Title
Size Changes within a Southeastern United States Coastal Shark Assemblage: 1975–2018
Date Issued
01 June 2021
Access level
open access
Resource Type
journal article
Author(s)
Fodrie F.J.
Fegley S.R.
Bargione G.
University of North Carolina at Chapel Hill
Publisher(s)
John Wiley and Sons Inc
Abstract
Harvest may have myriad effects on target species, including a change in population size structure. To assess whether size shifts have occurred among managed coastal species of shark (superorder Selachimorpha), we examined the population size structure of 12 species caught during a nearly five-decade-long fishery-independent survey conducted in Onslow Bay, North Carolina, using standardized longline gear. We evaluated trends in mean fork length (FL), median FL, and index of maximum FL (L90%) for each species separately across time using linear regression models. We also examined trends in size-classes (200-mm bins) and catch per unit effort for each species over time. For 10 of the 12 species (excluding sample-size-constrained Tiger Shark Galeocerdo cuvier and Bull Shark Carcharhinus leucas), size structure metrics indicated decreasing sizes over time, although statistical confidence for these patterns varied across species and metrics. Strongest statistical support for declining sizes was observed for Blacknose Shark Carcharhinus acronotus (mean FL, median FL, L90%), Dusky Shark Carcharhinus obscurus (L90%), Smooth Dogfish Mustelus canis (L90%), and Atlantic Sharpnose Shark Rhizoprionodon terraenovae (L90%). Magnitude of decreases in L90% among these 10 species during the survey ranged from roughly 9% (Silky Shark Carcharhinus falciformis; 83-mm decrease) to 35% (Sandbar Shark Carcharhinus plumbeus; 541-mm decrease). Our findings indicate a potential for fishing pressure to exert directional selection on these coastal shark species, although further research is needed regarding the nature of size-dependent catchability and species-specific vital rates to adequately evaluate these dynamics. Furthermore, in addition to the removal of “great sharks,” decreasing sizes of small coastal sharks, such as Blacknose Shark, Smooth Dogfish, and Atlantic Sharpnose Shark (i.e., “mesopredators”), suggest that harvest may have pervasive effects on species throughout this assemblage.
Start page
228
End page
239
Volume
13
Issue
3
Language
English
OCDE Knowledge area
Pesquería
Scopus EID
2-s2.0-85109326507
Source
Marine and Coastal Fisheries
Sponsor(s)
Collection of shark abundance and size data in Onslow Bay has been supported by Carolina Power and Light (~1975–1985) and by resources from the Institute of Marine Sciences of the University of North Carolina at Chapel Hill. The first author was supported by a PhD scholarship from the Peruvian Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica (CONCYTEC), award 292‐2014‐FONDECYT. The chief scientist who managed the survey over its first 35 years was Frank J. Schwartz. Numerous students, research technicians, staff, and volunteers have contributed assistance on deck and in the laboratory over the years—far too many to identify by name, although we remain in their debt. Captains John Wegner, Otis Lewis, Joseph Purifoy, and Stacy Davis guided the research ships, RV and then RV , from which the survey has been conducted. Matthew Kenworthy, Amy Yarnall, Charles Peterson, Johanna Rosman, and Nathan Bacheler aided with data curation, processing, and analyses. There is no conflict of interest declared in this article. Machapunga Capricorn
Sources of information: Directorio de Producción Científica Scopus