AbstractCommercial fishing for Pecten maximus and Aequipecten opercularis
has taken place in Shetland since the late 1960’s and early 1970’s,
respectively, with fluctuations in landings of both species during this time.
Recognition of the importance that shellfish fishing contributes towards
maintaining a diverse economy in a rural area, coupled with concerns in the
1990’s about the potential for overfishing, prompted by reductions in the
abundance of some shellfish species, the Shetland Shellfish Management
Organisation Ltd. was formed, with a remit to implement local management of
shellfish stocks, where necessary. The collection of biological data was started
and the completion of log books begun in 1999 and 2000, respectively, to
provide data to assess the species, with a view to their sustainable
Von Bertalanffy growth parameters were determined for contemporary
samples on both species and on historical samples of P. maximus. The
asymptotic shell length, as a measure of growth, was examined in relation to
the environmental variables of sediment composition and depth. Growth
studies were carried out on juveniles to measure sub-annual growth.
The gonadal condition through time in the adult stocks was assessed,
changes in gonad condition were related to spawning activity by collection of
spat on artificial collectors. Seasonal and spatial differences in yield of
adductor muscle and gonad from experimentally derived, and commercial
yield data, was analysed.
The assessment of the fishery utilised fisher knowledge on the
distribution of stocks. Catch Per Unit Effort and mortality rates data were
calculated. The overall Spawning Stock Biomass was estimated for P.
maximus using the swept area method. Long-term data from processing
factories were incorporated into the fisheries assessment. The assessment
indicates poor catches of A. opercularis for many years, and a recovery in
abundance of P. maximus on some fishing grounds since the low catches
experienced in 2000.
|Date of Award||11 May 2010|