Excavating Otata

Our changing climate and rising sea level is having an impact on our archaeological heritage. New Zealand Archaeology Week provides an opportunity to raise awareness of these changes.

In March 2020, prior to New Zealand’s Covid-19 lockdown, Auckland Museum archaeologists carried out a small excavation in a large coastal midden on Otata Island in the Hauraki Gulf, Tikapa Moana, in partnership with landowners and Ngāi Tai ki Tāmaki. The aim of the excavation was to record information from the important site before it is lost to erosion.

The results of this project will also provide a baseline for understanding the changing marine environment around Otata and a valuable comparison for modern surveys being carried out.

In January 2018, huge swells in the Hauraki Gulf caused widespread damage to coastal areas. In only a few hours the previously stable, vegetated coastline of Otata had been reduced by up to five metres, exposing the 50 meter length of midden. The waves removed shingle from the beach, which previously offered protection to the midden, which put it at increased risk of damage from further storms.

The Otata midden highlights the vulnerability of heritage sites as more intense weather events, coastal erosion and sea level rise is expected in the future. There are more than 2000 recorded archaeological sites in the inner Hauraki Gulf, including defensive pa sites, kumara pits and midden, with many of these in low lying at-risk areas. These sites are important to help understand early Māori use of the Gulf.

As it is not practical or feasible to build sea walls to protect them, archaeological excavation is the only way to preserve this important information.

A midden is a rubbish heap of domestic waste and is an invaluable source of information about how people lived in the past and about the natural environment at the time.

The exposed face of the midden we were excavating on Otata indicates at least two stages of occupation. These signs of occupation are characterised by dark layers of soil containing dense shellfish, bird and fish remains as well as stone and charcoal filled hangi and several postholes indicating where shelters may have been. A few postholes exposed in the section still have a large stone wedged down the side to keep the post stable.

Image caption: Close up of midden layers containing shell, bird and fish bone, hangi stones and stone flakes

The archaeologists, along with the Neureuter Family (landowners) and representatives from Ngāi Tai, set out for Otata on a clear autumn day. Planning for fieldwork on remote islands often requires a few Plan B’s and continuous checking of weather forecasts in the week prior. The weather must be fine for archaeological work to take place easily. Otata, the largest island in the Noises group of islands, lies northeast of Rakino Island on the outer edge of the Inner Gulf and is about one hour by boat from downtown Auckland.

The excavation of three 1x1 metre squares was conducted over a week. Each layer was carefully removed using a trowel, the contents of each square was then sieved and bagged. An enormous hangi was uncovered in square A with a dense charcoal layer and large hangi stones measuring over 20cm.

The actual size of this hangi is unknown because it extended into all four walls of the excavation. The hangi was topped by a dense concentration of large mussel shells.

Image caption: Interior of one of the 1x1 metre squares. Note the different layers, including the dense charcoal layer indicating a hangi pit

There is always debate about how much sample material is required to be representative. In this case 500kg of shell and bone was taken to Auckland Museum where analysis will be carried out. This will involve identifying all shell, fish and bird species present and in what quantities. From this it will be possible to look at foraging behaviour, food preferences and the season in which the different foods might have been taken. Obtaining radiocarbon dates will also be important.

Image caption: bags of excavated material to be taken to Auckland Museum for analysis

Archaeological sites can also be of interest to environmental scientists as they can provide a picture of what the environment was like at a particular time. This project will give a baseline for understanding the changing marine environment around Otata and will be a valuable comparison for modern surveys being carried out by scientists at the University of Auckland Leigh Marine Laboratory.

In addition, fish length can be estimated from measuring head bones to determine whether fish size has declined over time, and oxygen and nitrogen isotope analysis of shells can reveal environmental changes such as water temperature and sedimentation. Oetoliths, or ear bones of snapper, can also provide information on what season the fish were caught.

For archaeologists the most exciting feature of the Otata midden is the rich diversity of species contained within it. Middens with an abundant range of species are rare in the Hauraki Gulf and only a few have undergone full analysis.

The Otata project is enriched through its partnership with Ngāi Tai ki Tāmaki, incorporating Te Ao Māori into the results by looking at traditional knowledge and oral history alongside the archaeological record. Climate change, sea level rise and increased storm surge is already having a detrimental impact on coastal archaeological sites. Unfortunately, with many likely to be destroyed or severely damaged in the coming years, a huge amount of information about the past will be lost. This project hopes to demonstrate how archaeological investigation, coupled with mātauranga Māori, can be used to support anecdotal and contemporary climate data in the development of climate change responses, resource management plans and conservation. For further developments, watch this space.

Image caption: Auckland Museum archaeologists, Auckland Museum staff, Ngāi Tai ki Tāmaki representatives and members of the Neureuter Family on Otata Island

Blog: Excavating Otata Island: A Midden Revealed by Auckland Museum Assistant Curator, Archaeology Emma Ash. Published 30 April 2020