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Determining the causes of natural mortality in wild marine fish populations is extremely challenging. Scientists at WFRC and University of Washington introduce a new approach that can be used in annual fisheries stock abundance assessments.

Juvenile herring with classic signs of VHS
Juvenile herring with classic signs of VHS including focal hemorrhaging around the eyes, mouth, and fin bases. Photo provided by Paul Hershberger, USGS.

In wild fish populations, common disease surveillance data such as infection prevalence at time of sampling isn’t always informative, especially for fast-acting diseases that may go unobserved in infrequently sampled populations. Finding more effective ways to estimate mortality from disease in fish population models is critical for predicting populations and developing stock assessments. But what alternative methods and approaches for incorporating disease impacts in fisheries can provide the tools and strategies necessary to better understand and manage important fish stocks?

In a new publication of the Canadian Journal of Fisheries and Aquatic Sciences, scientists from WFRC and University of Washington present a novel method of estimating disease in wild marine fish populations. Since acute diseases may go unobserved in infrequently sampled wild populations, surveillance for antibodies against a pathogen may be more informative than screening for the pathogen itself. In these cases, seroprevalence — the proportion of fish with measurable antibody levels in their blood — may be more useful. In cases of life-long immunity, seroprevalence data require less frequent sampling intervals than infection prevalence data and can reflect the cumulative exposure history of fish. The scientists’ simulation-tested the usefulness of seroprevalence data in an age-structured fish stock assessment model using viral hemorrhagic septicemia virus (VHSV) in Pacific herring as a case study. They found that surveillance for antibodies against a pathogen may be more informative than screening for the pathogen itself. In the publication, authors report this novel approach for incorporating infection history and disease-associated mortality into annual fisheries stock assessments.

The next step will be to compare actual VHSV seroprevalence data in Pacific herring populations with annual demographic patterns to determine whether changes in exposure history are associated with changes in biomass, year class abundance, and recruitment.

To learn more about this study check out the publication at:

Trochta, J.T.  M.L. Groner, P.K. Hershberger, and T.A. Branch. 2022. A novel approach for directly incorporating disease into fish stock assessment: a case study with seroprevalence data. Canadian Journal of Fisheries and Aquatic Sciences. 79(4): 611-630.  https://doi.org/10.1139/cjfas-2021-0094.