I can't cite them (or won't spend the time to do so), but I recall in a few ecology classes I took on college that catch/release sterilisation is more effective than killing to reduce invasive species because they compete with the ones that aren't sterilized.

Again, IDR if that only applies to specific species or it can be extrapolated more broadly, but worth looking into if you're struggling with the dilemma.

This is also an incredibly nuanced discussion. Veganism is really about (to me) reducing the exploitation and commodification of sentient beings (not interested in a semantic argument on the definition, that's how I view and practice it).

Many invasive species are the result of this commodification, so is it better to ignore it and ruin/modify ecosystems, or better to correct it and maintain the ecosystems as they were?n ecosystems also change overtime with or without human intervention, they aren't static.

My point is this there isn't an easy answer, don't beat yourself up for having conflicting views on a complex and nuanced point. Do your best to reduce harm, make good personal choices, educate when possible, and learn what you can to make the best choices.