Relevance for Economic and Biological Management Objectives of MSY-based Reference Points for Multispecies, Multifleet Fisheries: a North Sea Plaice and Sole Case Study

Maximum sustainable yield (MSY) has been recommended as a reference point for fisheries sustainability. However, like other reference points it is generally applied on a single-species basis. This has potentially significant biological implications in a complex multispecies fishery. MSY-based reference points also have economic implications for fisheries prosecuting the resource. To examine these issues, interactions between North Sea plaice (Pleuronectes platessa) and sole (Solea solea) stocks and two fishing fleets (northern and southern) will be modelled, incorporating changes in stock distribution, productivity and resilience. Fleet- and species-specific implications of a range of management objectives, including MSY, for fishery sustainability and profitability will be examined

A comprehensive study to assess the impact of impulsive sound on juvenile sea bass

Given the increasing amount of anthropogenically induced underwater sound into the marine environment, a better understanding of the impact of impulsive underwater sound on marine life is needed. This study tackles the impact of impulsive sound, related to pile-driving activities for offshore wind energy development, on the mortality, stress and behaviour of post-larval and juvenile European sea bass Dicentrarchus labrax. A 'worst-case scenario' field experiment was carried out on board of a piling vessel, exposing 68 and 115 days old fish (<2 g wet weight) to the sound generated during 1.5 hours of pile-driving. The number of strikes ranged from 1740 to 3070, with a single strike sound exposure level between 181 and 188 dB re 1 μPa².s, resulting in cumulative sound exposure levels ranging from 215 to 222 dB re 1 μPa².s. Immediate and long-term survival of the exposed fish was high and comparable to the control groups. However, juvenile fish responded to the impulsive underwater sound by a 50% reduction in their oxygen consumption rates, an indicator of secondary stress response. Primary stress responses, measured through cortisol levels are still to be analysed. We didn't find any effect on the condition and fitness of the exposed fish on the long term. Lab experiments performed with a SIG Sparker and a larvaebrator, respectively producing mid-high and lower frequencies, were inadequate to distinguish the determining sound metric or to pursue the exact origin of the stress response. Further away from the sound source, behavioural and masking effects can be expected. A lab experiment was carried out to study the behaviour of juvenile sea bass before, during and after one hour of impulsive sound exposure. In the aquaria, single strike sound levels reached 162 dB re 1 μPa².s, leading to a cumulative sound exposure level of 196 dB re 1 μPa².s after 2400 strikes. We observed that normal behaviour was disturbed, with an increase in startle responses and stationary behaviour at the beginning of the sound exposure experiment. Also, fish dived to the bottom of the aquaria, which is a typical anxiety-related response. However, no spatial preference was observed and normal behaviour was re-established shortly after the sound exposure ceased. These results indicate that impulsive sound close to the sound source creates sound pressure levels that are below the lethal threshold for fish, but above the stress threshold, at least for sea bass <2 g. Furthermore, lower sound levels at a distance from the sound source (in this case pile-driving) can disturb fish behaviour. Under optimal lab conditions, we did not see effects beyond the sound exposure period, but it remains unknown whether the reduced fitness of juvenile fish after exposure is limited in the real world as well

Common Sole Larvae Survive High Levels of Pile-Driving Sound in Controlled Exposure Experiments

In view of the rapid extension of offshore wind farms, there is an urgent need to improve our knowledge on possible adverse effects of underwater sound generated by pile-driving. Mortality and injuries have been observed in fish exposed to loud impulse sounds, but knowledge on the sound levels at which (sub-)lethal effects occur is limited for juvenile and adult fish, and virtually non-existent for fish eggs and larvae. A device was developed in which fish larvae can be exposed to underwater sound. It consists of a rigid-walled cylindrical chamber driven by an electro-dynamical sound projector. Samples of up to 100 larvae can be exposed simultaneously to a homogeneously distributed sound pressure and particle velocity field. Recorded pile-driving sounds could be reproduced accurately in the frequency range between 50 and 1000 Hz, at zero to peak pressure levels up to 210 dB re 1µPa2 (zero to peak pressures up to 32 kPa) and single pulse sound exposure levels up to 186 dB re 1µPa2s. The device was used to examine lethal effects of sound exposure in common sole (Solea solea) larvae. Different developmental stages were exposed to various levels and durations of pile-driving sound. The highest cumulative sound exposure level applied was 206 dB re 1µPa2s, which corresponds to 100 strikes at a distance of 100 m from a typical North Sea pile-driving site. The results showed no statistically significant differences in mortality between exposure and control groups at sound exposure levels which were well above the US interim criteria for non-auditory tissue damage in fish. Although our findings cannot be extrapolated to fish larvae in general, as interspecific differences in vulnerability to sound exposure may occur, they do indicate that previous assumptions and criteria may need to be revised

