Shore zone habitat use by fishes and crabs in Delaware Bay: beach vs riprap shorelines
Date
2014
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Publisher
University of Delaware
Abstract
Estuarine habitat loss and fragmentation are among the most serious threats facing coastal fisheries. A major component of habitat loss is coastal development in the form of shoreline hardening, the process of placing hardened structures along soft shorelines to reduce erosion and protect upland property. Shoreline hardening drastically alters morphology of the intertidal zone, and has been shown to disrupt local patterns of habitat usage among shore zone biota. Several types of hardening structures are becoming more common within the Mid-Atlantic, and coastal population growth coupled sea level rise will further increase the demand for shoreline stabilization in the future. In this context, it is crucial to determine the importance of the shore zone as fish habitat, and the effects of anthropogenic modification. This study will assess differences in the usage, value, and function of unhardened shorelines relative to hardened shorelines for estuarine nekton communities within the Delaware Bay. In the first part of this study, I used quantitative sampling to measure species composition, overall density, and densities of individual species among natural (beach) and hardened (riprap) shorelines to evaluate spatial and temporal changes in the estuarine shore zone assemblage associated with shoreline modification. Fishes and crabs along the western shoreline of Delaware Bay were sampled from June through late September, 2012 and 2013. During 2013, the shore zone assemblage at one site in lower Delaware Bay was also sampled during both day and night hours. Over the two years of this study 14,198 fish and crabs were captured within the shore zone in total, comprised of 51 individual species. Overall nekton density was higher along beach shorelines at 2 of 3 locations. Nekton density was also higher at night along both beach and riprap shorelines. Habitat preference between hardened and unhardened shorelines existed among several abundant species. Usage of shore zone habitat also changed among several abundant species between day and night hours. Distinct assemblages of fish and crabs were present among beach and riprap shorelines at 2 of 3 locations and among day and night hours. In general, the results demonstrate altered usage of shore zone habitat along hardened shorelines and changes to overall use of shore zone habitat between day and night hours. Chapter 2 addressed changes in the feeding habits of top piscivorous fish species within the Mid-Atlantic estuarine food web. Diet composition and stomach fullness were measured in weakfish, bluefish, and striped bass captured during shore zone sampling. Striped bass and weakfish diets did not show changes in prey composition or feeding intensity among shoreline types. However, weakfish diet composition shifted among sites, indicating an effect of location on either prey selectivity or availability. Bluefish diet reflected differences in the predation of prey species associated with shoreline type in the month of July, with individuals captured along the beach foraging on fish prey and those captured along the riprap foraging on mysid shrimp. Bluefish captured in August exhibited similar diet composition overall, but different stomach fullness values indicating a difference in feeding intensity. In general, these findings show that shoreline hardening has the potential to alter shore zone habitat use and function for estuarine fishes, and that these effects appear to be inconsistent among species and size-classes.