The empty feeling of no conclusions

When I started the PhD, the cod stocks were in very bad shape.
On the opposite, sardine is a fish from low level of the marine food web; catch with purse-seining, a fishery with relatively low environmental impacts, and had greater potential of consumption in Portugal, since Portuguese love more sardines than any other people.
Because Portuguese eat so much cod, it would be great if they would eat more sardine (or other small pelagic fish) instead.
It turns out that after some years of trying to have something interesting to say in a PhD thesis...
The cod is not so bad because some stocks (not all!) as for example the Norwegian, recovered and are now certified by MSC.
Plus this year the North Sea cod stock seems that had finally recovered.
And Portuguese sardine stock (Iberian stock) had problems, with consequent suspension of the MSC certification in 2012.
Now more and more evidences show that it is a threat to marine life the depletion of sardine stocks, with important consequences for organisms, as marine mammals and birds.

The Pacific coast of North America supports one of the most vibrant and diverse marine ecosystems on Earth, largely because of the presence of thick schools of small prey fish such as Pacific sardines.
Unfortunately, this crucial forage fish appears to be in the midst of a severe population decline. 
Its absence will be felt by dozens of species of West Coast seabirds, whales, sharks, dolphins, and commercially important fish such as salmon and tuna that depend on sardines as a major food source. 
In addition, because sardines have been a staple of commercial purse-seine fishing on the West Coast, their decline raises the potential for fishing pressure to shift to similar, but more abundant, schooling species of forage fish. 


So what can I say about sustainable seafood consumption in Portugal?
Maybe just do not eat fish.
Or at least not too much!
Or try to be vegetarian.
Was it worth 4 years to do not have a clue what to conclude?