1. High-grading and over-quota discarding in mixed fisheries.
Batsleer J., Poos J.J., Hamon K., Overzee H.M.J., Rijnsdorp A.D.
Working as scientist in VisNed. Work that I will present today however is part of my PhD.
Controversial subject in fisheries.

2. High-grading
“The decision by fishermen to discard or retain fish of low value to make room for more valuable fish ...”
Gillis et al. 1995
I’m not sure if everybody knows the term high-grading but it is defined as…
In other words, fishers discard marketable fish while they still have sufficient quota available to land the catch. High-grading, or for that matter discarding of marketable fish in general, are seen as a wasteful practices in terms of food provision as well as for the sustainable exploitation of the stock. It is assumed that those fish do not survive the catching process. As such in 2009 the EU has declared high-grading as being an illegal practice

3. Fishers use adaptative strategies
Fishers are very capable, I would almost say masters in using adapting strategies to keep their bussiness viable given the dynamic environment they are operating. Discarding is one these adaptieve strategies. This dynamic environment is created by economic conditions including fluctuating fuel prices, fish prices, market demands, productivity of the fish stocks (how much can be harvested) and constraints imposed by management. For discarding specifically, there may occur a mismatch between the fishing opportunities and the fishing capacity.

4. Outline
Literature review
Model predictions
Control?

5. Literature review
Model predictions
Control?

6. Literature review
Query in Scopus resulting in 336 papers on discarding
Only papers with observations of high-grading or interviews selected
Generally on-board observers with discarding > MLS
When doubt, then we did not accept
Results in 44 papers with direct observations or interviews of high-grading
Hypothesis
Over-quota search 314 papers only 5 papers for which over-quota discarding could be inferred.

7. TAC Literature review Hypothesis
High-grading occurs worldwide, however dominant areas are also the areas where the majority of fisheries research is taking place.
High-grading occurs mainly in fisheries which are managed by individual quota or total allowable catches.
Surprisingly it does not only occur in (large) commercial fisheries, but high-grading is also found in recreational angling. Legal bag limit is

8. Literature review
Model predictions
Control?

9. Optimal annual strategy for an individual fisher
Dynamic state variable model
Annual
individual quota
Fish price
Variable costs
Plaice
Sole
Cod
1) Our modelling approach is based on Dynamic state variable modelling which is extensively described in a book of Clarck and Mangel. The DSVM is an Individual Based Model that has been used to predict behaviour for birds, fish, and insects.
2) We will use this model to evaluate the optimal annual strategy for a fishing vessel in the Dutch mixed flatfish fishery under annual landing quotas, while harvesting size structured fish populations. In this case plaice, sole and cod. These 3 species combined make up a total of 80% of the annual revenue of the Dutch demersal fleet.
3) The model is parameterized using spatio-temporal size-structured LPUE’s and includes some detailed economic information, such as fish price and variable costs (fuel, crewshare, landing costs, gear maintenance and other variable costs).

10. Make spatio-temporal predictions for three species each having five size classes using GAM.
No perfect knowledge: weekly catch rates within a year are random variable with seasonally changing mean
First, a statistical analysis using a Generalized Additive Model to make spatial and temporal predictions of means and variances of the catch rates of three commercial valuable species targeted by Dutch beam trawl fisheries in the North Sea (15 areas). Each species is divided into 5 size-classes.
Examples: left panel plaice < MLS (discards) High catch rates in areas bordering the plaice box. Middle panel is marketable plaice, higher Lpues in Northern areas. Right hand panel being predictions of Sole (cat 2 being of size 33-38cm). High catch rates in the Southern North Sea.
Knowing the spatiotemporal distribution of means and variances of the catch rates, these are used to parameterize an optimal choice model for individual fishers.
Cod<-gam(number ~ area + gear + te((sizeclass,week), by area) + log(hp) + te(yrwk, sizeclass) + offset(log(fishhour)) , family=negbin)

11. Size-structure implies price structure in fish populations
Season (weeks)
Price (€ kg-1)
1) The three fish species in the model are represented as size structured populations, whereby sole and cod are all marketable size-classes, but plaice consist of 4 marketable and 1 undersized size-class!
2) The different size classes of fish have different auction prices per week. Hence, the size structure is thus an important determinant for the value of a catch comprising of different size classes.
3) In the model we assume a single quota species, in this case plaice, constraining the individual vessel. We only have a single state variable, being the cumulative landings of quota fish caught. This facilitates computation.
(Buisman et al. 2011)
< MLS

