The U.S. east coast has already seen shifts in the distribution of major fisheries, influencing catch limits and complications with permitting across states. As black sea bass, summer flounder and scup populations have shifted away from their habitat in the southeast, they have moved to northern regions where fisheries may have lower catch limits and lack the same processing infrastructure needed to support fisheries, branching into areas where the fishing industry is not equipped to target them.
These major changes in species distribution lead fisheries managers to negotiate and agree on joint jurisdiction over certain species – and these changes are likely to continue, emphasizing the need for advanced models that take a holistic approach and effectively predict these shifts among species.
A new study led by scientists at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and the Cooperative Institute for Marine and Atmospheric Studies (CIMAS) integrating reef fish monitoring surveys with advanced climate modeling indicates potential poleward shifts in suitable thermal bottom habitat for six commercialized species of reef fish along the U.S. East Coast. This demonstrates how global climate models and environmental monitoring programs can be combined to explore potential changes in suitable thermal habitat of commercialized fish species.
“Climate models play a valuable role in predicting how environmental stressors will impact key natural resources over decades,” explains Brittany Troast, a CIMAS Senior Research Associate with AOML’s Ecosystem Assessment team and lead author on the study. “Here, we wanted to see how they perform on a more local scale, estimating changes that will influence major fisheries across the U.S. East Coast until the end of the century.”
In a study area spanning from Cape Canaveral, Florida to the Gulf of Maine, scientists wanted to demonstrate how well an ensemble of six models that are the standard for predicting global environmental changes – the Coupled Model Intercomparison Project Phase 6 (CMIP6) – can be used to capture shifts in the suitable thermal habitat on this smaller scale until the end of the 21st Century.
While many studies focus on sea surface temperature, this study used bottom temperature to examine fluctuations within marine habitats that directly impact selected fish species of interest and other natural resources. However, at the current scale, CMIP6 models estimate bottom temperature better at some locations than others. Small eddies and fluctuating currents that impact bottom temperature can be smaller than the resolution of the model. This leads to bias in the models, creating differences in bottom temperatures compared to existing data.
Practically-speaking, the CMIP6 models were developed to predict changes to entire Earth systems under various future scenarios – known as Shared Socioeconomic Pathways (SSPs). However, global models use lower resolutions while regional models are able to use a higher resolution, capturing complex environmental conditions with greater detail. Downscaling any model to a specific region requires calibration and using data collected across decades before the model can produce more precise, accurate predictions of future changes.
Troast along with researchers at NOAA Fisheries’ Southeast Fisheries Science Center and Office of Science and Technology, and Mississippi State University’s Northern Gulf Institute used long-term, historical data from the World Ocean Atlas to adjust the models’ bias. Integrating data spanning from 1981-2010 enabled the team to explore how historical changes in bottom water across marine habitats compared to projected changes under multiple climate scenarios.
Leveraging the Southeast Reef Fish Survey — a combination of trap-video surveys performed at designated stations along the continental shelf and the shelf edge across years – scientists were able to roughly determine thermal ranges for six target species of reef fish between Cape Hatteras, North Carolina and St. Lucie, Florida. After analyzing differences between the CMIP6 models’ estimates and survey temperatures, the climate model temperatures were adjusted to better agree with real-world observations and the temperature ranges at which the selected species were observed. That enabled the team to then explore how historical changes across marine habitats compared to projected changes under multiple climate scenarios.
Even under conservative scenarios, the model demonstrated significant increases in bottom water temperature potentially leading to major shifts in the suitable thermal habitat of six species currently regulated under the snapper-grouper fishery management plan between 2015 and 2100.
The CMIP6 models indicated the greatest increase in mean bottom temperature occurred outside of Chesapeake Bay while the smallest changes were seen around North Carolina. The study also found the area of suitable thermal habitat for all six species could decrease compared to the historical area.
It’s essential to note the study solely investigates changes in bottom water temperature but the movement of species to new regions will be influenced by a variety of other environmental variables including availability of suitable habitat, turbidity and prey abundance. However, the shift of one target species could create cascading effects on the distribution of other species in the ecosystem.
Modeling these changes over decades is complex, as it requires accounting not only for how environmental stressors affect individual species, but also how they holistically impact the distribution of species across an entire ecosystem.
According to the NOAA Fisheries’ Status of Stocks 2024 report, U.S. South Atlantic stocks of red snapper, red porgy, gag grouper and red grouper are already experiencing overfishing. With future shifts in habitat suitability, these valuable fisheries may experience added pressures in the near future with implications for fisheries management to strategize for these changing conditions.
As part of the greater Changing Ecosystems and Fisheries Initiative (CEFI), this study emphasizes the utility of developing regional climate models to assess changes in species distribution over years. Advancing our understanding of how exacerbated environmental stressors and changing conditions impact essential habitats across entire coastlines enables scientists to support the management of fisheries and resources among greater calls to ensure the health and sustainability of viable markets.