I've sketched out my coastlines, my mountains, my wind currents, and my climate zones. If its Earth-like in all respects but geography, where should the inhabitants of my world expect to find fish, and other marine life, in abundance? How can I get (at least approximately) to a map this this:
Why is Newfoundland and the whole far-north-Atlantic area one of the worlds great fisheries? Why Alaska, and Peru? Why is northern California blessed with so many different sea animals?
Here are a few factors I've heard suggested, but I have no background in oceanography or zoology to judge which of these are most important, or even true. The Wikipedia article outlines the factors affecting sea currents, but has little to say about how they relate to productivity.
- Photosynthesis is the basis of life in the sea as on land, so warm sunny places should have the most phytoplankton and thus other forms of life. Yet many real-world fisheries are based on cold water currents.
- Nutrients tend to drift down to the sea bed. Storms can stir this up and return them to the high-biomass sea surface (but do storms reach the sea bed outside of very shallow areas?). Likewise when deepwater currents are forced upward by the continental slope.
- River estuaries can bring dissolved minerals to the ocean. If industrial civilization is present, runoff of fertilizer from industrial farms, or pollution from industry, can cause algae blooms or poison sea life. However, I'm most interested in an untouched world.
A perfect answer would address a few of these related points:
- What factors affect freshwater productivity? This question is 90% about oceans, but in so far as lakes and rivers have different important factors, I'd love to hear about them.
- Seasonality and migrations: many animals travel long distances to breed or to follow prey animals. Should I expect to see shoals of fish in cold seas in the local summer, which migrate to warmer areas in the winter?
- What are some factors that a worldbuilder can use to steer things? If I'd like an area to have abundant sea life, should I make the nearby seas shallow or deep? One could add or remove undersea ridges to deflect sea currents, but how does that affect the fishing?