Wild populations of mussels, Perna canaliculus, in northern New Zealand supply the majority of seed mussels to the >70,000 tonnes per annum green-lipped mussel aquaculture industry. However, surprisingly little is known about the reproductive cycle in this mussel species or
in these northern populations at Ninety Mile Beach. An extensive histological study of P. canaliculus found that their reproductive biology was similar to that recorded for other mussels. The mussels were dioecious with a 1:1 sex ratio throughout all sizes; only one hermaphrodite individual
was found. Mussels began to mature from 27 mm shell length, and by 40–50 mm, most individuals were sexually mature. Both female and male mussels appeared to have a consistent gonad cycle of gamete development, discharge, and redevelopment. Both sexes were well-synchronized reproductively,
with a prolonged spawning season from June to December (Austral winter-spring) when water temperatures were at their lowest and rising. However, a small proportion of mussels was found spawning ripe gametes throughout the year, which could account for the continuing appearance of mussel seed
outside the main spawning season. The spawning-spat catching season is more extensive at Ninety Mile Beach than has been recorded in more southerly parts of New Zealand, and these differences may be related to the generally warmer water conditions recorded in northern areas.
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