Looking after little fish.

This is an interesting story because it highlights the way in which animals are so interconnected and it demonstrates the importance of the smaller, and arguably less exciting, little fish, like sardines, anchovies and the even smaller crustaceans known as krill. These smaller species, known as forage species, often occupy a key position at the center of the food web. This means that they are a key link between the species low down in the food web (at a lower trophic postion) and those higher up (at a higher trophic position). Small fish and krill occur in really high numbers and are often densely packed since their natural instinct is to swarm together. They are eaten by a number of much larger predators, i.e. bigger fish, sea birds and even whales. Blue whales, for example, can eat around 2000 kg a day worth of krill during their 3-month feeding season. 


But these little chaps are also consumed by humans and so the concern is that the current levels of fishing are having severe knock-on effects on other groups, because of the important position of these little forage species in the food web. To look into this further, researchers at CSIRO's Wealth from Oceans Flagship (http://www.csiro.au/csiro/channel/_ca_dch2t.html) constructed mathematical models of food webs, which showed that current fishing levels may have produced a 60% decline in groups such as marine mammals and sea birds. They go on to recommend a 50% reduction in fishing rates, which would still give 80% of the maximum sustainable fishing yield.


Just a quick word about the maximum sustainable yield or MSY: it is the maximum number of fish that you can take without the number of new born fish (knowns as recruits) severely dropping, i.e. without unsustainable exploitation of the fishery.  


See the review article at Science Daily:
http://www.sciencedaily.com/releases/2011/08/110810093837.htm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+sciencedaily%2Fearth_climate%2Foceanography+%28ScienceDaily%3A+Earth+%26+Climate+News+--+Oceanography%29