We assessed the effect of the European discards ban on the profitability of bottom trawlers in a case study fishery (GSA06, NW Mediterranean) in the transition period 2017-2018, when the species that characterize the fishery, viz. hake and red mullet, fall under the discards ban. We used the results of
Se evaluó el efecto de la prohibición de descartes sobre los beneficios económicos de la flota de arrastre del área GA06 (Mediterráneo noroccidental) en el periodo transitorio 2017-2018 durante el que las especies que caracterizan la pesquería, es decir la merluza y el salmonete, deben desembarcarse obligatoriamente. Usamos los resultados de
The reform of the European Union Common Fisheries Policy brought into force the prohibition of discarding catches of regulated species (
Geographical SubArea GSA06 (“Northern Spain”) is one of the 30 areas established by the General Fisheries Commission for the Mediterranean (GFCM) for fisheries stock assessment and management (
Demersal fisheries in GSA06 are carried out with a variety of fishing gear, although in terms of production otter bottom trawl is by far the most productive (
Regardless of the LO, many studies point to the benefits of improving selectivity in trawl fisheries under biological and ecological criteria (
The most important species in the two fishing strategies practised in GSA06 by bottom trawlers, the continental shelf mixed demersal fishery and the deepwater crustacean fishery, are subject to regular stock assessments by the European Commission Scientific, Technical and Economic Committee for Fisheries (STECF) and the GFCM. Specifically, in recent years, the target species of the mixed demersal fishery (hake, red mullet, black anglerfish and blue whiting), as well as the three deepwater crustaceans (deepwater rose shrimp, Norway lobster and red shrimp) have been assessed by means of catch-at-age models from data submitted by national authorities to the STECF in the Data Collection Framework (
The economic parameters for the model were obtained from data sources such as the Annual Economic Report (
The model was projected for 15 years, with 2015 as year 0 and 1000 iterations in each scenario (
Scenario 0 | |
---|---|
Scenario 1 | Introduction of a modified bottom trawl design in 2017 (see |
Scenario 2 | As in Scenario 1, but with the existence of a market for unwanted catches paying 0.20 € kg–1. The world market value of fishmeal ranged between 1400 and 2400 US$ t–1 in the period 2012-2015 ( |
Scenario 3 | As in Scenario 1, and no market for unwanted catches. Producers are obliged to meet the costs of disposal, at 0.50 € kg–1 ( |
Stockname | Age | Number (000s) | mat | M | F |
---|---|---|---|---|---|
0 | 100,806 | 0 | 1.240 | 0.119 | |
1 | 26,126 | 0.15 | 0.580 | 1.227 | |
2 | 2,788 | 0.82 | 0.450 | 1.605 | |
3 | 225 | 0.98 | 0.400 | 1.340 | |
4 | 30 | 1 | 0.370 | 0.282 | |
5 | 4 | 1 | 0.350 | 0.282 | |
0 | 11,817 | 0.09 | 1.080 | 0.010 | |
1 | 4,387 | 0.14 | 0.480 | 0.380 | |
2 | 2,481 | 0.21 | 0.370 | 1.630 | |
3 | 295 | 0.3 | 0.320 | 1.340 | |
4 | 50 | 0.41 | 0.290 | 0.290 | |
5 | 24 | 0.54 | 0.270 | 1.320 | |
6 | 10 | 0.66 | 0.260 | 7.050 | |
7 | 0 | 0.91 | 0.250 | 2.940 | |
8 | 0 | 1 | 0.240 | 2.940 | |
0 | 109,502 | 0 | 1.250 | 0.000 | |
1 | 27,656 | 0.13 | 0.820 | 0.110 | |
2 | 11,657 | 0.5 | 0.390 | 0.933 | |
3 | 2,779 | 0.79 | 0.280 | 1.523 | |
4 | 396 | 0.9 | 0.240 | 2.007 | |
5 | 44 | 0.97 | 0.220 | 1.494 | |
6 | 3 | 1 | 0.210 | 1.494 | |
0 | 93,000 | 0.46 | 0.990 | 0.118 | |
1 | 29,100 | 0.76 | 0.460 | 2.220 | |
2 | 2,050 | 0.88 | 0.300 | 2.082 | |
3 | 103 | 0.93 | 0.240 | 1.665 | |
4 | 50 | 1 | 0.210 | 1.665 | |
0 | 279,420 | 0.08 | 1.250 | 0.001 | |
