NIWA Ocean Survey 20/20

Coastal and Marine Data Portal

Tasman Bay Golden Bay Scallop Assessment

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The wild shellfish fisheries in Golden and Tasman Bays were once very valuable, but their production levels have declined significantly. We were asked to help stakeholders understand what had happened, and why, so that these valuable resources could be restored.

Rebuilding shellfish fisheries in Golden and Tasman Bays

The wild shellfish fisheries in Golden and Tasman Bays were once very valuable, but their production levels have declined significantly. We were asked to help stakeholders understand what had happened, and why, so that these valuable resources could be restored.

Overview

At their peak, wild fisheries for scallops, oysters, and mussels in Tasman and Golden Bays had combined revenues of about $90M a year. They also provided significant socioeconomic benefits to non-commercial stakeholders such as customary and recreation fishers, and to iwi.

However, these fisheries have declined over the last decade and commercial fishing has all but ceased. The causes of the observed decline are unknown, but are likely to be a combination of man-made and environmental effects.

We were asked to help the stakeholders of these fisheries develop potential approaches for restoring the sustainable production of wild shellfish fisheries in Golden and Tasman Bays.

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A satellite view of the Tasman Bay region.

Ecological importance

These fisheries and the ecosystems of which they are part occur in sheltered bays sheltered from oceanic swells; and these low energy environments are less resilient that those in high energy ecosystems on exposed coastlines.

These vulnerable ecosystems are not only subjected to the effects of fishing, but also to environmental, climatic, and other man-made stressors. These may include:

  • The effects of bottom fishing activities
  • Land use including toxins, pollutants, and the effects of sediment loadings in waterways
  • Climate and variability in primary production
  • Diseases and toxic algae

Our research will provide a case study for other fisheries in vulnerable ecosystems.

Socio-economic importance

The visions for the fisheries is to “to maintain healthy, productive and sustainable fisheries for commercial, recreational and customary use”. Maximising sustainable production in shellfish fisheries is important both regionally and nationally. Scallops represent the highest value shellfish stock in Tasman and Golden Bays and even a modest rebuild would have significant economic, social, and conservation benefits for all stakeholders.

Iwi (Te Tua Ihu) have interests in customary, commercial and, recreational fishing, and guardianship of coastal resources; this research has indirect links to Iwi aspirations consistent with their Iwi Fisheries Plan. Scallops are also an iconic recreational fishery in these bays and the New Zealand Recreational Fishing Council (NZRFC) supports rebuilding these fisheries to increase recreational opportunities.

Complex problems need sophisticated approaches

The declines are likely to be caused by several factors, with complex interactions.

Ad hoc changes to the management of these fisheries, or completely stopping commercial fishing, are unlikely to change their medium to long-term status. Increasing production of the fisheries will require research in order to provide tools and information for an ecosystem approach to managing them.

Approach

The complex issues affecting wild shellfish production in Tasman and Golden bays are most likely beyond the single stock management measures currently available, and need ecosystem approaches to rebuild shellfish production.

Because of this, we have established a group of stakeholder representatives so that we can to understand their management goals. This will allow us to clearly identify the information and tools they require, and to help develop a strategic research plan to get this information. Stakeholder engagement and collaborative research with the Cawthron Institute and Landcare Research underpin our research approach.

The development of a tool for ecosystem approaches will enable stakeholders to evaluate the trade-offs and benefits of different management options. At fishery and multi-fishery levels, we aim to build the capability of industry to maximise the production of wild shellfish through the development of technology and information

The identification of the primary drivers of, and constraints to, shellfish production is a key outcome of this research. These may be factors such as climate- or oceanographically-related drivers which we cannot control, but our ability to explain and predict when these drivers are likely to produce beneficial or detrimental effects will better inform management and fishing strategies. For other, man-made factors, information from this research may inform the development and evaluation of strategies to minimise or mitigate negative effects and to maximise the influence of positive effects.

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A sediment  plume from the Motueka River, in western Tasman Bay. Deposition of sediments from land based activities can have significant impacts on the coastal and estuarine environment.

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