Date Published: April 7, 2017
Publisher: Public Library of Science
Author(s): Tom Savoy, Lorraine Maceda, Nirmal K. Roy, Doug Peterson, Isaac Wirgin, Zuogang Peng.
Atlantic Sturgeon is listed under the U.S. Endangered Species Act as five Distinct Population Segments (DPS). The “endangered” New York Bight (NYB) DPS is thought to only harbor two populations; one in the Hudson River and a second smaller one in the Delaware River. Historically, the Connecticut River probably supported a spawning population of Atlantic Sturgeon that was believed extirpated many decades ago. In 2014, we successfully collected pre-migratory juvenile specimens from the lower Connecticut River which were subjected to mitochondrial DNA (mtDNA) control region sequence and microsatellite analyses to determine their genetic relatedness to other populations coastwide. Haplotype and allelic frequencies differed significantly between the Connecticut River collection and all other populations coastwide. Sibship analyses of the microsatellite data indicated that the Connecticut River collection was comprised of a small number of families that were likely the offspring of a limited number of breeders. This was supported by analysis of effective population size (Ne) and number of breeders (Nb). STRUCTURE analysis suggested that there were 11 genetic clusters among the coastwide collections and that from the Connecticut River was distinct from those in all other rivers. This was supported by UPGMA analyses of the microsatellite data. In AMOVA analyses, among region variation was maximized, and among population within regions variation minimized when the Connecticut River collection was separate from the other two populations in the NYB DPS indicating the dissimilarity between the Connecticut River collection and the other two populations in the NYB DPS. Use of mixed stock analysis indicated that the Connecticut River juvenile collection was comprised of specimens primarily of South Atlantic and Chesapeake Bay DPS origins. The most parsimonious explanation for these results is that the Connecticut River hosted successful natural reproduction in 2013 and that its offspring were descendants of a small number of colonizers from populations south of the NYB DPS, most notably the South Atlantic DPS. Our results run contrary to the belief that re-colonizers of extirpated populations primarily originate in proximal populations.
Atlantic sturgeon Acipenser oxyrinchus is a large, long-lived, anadromous species that is widely distributed along the Atlantic coast of North America . Spawning populations are found in most major river systems extending from St. Lawrence River, Quebec, to the Satilla River, Georgia . Atlantic Sturgeon have a complex life history with considerable variation in growth, age of maturity and maximum longevity. Historically, there were at least 25–30 spawning populations of Atlantic Sturgeon coastwide , but that number has dwindled in recent decades to 15–20 populations [4, 5].
In 2014, 64 juvenile Atlantic Sturgeon ranging from 22.5 to 71.0 cm TL were collected within the lower portion (rkm 6–18) of the Connecticut River from May through October during CT DEEP Marine Fisheries sturgeon research efforts (Fig 2). In total, the 45 smallest specimens (22.5 to 64.0 cm TL) were genetically analyzed. Twenty-three larger Atlantic Sturgeon were also collected and are depicted in the length frequency histogram (Fig 2), but were not analyzed genetically because they were likely older than the one-year old pre-migratory specimens that were the focus of our study.
Although the Connecticut River probably once hosted a spawning population of Atlantic Sturgeon, there has been no evidence of successful natural reproduction there for many decades. Our collection of a moderate number (n = 64) of specimens in 2014 of which a subset (n = 45) were juveniles indicates that successful natural reproduction occurred in the Connecticut River in 2013. Furthermore, our genetic results on a subset of the 2014 collection (n = 45) indicate that the juveniles collected there were most likely offspring of a small number of recent colonizers from spawning rivers outside of the NYB DPS, mostly from the SA, CB, and Carolinas DPS. These results are contrary to expectations that recolonizers would most likely be migrants from proximal, not distant spawning populations. The low levels of microsatellite and mtDNA diversity exhibited by the Connecticut River collection is consistent with its much smaller Ne compared to juvenile collections from other population within the NYB DPS and coastwide.
We report the first detection of successful natural reproduction of Atlantic Sturgeon in the Connecticut River in many decades. These were the smallest Atlantic Sturgeon collected in Connecticut waters in 28 years of sampling. Although our Connecticut River juvenile collection was genetically distinct from other collections coastwide, including the two other populations in the NYB DPS, it was surprisingly most closely genetically related to populations in geographically distant DPS. We recommend that directed sampling for juvenile Atlantic Sturgeon be conducted in the future in the Connecticut River to determine if successful spawning continues to occur, and if so, determine its genetic sources. It will also important to monitor the persistence of the 2013 cohort in the Connecticut River as they develop into subadults and to determine if additional successful spawning events reoccur.