MEPS 528:267-275 (2015)  -  DOI: https://doi.org/10.3354/meps11285

ABSTRACT: Niche segregation models underpin our understanding of speciation, population dynamics, and the evolution of foraging strategies. Many studies have evaluated changes in niche segregation dynamics over seasonal and decadal scales, but the influence of short-term stochastic processes like weather are poorly understood. This represents a problem for predicting ecosystem-level responses to the changes in weather patterns that are anticipated to occur over the coming decades. By simultaneously monitoring spatial and temporal segregation in a large estuarine piscivore and smaller benthic carnivore (mulloway Argyrosomus japonicus and sand whiting Sillago ciliata, respectively) before and after rainfall, we tested for disturbance-driven changes in species segregation. During non-rain conditions, both species were diurnally active but spatially segregated in the vertical plane (i.e. water depth). After rainfall, mulloway encroached on the whiting’s vertical habitat and reversed their activity rhythm, while whiting did the opposite, strengthening their diel activity rhythm. Long-term fishery catch data were broadly consistent with this pattern, with rain-associated increases in mulloway catchability contrasting a decrease in catchability of whiting. Our example suggests short-term stochastic disturbances can drive drastic changes in fish dynamics, and highlights the significance of future changes to rainfall regimes in structuring ecosystem processes.

KEY WORDS: Accelerometer · Acoustic telemetry · Anti-predator behaviour · Biologging · Circadian rhythm · Context-dependent · CPUE · Interaction · Plasticity · Risk-allocation hypothesis