We study the moduli space $I_{n,r}$ of rank-$2r$ symplectic instanton vector bundles on $mathbb{P}^3$ with $rge2$ and second Chern class $nge r+1, n-requiv 1(mathrm{mod}2)$. We introduce the notion of tame symplectic instantons by excluding a kind of pathological monads and show that the locus $I^*_{n,r}$ of tame symplectic instantons is irreducible and has the expected dimension, equal to $4n(r+1)-r(2r+1)$. The proof is inherently based on a relation between the spaces $I^*_{n,r}$ and the moduli spaces of 't Hooft instantons.
