So Genesis does it again, as confirmed by science animal forms start in the sea.
But why Bird life without land animals?
We now have air enriched for the faster respiration of animal forms, a long preparation job has been done for this. Though the sea will be a fairly balanced nutrient source the land was probably in a low or inconsistent nutrient condition in most places. Some land will be fine, the local rock breaking down into a rich nutrient soil. In many places the local rock may lack a mineral [element] or more and plant growth will be very slow.
[NB; rock needs to be broken down very small to become soil, weather erosion does some but it's slow, water does plenty but washes it downhill, glaciation benefits colder areas as this both crushes and mixes the particles, plants require about twenty minerals to live.]
Just a small point of note, Genesis actually says "waters" and “sea,” evidently it includes all water environments, "sea fish" would underestimate things. So I will suggest we may assume, any sea, river or lake animal including those where water is only a partial environment, may also have been included. Therefore all animals will have access to plants, as the plants are by now along [all?] water margins.
The Birds [flying animals] do a job in Nature which needed doing now, to start distribution of nutrient and seed inland. Seed would be spread, bird droppings would be spread [nutrients] in a random pattern almost everywhere. The Salmon [fish] come up rivers to spawn and die, a nutrient reversal on rivers.
So the animal creation is completed in water and the air, in so doing the animals advance land plants [nutrient] supplies.
The question of meat eating animals still divides those believers with a more detailed interest. In Nature's systems what must be considered is nutrient. Animals die and the minerals of their bodies must be taken back into service or maybe lost. A dead animal when eaten yields up mineral and sugar components, preventing waste.
1/... There would need to be scavenging or carrion feeders in the design.
2/... There seems to be production of small animals as food for larger animals (insects – birds).
3/... Animals which look designed to kill often seem able to withstand going without for a time.
4/... Because of the later failure of Mankind the natural system is not cared for in the manner of the Creator's direction, for that we must wait and see.
This is well before the time of Moses, so applying Jewish food rules here might be unwise. I will suggest [for Genesis] the clean animals are the vegetation eaters and unclean are the carrion/meat eaters until Moses.
Meantime avoid projecting human aspirations onto animals [Anthropomorphism].
Here we note the second heaven as the flying place of Birds.
next: 1 v 24,25 Sixth Day, part 1, Livestock and wild