vtsnowedin wrote: When they get the seas sufficiently empty of fish there will be no profit in it even with subsidies. At that point they will stop fishing and with time the fish stocks will recover. What happened with the whaling industry foretells the outcome.
Provided they do not pass the tipping point of the particular species this is likely true, however some fish like Cod for example have a very long maturation cycle. They reach a salable weight a long time before they become reproductively active.
There are also issues with ecosystem degradation, a new study from Australia was on the news yesterday about endocrine disruption from degraded plastic in the South Pacific and Indian oceans. It turns out that all the measurements of 'plastic pollution' have a serious problem because measurements in earlier studied had a cut off point that was too high. These folks used water filters and determined that millions of sand grain and smaller pieces of plastic can be in places of high surface evaporation. The plastic is buoyant and stays near the top of the water column. In places of high evaporation the surface water blows away on the breeze leaving the solid plastics behind, something you see in places like the eastern Mediterranean or southwest Pacific near Australia and Micronesia.
The smaller the fragments get the more they enter the food chain. When they get down to 1-2mm in size many predatory species mistake them for floating eggs of fish or crustaceans and swallow them. When they get sand to dust sized the filter feeders, most of which live close to the surface relatively speaking, filter them out of the water along with the plankton they normally eat. For most species a little bit is no big deal, but the chemicals seeping out of the plastics are frequently endocrine disruptors that alter or destroy the life cycle of the animals that eats them depending on species sensitivity and total dose ingested.
On the flip side of that coin we have discovered several species of bacteria now that can break down plastics into digestible carbon containing molecules. We have not found them for all plastics by a long stretch and they are not very common at this point in history, but if the plastic in the oceans remains a long term problem nature will eventually clean it up by dint of bacteria that can digest the polymer chains into digestible fragments. On the Gripping hand it took nature many millions of years to develop and spread bacteria that can break down Lignin from woody plants, which is part of the reason so much Lignite coal exists. Nothing could digest it in the distant past so decay of wood would only proceed until the Lignin remained and layer after layer built up in the soil. Once one bacteria developed the digestive enzymes needed the inter species gene exchange spread that ability to other types of decay bacteria.
From a chemical viewpoint plastic polymers are not unlike Lignin or Starch, they require specialist enzymes to 'unzip' the molecules into individual, digestible fragments. This makes it is plausible that the kind of bacteria which have developed the enzymes for breaking down plastic polymers will cross spread that capability to assorted other decay bacteria. Especially if we give nature a hand by deliberately spreading the genes for the polymer breakdown to many other species of bacteria that already live in the surface water of the world oceans and topsoil where plastics get discarded constantly.