Ecologisch Gericht Suppleren: meetplan geïntegreerde ecosysteem survey 2017

Suppleties van zand op vooroever of strand worden in opdracht van Rijkswaterstaat uitgevoerd om de Nederlandse kust tegen erosie te beschermen en om voldoende zand in het kustfundament te houden. Een groot deel van de suppleties vindt plaats in of nabij de kuststrook die binnen de Natura2000 regelgeving wordt beschermd, de Noordzeekustzone. Het is dus van belang de eventuele effecten van deze praktijk op de natuur zorgvuldig te bestuderen, zodat dit effect kan worden afgezet tegenover het algemene nut voor de maatschappij. Betere kennis van de effecten kan leiden tot beperking van eventuele schade aan- en mogelijk zelfs tot versterking van- gewenste natuurwaarden en ecosysteemdiensten. Tot nog toe is er relatief weinig aandacht geweest voor de gevolgen van suppleren op vispopulaties in vergelijking met benthos, terwijl de kinderkamerfunctie van de ondiepe kustzone een zeer belangrijke economische ecosysteemdienst levert. Kennis van de habitatfactoren die het voorkomen van juveniele vis in kinderkamers bepalen leidt tot een verbeterd inzicht van de gevolgen van suppleties op vispopulaties en van de voedselketen van viseters in de ondiepe kustzone. In overleg met natuurorganisaties en de kennisinstituten Deltares en Wageningen Marine Research is in 2016 het document `Ecologische effecten van zandsuppleties’ (Herman et al., 2016) geschreven met als doel onderzoek te formuleren naar ecologische effecten van zandsuppleties. In het onderdeel ‘uitvoeringsplan’ (deel C in Herman et al. 2016) zijn 3 onderzoekslijnen (ook wel Krachtlijnen genoemd) gedefinieerd, te weten: Vooroever, Duinen en Waddenzee. Het hier beschreven meetplan voor een survey in 2017 valt onder de onderzoekslijn Vooroever. De onderzoeksvraag die in dit meetplan wordt behandeld volgt uit de prioritering van de krachtlijn Vooroever: (Cumulatieve) gevolgen van reguliere suppleties op samenstelling en functioneren van het ecosysteem van de vooroever. Deze onderzoeksvraag luidt: “Wat zijn de cumulatieve gevolgen van reguliere suppleties op samenstelling en functioneren van het ecosysteem van de ondiepe vooroever van de Nederlandse kust?” Conform het plan van aanpak voor dit programma (Herman et al., 2016) wordt voorgesteld om een survey uit te voeren in de vooroever (0 tot 10-12 m diepte), waarbij benthos, vis en habitatkarakteristieken worden bemonsterd. Deze geïntegreerde ecosysteem survey is daarmee een onderdeel van een groter pakket van geplande dataverzameling in het kader van Ecologisch Gericht Suppleren II. Het hoofddoel van de survey is om data te verzamelen over het voorkomen van (juveniele) vis in relatie tot relevante omgevingsvariabelen, zowel abiotisch als biotisch. De survey zal inzicht verschaffen in het functioneren van het kustecosysteem en kennis opdoen over de wisselwerking met biotische en abiotische omgevingsvariabelen. De resultaten van de survey zullen dienen voor het opstellen van habitatmodellen voor juveniele vis om hiermee effecten van suppleties te kwantificeren. Dit rapport beschrijft de meetstrategie, de meetmethoden, de te meten variabelen (vis, benthos en omgevingsvariabelen) en de bemonsteringslocaties voor de ondiepe geïntegreerde ecosysteem survey 2017

Modelling dispersal dynamics of the early life stages of a marine flatfish (Solea solea L.)

Connectivity throughout the life cycle of flatfish remains an open question, especially during the early life stages. Their effective management requires understanding of how spawning grounds and nurseries are connected and what processes influence larval retention and dispersal. The case of sole (Solea solea L.) is of particular interest because it is one of the most valuable commercial species in the North Sea, although stocks are chronically overexploited and variability in interannual recruitment is high. The transport of sole larvae from the spawning grounds to the nurseries is driven by hydrodynamic processes, but the final dispersal pattern and larval survival/abundance might be influenced by both behavioral and environmental factors. Therefore it is important to understand the relative impact of hydrodynamics, environment, behavior and ecophysiology on sole larval dispersal. Here we use a particle-tracking transport model coupled to a 3D hydro-dynamic model of the North Sea to investigate interannual variability of the transport of sole larvae over a 12-year period (1995–2006). A sensitivity analysis is performed to assess the relative impact of hydrodynamics, temperature and behavior on the recruitment dynamics to the nurseries. Four scenarios have been tested: (i) constant forcing of sea surface temperature during all years but varying meteorological forcing and river runoff, (ii) constant meteorological forcing during the whole period but varying sea surface temperature and river runoff, (iii) no vertical migration and (iv) an extended drift period (max. 30 days) before settlement if the larvae are not close to a suitable sediment type. Results suggest that year-to-year variability of larval supply to the nurseries is high, both in terms of abundance and larval source (balance between retention and dispersal). Sensitivity analysis shows that larval abundance at the end of the larval stage increases considerably if a settling delay is included. The impact of vertical migration on larval transport and the variations in larval retention at the nurseries due to varying meteorological conditions and sea surface temperature forcing are not spatially consistent

