A few years ago I remember being challenged by a motorcycle mechanic in a pub about discards. I remember feeling quite indignant that while a mechanic could see the evils of throwing good fish back into the sea again the fisheries community couldn’t do anything about it. It seems blindingly obvious that discards are a bad thing. However, I’m a born cynic and when something is too good to be true I generally think it cant be true. Same with blindingly obvious. To many it seems blindingly obvious that MCZs are THE solution to the perceived problem of overfishing. Actually that is an example of a solution that is too good to be true. To easy.

But surely discards are different? Surely the fact that they are a bad thing is an example of something that is actually true?

Maybe not.

Consider first, what are we going to do with the fish that would have been discarded. As far as I understand it at the moment, ports and markets are not geared up to deal with tonnes of poorly treated, low value fish.

Consider second – what will we use it for? Maybe we can use it as fertilizer? Is that a good use of fish? Maybe we can feed it to Salmon? Feeding fish to fish seems wrong to me. Both of these options may induce high carbon costs. If it ends up as landfill that would be more illogical than continuing to put up with bycatch where at least the waste usefully feeds back into the system. It could be used as bait by static gear fisheries which could be good for that sector as this has become an increasingly expensive aspect for them.

Consider third. What has been happening to discarded fish in the past? It is either snapped up by eager sea birds, such as gannets, snapped up by predators or sinks to the bottom where it forms part of the food chain for other wild fish and benthic organisms. In some parts of the world it has been estimated that 40% of the diets of lobster and crab comes from discarded fish. I have a feeling that a lot of birds are going to starve when discards are banned. We could also see some declines in fished species that need discards.

Consider fourth. How will the discard ban impact on the behaviour or fishermen? If technical measures such as Trawl Exclusion Devices (TEDs) don’t work in their favour, they will perhaps target species that have low levels of bycatch. Perhaps everyone will target species with low levels of bycatch – what will the knock on effects of that be?

Consider fifth. Just because something doesn’t make it onto the deck doesn’t mean it has not been impacted by fishing gear. You could design gear that was more selective but not necessarily less harmful but it would reduce “bycatch”. In order to survive the vagaries of EU management, fishermen have become adept at working around regulations and this seems like me to be an area ripe for exploitation. From a management point of view just trying to estimate bycatch has been tricky enough and that is at least visible. How will we estimate the impacts of injury to animals that are not landed?

Consider sixth. What about the effects of differential survival rates of different species? The grand banks cod fishery was a victim of this because discarded dogfish survived quite well. Eventually dogfish replaced cod. It seems likely from what the fisheries minister has said that there will be investigations into which species survive discarding and I assume fishermen will not be forced to keep these. It would be, for example, extremely daft if potters had to keep all crabs and lobsters that ended up in their creels.

I don’t know the precise answers to some of the above, but my point is that we need to think hard about what the effects of the discard ban might be and find sensible solutions.

Dr Magnus Johnson is a lecturer in Environmental Marine Biology at the Centre for Environmental and Marine Sciences, University of Hull