How could my island-country mostly populated by massive humanoids subsist its inhabitants?

Question

In my prospective dramedy science-fantasy children's videogame Salade de Fruits (which means naturally Fruit Salad), there is an island-country comprising a total of eight islands:

1. The smallest has an area close to Manhattan Island (0.5 % of the country's human population inhabit there) (this island is the westernmost).
2. The second smallest has an area close to Staten Island (1 % of the country's human population inhabit there) (this island is the easternmost).
3. The third smallest has an area close to Montreal Island (3.5 % of the country's human population inhabit there) (this island is the southernmost).
4. The fourth smallest has an area close to Atka island (7 % of the country's human population inhabit there) (this island is the northernmost).
5. The fourth largest has an area close to Tahiti (11 % of the country's human population inhabit there) (this island is the north-eastern part of the country).
6. The third largest has an area close to Réunion Island (12 % of the country's human population inhabit there) (this island is the south-western part of the country).
7. The second largest has an area close to Socotra (25 % of the country's human population inhabit there) (this island is the north-western part of the country).
8. The largest has an area close to Anticosti Island (40 % of the country's human population inhabit there) (this island is the south-eastern part of the country).

This archipelago has a subpolar climate, a subantarctic climate to be exact. An inhabitant says: Dans mon pays, il n'y a que deux saisons: l'hiver et janvier ! (which means: In my country, there are only two seasons: winter and January!) (I want that French will be the original language of my videogame, sorry). Naturally, the archipelago is in the Southern Hemisphere, so they celebrate Christmas the 25th June, they celebrate Liberalia (Roman pagan and Roman neopagan festivity honoring Liber Pater) the 17th September, and they celebrate Halloween the 30th April, and naturally, I am semi-joking.

The human population of this country is ten millions. By human population, I mean the Homo genus: in my world, there are anatomically modern humans often just called humans, and other humanoids: angels, demons, merfolk, ogres, trolls, vampires, therianthropes, gnomes, elves, dwarfs, giants, halflings, goblins, orcs, and wizards.

1. 70 % of the human population of this island country is populated by massive humanoids: merfolk, ogres, and giants (respectively, 20 %, 35 %, and 15 %) (merfolk are as large as belugas, ogres are on average as heavy as adult male gorillas and as tall as the average male anatomically modern human professional basketball player, and giants are as large as polar bears) (all these species have a blubber like pinnipeds).
2. 16 % of the human population is populated by anatomically modern humans.
3. 10 % of the human population is populated by hybrids.
4. 4 % is populated by other humanoids.

So, how could my island-country mostly populated by massive humanoids subsist its inhabitants?

Note 1: in my story, individuals of any humanoids species can be of any morality and ethics (I hate the trope Exclusively Evil) (I also do not like the trope Always Good).

Note 2: giants are omnivores with herbivorous tendencies like American black bears, also, they are as solitary as cheetahs, and ogres and merfolk are both true omnivores like brown rats, also, they both are as solitary as blue whales (which are less social than other rorquals species).

Answer 1

Fishing

There's many islands and areas in the world that can't survive on agriculture, hunting or gathering. Still they can survive. Iceland comes to mind, but I've been also to rocky, sandy or otherwise harsh environments of which you can tell the same. All are difficult to live off the land.

These examples often still had water in the form of oceans or river/lakes. This gives them the option to fish. Fishing is a great main or supporting food source. Depending on where you are it can even give food all year round. If we're not talking about modern fishing, it's a relatively renewable and endless supply. This takes away many size restrictions that islands and population might bring.

Answer 2

Given the climate zone you have selected you will almost certainly have to increase the size of the island chain's land mass or decrease the size of your population (or both) - significantly.

For example by the end of the middle ages just before the great famines and black death episodes demographers estimate the population of Britain (including Scotland and Wales) to have been somewhere in the 5-7 million range. And these were 'normal' sized people remember with metabolisms to scale, not the 'giants' your talking about using. Add to that the fact that the British Isles are at a far lower latitude than your considering and hence have a milder climate, much more suited to agriculture and you start to see the problem.

Add in all the other races your talking about on top and I'm afraid somethings got to give, unless you posit a modern setting where scientific agriculture (e.g green houses etc) lets you overcome the problem.

Answer 3

Being on an island that does not support extensive agriculture fish is the first thing that comes to mind. However fish is missing something otherwise scurvy would not have been such a problem in the age of sail. You will need some kind of algae to complement the diet. Better would be a floating type of algae brought by a constant sea current from warmer latitudes, in this way you might have a constant supply.

Another source of vitamins could simply come from trade, a lot of modern industrial countries already don't produce enough food to feed their population and rely on imports. So it depends on what is valuable on your island, a precious mineral might support the population (even if King Midas would not agree).