Fisheries management 101

Yeah, I know I said the list didn't have any particular order, but now that I think about it, why not start with the basics? I mean, if you're not a fisheries scientist, this would make your reading easier (=you will keep reading, right?). I will try to explain a few concepts that I will use over an over again. So, is the band ready?

• Fish stock:

Wow, I just started and this is already difficult. There is quite a bit of discussion on how we should define stock. My favorite definition is the one by Ray Hilborn and Carl Walters, and it says that a stock is a group of fishies that is large enough to maintain itself, and where all the little fishies have similar lives (that is, they grow at the same speed, become mature at the same age, eat the same things, like the same tv-shows, etc.). This is a very practical definition, but just because of this, it is a somewhat artificial one. Other people say that we should define stock according to a lot of genetic parameters and that stuff (the idea that we're all part of the same family), and it would be nice but it is also very difficult to establish, so I will use the one I told you before.

• Recruitment:

Ok, this one is easier. In not-so-many words, it means how many of all the baby fishies born in a given year (or any other time frame used) survive and grow up to either sexual maturity, or the age at which they are first caught (the age where they become vulnerable to fishing gear). What definition to use depends on what we want the data for.

• Spawning stock (also known as spawner stock):
  

I guess the name is quite self-explaining, right? It makes reference to the parental stock, the part of the stock who is sexually mature. So, if I say spawning stock biomass, I guess you'll know what I'm talking about... yup, that's right, it is the total weight of the spawning stock.

• Maximum sustainable yield (MSY):

This is a rather tricky concept, but it is very important to know more-or-less what it means if you want to ever grasp what is wrong with fisheries. The main idea goes like this: on one hand, the more fishies you have, the more eggs and fishies that could be born, at least theoretically. On the other, the more fishes you have, the less food there is going to be for each fish, these won't grow as large and more of them will die of starvation, so the more fish you have, the less fish you have (well, this is a little more complicated, but you get the idea). If these two things happen, then there should be some kind of theoretical optimum value where we can take the largest yield, and ensure we will keep getting such large yields into the future. If we fish more, then less fishies will be born and we will have less, but if we fish less there will be less and less food, so we won't get as many fat fishes and our yields will be smaller.

So far everything sounds perfect and we shouldn't have any problems with fisheries, but there are lots of issues with this. There's for instance, uncertainty, that is, we can never know for sure how many fishes there are in the sea, so we don't know for sure where the optimum is and how close (or far) we are from it. But there is even a bigger problem, maybe you noticed that I was mentioning the word 'theoretical', which obviously implies that we're not even sure if such an optimum value even exists! Things in nature vary just too much for us to sit and hope that they will behave the same way over and over again, that's a little bit too much optimistic. I guess you can get an idea on how some fishery managed only by using the MSY idea can easily get out of control and collapse. If you don't, you can ask me :)

• Total allowable catch (TAC):

One of the most famous concepts in this whole area of fisheries, a TAC is a quota set by the managers to the fishermen, and it states how much can be caught during a given year. There are lots of ways in which TACs are set, how they are distributed among fishermen and other things, but I won't get into it now.

• Marine protected area (MPA):
  

This is a very trendy thing these days. The idea behind it is very simple, and so far it seems to work. As its name implies, an MPA is a place where no fishing can take place, so every fish living there will be safe from us. In a way, it works the same way as a national natural park almost anywhere. There are some issues though, like for example, how do you design a reserve for species like tuna, who travel thousands of miles during their migrations? well, I will talk about that some other day.
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Ok, I think that is enough for now. If you know what the things above mean, you will easily understand the subject of the following discussions.

Please, let me know if you understood or not.