State of the GBI Environment Report
by John Ogden

 

At Mulberry Grove beach, in February this year enterococci counts exceeded the Ministry for the Environment’s guideline of 140 enterococci per 100 mls of seawater level on two of the four monitoring days (ACC website). Retesting gave lower values, but, combined with algal blooms (see ENV NEWS 15) in the area, the results are cause for concern. D.o.C’s island-wide brown teal counts were down in 2008 compared to previous years, perhaps coinciding with an outbreak of colesi virus reducing the numbers of rabbits and hence causing ‘prey switching’ (to ducklings) by harrier hawks. Deer, pigs, rats and cats may have been eliminated from Kaikoura Island, and a rat-proof fence has been erected at Glenfern Sanctuary. Kanuka scrub may turn out to be a valuable asset for saleable ‘carbon credits’, but then again, it might not. The island’s human population has declined since the previous census, to the point where essential services are threatened. On the other hand tourist numbers may be up, and there appear to be more cars on better roads. About 70 new building permits were issued every year from 2000 to 2004, but since then the level has dropped to about 50 – still nearly one a week.

These and many other issues are all about the environment in which we live. The Resource Management Act (however it might be altered in future) requires us as individuals, and the statutory authorities who act on our behalf, to take account of our impacts on the environment. The elimination of such major pests as rats and cats, throughout Great Barrier, would have repercussions on many aspects of the biological, physical and social environment on the island. A charitable trust pressing for serious consideration of such a plan runs into serious issues regarding its relationships with all the authorities and individuals that must be involved, including of course the elected Community Board. This reasoning led us, in 2007, to propose writing a “State of the Environment Report” (SOE) for the island. An SOE is meant to provide a factual snapshot of the current health of the environment, to identify trends and indicate possible solutions or areas where more data are required. Most, if not all, SOEs have been produced by government agencies or regional bodies, such as the ARC. The most recent, and relevant, is that on the state of the environment in the Hauraki Gulf by the Hauraki Gulf Forum (H.G.F. June 2008; available on line as a summary or in full: www.arc.govt.nz/albany/).

So, as a bunch of amateurs, we started on the SOE for Great Barrier in early 2008 and soon realised what a huge – almost limitless – task we had set ourselves. There are so many aspects to what we mean by “environment” and the factual data are continuously changing, so that what is ‘true’ today, may not be so in six month’s time. Also there is so much data on some topics, and so little on others, and some is easy to get, and some is not. All I can say is that we are doing our best; we know we will miss some things and be out-of-date with others. Our aim is to produce a document which can be added to and improved on in future, but will have value as a summary of the current state of environmental trends on Great Barrier, and as a resource for information.

Liz Westbrooke has compiled the data for the first four chapters, which are almost finished. The introduction draws attention to the unique nature of the island’s biota and the risks it faces. Chapter 2 (‘Place and People’) deals with the physical environment and with population issues. Liz compiled old climate records to give a better picture of our changing weather patterns. However, the drivers for environmental change are mostly related to human activities; human demography shows the population peak (c. 1200) in the late 1990s, the fall since then, and the rapid shift to a population dominated by the over-50 age-group (Fig 1) . Median house prices have doubled over the same period. Chapter 3 describes production and consumption patterns, beginning with a ‘bullet point’ historical survey. “Commercially sensitive”, but vitally important data, such as the consumption of petrol and diesel proved impossible to get. Information concerning vehicle registrations in 2008 on the island had to be purchased from the Land Transport Safety Authority. Getting anything factual about the island’s economy has not been easy.

Chapter 4 covers Environmental Management and outlines the (often contentious) roles of Auckland City Council, Auckland Regional Council, the Department of Conservation and the Hauraki Gulf Forum. Great Barrier Island comprises 44% of Auckland City’s land, but the population is only 0.2% of the City’s! The Department of Conservation manage two-thirds of GBI, described by them as “one of the region’s last great wilderness areas”. (Wilderness with boardwalks? A re-classification might be in order). ARC works with D.o.C on pest management and biosecurity.

Chapters 5 and 6 deal with the vegetation and flora of the island, drawing together and summarizing unpublished information. Detail lists of species are relegated to Appendices. Stress is placed on the long-term but on-going changes as kanuka scrub turns to forest, or wetlands are drained. Rare plant species are mentioned and a list of the most important ‘environmental weeds’ presented. There is also a Chapter on carbon sequestration which discusses the potential monetary value of kanuka scrub. Three Chapters (7, 8,9) deal with invertebrates, reptiles and frogs, and marine life. The island has a particularly rich fauna of small land snails, and thirteen different kinds of lizards! The endangered tiny Hochstetter’s frog is still present in very small numbers, but tuatara, present on several sea-stacks and off-shore islands within living memory, have probably become extinct. Marine life is a big issue, which we can only cover in a summarized format; a great deal of relevance has been covered in more detail in the SOE for the Hauraki Gulf (see also the first H.G.F. SOE, 2004).

I am currently working on the Birds Chapter, drawing together historic data showing how we compare with New Zealand trends generally (Fig 2). Counts of common birds from the GBICT’s counts (see previous issues of ENV NEWS ), data from counts at Windy Hill and Glenfern Sanctuary, and other information will be summarized. I will be stressing the (mostly downwards) trends in the data for our iconic rarities (brown teal, black petrel, New Zealand dotterel) and drawing attention to how little we know about trends in other species, such as kaka, kakariki, tomtit, banded rail, bittern, reef heron, fern bird etc. Common ‘predators’, such as harrier hawks, pukeko and morepork owl also deserve more study. My bird data base currently includes 113 species for Great Barrier, but 13 of these are probably now extinct here or were erroneously recorded. However, the island and its surrounding seas have c. 100 bird species, which is roughly a third of the entire New Zealand list (excluding extinct species).

 

Fig 2. Indigenous bird species extinction rate on Great Barrier Island compared with the overall New Zealand rate, since the arrival of Europeans.

 

(NZ data from Tennyson, A. & Martinson, P. 2006. Extinct Birds of New Zealand. Te Papa Press.
Pp 180.; GBI data from Hutton, F. W. 1869. Trans. & Proc. NZ Institute vol 1. (Hutton visited GBI in 1868)).

 

The final two Chapters discuss the threats to the biodiversity posed by vertebrate pests, and some of the options and problems presented in their control or elimination. Linkages between these and the human economy are alluded to.

The final section will summaries the “State of Great Barrier Island’s Environment” and emphasize the main findings of our survey.