Multidisciplinary acoustic survey PELACUS0314: preliminary results on fish abundance estimates and distribution

PELACUS 0314 was characterised by relative stable weather conditions along the surveyed area. Besides, there was an important increase in backscattering energy as compared with the previous year. This resulted in an increase of the biomass estimated for the majority of the fish species, but still sardine is at lowest productivity ever recorded. Good recruitment would be observed in horse mackerel, but for the rest of the fish species, no strong signals for age group 1 have been detected. The reasons for this increase would be related to the weather stability which could have increased the fish availability either for a change in the behaviour (i.e. spatial pattern distribution) or for an increase in the food availability. This is relevant accounting the increase of the occurrence of mackerel subsurface layers observed this year. As PELACUS is a multidisciplinary survey series (we collect environmental and biological ancillary information, stomach contents, including CTD cats, plankton tows or continuous records of plankton, eggs, S, T and flourometry), we will try to explain this change of behaviour. Our main hypothesis is that these species could follow mackerel when is undertaking vertical migration, probably related with the spawning activity, just for feeding eggs and, therefore, changing the expected schooling behaviour by the dispersed one, used during the feeding activity

Preliminary results of the PELACUS0315 survey: estimates of sardine abundance and biomass

A total of 10 384 tons of sardine (191 million fish) was estimated to be present in northwest and northern Spanish waters by the Spanish spring acoustic survey PELACUS0315, carried out from 13th March to 16th April 2015. These values are virtually identical to those recorded in 2014, which shows a stable trend at the lower level of the time series. Sardine distribution was wider than previous years, but the energy allocated to this species was in general very low. Sardine was presented throughout the whole sampled area, but the energy attributed to this species was in general very low. Higher sardine concentrations were detected in Galicia and in the Vasque Country area. Most fish in the entire surveyed area were assigned as belonging to the age 1 (29% of the abundance and 20% of the biomass), age 2 (28% of the abundance and 26% of the biomass) and age 3 (27% of the abundance and 29% of the biomass) years classes. By sub-area, IXa subdivision represents 21.1%, VIIIc West 0.3%, VIIIcEast-West 25.4% and VIIIcEast- East 53.1% of the total abundance. Galicia populations (IXaN and VIIIcW subdivisions) were dominated by age 1 fish whilst the Cantabrian area was mainly composed by older individuals. The distribution of sardine eggs indicates a coastal distribution, agreeing with that observed in previous years. Sardine eggs showed a widespread distribution in the surveyed area, with higher percentage of positive stations than in earlier years

CRUISE REPORT INTERPELACUS 0414

An intercalibration survey aiming at to verify if the PELACUS survey time series could have been affected by the change from R/V Thalassa to R/V Miguel Oliver has been carried out off the Garonne mouth. To do that, the inter-ship variability in some sampler devices (mainly acoustics, CUFES and fishing gears) have been compared with the intra-ship variability in order to give coherence to the time series (i.e. small vessel effect). Accordingly, the null hypothesis the characterisation of the pelagic ecosystem by means of an acoustic-trawl survey would give significant differences on account the vessel effects was tested. Acoustic sampling consisted in two tracks 2.5 espaced and divided in two areas, shallower, with 22 nmi from 40 to 60 m, and deeper , with 10 nmi, from 110 m to the slope. These four track were surveyed three times for each vessel, first in parallel and the others with one of the vessels leading. In the same way 15 parallel fishing station were also perfomed. However, the intercalibration has been made in a small area and only during the light hours of four days and a half of effective work. It is, therefore, complicateto extract conclusions for a large scale survey such as PELACUS time series. In spite no significant diffences in mean backscattering energy was found, it seems that R/V Miguel Oliver, although showed worse noise spectra than R/V Thalassa specially at higher frequencies (200 kHz), consistently accounted higher cumulated backscattering energy values than Thalassa. In addition. Contradictory, the high level of cavitation showed by R/V Miguel Oliver would not result in a higher fish avoidance and the low cumulated backscattering energy values ahchieved by R/V Thalassa could be related with a higher fish avoidance or more presumably with a higher diving response to R/V Thalassa. This kind of response changes the tilt angle and TS becomes lower than expected, which in turn results in an underestimation of the fish abundance. This contradictory response has been already observed in other ship comparisons. Fish reactions cannot be explained only by considering noise spectra but also sound pressure fields and particle acceleration. This later feature would explain the results obtained. In the same way the different fishing gear used for both vessels would not result in significant differences between catch composition and length structure as the intra-ship variability was similar to the inter-ship one. However it should be mention that R/V Miguel Oliver has had higher accessibility to horse mackerel and hake than R/V Thalassa. Finally CUFES performance was similar for both vessels as the intra-ship variability is of the same order as the inter-ship one. Given these results, it seems that the PELACUS time series would not be affected by the change from R/V Thalassa to R/V Miguel Oliver

