Variations in North Sea sole distribution : variation in North Sea sole distribution with respect to the 56°N parallel perceived through scientific survey and commercial fisheries

The Dutch commercial fisheries report that sole (Solea solea) catches in the north of the North Sea have been increasing over the past years. While the large majority of North Sea sole catches are taken by beam trawl with 80mm mesh size, fishing with this gear is currently not allowed north of 56°N. In order to be able to get permission for a dedicated sole fishery (80 mm) in that area, scientific proof is needed for the increase in sole in the area north of 56°N. This study analyses data collected during the Beam Trawl Survey and STECF landing and effort data to investigate whether the spatial distribution of North Sea sole has changed over the last two decades. The study focusses in particular on the part of the North Sea to the north of the 56°N parallel where the main sole targeting fishery (beam trawl with 80mm mesh size) is currently not allowed to fish. Results based on the survey data show that the abundance and the extent of the distribution of sole in the area north of 56°N has increased (nearly doubled) since 2010. The proportion of the stock distributed north of 56°N also increased, but remains overall low (less than 7.5%). Over the same period, the centre of gravity of the stock has remained at a similar location. The only fleet operating at a scale large enough to provide information on sole at the scale of the North Sea was the Danish gillnet fishery. The proportion of landings of this fleet taken north of 56oN (in front of northern Denmark) has increased markedly since 2012, even when potential changes in the spatial distribution of the effort are taken into account. These results suggest an expansion of the stock at the margin of the distribution, while the core of the distribution of the stock has remained in the southern and central part of the North Sea (south of 54°N)

Best practices II : spatial distribution of the discards of the Dutch beam trawler fleet

This study aims at describing the spatial distribution – and its temporal variations - of discarding intensity (i.e. expected weight of discards for a standard trawl haul) for the 6 main species discarded by the Dutch beam trawl fisheries. For each species, the spatial distribution (quarterly maps for the period 2013 to 2017) is estimated using statistical models that take spatial and temporal correlation into account, which also allowed to test for the effect of a number of factors related to geography, environment, fishing practices and operational aspects on discarding. The data used to fit those models came from the observer trips and self-sampling program conducted at Wageningen Marine Research and from discards sampling trips conducted by the fishing industry. As by-product, the models provide descriptors of the temporal and spatial scales at which the discards of a given species are structured. The distribution of the expected discards per haul for dab was highly variable from quarter to quarter, with generally high discarding intensity in front of the southern coast of the Netherlands in quarter 1, a discarding intensity which is high on the German bight and low in front of the Dutch coast in quarter 3, and variable distributions for quarter 2 and 4. For plaice, the distribution was more stable, with high values consistently observed in the south of the area (between the south of the Netherlands and England), with occasional hot spots on the German bight. For sole, discards were not observed on the north-western part of the area, and a hotspot of sole discarding was found consistently in front of the southern coast of the Netherlands, occasionally expanding towards England or to the northern coast of the Netherlands. Discarding of turbot first occurred with a low intensity along the coast from Belgium to Germany. After the fourth quarter of 2015, high discarding started to occur, first limited to the small area in the southern North Sea, but progressively expanding to a larger area in the southern and central part of the North Sea, while discarding intensity remained low in the northern part of the area and in front of England. The distribution discarding intensity for whiting was highly variably, characterised by hotspots suddenly appearing for most years in the fourth quarter, and disappear in the following first quarter. Discarding of rays occurred mainly in the western part of the area, especially in front of southern England, with an increasing level since the fourth quarter of 2016. The distributions observed and their variability were further discussed in the light the available information on the distribution and migration of the species and on the management measures potentially influencing discarding

Best practices II : Effect on future development of sole and plaice of changing mesh size from 80mm to 90mm in the beam trawl fishery

This study investigates the consequence for future development of stock size, catches, landings and discards of sole and plaice of changing the mesh size of the cod-end from 80mm to 90mm for the Dutch beam trawlers in theTBB 70-99 fleet currently fishing with 80 mm.This study investigates the consequence for future development of stock size, catches, landings and discards of sole and plaice of changing the mesh size of the cod-end from 80mm to 90mm for the Dutch beam trawlers in theTBB 70-99 fleet currently fishing with 80 mm. The question is addressed by means of long term stochastic simulations. Using the simulation framework developed to test the effect of implementing the landing obligation, the future fishery selection pattern (how the fishing mortality is distributed across ages) is modified based on the results of the selectivity experiment to represent the consequence of changing mesh size. Simulations were then run for the next 50 years for different assumptions on the survival rate for both stocks: a 0% survival rate, and the lower and upper bounds of the current estimates of survival for each species. The differences in the effect on sole and plaice of using a 90mm net are related to both the direct effect of exploiting the stock with a different selection pattern and of applying different Fmsy values. The effects of changing mesh size are larger for sole than for plaice, because the share of the landings taken by the Dutch beam trawlers currently fishing with 80 mm is much larger for sole than for plaice. For sole, fishing with the 90mm net results in lower discards (10 to 16%). Landings are also lower (up to 4%) in the short term, but the situation reverses and landings become higher in the medium and long term (up to 3% after 5 years). These results are explained by the fact that when the 90mm net is used, the cohorts are exploited at a slightly later age combined with a stronger targeting of the older ages. This exploitation patterns leads in the medium and long term to a larger stock (by 3 to 13%), which explains the higher landings. Those benefits (in the medium and long term) of using the 90mm net are largest for the 0% and 10% survival assumptions, but are smaller (especially for the landings) for the assumption with 30% survival: the higher the chance for a discarded fish to survive, the less it pays to increase the selectivity of the gear because fish caught and discarded have still a chance to join the stock and further grow and reproduce. For plaice, in the scenarios with 0% and 10% survival, the Fmsy value for the 90mm net is higher than for the 80mm net. As a result, stock size is lower and catches, landings and (despite the improved selectivity of the net) discards are higher if the 90mm net is used. For the scenario with 20% survival rate, Fmsy values are similar for the 80mm and 90mm mesh size and the improved selectivity of the 90mm net indeed results in slightly lower discards, which in the medium and long term result in a slightly larger stock with slightly higher landings. One important assumption in these simulations is that the stocks are exploited at Fmsy in the future. However, if the beam trawl fleet switches to the 90mm net, its catchability (at least for sole) will decrease, meaning that a higher fishing effort will be necessary to achieve a same fishing mortality on the stock. The present study does not model explicitly catchability and effort, and therefore cannot quantify the change in effort implied if the stocks were to be exploited at Fmsy with the 90mm net

