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The present working document summarises the main results obtained during the ECOCADIZ‐RECLUTAS 2017‐10 Spanish (pelagic ecosystem‐) acoustic survey. The survey’s main objective is the acoustic assessment of anchovy and sardine juveniles (age 0 fish) in the recruitment areas of the Gulf of Cadiz. The survey was planned to be conducted by IEO between 12nd and 31st October 2017 in the Portuguese and Spanish shelf waters (20‐200 m isobaths) off the Gulf of Cadiz onboard the R/V Ramón Margalef. However, a serious breakdown of the vessel’s propulsion system detected in the afternoon of the 22th October led to the early termination of the survey in that day. Only the seven (7) easternmost acoustic transects were sampled, which were accompanied by the conduction of eight (8) fishing hauls. The resulting estimates are therefore referred to this surveyed area, which corresponded to the eastern sector of the Spanish shelf waters, comprising the shelf between Doñana and Cape Trafalgar, and they are not comparable to the previous available estimates. Anchovy abundance and biomass in that surveyed area were 1 492 million fish and 7 641 t. The abundance and biomass of age 0 anchovies in the surveyed area were estimated at 1 433 million fish and 7 290 t. This juvenile fraction accounted for 96% and 95% of the total estimated population abundance and biomass, respectively. The estimates for Gulf of Cadiz sardine in the surveyed area were of 591 million fish and 12 103 t. Estimates of age‐0 sardine were of 483 million fish and 8 778 t, 82% and 72% of the total population, respectively. These estimates cannot be compared with the remaining data points in the series because the abovementioned problems with acoustic sampling coverage.

In the Mediterranean Sea, the European anchovy (Engraulis encrasicolus) displays a key role in ecological and economical terms. Ensuring stock sustainability requires the provision of crucial information, such as species spatial distribution or unbiased abundance and precision estimates, so that management strategies can be defined (e.g. fishing quotas, temporal closure areas or marine protected areas MPA). Furthermore, the estimation of the precision of global abundance at different sampling intensities can be used for survey design optimisation. Geostatistics provide a priori unbiased estimations of the spatial structure, global abundance and precision for autocorrelated data. However, their application to non-Gaussian data introduces difficulties in the analysis in conjunction with low robustness or unbiasedness. The present study applied intrinsic geostatistics in two dimensions in order to (i) analyse the spatial distribution of anchovy in Spanish Western Mediterranean waters during the species’ recruitment season, (ii) produce distribution maps, (iii) estimate global abundance and its precision, (iv) analyse the effect of changing the sampling intensity on the precision of global abundance estimates and, (v) evaluate the effects of several methodological options on the robustness of all the analysed parameters. The results suggested that while the spatial structure was usually non-robust to the tested methodological options when working with the original dataset, it became more robust for the transformed datasets (especially for the log-backtransformed dataset). The global abundance was always highly robust and the global precisión was highly or moderately robust to most of the methodological options, except for data transformation.

During the 2015 routine acoustic survey for stock assessment carried out in the Spanish Mediterranean continental shelf, krill swarms were localized in two different places using an EK60 scientific echosounder, operating at multiple frequencies. Biological identification was performed by mean of a plankton net (bongo 90) equipped with two different mesh sizes (500 to 2000 microns). Although krill frequency response was similar in both localizations, samples analysis revealed the presence of two different species: Nyctiphanes couchii (Bell, 1853) and Nematoscelis megalops (Sars, 1883).

In this study we present the abundance and biomass of European anchovy (Engraulis encrasicolus) estimated by acoustic methods in the Northwestern Mediterranean Sea (GSA06). during two different seasons, winter, the anchovy recruitment season and summer, when the majority of the anchovy stock belongs to the spawner fraction of one year-old. Four standardized acoustic surveys carried out covering the study area during two consecutive years (every six months), two of them during the peak of anchovy recruitment and the other two during the peak of anchovy spawn, allow to observe changes in the anchovy stock abundance and biomass in this area. Acoustic data from summer and winter echo-surveys were analyzed in an effort to better understand the life cycle of anchovy in relation to the survival during its first year of life.

