Surveys of mussels (Mollusca: Lamellibranchia) in the firth of Thames, 1961–67

Abstract

Surveys are described which were made to determine distribution and relative density of stocks of mussels, Perna canaliculus Gmelin (Lamellibranchia: Anisomyaria; Mytilidae), in the Firth of Thames, North Island, New Zealand, during the late autumn‐early winter of each year 1961–63 and 1965–67. Two dredges available for sampling were tested against one another over similar ground. Both gave comparable results, but although the one chosen was never actually calibrated, it gave consistent results which allowed relative changes of abundance to be studied. In 1961, 206 stations were sampled on a grid of 1 square mile which covered most of the Firth. Early results showed that the densest beds were along the western shore line; there were only small patches of mussels off Coromandel and along the eastern shore. A well‐stocked and readily identifiable area of 2 square miles off Matingarahi Point was selected for more intensive sampling on a 1/16 square‐mile grid. Samples collected there annually showed a rapid decline of the population after commercial dredging in 1961–62; there was no substantial regeneration on the bottom after this, though satisfactory settlement occurred above the bottom on experimental moorings. Declining yields are shown for other areas (Ponui Island and New Brighton) which were also sampled on a 1/16 square‐mile grid. Commercial landings of mussels decreased rapidly after 1961, and have not recovered. There have been no regular landings since 1966 but a promising private experiment in small‐scale cultivation is described. © Taylor & Francis Group, LLC.