So here's the old news.... fish targeted by fisheries have been in decline for some time.  Removal or reduction of populations can alter ecological interactions, meaning that other species may become more abundant (or less) in their place.  This is typically done through something called competitive release (the species you compete with are gone, so there is more of a given resource for you) or trophic cascades (as one predator species is removed, its prey becomes more abundant because nothing is eating it.  Of course that means that there is more of those species to nibble away at whatever they eat, causing a population decline in that prey species).

Here's the new: The UK prawn fishery - the most valuable of the UK fisheries - only came about because of overexploitation of other marine species. The industry, a new study finds, is not built on solid grounds.

It seems that the paper has some backing from the industry too, with the Sustainable Inshore Fisheries Trust - a Scottish based charity - supporting the findings.

For those with access to the journal 'Fish and Fisheries' you can see the original paper here  http://onlinelibrary.wiley.com/doi/10.1111/faf.12041/abstract

If you don't have journal access, you can read the press release which gives an overview of the paper.