1 | 72,120 | 0.77 | 0.580 | 0.608 | |
2 | 15,798 | 1 | 0.440 | 0.274 | |
3 | 2,291 | 1 | 0.390 | 0.689 | |
4 | 609 | 1 | 0.350 | 0.267 | |
5 | 200 | 1 | 0.310 | 0.267 | |
1 | 34,479 | 0.05 | 0.470 | 0.010 | |
2 | 31,867 | 0.14 | 0.370 | 0.316 | |
3 | 16,107 | 0.32 | 0.290 | 0.780 | |
4 | 4,264 | 0.58 | 0.260 | 0.732 | |
5 | 1,289 | 0.8 | 0.240 | 0.647 | |
6 | 448 | 0.92 | 0.230 | 0.480 | |
7 | 105 | 0.97 | 0.220 | 0.438 | |
0 | 103,067 | 0 | 1.180 | 0.019 | |
1 | 34,144 | 0.01 | 0.530 | 1.113 | |
2 | 3,709 | 0.61 | 0.390 | 2.387 | |
3 | 253 | 1 | 0.340 | 1.508 | |
4 | 25 | 1 | 0.310 | 1.969 | |
5 | 3 | 1 | 0.290 | 1.969 |
The objective of this work was to assess the effect of the discards ban in the transition period 2017-2018 when only two species, viz. hake and red mullet, fall under the discards ban. The MCRSs are 20 and 11 cm total length for hake and red mullet, respectively. We used the results of
The bioeconomic model used was the same as the one described in
The dynamics of the number of individuals by age class
(1) |
(2) |
where
(3) |
where
The natural mortality vector was considered constant throughout the simulation horizon. The fishing mortality vector was kept constant at the values produced by the stock assessments in Scenario 0, but a new
(4) |
where
The mean annual biomass of the population (
(5) |
where (
(6) |
The spawning stock biomass for each species was projected with the formula
(7) |
where
The catches by species were produced with the classical Baranov catch equation (
(8) |
The combined catches of the main species are
(9) |
In the economic submodel, the catches of the seven main species are complemented by catches of other commercial species whose population dynamics are not explicitly modelled to produce the total fishery yield (
(10) |
Species | Ex-vessel price (€ kg–1) |
---|---|
6.80 | |
7.80 | |
9.90 | |
5.00 | |
29.80 | |
18.90 | |
3.10 |
Gross profit π of the fleet was computed from the difference between income and costs (
(11) |
Cost 1 | Commercial costs as a function of total revenues (common costs). | τ=19%, including sales tax, harbour dues, crates and boxes. |
---|---|---|
Cost 2 | Costs related to fishing effort, mainly fuel or energy costs (common costs). | CC=1185.5 €/DAS/vessel, which comprises mainly fuel costs and other minor running costs such as lubricants and crew food. |
Cost 3 | Labour costs, following the share system, where common costs are deducted from the total revenue and split between the owner and the crew. | γ=50% to the owner; additionally, an average salary for the crew (AL) was computed, assuming a crew of four in each vessel. |
Cost 4 | Variable costs, including engine repair and vessel maintenance, and fixed costs, including licence and mooring fees. | CVF= 113.48 €/DAS |
where τ is the commercial cost coefficient,
The labour costs are given by the following expression:
(12) |
The gross profits were computed without subsidies because it is uncertain whether direct subsidies to the fishery will be available from 2017. However, the subsidies received annually by the trawl fleet in GSA 06 are estimated at approximately 3% of the value of landings in
Discards
Estimations of discards are available from official sources (DCF) for the period 2011-2014 for some of the species considered here, although these estimates should be considered as minimum values only. Typically, the estimates produced in the reports (
An age-length transition matrix (
The probability of individuals of age a being in length class i is
(13) |
where φ is the standard normal cumulative distribution function, is the upper bound of length class l, and L is the total number of length classes.
