"We run regular fish surveys inside and outside the reserve to try and compare fish numbers and size and to understand what factors influence the effectiveness of marine reserves.
"Illegal fishing confounds that data and in extreme cases can render the entire research programme invalid."
He said the reserve had shown "very encouraging signs of recovery over the past 25 years", meaning more and large fish for people to catch outside of the reserve restrictions.
"These illegal fishers are killing the goose that lays the golden egg in the sense that the significant numbers of fish and their larvae that are spilling out of the reserve and into the wider marine area are then made available to be caught legally outside of the reserve.
"Illegal fishing significantly reduces the effectiveness of the reserve to act as a source of fish stock recruitment for the wider area."
Steve Anderton, a Guardians trustee well as their compliance and law enforcement adviser, was pleased to see the incidents reported.
"We hope these reports will alert the Department of Conservation to be more proactive with patrolling the reserve and its boundaries now that summer has arrived.
"Fishers should be aware that illegal fishing in the reserve not only carries heavy penalties including fines and imprisonment or both, but also forfeiture of vessels, vehicles and fishing gear.
"Marine reserve infringements can have a serious impact on the marine life within the reserve and we will be doing our utmost to ensure any suspected illegal activity is reported to the responsible authorities for early attention and possible prosecution."
To report suspicious fishing in the marine reserve call the DOC hotline 0800 DOC HOT (0800 362 468). Kapiti Marine Reserve info www.doc.govt.nz/parks-and-recreation/places-to-go/wellington-kapiti/places/kapiti-marine-reserve/