1. Update on previous year’s discussion on Descriptor 3
Approaches to improve assessment of data-limited stocks
Carl O’Brien, Cefas
Challenges offered by D3.3
Inigo Martinez, ICES
Making regional assessments of D3
Constanҫa Belchior, EEA

2. i) Approaches to improve assessment of data-limited stocks
Dr Carl M. O’Brien

3. Assessed stocks E.g. North-east Atlantic % Analytical 38 Trends based
stocks with both F & SSB estimates
stocks with only SSB estimates
stocks with only F estimates
stocks with no good environmental status assessment
E.g. North-east Atlantic %
Analytical 38
Trends based 10
Trends, survey only 39
Catch only 13
More uncertainty
Reduced quality and utility of advice for management

5. 1 2 4a 3a 4b 3b Development and simulation work undertaken since 2010
Simulation work for: 3a
ADGINTRO 3b
RGLIFE 4b

6. 2014 4c
Focusing on MSY for categories 3 and 4

7. Survey-, Catch- and Size-based methods
Survey-based method
hsCPUE applied to some stocks
North Sea brill: Rule-based hockey-stick fitted to proxy for recruitment and proxy for spawners, with indication of proxies for Blim and Bpa (left-hand panel) and results from hsCPUE (right-hand panel)

8. Conclusions (WKLIFE IV)
Results for lemon sole and North Sea brill seem consistent with other indications of stock status.
Survey data may not represent both components of the stock (recruitment and spawning biomass).
The approach appears promising and makes good use of the available data.

9. Catch-based method
Improved version of CMSY - applied to many stocks at WKLIFE IV
Results for North Sea brill (catch and CPUE):
CPUE data are shown directly on a second vertical axis in red in the
Pred. biomass vs CPUE graph.
In the Exploitation rate graph, the catch/CPUE ratio is shown in red against a second vertical axis.

10. Conclusions (WKLIFE IV)
Produced reasonable predictions for relative biomass and relative exploitation rate when compared with fully assessed stocks, simulated stocks and data-limited stocks for which CPUE data were available.
Application to stocks for which only landings data are available requires assumption that the proportion of discards are about the same throughout the time-series.
Extra caution needs to be applied when the assumption of average recruitment is likely to be incorrect; e.g. during periods known to be unfavourable for recruitment.

11. Size-based method
- Catches of fish (numbers) as a function of size (weight) for one year at least (fishery or survey).
- Case-specific life-history parameters characterising growth, mortality and recruitment, if available.
- Model follows size-based theory of exploited fish stocks and assumes steady-state; model output is ratio F/FMSY.
North Sea witch flounder: stock status estimated using survey data.

12. Conclusions (WKLIFE IV)
Method applied to North Sea ling, long rough dab and witch flounder and to Nephrops in FU 28-29: ling and witch flounder are exploited below or at MSY, while long rough dab is exploited close to MSY with a declining trend; Nephrops in FU seems to be undergoing overfishing in the recent years.
The method is currently being validated using real data; i.e. treating well-assessed stocks as data-limited.
The method is currently being implemented (s6model - single-species, size-based, steady-state model). It is expected to be in a stable, well-documented state shortly.

13. Topic for discussion: Data-limited fisheries in Europe
Question 1 – Is ICES’ science/advice development (WKLIFE) sufficient to identify FMSY proxies for category 3 and 4 stocks?
Question 2 – Should proxies be considered for biomass reference points? If not, should these be investigated as part of a management strategy evaluation (advice rule) to enable trade-offs to be explored?