Growth, age estimation and corroboration of northeast Atlantic chub mackerel (Scomber colias) in northern Iberian waters: a first attempt.

Updated information on growth of Atlantic chub mackerel in several areas of its distribution is required for the first stock assessment. Its growth pattern in Northern Iberian waters (2011-2017) is here analyzed with different approaches: those based on otoliths analyses (direct age estimation-DAE, back-calculation-BC and otolith marginal analyses) and those based on length frequency analyses (Bhattacharya, SLCA and PROJMAT methods). Two main different growth patterns are obtained, a "slow" one based on DAE, BC and LFDA from surveys; and a "fast" one based on Bhattacharya and LFDA from commercial landings. The divergence between both patterns begins to be evident at age 3 and older. Otolith marginal analyses that show an annual periodicity in the formation of the hyaline and opaque edge, the unimodal distribution of the annuli radius and the similarity of the back-calculated mean lengths to those obtained by DAE, support the age estimation criteria used in our analysis. The VBGF growth parameters (L∞=45.34, k=0.28, t0=1.18) obtained by otolith age estimation are available for the upcoming stock assessment process

Advances in the study on sexual maturity of Atlantic chub mackerel (Scomber colias) in Cantabrian Sea.

Atlantic chub mackerel (Scomber colias) is a middle size pelagic species distributed on both sides of the Atlantic Ocean. Landings of this species have increased recently in the Iberian Peninsula, likely associated to the increase of its abundance and expansion northwards, probably related to an increment of the sea temperature. The aim of this study is to improve the knowledge of the reproductive biology of the Atlantic chub mackerel and to present updated information on spawning period and maturity ogives that can be used for analytical stock assessment in ICES and its management

Preliminary observation on sexual maturity of chub mackerel (Scomber colias) in the Northern Iberian Atlantic waters (ICES Divisions 27.8.c and 27.9.a.N)

A study of the reproductive biology of the Atlantic chub mackerel (Scomber colias) has been performed in Northern Iberian Atlantic waters (ICES Divisions 27.8.c and 27.9.a.N) based on samples of 14538 specimens (11-50 cm total length) from commercial landings and scientific surveys from 2011-2019. The spawning period was defined based on the monthly prevalence of active females (maturity stages 3, 4 and 5 according to Walsh maturity scale) and temporal variability of females gonado- and hepatosomatic indices (GSI/HSI). Length and age maturity ogives were also estimated for males and females pooling all sampled years together. The spawning period occurred from March to July, with a peak in June. In the 27.8.c area, the GSI, HSI and prevalence of active females increased from March to June and then GSI and prevalence decreased abruptly. In the 27.9.a.N, the peak of spawning was observed earlier (April-May) and with lower intensity than in 27.8.c, but sampling in 27.9.a area was limited to the northern zone (Spanish waters) and are not conclusive. L50 and A50 values estimated with annual data were 22.9 cm and 1.6 years old respectively for both sexes combined, similar to the values estimated with data only from the spawning period: 22.7 cm and 1.5 years old respectively for both sexes combined. Our results were compared with those from previous studies in the NE Atlantic

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

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 water