My PhD work utilizes modern molecular genetics tools to investigate the contemporary and historical ecology of large open ocean and coral reef fishes (sharks, billfishes, groupers) that are of national management and conservation interest. Global declines of many marine apex predator fishes have occurred throughout the past few decades, and urgent management and conservation actions are required to prevent further declines and facilitate their recovery. To assist fishery managers in these actions, I am investigating a suite of biologically important questions pertaining to three commercially and recreationally exploited species: the roundscale spearfish, the Nassau Grouper, and the tiger shark. My research focuses on investigating the current stock structure of these species across their distribution, the relative size of their populations, their genetic diversity, and their contemporary and historical population demographic trajectories.
Four peer-reviewed journal publications have thus far resulted from this work (listed below), and five more planned publications are in various stages of writing. This work has also been presented at seven professional conferences to date.
Synopsis of Projects
Over the past few decades, there has been increasing concern about the population status of many billfish species as they are heavily fished in pelagic fisheries either as targets or as by-catch, and their management is made complex due to the international nature of their fisheries. Adding to this management complexity is that one billfish, the roundscale spearfish, was only recently validated in 2006 as a legitimate species by my advisor's lab. The lack of historical recognition of the roundscale spearfish is due to its strong morphological similarity to the heavily overfished and highly prized, recreationally fished white marlin. To make matters worse, it is now clear that the roundscale spearfish has frequently been misidentified as the longbill spearfish as well. To aid in the management of all billfish species, some of my PhD work has centered on using genetic tools to provide managers with information regarding the biology, distribution and stock structure of the roundscale spearfish. I developed genetic tools which have been used to (i) investigate and define the Atlantic distribution of the roundscale spearfish, (ii) assess the connectivity of North and South Atlantic populations of the roundscale spearfish for management purposes, and (iii) compare the demographic history and relative population sizes of the roundscale spearfish and the white marlin.
During my time as a PhD student, I have also had the opportunity to study the charismatic Nassau Grouper, a species of great conservation concern on coral reefs. Due to high levels of historical commercial and recreational fishing, the Nassau grouper has sustained alarming declines across its geographic distribution, resulting in an Endangered listing on the IUCN Red List and current consideration for Endangered listing under the US Endangered Species Act. In the US Virgin Islands, recognized Nassau grouper spawning aggregations have declined to very low levels; however, a remnant spawning aggregation historically numbering over 1000 individuals at Grammanik Bank, St. Thomas, has seemingly begun to recover since implementation of protective measures in 2005, and may now comprise approximately 200 individuals. The genetic consequences of such large aggregation declines and its incipient recovery are unknown. My genetic analyses of these fish is revealing several key, conservation relevant findings, including (i) the good news that high levels of genetic diversity remain in the aggregation despite overfishing, and (ii) strong indications that migrations from neighboring Caribbean spawning aggregations, rather than local replenishment, may be driving the recovery of the St. Thomas population; these neighboring populations and their conservation may therefore be essential to the continued persistence of the Nassau grouper in the USVI.
Finally, I am also investigating the biology and population connectivity of tiger sharks across their global distribution. As one of few sharks categorized as a coastal-pelagic species, the tiger shark inhabits a variety of marine habitats and often demonstrates complex patterns of migratory behavior and habitat utilization. Given its global distribution, information pertaining to the connectivity of the species is needed to help international managers and decision-makers properly conserve this large marine species. My work on the tiger shark is focusing on identifying several key factors which will aid both conservation and management of this species. Using genetic tools, I have found that (i) tiger sharks comprise at least two separate populations, one inhabiting the western Atlantic, and one within the Indo-Pacific, (ii) these animals appear to be connected on broad spatial scales within ocean basins, and (iii) tiger sharks inhabiting different geographic areas show varying levels of genetic diversity which has implications regarding how to prioritize conservation efforts for this large apex predator.
Journal Publications from this research
Bernard, A.M., M.S. Shivji, R.R. Domingues, F.H.V. Hazin, A.F. Amorim, A. Domingo, F. Arocha, E.D. Prince, J.P. Hoolihan and A.W. Hilsdorf. 2013. Broad geographic distribution of roundscale spearfish (Tetrapturus georgii) (Teleostei, Istiophoridae) in the Atlantic revealed by DNA analysis: implications for white marlin and roundscale spearfish management. Fisheries Research 139: 93-97.
Bernard, A.M., K.A. Feldheim, V.P. Richards, R.S. Nemeth and M.S. Shivji. 2012. Development and characterization of fifteen novel microsatellite loci for the Nassau grouper (Epinephelus striatus) and their utility for cross-amplification on a suite of closely related species. Conservation Genetics Resources 4: 983–986.
Bernard, A.M., K. A. Feldheim and M.S. Shivji. 2012.. Development and characterization of eleven novel microsatellite loci for the roundscale spearfishTetrapturus georgii and their cross-species amplification among other billfish species. Journal of Fish Biology 81: 1781–1786.