Abstract
The midget octopus Octopus huttoni is an important link between trophic levels as a food source and a predator, but little is known about its life history or growth. This is the first study to age and quantify growth in O. huttoni from three populations in Southern New Zealand, namely Foveaux Strait, Otago Harbour, and the Otago continental shelf. Morphometries were measured for 121 individuals, ages were estimated for 109 individuals using beak and stylet increment analysis, and lipofuscin quantity was analysed for 106 individuals. Assuming that one increment equals 1 day, beaks provided the highest age estimate (up to 250 days), but are suspected to be an underestimate (40-70 days) because increments were not found on laboratory-reared paralarval beaks, suggesting that the first increment may form after settlement. Daily growth rings in stylets were validated by tetracycline marking, but low estimates of age were attributed to poor visualisation of the stylet nucleus. The relationships between lipofuscin volume ratio and age or size of the individual were not significant, lipofuscin density was low, and individual variation was high. Results indicated that this species displays indeterminate growth until death, with a maximum mantle length of 50-60 mm at an age of 200-250 days. Further, individuals from Foveaux Strait were smaller and younger than those found in the Otago Harbour, supporting an hypothesis of an ontogenetic migration onshore.