Acoustic assessment and distribution of the main pelagic fish species in ICES Subdivision 9a South during the ECOCADIZ-RECLUTAS 2021-10 Spanish survey (October 2021).

The present working document summarises the main results obtained from the ECOCADIZ-RECLUTAS 2021-10 Spanish (pelagic ecosystem-) acoustic-trawl survey conducted by IEO between 21st October and 07th November 2021 in the Portuguese and Spanish shelf waters (20-200 m isobaths) off the Gulf of Cadiz (GoC) onboard the R/V Ramón Margalef. The survey suffered a ten-day delay in relation to the usual starting dates. The survey’s main objective is the acoustic assessment of anchovy and sardine juveniles (age 0 fish) in the GoC recruitment areas. The 21 foreseen acoustic transects were sampled. A total of 18 valid fishing hauls were carried out for echo-trace ground-truthing purposes. Chub mackerel, anchovy and sardine were the most frequent captured species in the fishing hauls, followed by horse mackerel, bogue, Atlantic mackerel, Mediterranean horse mackerel and blue jack mackerel. Boarfish, longspine snipefish and pearlside showed an incidental occurrence in the hauls performed in the surveyed area. Sardine and chub mackerel showed the highest yields in these hauls, followed by anchovy and Mediterranean horse mackerel. Total and Spanish estimates of total NASC allocated to the “pelagic fish species assemblage” in this survey showed lower values than those recorded last year, whereas the Portuguese estimates showed an increasing trend. GoC anchovy was widely distributed in the surveyed area, although avoided the easternmost waters. Higher densities were recorded between Alfanzina and west of Cape Santa Maria, in the Algarve, and between Isla Cristina and Bay of Cadiz. Anchovy acoustic estimates in autumn 2021, 17 512 t and 1973 million fish, experienced 38% and 51% decreases in abundance and biomass, respectively, in relation to the last year’s autumn estimates and they were lower than their time-series averages. The population was composed by fishes not older than 2 years. As usual, the bulk of the population, including juveniles, was located in Spanish waters. Age-0 anchovies accounted for 83% (1629 million) and 69% (12 063 t) of the total estimated abundance and biomass, respectively. Age-0 estimates experienced a similar decreasing trend than the one showed by the whole population in relation to the historical peak recorded in 2019, but with values close to the time-series average. GoC sardine was widely distributed all over the surveyed area (also avoiding the easternmost waters) and recorded a relatively high acoustic echo-integration in autumn 2021 as a consequence of the occurrence of dense mid-water schools in the Algarve coastal and inner shelf waters (20-78 m). Abundance (2986 million fish) and biomass (151 320 t) estimates were the second historical records within its respective series, although they represented 83% and 38% decreases in relation to the last year’s estimates. GoC sardine population was mainly concentrated in Portuguese waters. Age-5 group was the oldest age group in the population, although the occurrence of fishes older than 4 years was incidental. The population was mainly composed by fishes belonging to the age-0 to age-2 groups. Juvenile sardines (age-0 group) were not the dominant group, accounting for 21% (638 million) and 9% (12 854 t) of the total abundance and biomass, respectively. The bulk of this juvenile fraction was recorded in Spanish coastal waters. Chub mackerel was also widely distributed in the surveyed area, but showing higher densities in three between Cape San Vicente and Mazagón. Chub mackerel estimates were of 13 115 t and 106 million fish, accounting for 64% and 43% strong decreases in relation to the estimates in the previous year and with the above values being lower than their time-series average. The population was mainly concentrated in Portuguese waters and it was composed by fishes not older than 5 years, with the age-1 group being the dominant one. Age-0 fish was the second most important age group in the estimated population ((24%, 26 millionfish, and 13%, 1689 t, of the total abundance and biomass estimates). The bulk of the age-0 and age-1 groups were recorded in the Portuguese waters, whereas older age-groups were more frequent in Spanish waters.