pp. 753"761.