2.3 Fish biomass data
To determine the impact of food availability on survival and breeding probabilities in African penguins, we used estimates of sardine and anchovy spawner (fish aged ≥1 year) biomass from hydro-acoustic surveys conducted by the Department of Forestry, Fisheries, and the Environment (DFFE) in November each year between 2013 and 2019 (Coetzee & Merkle 2019, Coetzee et al . 2020). For detailed survey methods see Coetzee et al. (2008). We considered the portion of the biomass estimated to occur West of Cape Agulhas (WoCA), as prey availability in this region has previously been linked to measures of penguin survival and reproduction (e.g., Sherley et al . 2013, Robinson et al . 2015). Because the spawner biomass survey occurs during the penguins’ nonbreeding season, we related the biomass WoCA to survival using the biomass from the survey at the start of the nonbreeding period (i.e., for survival from 2013 to 2014, the WoCA estimate for November 2013 was used), and considered the biomass of the two species (sardine and anchovy) combined and for each separately in our modelling framework.