I wanted to see what I could do in Dwarf Fortress without resorting to 3rd party scripts, and while region-pops is useful, I don't want to cheat by building walls or killing off species, or doing things with hacks if there's a genuine method to do it!
Here's some interesting discoveries I found!
What I managed to do was line the perimeter of my world with drawbridges, and then raise them. This forced no land spawns. I left one tile open, and things still chose to pour through there, with NONE of them being sea creatures. At this point, I was convinced that the other biomes take priority to ocean biomes when it comes to spawning creatures. When I moved the edge tile to be in the ocean biome, but above ground and on the beach, land animals that live in ocean biomes came through (crabs, albatrosses, sea otters). Even when the only creatures that could spawn were ocean spawns, the game STILL prioritized land creatures.
Wanting to further experiment, I built drawbridges and walls to create an aqueduct that would feed to the edge of the map, where this one tile was. My pump did an excellent job of draining water from the ocean and feeding it into this tunnel I made, and then something interesting happened.
When I flooded this exit to the map and kept it flooded, sea creatures constantly poured through it. Absolutely none spawned in the actual ocean, despite there only being aquatic ocean spawn tiles. They would consistently come through the artificial water tile I had created on the beach.I don't know what exactly is causing this, as the only fundamental difference is that the aqueduct is one level above the ocean, and on the beach instead of offshore like the other edge tiles.
More experimentation is required! I'm very excited to hear what you all think of this. Thanks for the replies from everyone!
As far as embarks go... found one with this for region-pops output:
Creatures and vermin:
ALBATROSS_MAN 35
ANT innumerable
BARK_SCORPION 6356
BARK_SCORPION_MAN 43
BARN_OWL_MAN 52
BAT 8708
BAT_GIANT 523
BEETLE innumerable
BEETLE_MAN 57
BIRD_ALBATROSS 294
BIRD_BUZZARD 422
BIRD_COCKATIEL 7836
BIRD_EAGLE 534
BIRD_FALCON_PEREGRINE 402
BIRD_OSPREY 279
BIRD_OSTRICH 272
BIRD_OSTRICH_GIANT 189
BIRD_OWL_BARN 477
BIRD_OWL_GREAT_HORNED 422
BIRD_RAVEN 5998
BIRD_SWALLOW_CAVE 11343
BIRD_SWALLOW_CAVE_GIANT 201
BIRD_VULTURE 328
BIRD_WREN 5121
BLIND_CAVE_OGRE 189
BLOOD_MAN 760
BOBCAT 21
BOBCAT_MAN 50
BUGBAT 564
BUMBLEBEE innumerable
BUTTERFLY_MONARCH 9220
BUTTERFLY_MONARCH_MAN 64
BUZZARD_MAN 57
CAMEL_1_HUMP 309
CAMEL_1_HUMP_MAN 61
CAMEL_2_HUMP 477
CAMEL_2_HUMP_MAN 65
CAP_HOPPER 8910
CAVE_DRAGON 93
COCKATIEL_MAN 59
COYOTE 328
COYOTE_MAN 52
CRAB 4927
CRAB_MAN 31
CREEPING_EYE 10246
CREEPY_CRAWLER 14396
CROCODILE_CAVE 421
CRUNDLE 6153
CUTTLEFISH 5800
CUTTLEFISH_MAN 31
DAMSELFLY 7236
DESERT TORTOISE 384
DESERT_TORTOISE_MAN 50
DINGO 346
DINGO_MAN 59
DRAGONFLY 8717
DRALTHA 519
EAGLE_MAN 64
ECHIDNA 459
ECHIDNA_MAN 64
ELEMENTMAN_FIRE 886
ELEMENTMAN_MAGMA 745
ELK_BIRD 748
FIREFLY 8927
FIREFLY_MAN 57
FISH_ANCHOVY 7184
FISH_BLUEFISH 221
FISH_CAVE 14541
FISH_COD 222
FISH_CONGER_EEL 308
FISH_FLOUNDER 5043
FISH_HAGFISH 5398
FISH_HAKE 5727
FISH_HALIBUT 308
FISH_HERRING 8420
FISH_LAMPREY_BROOK 6302
FISH_LAMPREY_SEA 221
FISH_MACKEREL 5818
FISH_MARLIN 308
FISH_OPAH 423
FISH_RATFISH_SPOTTED 5159
FISH_RAY_BAT 3673
FISH_RAY_THORNBACK 5972
FISH_SALMON 5008
FISH_SEAHORSE 4324
FISH_SHAD 5852
FISH_SKATE_COMMON 294
FISH_SOLE 4987
FISH_STURGEON 265
FISH_SUNFISH_OCEAN 250
FISH_SWORDFISH 279
FISH_TROUT_STEELHEAD 4227
FISH_TUNA_BLUEFIN 479
FLESH_BALL 9943
FLY 87315
FLY_ACORN 16592
