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