12. Ψ=( + + ) – ( + ) A fisher evaluates optimal strategy based on:
Weekly behavioural choices:
Go out fishing or staying in port
Choose fishing area
Discard a part of the catch
Assumption is that fisher maximizes utility
We define utility as annual profit:
Ψ=( ) – ( )
1) In the model our individual fisher evaluates his optimal strategy in terms of weekly behavioural choices.
3 options: 1) fishing or not 2) choose the area 3) discard a part of the catch. The reason for choosing weekly time-steps is because most vessels make a trip of 4-5 days (1week)!
2) The choices an individual makes are based on a utility function, which can be seen as a fitness function and describes the result of the choices in a single currency. In fleet dynamics utility is defined as annual net revenue.
3) Profit depends on the expected direct contribution of the gross revenue that follows from the sales of fish in a week resulting from choices regarding area and discards. The direct contribution of the variable costs in a week resulting from the choice of fishing area. The expected value (i.e. mean) of indirect contribution of possible fines to the annual revenue, resulting from choices regarding area and discards

13. Increasing landings with increasing quota
High-grading is the dominant form of discarding > MLS
High-grading decreases with increasing quota
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Plaice landings and discards (tonnes yr-1)
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Quota are constraining for the fishery. Individual quota are fully exploited by the vessel. We have not reached the point where the fishery is able to fish unconstrained.
Projecting High-grading. Much high-grading at low individua quota. Vessel is trying to make optimal use of available quota by planning fishing activities in space and time.
Over-quota discarding seems not to depend on the available quota. Reason is that over-quota discarding is the result of the stochastic nature of the catches which prevents fishers from planning their catches perfectly.
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Plaice quota (tonnes yr-1)

14. High-grading early of the year when prices are low
Plaice discards (tonnes week-1)
Plaice discards (tonnes week-1)
Weekly pattern of decisions by an indivual vessel whether to land or discard fish. When IQ are large the majority of marketable fish that are caught are landed and high-grading almost only occurs are the beginning of the year when fish prices are low. i.e. the spawning period for plaice from december to March. This also explains the small amount of high-grading at the end of the year. Fisher will plan to fill its quota to maximize economic profitability by allocating effort in areas where they target the more valuable sole. High-grading in the middle of the year as a new year-class recruits into the fishery. High catch rates of smallest size classes coincides with a relatively low price compared to the larger size classes.
If quota are reduced fishers wil high-grade throughout the year. Over-quota discarding occurs at the end of the year, but when more quota is available fishers take more time to reach their quota limit. Over-quota catches are a result of uncertainty in the catch rates, preventing the fisheries from optimizing the use of quota by high-grading alone.
when a large amount of individual quota is available over-quota discarding occurs at the end of the year. High-grading only occurs at the beginning of the year when prices for plaice are low. Spawning period of plaice…
Lower quota vessel will land the fish in weeks when prices are high 1 6 11 16 21 26 31 36 41 46 51 1 6 11 16 21 26 31 36 41 46 51
Week

15. High-grading distorts observations of size composition20 40 60 80
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Percentage
Percentage of given size classes of plaice in the catch and landings. Clear that the size distribution is influenced by the amount of quota. These distributions depend on the choices and individual fisher make in terms of where and when to fish (each fishing ground characterized by different size composition) and the discarding decisions.
At high quota discarding is low and the size distibution in the landings more or less resembles the distribution of the catch. If quota are reduced the distribution starts to deviate from the catch, towards having more large plaice in the landings, smaller low valued size classes are discarded.
Problem: if you would base stock assessment purely on landing data accuracy of the assessment and quality of the advice would be affected. Need to get insight in the quantity , size or age structure as well as conditions when discarding of marketable fish can/may happen.
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Plaice quota (tonnes yr-1)

16. Outline
Literature review
Model predictions
Control?

17. Enforcement and control?
Increasing catches of juvenile plaice
We expect some high-grading in North Sea demersal fisheries:
Observations in scientific literature review
Strong incentive suggested by model
EFCA public reports of “Joint deployment programs”
Detailed information
Control efforts
Number and type of infringements
High-grading is prohibited since 2009, but High-grading is difficult to detect. Could a ban on high-grading be enforced effectively? Tresure of information on the effort to contole and the number and type of infringements of fisheries conservations measures.

18. Enforcement and control?
Increasing catches of juvenile plaice
In more than 3000 inspections
Guess how many infringements in total?
~350
Guess how many of those are related to high-grading? 1

19. Conclusions Increasing catches of juvenile plaice
Scientific literature on high-grading observations scarce, but suggests that it is pervasive
High-grading is the result of planning use of resources by individual fishers
If knowledge on seasonal spatial and temporal distribution, then high-grading is dominant form of discarding > MLS
High-grading hardly observed in control; difficult?
At the time we developed the model plaice quota where still constraining, which is currently not the case. In general, if fishers have knowledge on the spatiotemporal distribution of the resources and are able to plan their fishing activiteis to economically optimize their fishing opertions high-grading may occur.
Low infringements because high-grading does not occur that frequently or because it is difficult to detect. Need to be caught in action, processing time on board is rather short.

20. Thank you Increasing catches of juvenile plaice
Batsleer et al. (2015) High-grading and over-quota discarding in mixed fisheries. Rev Fish Biol Fisheries