Use of a Fishery‐Independent Trawl Survey to Evaluate Distribution Patterns of Subadult Sharks in Georgia

Cecil A Jennings,Carolyn N Belcher

doi:10.1577/c08-019.1

Cecil A Jennings, Carolyn N Belcher

Open Access

https://doi.org/10.1577/c08-019.1

Copy DOI

Abstract

AbstractWe investigated the utility of a fishery‐independent trawl survey for assessing a potential multispecies shark nursery in Georgia's nearshore and inshore waters. A total of 234 subadult sharks from six species were captured during 85 of 216 trawls. Catch rates and size distributions for subadult sharks and the ratio of neonates to juveniles were consistent among areas. The highest concentrations of subadult sharks occurred in creeks and sounds. Species composition varied among areas. The Atlantic sharpnose shark Rhizoprionodon terraenovae was the most abundant species in sound and nearshore stations, whereas the bonnethead Sphyrna tiburo was the most abundant species in creeks. The aggregate of other species occurred with higher frequency in the sounds and nearshore. Sampling characteristics of the trawl survey were compared with those from a fishery‐independent longline survey of subadult sharks to assess the similarity of the two gears. A total of 193 subadult sharks from seven species were captured during 57 of 96 longline sets, whereas 52 subadults from four species were captured during 20 of 48 trawls. Selectivity and efficiency differed between the two gears. The trawl had lower catch rates, caught smaller sharks, and encountered a different suite of species than the longline. General seasonal trends in relative abundance also differed between the two gears; the longline showed an increasing trend in abundance, whereas the trawl showed a stable trend. Although trawls were not found to be efficient for sampling subadult sharks from most species, they can be a useful source of supplemental data.

Highlights

U.S Geological Survey, Georgia Cooperative Fish and Wildlife Research Unit, D.B
The two most abundant shark species, which accounted for 96.6% of the total shark bycatch, were the Atlantic sharpnose shark and bonnethead
The bonnethead catch rates differed among areas; catches in the offshore sector were significantly lower than those in the inshore sectors

Summary

Introduction

U.S Geological Survey, Georgia Cooperative Fish and Wildlife Research Unit, D.B. Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia 30602, USA. Sampling characteristics of the trawl survey were compared with those from a fishery-independent longline survey of subadult sharks to assess the similarity of the two gears. Prior to 1993, stock assessments for many shark species relied on fishery-dependent indices (Carlson and Brusher 1999). Three surveys currently monitor shark abundance in the Gulf of Mexico and along the U.S Atlantic coast (Carlson and Brusher 1999); these surveys are conducted in areas where older juveniles and adults congregate, generally in waters greater than 10 m deep (Carlson and Brusher 1999)

Methods

Results

Discussion

Conclusion