That's a good question!
Biologically, a dead perch is a dead perch and will never spawn again. This is probably a slight oversimplification, but population dynamics wise, it has a mostly negligible effect on when you kill an animal, only that you killed it. For instance, whether you are keeping a perch in April or July, it won't spawn again.
Spawning closures generally only make sense in a few situations, such as:
1) if there are giant spawning aggregations in small geographic areas that make fish more vulnerable than normal (like say, walleyes in a river below a dam)
2) if fishing itself will disrupt spawning behavior
3) if there is a ton of fishing effort during spawning time that would over-exploit a spawning population
4) fishing activity itself will damage spawning habitat (such as anglers wading on top of brook trout redds and crushing eggs)
Since none of these are significant concerns for LM perch, there is no pressing biological need for a fishing closure during the spawning period. Especially since perch are prolific spawners, there are more than enough perch to pull of a giant yearclass if the conditions are right (like in 2015). The thing governing perch reproductive success is environmental conditions, rather than the number of perch spawning (at least, above some threshold of available spawning stock biomass).
Therefore, the one thing we would be concerned about is limiting total exploitation (amount of harvest) relative to the population, whether during the spawning season or over the entire season.
However, in general there is not much harvest during the spawning period (late April-early June). Even if you include all of April and May you are talking about 11% of total harvest.
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