Increased Abundance and Nursery Habitat Use of the Bull Shark (Carcharhinus leucas) in Response to a Changing Environment in a Warm-Temperate Estuary

Charles W Bangley,Lee Paramore,David S Shiffman,Roger A Rulifson

doi:10.1038/s41598-018-24510-z

Charles W Bangley, Lee Paramore + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-24510-z

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Abstract

A general northward shift in marine species distributions has been observed in the western North Atlantic Ocean, which may have significant ecological consequences. Large coastal sharks can have wide migratory distributions but show fidelity to specific nursery habitats. Here we show evidence for nursery range expansion into Pamlico Sound, North Carolina by a marine apex predator, the Bull Shark (Carcharhinus leucas). Previous assessments have shown little to no use of estuarine North Carolina waters as nursery habitat by Bull Sharks from 1965–2011. Juvenile sharks were rarely captured in a fishery-independent gillnet survey conducted by the North Carolina Division of Marine Fisheries (NCDMF) from 2003–2011, but were present every year from 2011–2016. Juvenile Bull Shark presence in the Sound was strongly related to early summer temperatures and late summer salinities, which have increased in the estuary over the 13 survey years, and further evidence for increasing water temperatures in Pamlico Sound was found in a 45-year data set for the NCDMF estuarine trawl survey. These results suggest that increasing water temperature and salinity have allowed Bull Sharks to expand their nursery habitat. This shift will have unknown, but potentially strong, impacts on both the local ecosystem and interactions with humans.

Highlights

Shifts in biodiversity can result in significant changes to local food web dynamics, ecosystem productivity, and even fisheries[2]
YOY and Age 1+ Bull Shark catch per unit effort (CPUE) was greatest during 2012 and sharks within juvenile size ranges made up the entirety of the catch in every subsequent year
Our results provide strong evidence that an increase in the use of Pamlico Sound as a Bull Shark nursery is associated with changing environmental conditions in the estuary, with temperature as the likely primary driver of Bull Shark presence

Summary

Introduction

Shifts in biodiversity can result in significant changes to local food web dynamics, ecosystem productivity, and even fisheries[2]. These ecological effects may be even more pronounced if a species new to a region is an apex predator, such as a shark[8]. A previous study compiling fishery-independent survey data, fishery landings, and sightings of Bull Shark in the coastal and estuarine waters of North Carolina documented 113 individuals from 1965–2011, but only nine were within juvenile size range[20].

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