Improving the knowledge basis for advice on North Sea horse mackerel : developing new methods to get insight on stock boundaries and abundance

The North Sea horse mackerel stock is currently classified by ICES as a data poor stock, for which the catch advice is based on the trend in an abundance index. The development of an analytical stock assessment, necessary to give more accurate advice, is hampered by a number of limitations on the input data, among which the most important are the poor quality of catch-at-age data and the absence of a targeted survey for North Sea horse mackerel. The aim of this project was to study possibilities to improve the data quality used for an analytical stock assessment model

Report of the Regional Co-ordination Meeting for the North Sea and Eastern Arctic (RCM NS&EA) 2016

The Regional Coordination Meeting NS&EA met in Edinburgh from 5th to 9th September 2016. Thirty four participants from 12 members states, representatives from Commission and ICES were in attendance. The meeting was largely devoted to subgroup work relating to regional sampling, cost sharing models, data needs and the sampling of anadromous and catadromous specie

Discard self-sampling of Dutch bottom-trawl and seine fisheries in 2014-2016

In the European Union the collection and management of fisheries data is regulated through the Data Collection Framework (DCF) of the European Commission (EC). Within this context, Wageningen Marine Research (WMR) coordinates a discards monitoring programme in collaboration with the Dutch demersal fishing industry. A ‘reference fleet’ of vessels of which the owners are willing to participate in a self-sampling programme, was recruited. Fishermen within the reference fleet are requested to collect discard samples according to a definite annual sampling plan. After the discard samples are brought to shore, WMR collects and analyses these samples. This report summarizes data that has been collected within this monitoring programme in 2014-2016.In 2014-2016 the reference fleet consisted of 20-22 vessels. In total, 160, 172 and 157 trips were sampled in 2014, 2015 and 2016 respectively. All sampled trips were assigned to their respective metiers, based on gear type, mesh size and species composition of the catch. Within a trip, the crew retained a sample during two separate hauls, thus constructing two independent samples. Sampling was conducted on board vessels from eleven different metiers: beamtrawlers with 70-99 (Eurocutters (i.e. engine power ≤ 300 hp) and large vessels (i.e. engine power >300 hp)), 100-119, and ≥120 mm meshes, Scottish seiners with 70-99, 100-119 mm, and ≥120 mm meshes, and otter trawlers with 70-99 mm meshes, 100-119 and ≥120 mm meshes.Discard patterns are quite similar between all metiers; dab and undersized plaice are the most frequently discarded species. In addition, the flyshoot trips frequently discarded grey gurnard, whiting and horse mackerel. The majority of the benthos discards within the beamtrawl and otter trawl metiers consisted of echinoderms and crustaceans. In comparison, flyshooters discarded almost no benthos.An important element in the reform of the Common Fishery Policy (CFP) is the obligation to land all catches, i.e. a discard ban. Under this landing obligation all discards of quota regulated species have to be landed. For the demersal fisheries the landing obligation will be phased in over a number of years. The landing obligation will have a particular strong impact on the Dutch demersal fishing industry as this is a mixed fishery where catches can contain many different quota species

Best practice II: effect of discard survival on North Sea sole and plaice

This report investigates the effects of discard survival on the current stock assessment and perception of the North Sea sole and plaice stocks. By recalculating the discard fraction of the catches and rerunning the assessment model, the stock assessment of sole and plaice is corrected for discard survivability. Secondly, all discard survival corrected assessments of both stocks are forecasted over 50 years under a landing obligation and discarding (business as usual) scenario. This simulation shows the effect of discard survival under a landing obligation and under the discarding scenario. The trend and perception of both stocks do not change when discard survivability is taken into account. But the fishing mortality, stock biomass, and recruitment are overestimated. The effect of taking into account discard survivability is a scaling depending on the characteristics of the stock (such as maturity at age) and the extent to which the part of the stock is being discarded. The effect of discard survival is greater in North Sea plaice than in North Sea sole, since the plaice is discarded more. The Fmsy reference points increase with increasing discard survivability. However, the “F-targets”, the F corresponding to the maximal yield under the landing obligation, that are calculated to simulate the “landing obligation-scenario” do not show the same trend with increasing discard survivability. The forecast simulation of North Sea sole and plaice was performed by projecting the stocks with targets for fishing mortality that maximise the yield of both stocks. This method gives insight in the effects of the discarding and landing obligation scenario on the catches, recruitment, spawning stock biomass, and fishing mortality. Differences between scenarios increase with increasing discard survivability, although differences are marginal in the simulation of sole (compared to the differences between scenarios in plaice). Mainly the catches are effected by discard survivability under the landing obligation scenario