The present working document summarises a part of the main results obtained from the Spanish (pelagic ecosystem‐) acoustic survey conducted by IEO between 28th July and 10th August 2015 in the Portuguese and Spanish shelf waters (20‐200 m isobaths) off the Gulf of Cadiz onboard the R/V Miguel Oliver. The 21 foreseen acoustic transects were sampled. A total of 19 valid fishing hauls were carried out for echo‐trace ground‐truthing purposes. CUFES sampling (117 stations) was carried during the survey in order to describe the extension of the anchovy spawning area. A census of top predator species was also carried out along the sampled acoustic transects. This working document only provides abundance and biomass estimates for anchovy and sardine which are presented without age structure. The distribution of all the mid‐sized and small pelagic fish species susceptible of being acoustically assessed is also shown from the mapping of their back‐scattering energies. Sardine was the most frequent species in the fishing hauls, followed by horse mackerel, chub mackerel, anchovy and mackerel. However, the most abundant species in these hauls was anchovy, followed at quite a distance by blue jack mackerel, sardine, horse mackerel and chub mackerel. As usual, the bulk of the anchovy population was concentrated in the central part of the surveyed area, with the smallest anchovies mainly occurring in the surroundings of the Guadiana and Guadalquivir river mouths and Bay of Cadiz, and larger/older anchovies occurring in the westernmost waters. The total biomass estimated for anchovy, 21.3 kt (2 506 million fish), was slightly below the historical average, but it still in the range of population levels featuring to a recovered population. The comparison of these estimates with their spring counterparts from the PELAGO survey evidences almost identical values for the Portuguese waters, whereas the ECOCADIZ survey estimated in summer at about 1000 million and 11800 t less of anchovy in

ECOCÁDIZ-RECLUTAS 1112 survey is the second survey by the IEO of acoustically assessing the abundance of anchovy and sardine juveniles in their main recruitment areas off the Gulf of Cádiz. The survey was conducted between 10th and 27th November 2012 onboard the Spanish R/V Emma Bardán and its sampled area was restricted only to the Spanish waters of the Gulf of Cádiz between 10 and 200 m depth.

The PELACUS 0313 survey was undertook this year on board R/V Miguel Oliver, an oceanographic research stern trawler vessel similar to R/V Thalassa. The survey was characterised by a very bad weather conditions during the first two weeks which did not allow working properly. Moreover, the weather conditions during the rest of survey were almost similar. As a consequence, most of the coastal pelagic fish community remained very close to the coast, thus not accessible to the pelagic gear samplers. (33% of the total acoustic energy – NASC- was unable to be properly allocated into fish species). Outside the coastal area (>90 m depth) main abundance fish species was mackerel with 380.000 tonnes, corresponding to 1.725 million fish. On the contrary, sardine distribution was scarce, and occurred in small schools (probably as a consequence of the bad weather condition), with only 3.343 tonnes corresponding to 54.0 million fish. Age group 2 was the most abundant, which confirms the high abundance found last year at age group 1 of the 2011 cohort.

Identification of the potential habitat of European anchovy (Engraulis encrasicolus) at different life stages in relation to environmental conditions is an interesting subject from both ecological and management points of view. For this purpose, acoustic data from different seasons and different parts of the Mediterranean Sea along with satellite environmental and bathymetry data were modelled using generalized additive models. Similarly, egg distribution data from summer ichthyoplankton surveys were used to model potential spawning habitat. Selected models were used to produce maps presenting the probability of anchovy presence (adults, juveniles and eggs) in the entire Mediterranean basin, as a measure of habitat adequacy. Bottom depth and sea surface chlorophyll concentration were the variables found important in all models. Potential anchovy habitats were located over the continental shelf for all life stages examined. An expansion of the potential habitat from the peak spawning (early summer) to the late spawning season (early autumn) was observed. However, the most suitable areas for the presence of anchovy spawners seem to maintain the same size between seasons. Potential juvenile habitats were associated with highly productive inshore waters, being less extended and closer to coast during winter than late autumn. Potential spawning habitat in June and July based on ichthyoplankton surveys overlapped but were wider in extent compared with adult potential habitat from acoustics in the same season. Similarities and dissimilarities between the anchovy habitats as well as comparisons with sardine habitats in the oligotrophic Mediterranean Sea and other ecosystems with higher productivity are discussed

