Acoustic assessment and distribution of the main pelagic fish species in ICES Subdivision 9a South during the ECOCADIZ 2020-07 Spanish survey (August 2020)

Abstract

The present working document summarises the main results obtained from the ECOCADIZ 2020-07 Spanish (pelagic ecosystem-) acoustic-trawl survey conducted by IEO between 01st and 14th August 2020 in the Portuguese and Spanish shelf waters (20-200 m isobaths) off the Gulf of Cadiz (GoC) onboard the R/V Miguel Oliver. The 21 foreseen acoustic transects were sampled. A total of 26 valid fishing hauls were carried out for echo-trace ground-truthing purposes. Four additional night trawls were conducted to collect anchovy hydrated females (DEPM-adult ad hoc sampling). Chub mackerel was the most frequent captured species in the fishing hauls, followed by mackerel, anchovy, horse mackerel, bogue, sardine, blue jack mackerel and Mediterranean horse mackerel. Round sardinella, longspine snipefish, Atlantic pomfret and transparent goby showed a very low occurrence, whereas the occurrence of boarfish and pearlside was incidental. Chub mackerel, anchovy and sardine showed the highest yields in these hauls. The estimate of total NASC allocated to the “pelagic fish species assemblage” has shown a slight decrease in relation to the historical records in 2018 and 2019, mainly caused by the regional decrease in Spanish waters. However, both total and regional estimates are still above their respective historical averages. Such estimates are the result of the relatively high acoustic contributions of anchovy, sardine (both mainly in Spanish waters), and chub mackerel (in Portuguese waters). GoC anchovy was widely distributed in the surveyed area, showing the highest densities between Cape Santa Maria and Bay of Cadiz. Anchovy acoustic estimates in summer 2020 were of 5153 million fish and 44 877 tones, with the bulk of the population occurring in the Spanish waters. The population was composed by fishes not older than 2 years, with age-0 fish contributing 75% of the total population. The largest (and oldest) fish were distributed in the westernmost waters and the smallest (and youngest) ones concentrated in the surroundings of the Guadalquivir river mouth and adjacent shallow waters. The current biomass estimate becomes in the second historical maximum within the time-series. GoC sardine distributed almost all over the surveyed area (avoiding the Spanish easternmost waters), but was mainly concentrated between west Cape Santa Maria and the Bay of Cadiz, especially in the Spanish central waters of the Gulf, where numerous dense mid-water schools were recorded in the coastal fringe (20-40 m depth). The estimates of sardine abundance and biomass in summer 2020 were 1923 million fish and 50 721 t, estimates close to the historical average, but lower than the values estimated last year and the most recent maxima reached in 2018. Although up to 5-year olds were recorded in the population, age-0 juveniles accounted for 71% of the total numbers, mainly occurring in relatively shallow waters along the coastal fringe comprised between Tinto-Odiel river mouth and the Bay of Cadiz. Chub mackerel was widely distributed in the surveyed area, mainly in the central and western shelf waters, although the highest densities occurred in the western Algarve. A total of 32 854 t and 448 million fish were estimated for Chub mackerel, estimates similar to the most recent ones and very close to the time-series average. Age-0 and age-1 groups were the dominant age groups and mainly occurring in the Portuguese waters. The oldest fish (3-5 years) occurred almost exclusively in Spanish waters