Within-region differences in growth responses of an herbivorous coral reef fish to local and regional climatic processes

Understanding how environmental stressors impact fisheries is imperative for the sustainable management of our marine resources. Synchrony in inter-annual growth patterns among individuals and populations has been identified across large spatial scales, both within and among species. This synchrony indicates a detectable sensitivity to changes in climatic or environmental conditions. We explored within-region effects of environmental and climatic variability using inter-annual otolith growth rates (increments) in a tropical coral reef fish, Naso unicornis. Dendrochronology techniques were applied to remove age-specific growth effects and extract a high-frequency variability signal indicative of short-term environmental change. Using linear mixed-effects models, we identified best predictors of the variation in growth at two adjacent latitude subsets in the Commonwealth of the Northern Mariana Islands. We found different latitude subset growth responses for the years 2000-2013 and 2005-2017, indicating independent fluctuations in growth across latitude however, synchrony was present among individuals within a latitude range. Local environmental processes were more important than regional climatic processes for explaining N. unicornis growth in the north, but in the central islands, neither process had a clear effect. Otolith growth in fish inhabiting the north had a positive response to increased annual average sea surface temperature (SST). In adjacent central islands, otolith growth responded negatively to warmer winter SST. Baseline information for most fisheries on the direct impact of external forcings on fish, especially in tropical coral reef fisheries, remains sparse. We provide information on how climate and environment have impacted past growth with implications for future fisheries productivity monitoring.