TASMANIAN GIANT CRAB FISHERY - 13/14

This assessment of the Tasmanian giant crab shery covers the period from 1st
March 2013 to 28th February 2014 and forecasts catch rates and biomass levels
under current management arrangements.
In the last two years, the total catch has decreased substantially. The catch re-
ported in the quota allocation system for the 2013/14 season was 25.95 tonnes,
representing only 55.7% of the 46.6 tonne TACC. In the 2012/13 season the catch
was similar at 26.41 tonnes, which was 56.7% of the reduced 46.6 tonne TACC.
State-wide catch rates were at records lows in the 2013/14 shing season, currently
23% of the standardised 1995/96 catch rate. Regionally, catch rates were 27% on
the West coast and 15% on the East coast. The state-wide catch rate in 2013/14
declined by 7% from 2011/12 and 5% from 2012/13, triggering the limit reference
point for a decline across two consecutive years. The regional catch rates o the
West and East coasts also declined by 9% and 8% respectively since 2011/12 but
this was less than 20% so the limit reference point was not triggered.
Catch rates of undersize crabs (which are released) provide an indication of un-
dersize abundance and consequently the strength of future recruitment to the
exploitable biomass. The catch rate of undersize giant crabs has been declining
since 2004/05 on the East coast and in 2013/14 was at 2% of the 2004/05 peak.
On the West coast, undersize catch rates have almost quadrupled since 2009/10
and were at similar levels to 2003/04, which is a positive sign for future exploitable
biomass. The reduction in the male size limit for the 2009/10 season can explain
some of the reduction in undersize catch rates on the East coast, however there
was already a substantial reduction in catch rate prior to the size limit change.
This dramatic reduction in undersize catch rates on the East coast is a concern
for the future health of the exploitable biomass.
Reference points relating to the weight structure of the catch landed at processors
are no longer assessed due to the availability of a stock assessment model. The
stock assessment model uses the length frequency data collected by shers in ad-
dition to commercial catch and eort data, to provide more reliable and higher
resolution size structure and biomass data.
The stock assessment model estimates that the state wide exploitable biomass
has declined from a maximum of approximately 1100 tonnes in the early 1990s
to 106 tonnes in 2013/14. This equates to 9% of the original unshed exploitable
biomass. Total biomass and egg production have both decreased to 13% and
14% respectively of their initial levels but have started to stabilise over the last
two shing seasons. Due to signicant undercatch, estimated harvest rates have remained steady over the last two shing seasons at around 25% state-wide.
Results for the West coast are indistinguishable from the state wide results when
considered relative to the virgin stock state. Total biomass and egg production
have both decreased to 14% of their initial levels but have been relatively stable
for the last three shing seasons with slight improvement. Estimated harvest rates
have remained steady over the last two shing seasons at around 22%.
The East coast stock is smaller but has had proportionately lower catches. Con-
sequently the stock is less depleted at 14% of Virgin exploited biomass and 20%
egg production. The harvest rate has declined to 22% (the same as the West
coast). There is more uncertainty about the East coast stock due to the limited
availability of length frequency data. Length frequency data from the East coast
is urgently required to reduce uncertainty in the assessment.
The stock assessment projections for the 2014/15 TACC with a 10% undercatch
(34.3 tonnes) over the next decade were positive at all three spatial scales. State-
wide catch rates, absolute egg production and exploitable biomass are projected to
stabilise and rebuild to 52%, 78% and 56% greater than present levels respectively
by 2023. East coast catch rates, absolute egg production and exploitable biomass
are also projected to stabilise and rebuild to 47%, 64% and 54% greater than
present levels respectively by 2023. Similarly, West coast catch rates, absolute egg
production and exploitable biomass are projected to stabilise and rebuild to 58%,
68% and 50% greater than present levels respectively by 2023.
Catch rates of giant crab in 2013/14 have continued to decline, which was not pre-
dicted by the previous stock assessment despite actual catches being substantially
lower than those that were modelled. This raises concern that the observed catch
rate declines are due to external factors not modelled. While model projections
indicate stability in the future, there is much uncertainty with these outputs be-
cause length frequency data is not available from the East coast stock and growth
information is limited. Consequently, the positive model based outlook should be
treated cautiously.

This dataset record is provided by Parks Australia to highlight research conducted within or relevant to Australian Marine Parks. The original publication and associated intellectual property remain with the source organisation.
This publication was previously made available via the Australian Marine Parks Science Atlas and is provided here to maintain access following the decommissioning of that platform



Tags: Australian marine parks, Fisheries, Giant Crab Fishery, harvest rates, tasman fracture
Organization: Parks Australia