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.