E - Iccat

ICCAT REPORT 2012-2013 (I)
5.2.1 East Atlantic and Mediterranean
The 2011 eastern Atlantic and Mediterranean bluefin tuna catch was 9,779 t, the lowest catch since 1950. Since
2008, a rebuilding plan and enforcement controls have been in place which resulted in a marked decrease in the
catch of mostly young fish in the Mediterranean. The quality and quantity of data and its collection continues to
need improvement.
The SCRS has strong concerns about the catch and catch-at-size quality/quantity of the data, the under-reporting
of fishing CPCs prior to 2007, the impacts of IUU fishing, and the loss of information at the time of caging.
However, both the data quantity and quality is improving with the introduction of individual quotas, better
enforcement of the controls and acquisition of new sources of information (BCDs, ship board observers, VMS
signals, cage site observers and the use of stereoscopic cameras during caging operations).
All CPUE indices displayed positive trends in recent years, including fisheries-independent information from the
aerial surveys performed on juvenile fish in the north-western Mediterranean Sea. Recent regulatory measures
significantly affected the CPUE values through a change of operational patterns. Fisheries-independent surveys
(e.g., aerial and larval surveys) and a large-scale tagging program are needed to provide more reliable stock
status indicators.
The Committee updated the 2010 stock assessment. In addition to improvements in the data quantity and quality,
the assessment methods applied must be modified in the future to better accommodate the substantial
uncertainties in the historical total catch, catch at age, and effort data. Testing of the methodologies envisioned to
improve robustness will require at least three years to complete.
The estimates of current stock status relative to benchmarks are highly sensitive to the selectivity pattern and to
the hypotheses about the recruitment levels. The perception of the stock status has improved in comparison to
previous assessments (F declined in recent years). All runs investigated showed a clear increase of the spawning
stock biomass (SSB), but both the speed and the magnitude of this upward trend remain highly uncertain as these
strongly depend on model specifications.
A higher abundance or higher concentration of small bluefin tuna was observed during aerial surveys conducted
in the north-western Mediterranean. This observation may reflect a response by the stock to an increase in the
minimum size regulation which also partly affected the selectivity patterns for several fleets operating in the
Mediterranean Sea and East Atlantic over the last five years. Improved yields-per-recruit were also observed in
comparison to the early 2000s as well as a greater recruitment to the SSB as a result of the regulation allowing a
higher survival of juvenile fish.
Sources of uncertainties have not yet been fully quantified and these include population structure, migratory
rates, key modeling parameters for bluefin tuna productivity and the fact that it is difficult to take the IUU catch
into account in the Kobe matrices. Despite these unquantified uncertainties, the 2012 updated stock assessment
confirmed the 2010 findings that the recovery plan would enable eastern bluefin tuna to return to B MSY with a
probability of at least 60% by 2022. Current estimates indicate that rebuilding could even be achieved before
2022, and that a slightly higher TAC would achieve the Commission’s objectives. However, given that the speed
and magnitude of the rebuilding of the SSB remains highly uncertain, verification of this outcome needs to be
confirmed by future data and analyses.
5.2.2 West Atlantic
This stock was last assessed in 2010 with slight increases being noted in the stock. The 2012 stock assessment
was an update of the previous analysis.
Virtual population analyses (VPA) were conducted with the same parameter specifications used in the 2010
base-case assessment using the most recent years of available data. Conclusions do not reflect the full degree of
uncertainty in the assessments and projections resulting from stock mixing, recruitment, maturity at age and
catch at age. Many of these deficiencies are being addressed by current research programs.
The Committee has no strong evidence to favour either recruitment scenario over the other. They are viewed as
reasonable (but not extreme) lower and upper bounds on rebuilding potential. The low recruitment scenario
suggests the stock is above the MSY level with greater than 60% probability and catches of 2500 t or lower will
maintain it above the MSY level and if the high recruitment scenario is true, the stock is not expected to reach
the MSY level by 2019 even with no catch.
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