Life History and Population Structure of Snowy and Warsaw Grouper in US Waters

Abstract

Important life history and population parameters are currently unavailable for Snowy Grouper (Hyporthodus niveatus) and Warsaw Grouper (H. nigritus), which represent two valuable and vulnerable components of the deepwater grouper assemblage. Since fisheries yields, population dynamics, and rebuilding plans are dependent on life history traits, genetic characteristics, and other population parameters, there is a clear need to close existing data gaps for these two species. Recent assessments indicate these species are overfished (Snowy Grouper) or experiencing overfishing (Warsaw Grouper) in the South Atlantic, while the stock status of both is currently unknown in the Gulf of Mexico. Both species appear on the International Union for the Conservation of Nature (IUCN) Red List of threatened species (2014.2), with Snowy designated “vulnerable” and Warsaw listed as “critically endangered,” indicating that fundamental data on the life history and population structure of each species is needed to reduce the “uncertainty” in stock assessments in the South Atlantic and allow for “initial” stock assessments of each species in the Gulf of Mexico. The goal of this project was to comprehensively investigate the life history and population structure of Snowy Grouper and Warsaw Grouper in U.S. waters by coupling three distinct but complementary research components: 1) age validation (bomb radiocarbon dating) coupled with the development of age-length keys for both species in the South Atlantic and Gulf of Mexico; 2) geochemical and genetic approaches to determine the population structure and connectivity of Snowy Grouper and Warsaw Grouper from four regions (South Atlantic, northwestern [NW], northcentral [NC], and northeastern [NE] Gulf of Mexico); and 3) histological examination to estimate several key reproductive parameters including sex ratios, maturity, the proportion of active spawning adults (i.e., spawning fraction) by age and size class, and spawning seasonality. Data from the project addresses specific research recommendations identified by our NOAA Fisheries colleagues, particularly the need for basic information on the age, growth, and reproductive biology of both Snowy Grouper and Warsaw Grouper.