Summer southerly winds blow young larvae 100's km offshore, against the mean near-surface onshore flow.
La Nina raises the northern sea level, strengthening the onshore flow, so the larvae go less far offshore.
Westerly winter winds may help larvae back onshore.
Still need to factor in other biological variables, eg primary production.

The Leeuwin current is anomalous and is responsible for WA having an oligotrophic (tropical) ecosystem. Lower northern sea levels, eg associated with a more El Nino-like mean state, could cause major ecosystem adjustments to happen in WA.