MarBlog

So these last couple of days I have attended WKMOR - a workshop on understnading and quantifying mortality in pleagic, early-life stages of marine organisms.

Don’t let the title put you off – this is interesting stuff. To put it in lay-mans terms – every fish or other marine animal that we enjoy eating throws out millions of eggs every year to reproduce. Only a tiny fraction of these survive, but with the big number you’re talking about, even a relatively small change in the survival of these eggs through their various larval phases into adulthood, can mean a huge change in what we are able to harvest. More over – the ability to harvest one species of what we regard as foods, may have a significant impact on other species in the foodweb – so, as ususal, it is not straight forward.

However, this workshop aims at addressing one of the issues that has been a hard nut to crack for decades – namely mortality – how many of the eggs and larvae die – why, how, and what drives it.

So far, ideas range from the downright depressing – “we don’t know anything”, to the “We’re getting there”.

One of the major complexities is that for small critters swimming aorund in a soup of plankton, the critical issue has been assumed to be able to grow fast so you have less predators eating you. While this idea still reamins valiud, there seems to be a shift towards the idea that just realising growth may not be enough – the predators will still get you if you aggregate, or if you are particular successfull in surviving in high numbers. In addition, once these larvae has made it to the end of their free-floating planktonic stages, it may simply be that there is only room for a limited number to settle to the seabed, which means that the number of survivors is limited no matter what.

Opinions still differs, and it is an areas that will require increased attention. Certainly one things is clear – the ability to model larval fish and their intricate prey feeding it noteworthy, but not enough!