Spatio-temporal patterns and morphological characterisation of multispecies pelagic fish schools in the North-Western Mediterranean Sea

Echosounder data from four surveys (1992, 1993, 1995 and 1996) is used to investigate the spatio-temporal variability of school behaviour in North-Western Mediterranean waters. The schools are described using morphological, energetic, spatial and temporal descriptors. The variability in the morphological, positional and energetic parameters of the schools is attributable more to the size of the school's individuals (juveniles or adults) than to the relative composition (percentage) of pelagic species in the area. This fact made difficult the identification of species in the studied area. The concentration of schools in certain geographic zones is determined by local oceanographic characteristics that favour the trophic or reproductive activity of these species. The diurnal aggregative behaviour of pelagic species is typical of the zone and no schools were detected at night. The biomass of the pelagic species in the area under consideration has diminished during the 4-year study period and no relationship was found between the number of schools and the biomass evaluated. This is the first time that the schools of small pelagic fishes from the Spanish Mediterranean Sea have been described and the information could be useful to the management and exploitation of the fisheries in the areaPublicado

The effect of environmental changes in the Galician sardine fishery

Annex 6The highest catches of the Iberian sardine stock are taken from the southern part of Galician waters (NW corner of the Iberian Peninsula) and northern Portugal. Landings are mainly composed of younger fish, which reflects the proximity of the main recruitment area to the fishery grounds. Since 1978 there has been an improvement in the knowledge of the biology and stock dynamics of sardine around the Atlantic Iberian waters. In the last decade a consecutive years with poor recruitments result in a depletion of stock below limits previously recorded. The recruitment processes seem to be driven by oceanographic (local) and climatic (global) events, this dependence on both phenomena may explain the fluctuations on the landings in the sardine fisheries in Atlantic Iberian waters. Given the dependence of the fishery in this area on the strength of the recruitment, different relationship between biotic components (spawning stock size, recruitment, landings and recruitment landings) and abiotic: climatic indices (NAO-winter, Gulf Stream and AMO) and local oceanographic coastal events (upwelling and poleward current) were analysed. In the analysis of the abiotic series in the period (1978–2005), there appears to be a shift in the general trend in 1995. In addition at the end of the nineties several consecutive years with poor recruitment result in a depletion of the stock below limits previously recorded as well as changes in the distribution area. Before the shift was observed the recruitment variability could be explain by the environmental variables, but since then the correlation is poor

In situ target strength measurements. Preliminary data of sardine (Sardina pilchardus W.) from the Mediterranean Sea

During the pelagic fishing stations of the acoustics surveys Ecomed 91 and Ecomed 92, carried out in november 1991 and 92, series on sardine TS were collected using a SIMRAD EK-500 38 kHz split-beam echo sounder and echointegrator. Only data with similar features in bottom depth, trawling depth and % of capture were used. The Least-Mean-Square regression of mean TS on the logarithm of the mean fish length of the form TS=m1og(1}+b was finally applied to 11 data series giving m=29.73 and b=-74.08 with r =0.94 or, requiring that m=20, b=-63.34, which is higher than ot~ers to similars species but close to the Love's one. This could be explained for the trawling depth or for the short range of length analyzed

Acoustic abundance estimates of blue whiting off the Spanish Atlantic coast in march-april 1991

This document describes the abundance and distribution whiting from an acoustic survey on the Spanish continental shelf (Divisions VIIIc and IXa2). The total biomass was 171 thousand tonnes, corresponding million fish. of b1ue Atlantic estimated to 4800 Only young fish were recorded in the whole area surveyed, with similar length and age distribution to those found in the fishery (Ages 0-5). Older fish were not detected in this area, at least in the spawning season. A comparison of the distribution and densities of blue whiting observed in this survey with those recorded in 1984 show that the distribution pattern in this area is quite stable

Depth and spatial distribution of blue whiting juveniles in Bay of Biscay

During March-April 1994 and 1996 two cruises have been performed around Bay of Biscay in order to check movements of blue whiting using acoustic methods. These cruises consisted in a double coverage of an area from 47°30' N, 7°15' W to 43°30' N, 6°30' W along the French and Spanish continental shelf-break (200 m to 1000 m). During these surveys juveniles of blue whiting were found in off-shore pelagic schools. This paper describes the spatial distribution and depth of these schools around the studied area