How overfishing depleted a natural resource

The demise of the Hauraki Gulf mussel beds is a cautionary tale of the unmanaged interaction of human activity and marine resources. The fishery's rise and fall is traced in a paper for Niwa's historical fisheries project by former Niwa fisheries scientist Larry Paul.

The reefs supported a significant dredge fishery from about 1910 to the 1960s, Paul writes. Mussels were sold fresh or pickled in the Thames area, or dried for sale to the Chinese community in Auckland - their health-enhancing properties were already known. Dehydrated soup powder was anticipated to be a major industry.

By World War II, about 1400 tonnes were landed annually and sold mainly fresh in-shell but also smoked or soaked in vinegar in tin drums.

During the war, canned mussel chowder was sent to New Zealand POWs.

In the 1950s, the Gundlock dredge brought increased catches but it proved more destructive of the seafloor. Landings peaked at about 2800 tonnes in 1961 but crashed to zero in 1969. The collapse was thought to be due to the dredges progressively fishing out beds, removing the substrate needed for juvenile mussels to attach to. Increasing sedimentation, from urban development and forest clearance for farming, may also have contributed to the mussels' decline and failure to recover since.

Paul says it was recognised early that quantity and quality was decreasing but little was done. The attitude was that if one area was fished out, boats would simply move further afield. Dredgers who tried to farm mussel beds rotationally to allow replenishment were thwarted by others who came and took the lot. As late as the 1950s, the department believed yields could be increased by fishing the densest ("over-populated") beds harder to encourage replenishment.

A relaxation of fishing regulations in the early 60s saw the number of boats double to eight and hastened the fishery's collapse.

Poachers played a part, illegally using scuba gear to reach the beds and raffling bagged mussels in bars or supplying fish shops.

Only towards the end was it fully appreciated the mussels were disappearing.

Paul concludes that the fishery failed because too little was known of mussel ecology. "Although this deficiency was recognised at the time, no management action was taken as the exploitation rate steadily increased."

Geoff Cumming