Local and Regional Drivers of Fish Growth Rates
How and why fish grow are heavily dependent on environmental conditions like climatic processes and water quality. Understanding how exactly these stressors impact fisheries as a whole is essential to informed, sustainable management. Environmental variations like wind dynamics and temperatures (air and water) can lead to increases—or decreases—in growth rates.
Drivers of Growth in Aquatic Ecosystems
Optimal water quality conditions are a key component to ensuring fish health and improved growth rates. Dissolved oxygen concentration, water temperature, and other environmental conditions impact aquatic life.
For example, high temperatures can lead to death and disease for temperature-sensitive species in fresh and saltwater environments. Additionally, temperature spikes can impact migration behaviors and delay the development of fry.
Water quality is closely related to climate conditions at both the regional and local scales. In ocean environments, the El Niño Southern Oscillation warms water, leading to changes in fish growth rates that vary depending on the species involved.
Due to this complexity, understanding preferred habitat conditions for fisheries and the influence of climate dynamics is a key component of fisheries management. In order to do this effectively, studying the growth rates of fish under various environmental conditions is necessary.
Evaluating Growth Rates
One of the most common forms of age assessment for fish is otolith surveys. Like trees, otoliths develop rings over time as the fish ages, as well as a unique chemical footprint that can help identify the conditions the fish faced while growing. Measuring fish length over time can also help measure growth rates and estimate fish age, though this is less precise than otolith assessments.
In order to understand the relation between environmental conditions and growth, age assessments should be done in tandem with water and climate monitoring.
Case Study: Bluespine Unicornfish Growth Rates in the Northern Mariana Islands
A 2025 study explored within-region effects of environmental and climatic variability using inter-annual otolith growth rates in Bluespine Unicornfish (Naso unicornis), a tropical coral reef fish. This species was selected because previous research revealed “synchrony in growth responses among different populations of the same species in the same ocean basin.”
According to the study, “This synchrony indicates a detectable sensitivity to changes in climatic or environmental conditions.”
The study hypothesized that there would be synchrony in growth rates across a small latitudinal range driven by regional or broad-scale climate indices in fish species. In addition to testing the influence of local (temperature and productivity) and regional-scale processes, the two were compared to identify the scale of influence.
Results found that local environmental processes were more important than regional climatic processes for fish growth in the northern portion of the Northern Mariana Islands. However, in the central islands neither local nor regional processes had a clear effect on growth rates.
In the north, fish saw positive responses to increased temperatures, while there was a negative response in the central islands.
Conclusion
Such results suggest that fisheries managers should consider the complex impacts of climatic processes and environmental conditions in the region they are managing. All of this means that informed management requires monitoring both the environment (water quality, climate/weather, and hydrology) and the fish.
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