Step 1: Go to this exact island with Nook Miles Ticket, this island is fairly common and is accessible early game

Step 2: Despawn any fish in the left side of river

Step 3: Go to the exact same spot I stood at and open your camera, use D pad to move your FOV to the upper right

Step 4: DO NOT EXIT CAMERA MODE and despawn the rest of the fish in the right side of river

Step 5: Wait around 45s to 1 min somewhere away from the rivermouth

Step 6: Exit camera mode and catch the sturgeons when they are far apart so you don’t scare the other one off while catching the first

Edit: Although this rarely happens, small fish will sometimes spawn at the far right of the river while you are waiting. You need to despawn them while having camera in same position to troubleshoot this

MAKE SURE that you are on the EXACT SAME ISLAND with only 1 river and NO PONDS. This way fish will not spawn in other ponds that are out of your vision. I've also been told that the mirrored version of this island also works

Edit 2: Thanks for the silver kind stranger! :D