Juvenile gadoids use multiple habitats and favour patch boundaries within seascapes

Fish nursery areas need to be determined at the appropriate spatial scale with an understanding of how juvenile fish are distributed across combinations and arrangements of habitat types within seascapes. A seascape approach allows the influence of seabed type, patch sizes, boundaries and habitat combinations on species distributions to be understood. This study investigated the influence of seascape ecology and species co-occurrence patterns on the distribution of three juvenile gadoids, Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus), and whiting (Merlangius merlangus), while also accounting for the interactions between species as latent variables. We used 757 stereo baited remote underwater video (SBRUV) deployments between 2021 and 2023 across two sea lochs and adjacent bays on the north and west coasts of Scotland to gather relative abundance data. A joint species distribution model was used to determine the seascape drivers of 10 fish species as well as using an unobserved random variable to understand how species co-occurrences influence individual species distributions. Atlantic cod, haddock and whiting distributions were driven by distinct ecological factors yet had limited areas of overlap. Atlantic cod and haddock were most abundant in areas with a diverse mix of habitats. However, whiting were most abundant in areas with lower habitat diversity. Consistently higher relative abundance of all species near habitat patch boundaries indicates that edge effects and access to multiple habitat types are critical determinants of nursery habitat. Despite their distinct distributions explained by environmental variables, species-to-species co-occurrence patterns were very similar across the three species. This may be indicative of similar ecological roles and biological interactions or similar response to an unrecorded variable. The inclusion of how species respond to seascape structures is valuable because it gives a greater level of understanding of what juvenile fish need in nursery areas at the relevant spatial scale.