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Understanding the land-sea connection
The Ministry of Fisheries is working to help regional councils and other
land managers and planners understand the effects land-based
activities are having on coastal fisheries and biodiversity.
Photo: Ministry of Fisheries
Good land-use planning supports one of our favourite pastimes – coastal fishing.
The link between water quality and healthy fisheries is a very clear one according to a new review covering the effects of land-based activites on our fisheries and coastal biodiversity.
The review brings together all the New Zealand studies on this issue, as well as drawing on overseas examples to ‘fill in the gaps’, says Ministry of Fisheries Science Manager Martin Cryer.
“There’s increasing evidence from both New Zealand and overseas that land-based activities can have significant effects on fisheries, as well as on the wider ecosystem,” Cryer says.
“We thought that having all this information together in one place would help land-use planning as well as fisheries management.”
Of all the land-based effects on our fisheries, the review suggests sediment is the biggest issue across New Zealand (although nutrient enrichment and other pollution can be significant in places).
Sediment impacts
Suspended sediment can make it harder for finfish to ‘breath’ and find food. It also makes it harder for filter-feeding shellfish to feed; so cockles, pipi, mussels and scallops can die off if the waters where they live get too muddy or silty.
When sediment settles, it can smother shellfish beds and other living creatures on the seabed, particularly if the silt/mud builds up in thick enough layers.
Layers of silt and mud also prevent shellfish like green lipped mussels attaching to the seabed, because these species need something firm to attach to.
In addition to this, sedimentation affects rocky reef areas because kelp spores need a hard surface to attach themselves to. Absence of spores means absence of kelp forests. Baby paua also find it hard to establish on surfaces covered by a fine layer of mud or silt.
Flow-on effects
“This is something we all have to work together on. Because we are all a part of this problem, we must all be part of its solution.”
These direct affects of sediment can flow-on into other parts of the ecosystem, causing more widespread harm.
For instance, rocky reef ecosystems are supported by the growth of kelp and other seaweeds there. By preventing attachment of kelp and seaweed spores, sediment can reduce the growth and extent of kelp forests. Where this happens, the whole productivity of the rocky reef ecosystem is reduced.
Sometimes these indirect (or flow-on) effects become felt over an extensive area. This can happen to species that have a life stage (or stages) that relies on a habitat that is vulnerable and in nearshore waters.
Snapper, trevally, tarakihi, john dory, garfish, parore, blue cod and mullet all rely on habitats that are sensitive to sediment – places like mussel beds, sub-tidal seagrass meadows, sponge gardens and bryozoan and tubeworm mounds. These provide important nursery and rearing areas, rich feeding grounds and safe havens from predators. They also frequently occur in sheltered bays or harbours – the very places most affected by sediment from the land.
The link between land use
and fisheries is crucial for
some of our northern
snapper fisheries.
Photo: Ministry of Fisheries
Of all the land-based effects on our
fisheries, a new NIWA review
suggests sediment is the biggest
issue across New Zealand.
Photo: Murray Hicks, NIWA
Working together
When a fishery gets stressed by sediment or other environmental effects, it becomes more vulnerable to further pressure – from fishing, for instance.
This means we need a healthy environment as well as effective fishing controls to keep our fisheries in good condition.
The Ministry of Fisheries is working to help regional councils and other land managers and planners understand the effects land-based activities are having on coastal fisheries and biodiversity.
“The Ministry can’t control what people do on the land, but we can work with the agencies that do control this,” says Sarah Omundsen, Inshore Fisheries Manager, Ministry of Fisheries, Auckland. “It’s important we make sure everyone knows what is at stake – in terms of how land-use practices affect fisheries.
“I’m sure that if people knew the effects their activities are having on their local fisheries and ocean, they would be more careful in some of the things they do in their daily lives. This is something we all have to work together on. Because we are all a part of this problem, we must all be part of its solution.”
Recently, a primary sector group working with the Auckland Regional Council identified the Hoteo River as a priority catchment to work together on to address water quality issues. The Hoteo flows into the Kaipara Harbour near the seagrass beds that are vital nursary grounds for North Island west coast snapper.
Ian Brown is the coordinator for the Primary Sector Water Partnership, and says his group’s work, together with the efforts of other agencies, will focus on working with rural land managers to help reduce sediment inputs into the Hoteo River catchment.
The Primary Sector Water Partnership is working with the Auckland Regional Council to help leverage off existing initiatives in this area. This work will aim to link to that of another group already involved in the issue – the Integrated Kaipara Harbour Management Group. The Ministry of Fisheries is a participant in this group, along with councils, other government agencies, industries and NGOs.
Other groups have already begun down this path. The Whaingaroa Harbour Care project is a case in point. Since 1995, the group has planted and fenced around waterways in the Raglan Harbour catchment, to improve water quality and biodiversity in the harbour. Benefits to local fisheries will hopefully follow.
“Projects like these are an investment that in time have the potential to increase the abundance of our fisheries – an endlessly renewable economic, culturally and socially valuable resource,” Omundsen says.
The Ministry of Fisheries’ commissioned NIWA review of land-based effects on New Zealand fisheries and ecosystems can be found at www.fish.govt.nz
