Writing a story and it requires that fishing not be a terrifically viable source for sustenance for an indigenous population in the south pacific circa 1942. Are there some islands that just due to currents or by virtue of some geographical anomaly they simply dont’ get a
lot of fish? I suppose I could do a manmade disaster like an oil spill but could that last nearly 40 years? Thanks as always all!
Insufficient local timber to make fishing boats?
Ever visited one of those “South Pacific Island Paradise” places? (Even Hawaii will do.) Or at least seen pictures, showing that brilliant crystal-clear water with all the little brightly-colored fish swimming around?
There’s a reason why that water is so crystal clear. Contrast with the rather turgid waters near-shore of larger land masses, especially in any areas where there are major river outfalls into protected bays. Monterey Bay, Ca., is an excellent example. Here, you have a lot of nutrients in the water, supporting a whole food chain hierarchies, from murky clouds of plankton, up through sea urchins, barnacles, lots of fish, sea otters, and whole forests of giant kelp, all the way up to seals, sea lions, dolphins and great whales.
Contrast that, again, with those sparkling crystal clear waters around islands (you see this in those snorkeling havens around Caribbean islands too). Far out in the ocean, away from any major land masses with shallow continental shelves and water outfalls (islands hardly count), you have no major sources of nutrients to build a food chain on. Your beautiful clear sandy bottoms are basically marine deserts, able to support only relatively sparse desert life communities.
I can think of a few possibilities. Senegoid took the basic explanation, though.
As another line of thinking: big storms like a typhoon, or other natural disasters like tsunamis or volcanoes can reshape a coastline pretty dramatically, messing up coral, moving (or removing) sand, etc. That could destroy the habitat for fish that were there before the accident and leave no good habitat for new ones.
And how about a crown of thorn starfish explosion? These are a problem for the Great Barrier Reef. The starfish eat coral and can turn a thriving reef into a graveyard overnight. (Wikipedia). I doubt the starfish themselves would be edible to a person.
Maybe the war between Japan and the US could be brought in…
Here’s “some” detail…
Basically, if island is surrounded by warm water, the algae and plankton grow, and consume all the nutrients,and this occurs in the deep water off the island… So the deep water fish eat all that. The reef fish, which the islanders can fish with canoe, becomes infertile.
If however a cold water current flows toward the island, this stirs up the nutrients and nothing grows in it, so the nutrients get to the reef/shore/estuary/lake and the reef fish get fed.
WW II saw many changes, such as ban on trade, and restriction or difficult fishing for deep sea fish (outside the reef…They may have been treated as enemy if they went out…) . Also the populations were moved, concentrated, so one area may be easily over-fished.
I’ve read (most likely in one of Jared Diamond’s books… “Collapse” maybe ?) that among the main reasons Easter Islanders got into trouble were:
- deforestation (they cut the trees to move around those big statues) –> no canoes, no fishing, as already mentioned by Mangetout
- the island itself is the top of a volcano with very steep slopes, so there are no reefs, sand or shallow waters where fish could live. IIRC, the diet of islanders consisted mostly of chickens.
So would “insufficient fringing reef” capture it adequately?
Or, you could have an invasive species that is poisonous to humans show up and out-compete all other fish species. The natives can go out and fish, but all they get is nets full of the poisonous fish.
Another reason fishing can be difficult is that the shore is lined with sharp coral that is dangerous to cross, and the water may be filled with toxic red coral making it extremely difficult to fish. Lucy Irvine documented this situation in her book Castaway. Might be a good resource for you.
ETA: In general fishing from the shore is not productive if there isn’t shallow protected water for the fish to live in. People who depend on ocean fish for their food almost always have boats.
Ok, but what kind of fishless island would support an indiginous population? Without food, who lives there?
People with boats.
Or people with pigs.
Correct. It’s gonna be pigs and coconuts.
Don’t forget rats. The Polynesian rat Rattus exulans was used for food on many Polynesian islands. Also dogs.
And people. The Maori in New Zealand didn’t have pigs or chickens. Their only sources for land mammal protein were dogs, rats, and people. They used all three.
And apples for sauce 
Eeew. They ate rats?
How is that different from eating rabbits? What’s eew about it?
whoosh.** Colibri **mentioned that they ate dogs, rats, and people.
The odd thing is that they would have had to bring the dogs and rats with them. So someone said “Skip the pigs, let’s bring rats”.