Drivers of the fish community size spectrum and its utility as an indicator of fish productivity: insights from three decades of monitoring data from a small boreal lake

Freshwater fisheries monitoring programs require indicators of fish community and population productivity and abundance. Two potential indicators include the slope and height of the community size spectrum, which are often interpreted as proxies for trophic dynamics and community abundance (or production), respectively. Previous studies have lacked alternative estimates of fish production and abundance to compare with community spectral parameters and have had limited limnological data to understand drivers of variability in spectral parameters among lakes. Using ∼30 years of monitoring data from a boreal lake, we showed that the height of the fish community size spectrum was related to independent mark/recapture-based estimates of abundance for the dominant large-bodied species, white sucker, but not to their biomass or annual production estimates. Further, limnological properties including the duration of ice cover, light, temperature, and the biomass of zooplankton prey were associated with inter-annual variation in spectral slopes and heights, often nonlinearly. Our results indicate that spectral parameters derived from fish communities can reflect long-term environmental change and provide new insights on drivers of fish community size structure.