Baltic Sea Cod Reproductive Volume from Reanalysis

'''DEFINITION'''The cod reproductive volume has been derived from regional reanalysis modelling results for the Baltic Sea BALTICSEA_MULTIYEAR_PHY_003_011 and BALTICSEA_MULTIYEAR_BGC_003_012. The volume has been calculated taking into account the three most important influencing abiotic factors of cod reproductive success: salinity > 11 g/kg, oxygen concentration > 2 ml/l and water temperature over 1.5°C (MacKenzie et al., 1996; Heikinheimo, 2008; Plikshs et al., 2015). The daily volumes are calculated as the volumes of the water with salinity > 11 g/kg, oxygen content > 2 ml/l and water temperature over 1.5°C in the Baltic Sea International Council for the Exploration of the Sea subdivisions of 25-28 (ICES, 2019).'''CONTEXT'''Cod (Gadus morhua) is a characteristic fish species in the Baltic Sea with major economic importance. Spawning stock biomasses of the Baltic cod have gone through a steep decline in the late 1980s (Bryhn et al., 2022). Water salinity and oxygen concentration affect cod stock through the survival of eggs (Westin and Nissling, 1991; Wieland et al., 1994). Major Baltic Inflows provide a suitable environment for cod reproduction by bringing saline oxygenated water to the deep basins of the Baltic Sea (see the OMIs: BALTIC_OMI_WMHE_mbi_bottom_salinity_arkona_bornholm and BALTIC_OMI_WMHE_mbi_sto2tz_gotland). Increased cod reproductive volume has a positive effect on cod reproduction success, which should reflect an increase of stock size indicator 4–5 years after the Major Baltic Inflow (Raudsepp et al., 2019). Eastern Baltic cod reaches maturity around age 2–3, depending on the population density and environmental conditions. There are a number of environmental factors affecting cod populations (Bryhn et al., 2022). Low oxygen and salinity cause stress, which negatively affects cod recruitment, whereas sufficient conditions may bring about male cod maturation even at the age of 1.5 years (Cardinale and Modin, 1999; Karasiova et al., 2008). '''CMEMS KEY FINDINGS'''In general, the cod reproductive volume fluctuates between 200 and 400 km3. There are two separate periods when cod reproductive volume has significantly increased where maximum values reach 1200 km3. These periods, from 2003 to 2005 and from 2015 to 2018, correspond to the post Major Baltic Inflow periods (BALTIC_OMI_WMHE_mbi_bottom_salinity_arkona_bornholm and BALTIC_OMI_WMHE_mbi_sto2tz_gotland). In 2022, the cod reproductive volume was at its base level between 200 and 400 km3. According to the study by Bryhn et al. (2022) an increase of spawning stock biomass in the eastern Baltic Sea has not been observed.'''Figure caption'''The time series of cod reproductive volume in the Baltic Sea from 1993 to 2022. The volume has been calculated from salinity, temperature and oxygen data extracted from Copernicus Marine Service regional reanalysis products BALTICSEA_MULTIYEAR_PHY_003_011 and BALTICSEA_MULTIYEAR_BGC_003_012."'''DOI (product):''' https://doi.org/10.48670/moi-00196