Potential impacts of climate variability and change on the recent declines in coastal species along the U.S. Gulf and South Atlantic Bight

Coastal migratory pelagic species, such as king mackerel and greater amberjack, are key
commercial and recreational fishery species in the U.S. Gulf of Mexico (GoM) and South
Atlantic Bight (SAB) regions that support a billion-dollar economy (Karnauskas et al. 2013). The
most recent stock assessments for this suite of species indicated that recruitment of most stocks
began declining in the late 2000s, a signal indicative of either reduced population productivity,
migration out of the management area, or a combination of both factors (SEDAR, 2013; 2014a,
b, c). Concurrently, the upper ocean temperatures in the SAB and GoM have abruptly increased,
partly due to the increased westerly and trade wind system in the North Atlantic and the
associated upper ocean heat accumulation in the subtropical North Atlantic (e.g., Volkov et al.,
2019). Therefore, it is reasonable to hypothesize that the recent anomalous accumulation of the
upper ocean heat in the subtropical North Atlantic increased the stratification to suppress the
vertical entrainment of nutrients and biological productivity along the GoM and SAB, and thus
affecting productivity of prey populations for the coastal pelagic species. A competing
hypothesis is that a series of La Niña events that prevailed from late 2005 to early 2012
decreased the river discharges of freshwater and nutrients across the northern GoM and west
Florida coast to cause the decline of the coastal pelagic species in the GoM (e.g., Gomez et al.,
2019). The primary objective of this proposed research is to elucidate potential large-scale
climate drivers of plankton biomass and range shifts – and their combined influences – for a suite
of coastal pelagic species in the GoM and SAB. In order to achieve this objective, we will first
explore the link between the two key environmental drivers (i.e., upper ocean heat content and
river discharge) and the coastal pelagic stocks in the GoM and SAB, by analyzing available
fisheries and satellite data, ocean reanalysis products and a high-resolution regional ocean-
biogeochemical hindcast simulation. Then, we will explore large-scale climate processes that
influence the upper ocean heat content, river discharge and the associated nutrient availability
and plankton biomass in the GoM and SAB, by using a series of high-resolution regional ocean-
biogeochemical model experiments. Such climate processes include North Atlantic sea surface
height (SSH) tripole mode, El Niño – Southern Oscillation (ENSO), North Atlantic Oscillation
(NAO), Atlantic Multidecadal Oscillation (AMO) and Atlantic Meridional Overturning
Circulation (AMOC). Finally, we will use a suite of CMIP6 models and dynamic downscaling
simulations to explore the potential influence of anthropogenic global warming (AGW) on the
coastal pelagic stocks.

The proposed work contributes directly to NOAA CPO FY2020 MAPP funding
Competition-4 Modeling Climate Impacts on the Predictability of Fisheries and Other Living
Marine Resources, Type-1, Priority Area-A: The proposed work will identify key climate and
oceanic processes that affect ocean-biogeochemistry of relevance to the coastal pelagic species
assessed and managed by NMFS/SEFSC and the regional Fishery Management Councils in the
U.S. Gulf and South Atlantic Bight.

Climate Risk Area: Marine Ecosystems