Research activities carried out by IEO in the Canary Islands during intersession

Regarding the research activities carried out by Oceanographic Centre of the Canary Islands (IEO-CSIC) during intersession, several studies on different topics were presented. Firstly, reproductive traits for the four main species have been analysed including all the data obtained since the monitoring system was launched in 2013. Although with some variations, the spawning season matched with winter and beginning spring for S. colias, T. picturatus and S. pilchardus. However, spawning individuals of S. aurita are present all year round. Sizes at first maturity (SFM) were also estimated, with slightly smaller sizes obtained for S. colias and T. picturatus (around 19 cm of total length) compared with the reference values (20 cm and 23 cm, respectively) (Jurado-Ruzafa and Santamaría, 2013; Lorenzo and Pajuelo, 1996). It seems that SFM remains stable for S. pilchardus (15 cm) (Méndez-Villamil et al., 1997). In the case of S. aurita, size at first maturity has been estimated for the first time in the Canary Islands, and has been recently published (Jurado-Ruzafa et al., 2022). Secondly, a first attempt to describe total catches of the Canary artisanal purse-seine fleet based on scientific observation shows that discards are more relevant than what was supposed, reaching the 25 percent of the total catches. The situation is even more concerning if only S. colias is considered, with discards around 40 percent of the total catches, mainly impacting on juveniles’ fraction, which is usually used as bait by commercial vessels but that are not officially reported. Finally, very preliminary results were shown to the working group about the potential adaptive plasticity in Scomber colias from the Canary Islands, based on otolith shape analyses. These results were obtained from analysing 748 otoliths extracted from August 2016 to December 2017. A DIvisive ANAlysis (DIANA) Clustering method using the fourth wavelet obtained from otolith contours resulted in the detection of five different morphotypes (or otolith phenotypes), with two of them representing 85 percent of the samples analysed, and whose individuals were slightly larger than for the other morphotypes. Further questions should be explored, addressing possible intraspecific variation in the growth rate among phenotypes; phenotypes proportions change in relation to seasonal variations; existence of different ecological strategies related to each phenotype and the presence of these otolith phenotypes in other geographical areas, as it has been described for T. picturatus (Tuset et al., 2019; Vasconcelos et al., 2021).ReferencesJurado-Ruzafa, A. and M.T.G. Santamaría. 2013. Reproductive biology of the blue jack mackerel, Trachurus picturatus (Bowdich, 1825), off the Canary Islands. Journal of Applied Ichthyology, 29(3): 526–531.Jurado-Ruzafa, A., B. Sotillo de Olano, Z. Santana Arocha, B. G. Mañé, C. Estil-las, E. Hernández, S. Jiménez, G. González-Lorenzo and C. Perales-Raya. 2022. Reproductive traits of the round sardinella in the Canary Islands (Spain, NW Africa). Journal of the Marine Biological Association of the UK, (early view) 1-7.Lorenzo, J. M. and J.G. Pajuelo. 1996. Growth and reproductive biology of chub mackerel Scomber japonicus off the Canary Islands. South African Journal of Marine Science, 17(1): 275-280.Méndez-Villamil, M., J.M. Lorenzo, J.M. González and R. Soto. 1997. Periodo reproductor y madurez sexual de la sardina Sardina pilchardus (Walbaum, 1792) en aguas de Gran Canaria (Islas Canarias). Boletín del Instituto Español de Oceanografía, 13(1-2): 47-55.Tuset, V.M., A. Jurado-Ruzafa, J.L. Otero-Ferrer and M.T.G. Santamaría. 2019. Otolith phenotypic variability of the blue jack mackerel, Trachurus picturatus, from the Canary Islands (NE Atlantic): Implications in its population dynamic. Fisheries Research, 218: 48-58.Vasconcelos, J., A. Jurado-Ruzafa, J.L. Otero-Ferrer, A. Lombarte, R. Riera and V.M. Tuset. 2021. Thinking of Fish Population Discrimination: Population Average Phenotype vs. Population Phenotypes. Frontiers in Marine Science, 8(1489).