Taking stock—the changes to New Zealand marine ecosystems since first human settlement: synthesis of major findings, and policy and management implications

New Zealand has a short and uninterrupted archaeological, historical and contemporary record of human exploitation of marine resources compared to most other places globally. Moreover, the human population trajectory for New Zealand is known from first settlement, a key parameter when estimating rates of resource exploitation. A large multi-disciplinary project (“Taking Stock” ZBD200505) was conducted to determine the effects of climate variation and human impact on the structure and functioning of New Zealand marine shelf ecosystems over the timescale of human occupation in New Zealand from about AD 1250 to the present day. In all, 18 separate reports have been prepared, some of which present results for the whole New Zealand region, while others focus on changes occurring in one or both of two study regions; the Greater Hauraki Gulf and the Otago-Catlins coast. In this report we summarise and synthesise the major findings of the project and discuss the overall implications of the results for marine conservation and management.

The project indicates that from first human arrival, marine environments in the Greater Hauraki Gulf and Otago-Catlins study sites underwent a profound change over the period. Fur seals (Arctocephalus forsteri) and sea lions (Phocarctos hookeri) were eliminated from much of the New Zealand coast within a few hundred years of Māori arrival, and seabird populations were impacted by sustained human harvesting, as well as by the arrival of the Pacific rat (Rattus exulans). Despite a high reliance by Māori on marine resources in both the Greater Hauraki and Otago-Catlins regions, the abundance of fish, invertebrates, whales and dolphins was reported as remarkably high by the earliest European visitors and explorers. However, following European arrival, fur seals were hunted to local extinction in their remaining foothold around the southern coasts of the South Island and Stewart Island and almost eliminated from the sub-Antarctic Islands. Southern right whales (Eubalaena australis) were hunted almost to extinction by the late 1840s and the other large whales were severely exploited during the 19th and 20th centuries. There was increasing exploitation of a range of fish and invertebrates once commercial fisheries were established in the 1860s, initially to supply a growing European settler population, and later to supply rapidly developing export markets. Laws and regulations to control fishing practices were introduced as early as 1866.

The historical data shows that the abundance of some exploited species of fish and invertebrates declined noticeably in both study regions, in the late 19th century and early 20th century prior to the start of New Zealand’s official landings records. The declines were first evident in species such as rock oysters (Saccostrea commercialis), grey mullet (Mugil cephalus), and flat fishes in sheltered, shallow, easily accessed areas, but later progressed to species with a wider distribution such as snapper (Pagrus auratus) and blue cod (Parapercis colias), or with a deep water refuge such as groper (Polyprion oxygenios and P. americanus). Declines in most species continued from the mid-1930s onwards during the ‘statistical era’ when fisheries landings data started to be comprehensively gathered nationwide and a variety of controls introduced. The most dramatic example during this period was the dredge fishery for green-lipped mussels (Perna canaliculus) in the inner Hauraki Gulf which collapsed in the 1960s, with significant ecological consequences, and has not recovered since.

Not until the introduction of the fisheries Quota Management System in the mid-1980s, were commercial harvests of marine fish and invertebrates finally brought under control allowing some stocks and populations to rebuild. Similarly, protection of most seabirds did not occur until the 1950s.

To determine the overall impacts of humans on a New Zealand shelf ecosystem this project aimed to build a mass balance model of the modern marine ecosystem in the Greater Hauraki Gulf, and then to estimate how this system operated at four earlier periods representing distinct phases of human marine resource exploitation over the last 1000 years (Pinkerton et al. 2015). These periods were ca. 1950, a period of a period of relatively stable domestic fishing activity; 1790, late Māori phase just prior to before the onset of European whaling and sealing; 1500, early to mid pre-European Māori phase; and 1000, before human settlement in New Zealand. There were insufficient detailed data to build similar models for the Otago-Catlins shelf. While all of the project reports contributed information to the mass balance modelling, individually they each provided details about particular trajectories of change for either the environment or specific groups of organisms and, as far as possible, explored the historical context of these changes.

In the sections below we summarise the main results of the project. In Section 2 we examine the evidence for climatological change in New Zealand during the period of human settlement and what that may have meant for the productivity and growth of marine organisms. In Section 3 we summarise archaeological, historical, and more recent information, including oral histories and fisheries landing histories, to construct narratives about the exploitation of shellfish, fish and sharks, seabirds, and marine mammals respectively. In Section 4 we summarise the findings from five mass balance models of the Greater Hauraki Gulf ecosystem spanning the last 1000 years. In Section 5 the overall results of the study are discussed. Then, in Section 6, we provide the overall implications of the study for marine conservation and management.