EARLY LIFE HISTORY OF LARVAL RIVER HERRING IN A COASTAL WATERSHED: ABUNDANCE, GROWTH, AND MORTALITY

Abstract

River herring are two closely-related, anadromous fish species, Alewife (Alosa aestivalis) and Blueback Herring (A. pseudoharengus), which have been historically, commercially, and ecologically important along the North American Atlantic coast for hundreds of years. However, recent decades have been marked by their dramatic population declines and a collapse of the fishery. Historical records show that the coastal watershed of North Carolina's Chowan River was an epicenter for river herring harvest and spawning from pre-1700 through the late 1980s. I spatiotemporally characterized the early life history of river herring larvae in the Chowan River and its tributaries in the spring spawning season of 2011 by calculating larval abundance, growth, mortality, and diet relative to water quality and chemistry. Results show that the Chowan River and its tributaries supported relatively high numbers of river herring larvae in 2011 compared to an early 1980s study, with mean catches per unit effort (CPUEs) ranging from 52.87 + 71.68 larvae/100 m3 to 1583.53 + 2698.18 larvae/100 m3 compared to a similar and neighboring riverine system - the Roanoke River - with mean CPUEs ranging from 4.1 + 20.9 larvae/100 m3 in 2008 to 30.8 + 149.8 larvae/100 m3 from a study in 2009. A concurrent study to my research indicated that larval river herring diets are very similar between the adjacent systems, consisting primarily of copepods and rotifers in both the lower Chowan and the lower Roanoke River. Also, analyses of abundance, growth rates, and mortality rates suggest that density-dependent mechanisms likely control larval river herring trends throughout the Chowan system. Although all nursery habitats are worthy of research and conservation efforts, the Chowan River has continually proved to be a regional epicenter for successful reproduction and early life history of river herring and, therefore, merits special attention as a Strategic Habitat Area (SHA) by the State of North Carolina.