Habitat selection of juvenile sole ( Solea solea L.): Consequences for shoreface nourishment

The shallow coastal zone is an essential nursery habitat for juvenile flatfish species such as sole (Solea solea L.). The increased frequency of shoreface nourishments along the coast is likely to affect this nursery function by altering important habitat conditions, including sediment grain size. Sediment preference of juvenile sole (41–91 mm) was studied in a circular preference chamber in order to understand the relationship between grain size and sole distribution. The preference tests were carried out at 11 °C and 20 °C to reflect seasonal influences. The juveniles showed a significant preference for finer sediments. This preference was not length dependent (within the length range tested) nor affected by either temperatures. Juvenile sole have a small home range and are not expected to move in response to unfavourable conditions. As a result, habitat alterations may have consequences for juvenile survival and subsequently for recruitment to adult populations. It is therefore important to carefully consider nourishment grain size characteristics to safeguard suitable nursery habitats for juvenile sol

Variability in transport of fish eggs and larvae. IV. Interannual variability in larval stage duration of immigrating plaice in the Dutch Wadden Sea

Larval immigration of plaice Pleuronectes platessa L. into the western Wadden Sea in spring was followed biweekly from 1993 to 2002. For each year (1993 excluded), 150 settling individuals were selected and used for reconstruction of larval stage duration based on otolith daily ring counts. In addition, prevailing water temperature conditions during drift as revealed from NOAA satellite images were determined. Mean larval stage duration varied between about 40 and 60 d, without any clear significant pattern between or within years. Year-class strength of plaice in the western Wadden Sea was not related to mean larval stage duration. Mean larval stage duration did not show a clear pattern during the period of immigration, nor with reconstructed temperature conditions. The observed decrease of larval stage duration with temperature in the field was lower than that observed under laboratory conditions, suggesting food limitation with increasing temperature during drift. The fact that both within-year and for all years combined the number of immigrating larvae was inversely related to temperature conditions during drift suggested that year-class strength could be affected by temperature-mediated predation, but simultaneously occurring food limitation at high temperatures cannot be excluded

Can guild- or site-specific contrasts in trends or phenology explain the changed role of the Dutch Wadden Sea for fish?

The Wadden Sea bordering the Dutch, German and Danish coast, is traditionally a region with important functions for many fish species: as a nursery area for juveniles (marine juveniles), as a feeding area, as a transit to and from fresh water, and resident species complete their whole life cycle there. Because of indications that the importance of the Dutch Wadden Sea has changed drastically for many species during the past decades, we analysed and classified trends of 24 common fish species in the last 45 years, whichwere assigned to 5 differentecological guilds. Trends were examined for threeWadden Sea regions and compared to trends in the adjacent two North Sea coastal regions. For these analyses we made a combined use of two longterm time series: an annual beamtrawl survey, the Demeral Fish Survey (DFS) with a high spatial but poor seasonal resolution and a fyke serieswith a high seasonal but poor spatial resolution.Weinvestigated forwhich species the DFS surveywas appropriate for trend analysis, and we evaluated whether a change in timing may contribute to patterns in DFS time trends. Total fish biomass showed a similar pattern in all tidal basins with an increase from 1970 to 1980, a peak in the mid-1980s and a strong decline from 1980 to 2000, with a subsequent stable trend. The pattern in the coastal region deviated especially in the past 10 years, with a further decline along the Dutch Wadden coast and an increase along the mainland coast. Most dramatic declines throughout the Wadden Sea occurred in speciesbelonging to the marine juvenile guild, notably plaice, sole and dab. A declining trend in marine juveniles is on-going in the western part, while it recently stabilised or even increased in the central and eastern part and in the coastal regions. Resident species showed more variable trends in the Wadden Sea with less pronounced directions: both increases and decreases occurred. In the coastal regions, several resident species have increased considerably in the last 15 years, a pattern not observed in the Wadden Sea. Also the size structure of the fish community changed in all regions,with generally the strongest declines in the largest size classes. The combined use of the two surveys showed that for some species the DFS was not timed in the period of peak occurrence. Althoughthe phenology of several species has changed, the DFS survey period still encompasses the peak period of most species