Fish stocks

In marine environments this may be less evident than on land because there are fewer topographical boundaries, however, discontinuities still exist, produced for example by mesoscale and sub-mesoscale circulations that minimize long-distance dispersal of fish larvae.

There is a tendency to form a structured series of discrete populations which have a degree of reproductive isolation from each other in space, in time, or in both.

Usually this is done through the medium of an intergovernmental regional organisation set up for the purpose of coordinating the management of that stock.

Pelagic species are more mobile, their movements influenced by ocean temperatures and the availability of zooplankton as food.

[6] The World Wildlife Fund and the Zoological Society of London jointly issued their "Living Blue Planet Report" on 16 September 2015 which states that there was a dramatic fall of 74% in world-wide stocks of the important scombridae fish such as mackerel, tuna and bonitos between 1970 and 2010, and the global overall "population sizes of mammals, birds, reptiles, amphibians and fish fell by half on average in just 40 years.

"[7] It is hoped that global efforts like the United Nations Sustainable Development Goal 14 meets its targets aimed at reversing these trends.