Age and Growth of Atlantic Sturgeon in the James River, Virginia, 1997-2011

Historically the Chesapeake Bay supported a large population of Atlantic sturgeon Acipenser oxyrinchus, but loss of suitable spawning habitat and overfishing coincided with dramatic in-system declines throughout the 20th century. Atlantic sturgeon harvest moratoriums were implemented in 1974 for Virginia waters and were expanded coastwide in 1998. In 1997, researchers became aware that commercial fishers in the James River, a tributary of the Chesapeake Bay, were catching juvenile and subadult Atlantic sturgeon as bycatch in various fisheries. Genetic studies showed that the Chesapeake Bay population has maintained genetic integrity and qualifies as a distinct population segment. Between 2007 and 2011, almost 150 adults have been caught in the tidal-freshwater portion of the James River during putative spawning runs. Pectoral fin spines from juveniles and subadults collected in the Burwell Bay (rkm 40) and Cobham Bay (rkm 60) areas and mature adult samples from vessel strikes in freshwater around or above rkm 120 were analyzed to create a length-at-age curve for Atlantic sturgeon in the James River. Five models were used to analyze the data, and the double von Bertalanffy (k(1) = 0.054, k(2) = 0.097, t(1) = -2.85, t(2) = 1.09, t(p) = 6.03 years, L-infinity = 2241 mm) provided the best fit to the observed data. We estimated an increase in growth coefficient at t(p), which could be an artifact of low sample size or due to ontogenetic changes in habitat use as older fish spend more time in oceanic waters than younger fish. Atlantic sturgeon in the 6-9 year age range are rarely encountered in the James River compared with younger and older age-classes, so a more in-depth analysis of the increased growth coefficient would require ocean sampling.