Contemporary and future distributions of cobia, Rachycentron canadum

Abstract

AimClimate change has influenced the distribution and phenology of marine species, globally. However, knowledge of the impacts of climate change is lacking for many species that support valuable recreational fisheries. Cobia (Rachycentron canadum) are the target of an important recreational fishery along the U.S. east coast that is currently the subject of a management controversy regarding allocation and stock structure. Further, the current and probable future distributions of this migratory species are unclear, further complicating decision‐making. The objectives of this study are to better define the contemporary distribution of cobia along the U.S. east coast and to project potential shifts in distribution and phenology under future climate change scenarios.LocationChesapeake Bay and the U.S. east coast.MethodsWe developed a depth‐integrated habitat suitability model using archival tagging data from cobia that were caught and tagged in Chesapeake Bay during summer months and coupled those data with high‐resolution ocean models to project the contemporary and future distributions of cobia along U.S. east coast.ResultsDuring the winter months, suitable cobia habitat currently occurs in offshore waters off North Carolina and further south, whereas during the summer months, suitable habitat occurs in waters from Florida to southern New England. In warmer years, the availability of suitable habitat increases in northern latitudes. Under continued climate change over the next 40–80 years, suitable habitat is projected to shift northward and decrease over the shelf.Main conclusionsHabitat distributions suggest cobia overwinter offshore and could inhabit waters further north during warmer months, into state jurisdictions that do not have strict management regulations for cobia. When waters are warmer, distributions are projected to shift poleward and seasonal migrations may begin earlier. These results can inform resource allocation discussions between fishery managers and resource users.

Estimating Shifts in Phenology and Habitat Use of Cobia in Chesapeake Bay Under Climate Change

“…The exact timing of both inshore and offshore migrations fluctuate each year and are thought to be driven by temperature cues (Smith, 1995;Lefebvre and Denson, 2012). Anecdotal evidence from fishermen suggests that cobia have been entering Chesapeake Bay earlier in recent years, consistent with habitat suitability models suggesting that future climate warming will result in arrival into inshore habitats, like Chesapeake Bay, earlier in the spring (Crear et al, 2020b).…”

“…The habitat model followed similar methods described in Eveson et al (2015) and Crear et al (2020b), which uses the ratio between habitat use and habitat availability to determine habitat suitability of the fish species. Habitat use was characterized by the temperatures utilized by tagged cobia (section "Habitat Use Densities" below) and habitat availability was the thermal distribution of the environment, as predicted via biogeochemical modeling (section "Habitat Availability Densities" below).…”

“…Along the east coast of the U.S., cobia migrate into bays and estuaries, such as Chesapeake Bay, in late spring/early summer to spawn and feed (Joseph et al, 1964;Smith, 1995;Perkinson et al, 2019). They remain in these habitats until late summer/early fall when they migrate primarily offshore to the shelf waters ranging from North Carolina to Florida (Crear et al, 2020b). The exact timing of both inshore and offshore migrations fluctuate each year and are thought to be driven by temperature cues (Smith, 1995;Lefebvre and Denson, 2012).…”

“…These studies have been used to identify both habitat reductions and range shifts. Although a recent study assessed climate impacts on cobia distribution along the U.S. east coast (Crear et al, 2020b), the spatial resolution of the analysis was too coarse to assess the changes in the habitat quality of Chesapeake Bay.…”

Sensitivity of a shark nursery habitat to a changing climate

“…It is clear that juvenile sandbar shark distribution shifts in latitude depending on whether environmental conditions are representative of an average, dry, or wet year. Assessing interannual variability in suitable habitat, although often ignored in most habitat modeling studies, is critical in understanding how a habitat may change (Crear et al 2020), particularly in dynamic habitats (bays and estuaries). For juvenile sandbar sharks, a southward shift in suitable bottom habitat occurred during a wet year because the low-salinity water extended farther south, whereas during a dry year, the low-salinity water receded farther up Chesapeake Bay, resulting in a northward shift of suitable habitat.…”