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Assessment of the Potential Impacts on Waders and Seabirds of Finfish Marine Farming in the Firth of Thames

Report: TR2008/50
Author: Paul Sagar (NIWA)


Currently, Environment Waikato is scoping a possible plan change to allow for the diversification of aquaculture within existing aquaculture management areas in the region. This plan change would allow for the cultivation of species other than mussels, including finfish. This assessment is one of several studies commissioned as part of the information gathering and consultation phase of the aquaculture plan change. The primary objective of this study is to:

Evaluate the impact of new types of aquaculture, such as kingfish farming, on waders and seabirds, and their habitat.

Key findings are:

  1. A total of 132 species of birds have been recorded from the Firth of Thames, primarily in the vicinity of Kaiaua/Miranda, at the north-western section of the Ramsar site. Of these, about 60 species are either abundant or common, the remainder being occasional or rare visitors.
  2. The Firth of Thames is of international importance for the numbers of Arctic-breeding bar-tailed godwits (Limosa lapponica) and red knot (Calidris canutus) and endemic pied oystercatchers (Haematopus finschi), pied stilts (Himantopus leucocephalus), black stilts (Himantopus novaezelandiae), NZ dotterels (Charadrius obscurus aquilonius) and wrybills (Anarhynchus frontalis) that it supports. All of these species forage on the intertidal mudflats. Of these, the species of conservation concern are black stilt (threat status B.1 Threatened - Nationally Critical); NZ dotterel and wrybill (B.3 Threatened - Nationally Vulnerable); pied stilt and pied oystercatcher (both D.1 At Risk – Declining).  
  3. Of the species that forage in open water, some feed on small fish either taken near the surface of the sea by plunge diving (e.g., Australasian gannet Morus serrator, Caspian tern Sterna caspia, white-fronted tern Sterna striata) or from greater depths by swimming underwater (e.g., pied shag Phalacrocorax varius, spotted shag Stictocarbo punctatus). Other species dive to feed on a range of small fish, crustaceans, and cephalopods (e.g., flesh-footed shearwater Puffinus carneipes, blue penguin Eudyptula minor) and others take mainly crustaceans from the surface of the sea (e.g., red-billed gull Larus noveahollandiae scopulinus, black-billed gull Larus bulleri). Among these, the species of conservation concern are black-billed gull (B.2 Threatened – Nationally Endangered); caspian tern, red-billed gull and pied shag (B.3 Threatened – Nationally Vulnerable); white-fronted tern, flesh-footed shearwater and blue penguin (D.1 At Risk – Declining).
  4. Waders within the Ramsar site may be affected indirectly via changes to habitats and invertebrate prey species caused by nutrient release driving primary production. Such effects could be either positive or negative. Positive effects may occur if any increase in phytoplankton production causes an increase in prey productivity. Negative effects could occur if an increase in nutrient levels led to either/or an increase in mangrove expansion, blooms of intertidal macroalgae, changes in the phytoplankton community that affected invertebrate prey species, severe eutrophication that affected the functioning of the intertidal ecosystem.
  5. However, these indirect effects are likely to be localised, and so not have any significant effects on the Ramsar site.
  6. Seabirds may be directly affected by entanglement, habitat exclusion, disturbance associated with farm activities, and increased prey availability with wild fish attracted to farms.
  7. Entanglement risk is well-managed in areas of New Zealand where marine salmon farming occurs, and so this is should be a minor risk that can be monitored effectively. Exclusion will be limited to the farm footprint. Limited anecdotal observations indicate that some seabirds become habituated to vessel movements and disturbance associated with finfish farming activities. Increased prey availability could become an additional food source of penguins, shags, gulls and terns. In addition, for some species, particularly shags, gulls and terns, marine farming structures are likely to provide roosts closer to the foraging areas of these birds resulting in them having to expend less energy commuting to the feeding areas. Overall, the potential consequences of these cumulative effects are likely to be minor.

Assessment of the Potential Impacts on Waders and Seabirds of Finfish Marine Farming in the Firth of Thames
(178 kb, 25 seconds to download, 56k modem)

Table of Contents


  Executive summary  i
1 Introduction  1
1.1 Background  1
1.2 Brief overview of ecological effects of finfish farming  2
2 Methods  3
3 Miranda Ramsar site  3
3.1 Bird species  3
3.2 Current risks to the Miranda Ramsar site  7
3.3.1 Extent of effects on benthic production  8
3.3.2 Extent of effects of nitrogen discharges  8
4 Risk and ecological consequences of identified effects within the Ramsar site  9
4.1 Changes to foraging areas and invertebrate prey through phytoplankton and macroalgal productivity  9
4.2 Changes to foraging areas through expansion of mangroves 11
5 Outside the Miranda Ramsar site 11
5.1 Bird species 11
5.2 Potential effects of finfish farming on seabirds 11
5.2.1 Entanglement, habitat exclusion and disturbance 12
5.2.2 Aggregation of prey and provision of roosting sites 13
5.3 Significance of effects on seabirds outside the Ramsar site 14
6 Research recommendations 14
7 Conclusions 15
8 Acknowledgements 15
9 References 16




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