Opportunities for improving stock assessment

Kristjan ThorarinssonPopulation Ecologist

The Federation of Icelandic

Fishing Vessel Owners

Ingredients for good assessment

Required as a minimum:

• Sound knowledge

• Good dynamic and statistical models

• The right info/data

Knowledge, model development and data collection progress in an interactive way

Assessing scientific advice:How good is it?

• Sound biological knowledge √• Expertise in modelling and statistics√• Full use made of all available data?

A gap in knowledge

• Fisheries data are produced by an interaction between fish stocks and fishing fleets

• Fisheries scientists make great effort to understand fish stocks

• Fisheries scientists make relatively little effort to understand fishing fleets

• Consequently, the interaction between fleets and fish stocks is poorly understood

Assessment not automatic

Many judgement calls must be made when assessing any given stock.

(Do I make this assumption or that assumption? Do I believe the results of this model or that model? What info can guide me?)

Many sources of information can and should affect such judgement calls.

Industry expectations

• The fishing industry will always demand improved performance

• Current post hoc explanations of failure not adequate. Catchability change? Can happen again if not fully understood.

Need for improvement

• Points illustrated with 2 Icelandic examples: 

• 1. Cod  - a stock assessed only on the basis of survey 

• 2. Saithe - a stock previously estimated only on the basis of commercial catch data

Recent asessments:Over and underestimates

MRI track record in recent years has led to doubts:

• Saithe stock -- underestimated

• Cod stock -- overestimated

MRI needs to rebuild confidence in its assessments and advice

Saithe: A trap

• Insufficient monitoring of recruitment and migration

• Most all data come from fishery (catch and CPUE)• Vicious circle: TAC => avoid saithe => catch

and CPUE => stock estimate => TAC • No way for TAC to go up? Requires independent

data, either stock survey or crew survey

Cod

• Overestimate => CCR gives too large catch => stock decline and serious disappointment.

• Groundfish survey CPUE has produced more accurate results than trawler log book CPUE. Reason: Technical change and changes in fleet behaviour.

Fleet data

• Fishing operations do not constitute planned scientific sampling of fish stocks.  Nevertheless there may be a useful (fixed) relationship between average CPUE and stock abundance if vessel and gear remain unchanged and if fishing objectives remain unchanged. 

• Info from vessel captains is needed for proper interpretation of log book data.

Survey data

• Surveys independent of commercial fishing operations are relatively reliable in some cases.  Survey results often need to be supplemented with information from the fishery, especially when area coverage is limited. 

Adequate data?

• Stock redistribution. An inshore shift in cod distribution suspected in 2000-2002. Annual groundfish survey does not appear to cover the inshore adequately

=> Need to institute a new inshore survey

Adequate systematic use of data?

Fishing fleet operations:

– technical change– mesh size change– quota transfers– target species– log books– interviews with captains– scientist participation in fishing trips– digital data on individual fish from processing

Systematic study needed

New and Trendy:

Ecosystem Based Fisheries Management

• Everybody talks about it• Nobody knows what it is!

• Some steps have already been taken• Appearing in official texts• A great deal of work ahead

Conclusion

In fisheries assessment and advice, it is in my opinion not sufficient to apply population dynamics models to standard data on and catch and CPUE.  It is very important also to follow the fishery itself in some detail, how the fishing boats operate, how the fishing effort and fishing techniques change, and what the fishermen have to say about fish behaviour and changes in fish availability.  This necessitates organised communication and cooperation between fishery scientists and the fishing industry.  A lot more can be done profitably in this regard than is current practice.