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Quantifying Spatiotemporal Patterns In Consumption And Habitat Of Spiny Dogfish In The Northwest Atlantic
Robert J Latour
Robert J Latour
Abstract
The spiny dogfish, Squalus acanthias, is a small, mesopredatory shark that preys upon and likely competes with a number of managed species in the Northwest Atlantic. These dogfish have a near-continuous two-year cycle of gestation, with low fecundity and late maturity, and support a targeted fishery on the Northeast US shelf that is managed jointly by Mid-Atlantic Fishery Management Council and the Atlantic States Marine Fisheries Commission. This thesis focused on two aspects of spiny dogfish ecology in this region: drivers of key prey consumption by spiny dogfish for each sex and maturity stage, and the role of gestation on spatiotemporal distribution and habitat utilization of mature female spiny dogfish. In Chapter 1, seasonal consumption of Atlantic menhaden (Brevoortia tyrannus), Atlantic herring (Clupea harengus), and longfin inshore squid (Doryteuthis pealeii), by spiny dogfish was quantified via multivariate vector auto-regressive spatiotemporal (VAST) models that combined survey catch and stomach contents data. Annualized indices for broad-scale environmental phenomena (North Atlantic Oscillation, Atlantic Multidecadal Oscillation, and Gulf Stream Index) and prey availability (prey harvest, seasonal prey abundance, seasonal prey-predator overlap) were assessed as potential drivers for seasonal consumption of key prey using Kendall-Tau tests and repeated-median (Siegel) regression. AMO and species-specific prey availability metrics were most frequently correlated with prey consumption, though there was also evidence of prey switching between Atlantic menhaden and Atlantic herring and a complex relationship between spiny dogfish, Atlantic herring, and longfin inshore squid. In Chapter 2, mature female spiny dogfish were separated into early term, late term, and nongravid reproductive groups based on embryo development. Species distribution models and ecological niche models were constructed to predict spatiotemporal distribution and habitat suitability for each life stage. These predictions were then used to calculate spatiotemporal and niche overlap, which was formally assessed for spatiotemporal and niche equivalency. Equivalency was rejected in a number of cases, indicating the existence of habitat partitioning within mature female spiny dogfish based on gestation. In particular, niche equivalency was rejected between late term females and both other groups in fall. While the abundance of the former declines linearly with depth, nongravid females exhibited a bimodal relationship while early term females showed no relationship indicating that spiny dogfish may utilize shallow waters for parturition and offshore locations for mating. Future research should further explore prey switching in the Northwest Atlantic and the role of reproduction on the distribution and habitat utilization of mature female fish.
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2024-01-01
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Virginia Institute of Marine Science
DOI
https://dx.doi.org/10.25773/v5-vcj8-c702