Dermal mycobacteriosis and warming sea surface temperatures are associated with elevated mortality of striped bass in Chesapeake Bay

Abstract

Temperature is hypothesized to alter disease dynamics, particularly when species are living at or near their thermal limits. When disease occurs in marine systems, this can go undetected, particularly if the disease is chronic and progresses slowly. As a result, population‐level impacts of diseases can be grossly underestimated. Complex migratory patterns, stochasticity in recruitment, and data and knowledge gaps can hinder collection and analysis of data on marine diseases. New tools enabling quantification of disease impacts in marine environments include coupled biogeochemical hydrodynamic models (to hindcast key environmental data), and multievent, multistate mark–recapture (MMSMR) (to quantify the effects of environmental conditions on disease processes and assess population‐level impacts). We used MMSMR to quantify disease processes and population impacts in an estuarine population of striped bass (Morone saxatilis) in Chesapeake Bay from 2005 to 2013. Our results supported the hypothesis that mycobacteriosis is chronic, progressive, and, frequently, lethal. Yearly disease incidence in fish age three and above was 89%, suggesting that this disease impacts nearly every adult striped bass. Mortality of diseased fish was high, particularly in severe cases, where it approached 80% in typical years. Severely diseased fish also had a 10‐fold higher catchability than healthy fish, which could bias estimates of disease prevalence. For both healthy and diseased fish, mortality increased with the modeled average summer sea surface temperature (SST) at the mouth of the Rappahannock River; in warmer summers (average SST ≥ 29°C), a cohort is predicted to experience >90% mortality in 1 year. Regression of disease signs in mildly and moderately diseased fish was <2%. These results suggest that these fish are living at their maximum thermal tolerance and that this is driving increased disease and mortality. Management of this fishery should account for the effects of temperature and disease on impacted populations.

Disease in Central Valley Salmon: Status and Lessons from Other Systems

“…Nonlethal testing methods to assess infection status are reliable for some but not all fish pathogens, but assessing disease status by non-lethal methods is often more difficult. However, diseases that can be assessed by visual or non-lethal methods allow disease state to be integrated with other populations assessments (e.g., markrecapture approaches; [Groner et al 2018]). Typically, more invasive techniques are needed to determine disease state.…”

Effects of Infectious Diseases on Population Dynamics of Marine Organisms in Chesapeake Bay

“…The mortality of striped bass increases with increasing disease severity, with moderately and severely diseased individuals having 16% and 46% year −1 higher mortality relative to healthy fish (Hoenig et al 2017). Mortality among severely diseased striped bass is especially high, with average mortality from 56 to 87% year −1 (Groner et al 2018b). At the population-level, Fig.…”

“…Mycobacteriosis was first detected in the population in 1997 and correlates with an increase in natural mortality in the Chesapeake Bay according to tagging estimates (Northeast Fisheries Science Center 2019). Prevalence of mycobacteriosis can vary among years and locations and can exceed 60% (Cardinal 2001;Gauthier et al 2008;Hoenig et al 2017;Groner et al 2018b). The mortality of striped bass increases with increasing disease severity, with moderately and severely diseased individuals having 16% and 46% year −1 higher mortality relative to healthy fish (Hoenig et al 2017).…”

“…Shifting environmental conditions may affect interactions between hosts and pathogens, which can tilt the balance toward or away from high disease states (Burge et al 2014;Barbieri et al 2018). Our understanding of how climate change will affect marine infectious diseases in the Chesapeake Bay is restricted to hosts for which there are long-term infectious disease datasets (Harvell et al 2002), in particular oysters and striped bass (Hofmann et al 2001;Bushek and Ford 2016;Groner et al 2018b). Predicting responses to climate change is further complicated by the synergistic effects of populations responding to multiple climate variables and subsequent changes in the marine community (Harvell et al 2002;Ward and Lafferty 2004).…”

“…Infectious diseases can have substantial effects on population dynamics and communities of marine organisms (Andrews 1979;Muehlstein et al 1991;Groner et al 2018b). For this paper, infectious disease is defined as a disease caused by bacterial, fungal, viral, or parasitic infections that can be transmitted from one individual to another (simply referred to as diseases hereafter).…”