Phenological Characterization and Effects of Environmental Attributes on River Herring Spawning Migrations within the Albemarle Sound Watershed.

LOMBARDO, STEVEN MICHAEL. Phenological Characterization and Effects of Environmental Attributes on River Herring Spawning Migrations within the Albemarle Sound Watershed. (Under the direction of Dr. Jeffrey A. Buckel). River herring, the collective name for alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), are anadromous fishes that are at or near historically low levels of abundance throughout their distributions. Historically, river herring supported one of the largest fisheries in North America. A combination of commercial pressure directly on the spawning grounds, offshore bycatch, and habitat degradation contributed to the collapse of river herring populations. Despite efforts to recover river herring stocks, which includes moratoria, bycatch caps, dam removal, and habitat restoration, stocks still have yet to rebound. We identified the spawning migration process as a potential bottleneck for recovery as it is particularly sensitive to environmental conditions. Our study objectives were to 1) characterize variation in the timing and duration of river herring spawning migrations within the Albemarle Sound watershed over a four-decade period and 2) elucidate whether agriculture/silviculture and development within the riparian zone impede the ability of river herring to migrate upstream, identify which habitat attributes are the most important for determining the suitability of habitat, and explore whether culverts are acting as a barrier for upstream migration. Using logistic Generalized Additive Models (GAMs) and NC Division of Marine Fisheries (NCDMF) river herring spawning habitat survey data that spans four decades (1973 – 2016), we observed phenological changes in the timing and duration of spawning migrations for both alewife and blueback herring. When comparing the alewife spawning migration in the 1970s to migration in the 2010s, alewife arrive to the spawning grounds 16 d earlier, the spawning migration peaks 12 d earlier, the egress is 27 d earlier, and 11 d less are spent on the spawning grounds. When comparing the blueback herring spawning migration in the 1980s to the migration in the 2010s, blueback herring are arriving 5 d earlier, the peak of the migration is 13 d earlier, the egress occurs 23 d earlier, and 18 d less are spent on the spawning grounds. We hypothesized age structure, abundance, or vernal warming to be potential drivers of the observed change in phenology. Water temperature data suggest that an increased vernal warming rate in recent decades (2000s & 2010s vs 1970s & 1980s), specifically in April and May, is driving earlier egress times for both species. In order to look at the effects of agriculture/silviculture, urbanization, and water quality on the ability of river herring to migrate upstream, we again used NCDMF river herring spawning habitat survey data (2007 – 2016) and logistic GAMs, in addition to 2010 land cover condition NOAA Coastal Change Analysis Program data. Presence/absence data from the NCDMF river herring spawning habitat survey was also used to evaluate culvert passability for river herring (observationally). We found no effect of agriculture/silviculture or development on upstream migration for either species. Water temperature and DO concentration were the two most important contributors for the presence of both alewife and blueback herring. The presence of culverts within the Albemarle Sound watershed currently does not appear to be restricting habitat availability or use. The 60 culverts sampled by the NCDMF were classified: 8 passable, 3 unpassable, 15 reached but undetermined passability, 1 potentially unpassable, 1 unknown, and 32 unreached. Overall, habitat conditions within the Albemarle Sound watershed appear suitable for river herring and efforts should be put forth to maintain those conditions. Phenological Characterization and Effects of Environmental Attributes on River Herring Spawning Migrations within the Albemarle Sound Watershed. by Steven Michael Lombardo A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfilment of the requirements for the degree of Master of Science Fisheries, Wildlife, and Conservation Biology Raleigh, North Carolina 2018