Research that proves marine reserves do act as fish nurseries may silence some of the opposition to their establishment.
A higher proportion of young snapper in fishing areas north of Auckland are related to adult snapper from the Goat Island Marine Reserve, confirming what scientists long suspected – that the reserve acts as a giant snapper nursery.
The study from the University of Auckland's Institute of Marine Science is the first time scientists have looked at a temperate commercial fishing species to find evidence of a direct parental link between adults in a marine protected area to juveniles outside.
Led by Professor John Montgomery, Dr Shane Lavery, and former University of Auckland postdoctoral fellow Dr Agnès Le Port, the research team used a combination of genetic testing and hydrodynamic modelling of snapper larvae.
They found at least 11 percent of juvenile snapper up to 40km away were the offspring of spawning adults from the reserve at Leigh, north of Auckland, whereas no offspring matches were found to adult snapper sampled from non-reserve areas.
“The contribution from the reserve is about 10 times higher than would be expected if snapper larval contribution was simply proportional to geographic area,” says Professor Montgomery. “Even though the reserve is a tiny percentage of the area studied, it is more than pulling its weight in contributing to snapper populations outside.”
An area of 400 square kilometres was included in the study, from Mangawhai in the north to Mahurangi in the south. Goat Island Marine Reserve makes up just 1.3 per cent of the area studied. It is a ‘no take' marine reserve, meaning fishing is strictly prohibited.
“This is the first estimate of the larval contribution of adult snapper from the reserve into the surrounding fishery,” adds Professor Montgomery.
Previous research has shown that while snapper move over a wide area, resident snapper within the reserve tend to stay put for some time, forming a significant breeding population of large individuals.
“Enough of them stick around within the reserve for our data to show a direct and significant link between the adults in the reserve and the juveniles many kilometres away.”
For the research, adult snapper within the reserve were caught, tagged and a fin clip sample was taken before being returned to the water. The same technique was then used in non-reserve areas.
Professor Montgomery says the hydrodynamic modelling work done for the study is the first time scientists have used the method alongside multiple genetic techniques.
“Hydrodynamic computer modelling uses our understanding of tidal currents and wind patterns to predict where snapper larvae end up,” he explains.
“The agreement between predicted dispersal and the genetic matches helps validate the modelling and its potential use in the design of future marine protected areas.”
He's unsure if the results are applicable to the Tuhua Marine Reserve at Mayor Island. The reserve, established in January 1993, covers around three square nautical miles at the northern end of the island and extends from the mean high water springs mark to one nautical mile offshore.
The reserve includes approximately five kilometres of coastline from Tumutu Point, east to Turanganui Point. It is one of more than thirty marine reserves protecting our seas around New Zealand.
While they know marine reserves are useful in terms of encouraging biodiversity recovery with the reserves protecting exploited species, a snapper nursery requires a stable adult population as well as a suitable area downstream.
“It depends a bit on the area downstream of that appropriate settlement area,” says Professor Montgomery.
“One of the things we found with Leigh is we studied the area north of the reserve. We know the larvae are being washed north of the reserve based on the modelling, but we found it difficult to actually capture newly settled animals up there because it's basically a big open surf beach.”
The reserve effect was more noticeable south of Goat Island where there are the harbours and sea grass that provide a settlement habitat.
“So those will be the reservations. You need a stable population and an area downstream that is effective for post larval settlement.”
“Further down the track it is something people could take into account in siting new marine reserves, if replenishing snapper stocks was one of the stated objectives.
“What we have done is provide an actual look at larval settlement areas and run the models backwards to see where those spawning populations are.
‘With the spawning populations known, they could be looked after so they basically keep fuelling the larval development areas.”