FLY_MAN 36
GECKO_LEOPARD 6506
GIANT PEREGRINE FALCON 7
GIANT_ALBATROSS 146
GIANT_BARK_SCORPION 134
GIANT_BARN_OWL 163
GIANT_BEETLE 127
GIANT_BOBCAT 15
GIANT_BUTTERFLY_MONARCH 92
GIANT_BUZZARD 168
GIANT_CAMEL_1_HUMP 175
GIANT_CAMEL_2_HUMP 168
GIANT_COCKATIEL 169
GIANT_COYOTE 99
GIANT_CRAB 56
GIANT_CUTTLEFISH 46
GIANT_DESERT_TORTOISE 189
GIANT_DINGO 113
GIANT_EAGLE 196
GIANT_ECHIDNA 113
GIANT_FIREFLY 71
GIANT_FLY 92
GIANT_GILA_MONSTER 50
GIANT_GRASSHOPPER 64
GIANT_GRAY_LANGUR 250
GIANT_GREAT_HORNED_OWL 162
GIANT_HAMSTER 85
GIANT_HORSESHOE_CRAB 2120
GIANT_IBEX 134
GIANT_JAGUAR 15
GIANT_JUMPING_SPIDER 127
GIANT_KANGAROO 106
GIANT_KINGSNAKE 127
GIANT_LEOPARD 8
GIANT_LEOPARD_GECKO 127
GIANT_LIZARD 57
GIANT_LOUSE 85
GIANT_MANTIS 216
GIANT_MOON_SNAIL 61
GIANT_MOSQUITO 99
GIANT_MOTH 127
GIANT_NAUTILUS 76
GIANT_OCTOPUS 86
GIANT_ORCA 131
GIANT_OSPREY 111
GIANT_PORCUPINE 120
GIANT_RATTLESNAKE 99
GIANT_RAVEN 99
GIANT_ROACH 99
GIANT_SLUG 120
GIANT_SNAIL 134
GIANT_SPARROW 158
GIANT_SPERM_WHALE 71
GIANT_SPONGE 2050
GIANT_THRIPS 99
GIANT_TICK 113
GIANT_VULTURE 189
GIANT_WEASEL 175
GIANT_WREN 148
GIGANTIC SQUID 81
GILA_MONSTER 121
GILA_MONSTER_MAN 29
GORLAK 318
GRASSHOPPER_MAN 36
GRAY_LANGUR 908
GRAY_LANGUR_MAN 61
GREAT_HORNED_OWL_MAN 65
GREEN_DEVOURER 442
GREEN_TREE_FROG 1281
GREMLIN 28
HAMSTER 8824
HAMSTER_MAN 50
HONEY BADGER 309
HONEY BADGER MAN 65
HONEY BADGER, GIANT 127
HONEY_BEE innumerable
HORSESHOE_CRAB 4584
HORSESHOE_CRAB_MAN 36
IBEX 272
IBEX_MAN 36
IMP_FIRE 567
JAGUAR 21
JAGUAR_MAN 57
JELLYFISH_SEA_NETTLE 1381
JUMPING_SPIDER_MAN 43
KANGAROO 422
KANGAROO_MAN 56
KINGSNAKE 402
KINGSNAKE_MAN 29
LEOPARD 21
LEOPARD_GECKO_MAN 57
LEOPARD_MAN 57
LIZARD 8395
LIZARD_MAN 57
LIZARD_RHINO_TWO_LEGGED 3411
LOBSTER_CAVE 12748
LOUSE innumerable
LOUSE_MAN 36
MAGGOT_PURRING 1734
MAGMA_CRAB 1256
MANERA 876
MANTIS 571
MANTIS_MAN 36
MOGHOPPER 2932
MOLE_GIANT 620
MOON_SNAIL innumerable
MOON_SNAIL_MAN 41
MOSQUITO 55288
MOSQUITO_MAN 50
MOTH 9182
MOTH_MAN 50
MUSSEL innumerable
NAUTILUS 6158
NAUTILUS_MAN 26
OCTOPUS 1092
OCTOPUS_MAN 31
OLM 9794
OLM_GIANT 535
ORCA 250
ORCA_MAN 36
OSPREY_MAN 22
OSTRICH MAN 65
OYSTER innumerable
PEREGRINE FALCON MAN 56
PLUMP_HELMET_MAN 657
POND_GRABBER 713
POND_TURTLE 7777
PORCUPINE 441
PORCUPINE_MAN 30
RAT 5159
RATTLESNAKE 441
RATTLESNAKE_MAN 29
RAT_LARGE 85
RAT_MAN 31
RAVEN_MAN 55
REACHER 418
ROACH_LARGE 5102
ROACH_MAN 43
RUTHERER 174
SEA OTTER 193
SEA_SERPENT 5
SHARK_ANGEL 423
SHARK_BASKING 279
SHARK_BLUE 250
SHARK_FRILL 207
SHARK_GREAT_WHITE 308
SHARK_HAMMERHEAD 221
SHARK_MAKO_LONGFIN 236
SHARK_MAKO_SHORTFIN 294
SHARK_NURSE 294
SHARK_SPINY_DOGFISH 393
SHARK_WOBBEGONG_SPOTTED 221
SLUG innumerable
SLUG_MAN 50
SNAIL innumerable
SNAIL_MAN 64
SNAKE_FIRE 10004
SPARROW 7254
SPARROW_MAN 50
SPERM_WHALE 236
SPERM_WHALE_MAN 46
SPIDER_CAVE 12972
SPIDER_CAVE_GIANT 107
SPIDER_JUMPING 6785
SPONGE_MAN 26
SQUID 5800
SQUID MAN 41
TERMITE innumerable
THRIPS innumerable
THRIPS_MAN 65
TICK innumerable
TICK_MAN 64
TOAD 5272
TOAD_GIANT_CAVE 368
TROGLODYTE 120
TROLL 304
VORACIOUS_CAVE_CRAWLER 92
VULTURE_MAN 57
WEASEL 309
WEASEL_MAN 43
WREN_MAN 63
Looks pretty good, ocean-wise, with squid, octopus, whales, many fish types, giant versions, and so on.
If you're interested, I can post the worldgen and embark location.
In that past, I used DFHack obsidian walls on the map edge to curtail spawns in certain locations. Might work here with getting only ocean spawns?
Thanks for the offer, but have you tried embarking there yourself? Did you see things spawning there, or are you only going by region-pops? It's quite similar to my own embark, honestly.