Resumen Las condiciones hidrográficas observadas durante la campaña Pelacus0411, realizada entre el 26 de marzo y 20 de Abril de 2011 en aguas de la plataforma continental Nord Ibérica, son las propias de comienzos de primavera, caracterizadas por una incipiente estratificación térmica y la presencia de agua de baja salinidad cerca de la costa, principalmente en las proximidades de las desembocaduras de los principales ríos. La fluorescencia (variable indicadora de la abundancia de fitoplancton –producción primaria) presentó los valores más elevados en superficie sobre el talud continental en la zona de Galicia, influenciada por la masa de agua de alta salinidad asociada a la contracorriente de talud (‘Corriente Ibérica hacia el Polo’). A partir del Cantábrico Central, frente a la costa Asturiana, y hacia la zona interna del Golfo de Vizcaya, se observó un máximo sub-superficial de clorofila entorno a los 20 o 30 m. La biomasa total de sardina en la zona de estudio estimada mediante métodos acústicos fue de 11.768 toneladas (t) (151106 individuos). Esta especie se localizó preferentemente en la plataforma de Asturias (sub-área ICES VIIIcE-w), en contraste con su práctica ausencia en aguas de la plataforma de Gallicia (sub-áreas ICES IXa-N y VIIIcW). Los individuos más jóvenes, de edades entre 1 y 2 años, predominaron en Galicia (sub-área ICES IXaN), mientras que los de mayor edad, 3 años, fueron más abundantes en la plataforma de Asturias y del País Vasco (sub-áreas ICES VIIIcE-w y VIIIcE-e respectivamente). Las estimas de abundancia de sardina en la campaña de 2011 son las más bajas de la serie desde 2001 y suponen un motivo de preocupación en relación al estado del stock. Si no tiene lugar un reclutamiento importante, el último de los cuales tuvo lugar en 2004, la previsión apunta hacia un descenso continuado de la biomasa de sardina en la plataforma Nord Ibérica. La biomasa estimada de anchoa fue de 2071 t, correspondiente a 142000 individuos. Éstos se localizaro

ECOCÁDIZ‐RECLUTAS 1009 survey is the first attempt by the IEO of acoustically assessing the abundance of anchovy and sardine juveniles in their main recruitment areas off the Gulf of Cádiz. The survey was conducted between 26th October and 5th November 2009 onboard the Spanish R/V Emma Bardán. In order to achieve a better sampling coverage of juveniles, the acoustic sampling grid was more intensive (4 nm‐spaced transects) than the adopted one in conventional surveys. Unfortunately, the initially planned survey area limits and the ship‐time available (17 transects over waters shallower than 50 m depth between Tavira and Chipiona, and 11 days) showed both insufficient due to a deeper bathymetric distribution of anchovy juveniles than expected and the sucession of a series of unforeseen problems which led to drastically reduce the actual sampled area to only 6 transects from the easternmost zone. Acoustic estimates from this last area are available for anchovy (2 771 t, 524 million fish), sardine (25 167 t, 500 millions), chub mackerel (17 627 t, 152 millions) and Mediterranean horse‐mackerel (17 005 t, 159 millions). The abundance and biomass of age 0 anchovies in the surveyed area were estimated at 2 588 t and 510 million fish, respectively, i.e. 93% and 97% of the total estimated anchovy biomass and abundance. Sardine estimates were not age‐structured but the abundance and biomass of juveniles smaller than 17 cm were estimated at 3 382 t and 130 millions, 13% and 26% of the total estimated species’ biomass and abundance. An approximate evaluation of the impact of the incomplete coverage of the anchovy juvenile distribution during the survey was carried out by comparison of our data with the resulting yields and location of positive fishing stations from a groundfish survey carried out just after the present survey.

The present working document summarises the main results from the Spanish acoustic (pelagic ecosystem‐) survey conducted by IEO between 25th July and 1st August 2010 in the Portuguese (but with an incomplete coverage) and Spanish shelf waters (20‐200 m isobaths) off the Gulf of Cadiz onboard the R/V “Cornide de aavedra”. The survey season was coincident with the anchovy (Engraulis encrasicolus) peak spawning to achieve an acoustic estimate of its SSB in the study area as well. This year the surveyed area was reduced to an area limited by the waters placed between Cape Trafalgar and Cape Santa Maria. Abundance and biomass estimates are given for all the mid‐sized and small pelagic fish species susceptible of being acoustically assessed according to their occurrence and abundance levels in the study area. The distribution of these species is also shown from the mapping of their back‐scattering energies. In the sampled area, anchovy was distributed all over the shelf of the study area with the densest concentrations being recorded over the middle‐outer shelf in the westernmost area. The total biomass estimated for anchovy was 12.3 thousand tonnes (954 million fish) and sustained, as an average, by maller anchovies than those observed the last year. Sardine (Sardina pilchardus) occurred all over the inner‐middle shelf, in shallower waters than anchovy, and also showing the highest densities in the westernmost coastal waters of the sampled area. The species was the most important one in terms of both biomass (67 thousand tonnes) and abundance (2 thousand million fish) and showed vidences of a relatively good recruitment. Chub mackerel (Scomber colias) was almost absent in the shallower waters and in the whole central part of the sampled area. This species was amongst the species which less contributed to the total biomass and abundance of the pelagic species assemblage, with almost 3 thousand tonnes and 43 million fish only. Acoustic estimates for jack and horse‐mackerel

