Decadal-scale decline of scamp (Mycteroperca phenax) abundance along the southeast United States Atlantic coast

Abstract

Scamp (Mycteroperca phenax) are a long-lived, economically important grouper species for which population trends are unknown along the southeast United States Atlantic coast (SEUS). We analyzed fishery-independent chevron trap (1990–2016) and underwater video (2011–2015) data using two-stage generalized additive models to elucidate changes in scamp relative abundance and mean size across the SEUS. A total of 1813 scamp were caught in 15609 trap samples across 27 years of sampling, and the proportion of traps catching scamp declined from a peak of 18.0% in 1994 to 2.5% in 2016. Likewise, mean scamp relative abundance declined 92% from its peak in 1995 to its lowest point (2016) in the time series. We observed a 29% decline of scamp relative abundance on videos between 2011 and 2015 (N = 6061 video samples), which closely matched the declining trend of trap relative abundance for the same years. Mean annual coefficients of variation were higher for traps (0.41) than video (0.20), but traps were essential given the much longer time series of trap data. Trap and video spatial predictions for scamp were consistently highest on the middle and outer continental shelf (40–100 m deep) between southern North Carolina and Georgia. Mean scamp total length increased approximately 130 mm over the course of the study due to the disproportionate declining catch of small scamp from traps since the early 2000s. Two hypotheses for potential recruitment failure of scamp in the SEUS are recruitment overfishing (increased F) and increased mortality on egg, larval, or juvenile stages (increased M).