I have a particular interest in Marine Protected Areas (MPAs) because I live on Wellington’s south coast overlooking Taputeranga marine reserve.
Every day I observe some of the positive aspects of marine protection – school kids learning about and enjoying the marine life – and some of the challenges – poachers, Undaria, and muddy stormwater discharges. Less visible, however, is the impact that the reserve is having on the recreational pāua fishery.
There has never been a commercial pāua fishery on Wellington’s south coast. Locals will tell you that back in the 1990s, the whole of the south coast supported a thriving and accessible recreational fishery and divers could readily get a decent feed of pāua (or crayfish). After the reserve was established in 2008, all fishing was displaced beyond the reserve boundaries. Most of the accessible coastline now lies within the reserve, so recreational fishing pressure is concentrated on just a few remaining reefs, unless you have a boat and can travel much further to dive. On calm weekends, these nearshore reefs are dense with divers, boats, and cray pots. Some weekends I join them, so I know from experience how this intense fishing pressure has affected the surrounding pāua fisheries. It’s now much more difficult to take home a feed from the south coast – you have to swim further, dive deeper, and the pāua are widely dispersed. Big aggregations of adults are mostly gone, a problem in itself for spawning success.
It should be a no-brainer that closing an area to fishing increases fishing pressure and threatens the sustainability of fish stocks beyond the closed area – it’s like a farmer trying to raise the same amount of stock on a smaller land area. And it really annoys me when I hear responses like, “but marine reserves enhance surrounding fish populations”. In the case of pāua, this is demonstrably not true. There is no empirical research that shows marine reserves enhance pāua populations outside reserve boundaries. While increases of abundance have been measured inside some marine reserves, it doesn’t follow that the fisheries outside the reserve will become more abundant. In order for MPAs to enhance neighbouring pāua populations, adult or juvenile pāua would have to move from the MPA and successfully settle in the surrounding habitat.
Anyone who is familiar with pāua behaviour will appreciate that spillover of adults from marine reserves is negligible – pāua are sessile organisms and, once settled, move only tens of metres. Pāua larvae do float for a few days and can disperse a little further, but that dispersal is still primarily local in scale. Published research shows that larval settlement occurs close to the parent pāua – the highest claimed dispersal distance in international literature for abalone is only a few hundred metres. Even if larvae do successfully move beyond a reserve boundary, adjacent fisheries won’t benefit unless the larvae successfully settle and recruit to the fishery – and that in turn depends on environmental conditions and availability of habitat. Juvenile pāua require a period of quiet sea and onshore winds to hold them in the intertidal zone that contains their preferred settlement habitat. Stretches of inhospitable substrate also constrain their ability to colonise new areas. For instance, pāua larvae won’t thrive on the sandy substrate of Lyall Bay immediately to the east of Taputeranga marine reserve.
I’m convinced from the available research and my own observations that Taputeranga marine reserve has contributed to a net decline in pāua abundance on the available road access parts of Wellington’s south coast. If an area is closed without considering the impacts of displaced harvesting – whether by recreational or commercial fishers – the surrounding fisheries will suffer. Let’s hope that the Ministers who make the decisions on the Otago MPA network recognise that effective marine biodiversity protection must complement and support our fisheries management regime, rather than undermining it.