In the face of climate change and exhaustive exercise: the physiological response of an important recreational fish species

Abstract

Cobia (Rachycentron canadum) support recreational fisheries along the US mid-and south-Atlantic states and have been recently subjected to increased fishing effort, primarily during their spawning season in coastal habitats where increasing temperatures and expanding hypoxic zones are occurring due to climate change. We therefore undertook a study to quantify the physiological abilities of cobia to withstand increases in temperature and hypoxia, including their ability to recover from exhaustive exercise. Respirometry was conducted on cobia from Chesapeake Bay to determine aerobic scope, critical oxygen saturation, ventilation volume and the time to recover from exhaustive exercise under temperature and oxygen conditions projected to be more common in inshore areas by the middle and end of this century. Cobia physiologically tolerated predicted mid-and end-of-century temperatures (28-32°C) and oxygen concentrations as low as 1.7-2.4 mg l −1 . Our results indicated cobia can withstand environmental fluctuations that occur in coastal habitats and the broad environmental conditions their prey items can tolerate. However, at these high temperatures, some cobia did suffer post-exercise mortality. It appears cobia will be able to withstand near-future climate impacts in coastal habitats like Chesapeake Bay, but as conditions worsen, catch-and-release fishing may result in higher mortality than under present conditions.

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

“…The relationship between fish physiology and the environment is one way to understand the impacts of climate change on fish. A recent physiology study found that cobia are able to withstand temperatures as warm as 32 • C; however, when exercised to exhaustion in these conditions, 30% of individuals suffered mortality (Crear et al, 2020a). Furthermore, this study showed cobia had a very high hypoxia tolerance, where individuals could tolerate oxygen levels as low as 1.7-2.4 mg l −1 at temperatures between 24 and 32 • C (Crear et al, 2020a).…”

“…These experiments showed that hypoxia tolerance declines in warmer waters (Crear et al, 2020a). To remove those portions where habitats were physiologically unavailable to cobia, we adjusted cells from depth bins to not available values (NAs) where temperatures were between 24 and 28 • C and dissolved oxygen levels were less than or equal to 1.7 mg l −1 , where temperatures were greater than 28 • C and less than 32 • C and dissolved oxygen levels were less than or equal to 2 mg l −1 , and where temperatures exceeded 32 • C and dissolved oxygen levels were less than 2.4 mg l −1 (Crear et al, 2020a). Because salinity preference is unknown for adult cobia while inhabiting Chesapeake Bay, we generated an area based on where cobia are caught while in Chesapeake Bay.…”

“…Cobia may have the ability to behaviorally adapt to climate change within Chesapeake Bay. The fact that cobia could withstand water temperatures as warm as 32 • C (Crear et al, 2020a), suggests that if waters warmed throughout Chesapeake Bay, areas with water temperatures up to 32 • C could still be habitable or maybe even suitable. Meaning, temperatures between 22.5 and 28 • C may be preferred, but if unavailable, cobia could still inhabit warmer temperatures.…”

“…A recent physiology study found that cobia are able to withstand temperatures as warm as 32 • C; however, when exercised to exhaustion in these conditions, 30% of individuals suffered mortality (Crear et al, 2020a). Furthermore, this study showed cobia had a very high hypoxia tolerance, where individuals could tolerate oxygen levels as low as 1.7-2.4 mg l −1 at temperatures between 24 and 32 • C (Crear et al, 2020a). Based on these results, it appears cobia are more hypoxia tolerant than many active predatory species and therefore might be less impacted by future decreases in dissolved oxygen concentration.…”

“…To predict future changes in phenology and habitat suitability for cobia within the Chesapeake Bay, we developed a habitat model parameterized with our physiology data (Crear et al, 2020a) and archival tagging data. This model was used to project the current arrival and departure times of cobia into Chesapeake Bay and the changes to this phenology in the future under climate change.…”