Why do some animals, like sea turtles and salmon, lay eggs away from their natural habitat?


This might be a strange question, but why do sea turtles lay eggs on land and not for example dig up holes inside the ocean? They live their whole lives in the ocean, so why do they lay eggs on land? Why travel so far just to lay eggs?

Same goes for some salmon, why do they leave the oceans and lakes, and go upstream on rivers and not lay their eggs where they live?

It is probably something to do with protecting their offspring, but it seems to me that they still have predators that hunt their offspring fairly easily where they hatch/lay their eggs, so maybe there is another reason as well?

In: 146

Turtles breath air, and the embryos in the eggs must get their air through the membrane of the egg which they wouldn’t be able to under water. Also, the right temperatures for the eggs don’t exist in the water.

Salmon are incapable of living in salt water when they are first born, so the eggs must be laid in fresh water. Going back to the same place they spawned makes sense: it’s a known quantity capable of supporting salmon eggs.

So the general reason behind both is that these are creatures that have adapted to live in environments as adults that they could not survive in as newborns, so it is necessary to return to the place (or a similar place) to that in which they themselves were born.

All of evolution is a game of cat and mouse between a species and the various things in the environment that want to kill it. If something has even a marginal benefit to survival, it will likely become a dominant trait given enough time. The adaptation doesn’t have to be _perfect_, just _better_.

So, in both cases, some ancestor of the modern animal decide to lay its eggs in a non-traditional location due to a quirk of genetics and those offspring were better able to survive to adulthood.

I don’t know about fish, but turtles lay their eggs in sand so the embryos can breath. Sea turtles have to come up for air every so often.

Baby turtles would drown if they were born in the ocean. I don’t think anything more really needs to be said about that one.

Good answers so far but there could be one additional reason: By sheer happenstance, the hatching of turtle eggs on a beach creates a kind of selection pressure that wouldn’t otherwise be created in a “safer” environment(Let’s assume that there were no environmental problems like temperature and O2 for laying eggs under the ocean floor, which are the main answers to this question).

So in simpler words: Making your hatchlings run a predator filled obstacle course offers more selection pressure, which leads to more robust turtles