Developing spatio-temporal models using multiple data types for evaluating population trends and habitat usage

Spatio-temporal models have become key tools for evaluating population trends and habitat usage. We developed a spatio-temporal modelling framework employing a combination of encounter/non-encounter, count, and biomass data collected by different monitoring programs (“combined data”). The three data types are predicted using a computationally efficient approximation to a compound Poisson-gamma process. We fitted spatio-temporal models to combined data for Gulf of Mexico (GOM) red snapper (Lutjanus campechanus) for 2006–2014. These spatio-temporal models provided insights into GOM red snapper spatial distribution patterns, which we corroborated by comparing to past predictions generated using only encounter/non-encounter data. However, relying on biomass and count data in addition to encounter/non-encounter data also allowed us to reconstruct biomass trends for GOM red snapper and to examine patterns of distribution shifts and range expansion/contraction for this population for the first time. Moreover, combining multiple data types improved the precision of reconstructed population trends and some variables quantifying habitat usage. Finally, scenarios and simulation experiments conditioned upon red snapper data showed that the improvement in fitting to combined data is greater when biomass data for the study population are lacking for an entire subregion and, to a lesser extent, for an entire time period (e.g. in early years).

Ontogenetic Habitat Usage of Juvenile Carnivorous Fish Among Seagrass-Coral Mosaic Habitats

Seagrass beds and coral reefs are both considered critical habitats for reef fishes, and in tropical coastal regions, they often grow together to form “mosaic” habitats. Although reef fishes clearly inhabit such structurally complex environments, there is little known about their habitat usage in seagrass-coral mosaic habitats. The goal of this study was to examine potential factors that drive habitat usage pattern by juvenile reef fishes. We quantified (1) prey availability, (2) potential competitors, and 3) predators across a gradient of mosaic habitats (n = 4 habitat types) for four dominant carnivorous fishes (lethrinids and lutjanids) in the main recruitment season at Dongsha Island, South China Sea. We found that the coral-dominated habitats had not only a higher availability of large crustacean prey but also a higher abundance of competitors and predators of juvenile fishes. Food availability was the most important factor underlying the habitat usage pattern by lethrinids and lutjanids through ontogeny. The predation pressure exhibited a strong impact on small juvenile lethrinids but not on larger juveniles and lutjanids. The four juvenile fishes showed distinct habitat usage patterns through ontogeny. Collectively, mosaic habitats in the back reef system may be linked to key ontogenetic shifts in the early life histories of reef fishes between seagrass beds and coral reefs.