The present working document summarises the main results from one IEO’s coastal (50 – 7 m depth) survey (ECOCÁDIZ-COSTA 0709) complementary and almost synchronous (2nd-9thJuly 2009, R/VFrancisco de Paula Navarro) to the Spanish “standard” acoustic (pelagic ecosystem-) survey (ECOCÁDIZ 0609; 27thJune-6th July 2009; Portuguese and Spanish shelf waters off the Gulf of Cadiz: 20-200 m isobaths; R/V Cornide de Saavedra). Unfortunately, the impossibility of fishing in waters deeper than 25 m depth with an appropiate gear resulted in a relatively high percentage (51.5%) of Not Identified NASCs in relation to the total sampled back-scattering energy attributed to fish, although these energies were mainly concentrated in the deepest ESDUs previously sampled and assessed by the conventional survey. Acoustic energies in the coastal survey were not very high in the shallower waters, which is reflected in the contribution to the total energy by the most coastal species.

Acoustic surveys are used worldwide for the assessment of pelagic fish stocks. In the Spanish Mediterranean area acoustic surveys are performed annually in late autumn and cover the entire continental shelf between 30 and 200 m depth. This survey was initiated to obtain estimates of anchovy recruitment (Engraulis encrasicolus), but additionally provide a general overview of the whole pelagic fish community in the study area during the time of the year it is performed. Our study area has a diverse assemblage of small and medium-sized pelagic fish (up to nine species) and thus we rely on the proportion of species obtained in middle-water pelagic fishing trawls to attribute the amount of echo corresponding to every single species and estimate their abundance. Although uncertainties may arise from many different sources (e.g. transducer motion, target strength, migration) we focus our study on the estimation of overall sampling uncertainty, one of the main contributors to random error. We apply geostatistical techniques to deal with spatial correlation and discuss benefits and pitfalls in their application. Although transitive geostatistics have seldom been used, most probably due to their inability to produce spatial maps of abundance and variance estimations, they constitute a powerful tool to routinely estimate sampling variance and its variation in time in a multi-specific context. They may also help to assess the effects of varying sampling intensity and could potentially be useful to detect possible processing errors, for example, in echogram scrutinizing. These techniques may therefore potentially help improve both the precision and the accuracy of acoustic data

Results of the Spanish spring acoustic survey PELACUS0407, carried out from the 27th March to the 23rd April 2007, indicated a stock biomass of 96,390 tons of sardine (1482 million fish) in northwest and northern Spanish waters. The main bulk of the resource was found in Galician waters (ICES sub-areas IXa-N, VIIIc-W) and consisted of age 3 fish (fish born in 2004). Age 3 fish also predominated in ICES sub-area VIIIcE-w but not in the eastern part of the surveyed area, where older fish were more abundant (ICES sub-area VIIIcE-e). The abundance and biomass obtained from PELACUS0407 are similar to the values estimated from the last 2 surveys (with a slight increase in the biomass but not in the number of fish). These figures seem to indicate that the last strong sardine recruitment (2004) probably halted the downward trend in stock size apparent since 2001 in Spanish waters. However, there is also evidence that the 2004 recruitment in the surveyed area was not as strong as the previous recruitment peak in 2000, since both biomass and abundance values are at their lowest since 2001. In addition, the area occupied by the sardine stock in Spanish waters appears also to have diminished continuously since 2001, which could make the resource even more vulnerable to fishing and/or predation. PELACUS0407 also obtained data on the distribution of sardine eggs and their number in the surveyed area: eggs were found in larger quantities and over a wider area than previously recorded by CUFES in the PELACUS series (2000-2007)