(14) |
where
The mean length-at-age
The ogive of unwanted catches by age was computed for hake and red mullet by adding the proportions in the age-length probability matrix in each age class:
(15) |
In the present work, we will consider perfect compliance with the LO in Scenarios 2 and 3, i.e. all undersize catches are either sold to processing markets or destroyed, at a cost to the producer.
The size frequency of bottom trawl catches in GSA06 for hake and red mullet are shown in
|
|
|
---|---|---|
Hake, age class 0 | 14.09 - 2.33 - 0.332 | 0.001 |
Hake, age class 1 | 23.20 - 3.84 - 0.449 | 0.065 |
Hake, age class 2 | 32.94 - 5.45 - 0.219 | 0.998 |
Red mullet, age class 0 | 13.38 - 1.92 - 0.266 | 0.001 |
Red mullet, age class 1 | 16.99 - 2.44 - 0.734 | 0.250 |
The projections of the biological indicators for each species, under the assumption of stochastic mean recruitment, are shown in
The amount of discards projected for 2015 and 2016, about 900 t for hake and red mullet combined, would decrease significantly, to about 100 t yr–1, from 2017 onwards after the introduction of the trawl modification (
Our results show that the volume of unwanted catches under the MCRS for hake and red mullet (under the remit of the LO from the beginning of 2017) is relatively low in terms of overall bottom trawl fisheries production. Their obligatory landing and sale for non-human consumption would produce small additional revenue to trawler operators, of the order of €0.2 million assuming a relatively high price of 0.20 € kg–1 for this product paid by fishmeal producers, for example. Adding the production of former discards from other demersal species that will produce unwanted catches from 2019, with the full implementation of the LO, is unlikely to double the additional revenue from former discards to trawl operators. In our analysis we have ignored the additional handling costs of former discards brought to land, but from personal interviews with producers (
year | Scenario 0 | Scenario 1 | Scenario 2 | Scenario 3 |
---|---|---|---|---|
2015 | 6.599 | |||
2018 | 14.115 (4.568-26.956) | –4.332 (–11.207-3.153) | –5.414 (–11.822-3.373) | –5.086 (–11.498-3.246) |
2020 | 15.120 (5.036-27.060) | 32.396 (18.306-51.525) | 31.726 (18.671-49.902) | 32.281 (18.725-50.997) |
All in all, the adoption of more selective fishing gear is expected to help rebuild stocks and increase the profitability of bottom trawl fisheries, regardless of the commercial fate of unwanted catches under the remit of the LO. Our scenarios provide only minimum estimates because the adoption of a more selective trawl design, such as the one described in
The adoption of simple but efficient technological changes to bottom trawls can be a positive step towards reducing catches of the unwanted fraction of regulated species. In the short term, the introduction of the new fishing gear would have negative economic consequences, which are unlikely to last more than one or two years given the rapid turnover rates of Mediterranean fish stocks. The real impact in the medium to long term is harder to forecast for two main reasons: First, the strong stock rebuilding predicted by simple biological models under constant recruitment assumptions may be far from the reality of dynamic ecosystems with complex relationships among the components (e.g. intra-specific density dependence and inter-species interactions).
This study received funding from the European Commission’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 634495 for the project “Science, Technology, and Society Initiative to Minimize Unwanted Catches in European Fisheries” (MINOUW). The authors thank the European Commission (DG MARE and the Joint Research Centre) for facilitating access to the fisheries Data Collection Framework database.