Reproductive biology and the use of photoidentification to study growth in Stichopus mollis (Echinodermata: Holothuroidea) in Doubtful Sound, Fiordland, New Zealand.

Lesley Raj
August 1998

Abstract

There has been some interest in developing a fishery for the sea cucamber, Stichopus mollis, in Fiordland and other parts of New Zealand for overseas markets. Unfortunately, little information is available on the biology of this species that can be used in the development of a management strategy for a potential fishery. One of the aims of this study was to obtain basic information on the reproductive biology of S. mollis in the fiord environment that might be useful in a management context.

Stichopus mollis from Elizabeth Channel, Doubtful Sound, were sampled monthly from April 1997 to March 1998. This population was dioecious with a 1:1 sex ratio. Gonad index (GI) was greatest between September and January 1998, peaking in October. The majority of sea cucumbers from July to January were in growth, mature or spawning stages of gametogenesis; the remainder of the time most inividuals were in post-spawning, recovery and growth stages. A resting gametogenic stage was documented in S. mollis during winter, although not all individuals sampled displayed this stage. Based on these data, S. mollis in Doubtful Sound possesses an annual breeding cycle with a peak in reproductive effort during spring. A number of environmental factors were recorded with daylength and chlorophyll a correlating best with GI. Size at first sexual maturity (SAFSM) was determined as 91g wet gutted weight.

Photoidentification was trialed as a means for re-identification of individuals in the wild. Photographs of individual Stichopu mollis from within the study site (Elizabeth Basin, Doubtful Sound) were taken neach month over a sixteen month period. Fourteen individuals could be re-identified due to characteristic warts, spots and colouring. The majority of sea cucumbers re-identified had detailed patterns of dots on their dorsal surface, giving the observer a larger, more distinct pattern to look for. Mean size of re-identified individuals was 24 cm. Length measurements, calculated for the re-identified individuals, suggested that growth was slow or negligible for sea cucumbers of this size.