Compare with chlorophyll levels in the ocean:<p><a href="https://svs.gsfc.nasa.gov/30786" rel="nofollow">https://svs.gsfc.nasa.gov/30786</a><p>Essentially there are small diatom things at the bottom of this food chain (and at the top of the ocean) that do the heavy lifting of converting sunlight into energy. Plankton (diatoms and the many, many, many variants) then get eaten by fish and then those fish get eaten by bigger fish and then the Japanese/Chinese/Spanish fishing fleet scoops them all up.<p>Temperature is important to the phytoplankton so there are places like the seas around Iceland that are extraordinarily rich for marine life. Also important is what flows out of rivers and gets blown off the land, grasses on land are therefore surprisingly important for fisheries - nitrogen has to come somewhere.<p>In conclusion I am surprised at how different the two maps are of where the fishing happens and where marine life as measured by chlorophyll happens.