National Marine 
Fisheries Service 
NOAA 
Abstract—Effective assessment and 
management of migratory species 
require an understanding of stock 
boundaries and habitat use during crit- 
ical life history periods. The blue crab 
(Callinectes sapidus) is considered a 
primarily estuarine species and has 
traditionally been assessed and man- 
aged on a state basis, relying on abun- 
dance estimates derived from estuarine 
sampling. Females undertake a sea- 
ward spawning migration, and recent 
evidence indicates that coastal and 
offshore waters may provide import- 
ant spawning habitat. We investigated 
occurrence and reproductive output of 
spawning blue crab in offshore waters 
of the northwestern Gulf of Mexico, 
and results indicate that these waters 
may be an important spawning area 
for this species. Densities of blue crab 
were low offshore compared with those 
in estuaries, but given the large extent 
of available offshore habitat, the total 
abundance of adult females is likely 
similar in offshore and estuarine 
waters. Analyses of the reproductive 
output of females collected offshore 
indicate that they continue to spawn 
after leaving the estuaries. Fecundity 
and measures of egg quality were 
assessed and were similar to previous 
estimates for estuarine regions. Future 
management and assessment efforts 
should account for this previously 
understudied portion of the blue crab 
spawning stock. 
Manuscript submitted 6 March 2020. 
Manuscript accepted 14 October 2020. 
Fish. Bull. 118:346—358 (2020). 
Online publication date: 11 December 2020. 
doi: 10.7755/FB.118.4.4 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
é established in 1881 << 
Spencer F. Baird 
First U.S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Distribution, relative abundance, and reproductive 
output of spawning female blue crab 
(Callinectes sapidus) in offshore waters 
of the Gulf of Mexico 
Adam A. Kemberling 
M. Zachary Darnell (contact author) 
Email address for contact author: zachary.darnell@usm.edu 
Division of Coastal Sciences 
School of Ocean Science and Engineering 
The University of Southern Mississippi 
703 E. Beach Drive 
Ocean Springs, Mississippi 39564 
Fisheries management is most effective 
when the scale of management matches 
the scale of the stock (Begg et al., 1999; 
Al-Humaidhi et al., 2013). The modern 
stock concept describes units of a pop- 
ulation that can be considered homoge- 
neous (in terms of life history, responses 
to environmental fluctuations, genetic 
diversity, etc.) and can inform the scale 
of assessments and management deci- 
sions (Begg and Waldman, 1999). The 
failure to correctly identify spatial 
complexity within a stock has been 
identified as one of the main factors 
contributing to the collapse of some 
high-profile fisheries in the recent 
past (Hutchinson, 2008), and studies 
examining genetic stock structure have 
identified cases with clear mismatches 
between the genetic stock structure 
and the management of the stock as a 
singular unit (Bonanomi et al., 2015; 
Kerr et al., 2017). 
Migratory stages are common in 
marine and estuarine species (e.g., 
Forward and Tankersley, 2001; Potter 
et al., 2015; Secor, 2015). Large-scale 
seasonal or annual movements can 
complicate fisheries management 
because different life stages may 
occupy different habitats. For these 
species, understanding habitat use 
during critical life history stages (e.g., 
spawning) is particularly important 
in the context of temporal or spatial 
management actions (e.g., season and 
area closures, spawning sanctuar- 
ies, migratory corridors, and ecosys- 
tem-based management). 
Blue crab (Callinectes sapidus) sup- 
port highly valuable fisheries along the 
Atlantic and Gulf coasts of the United 
States, with landings in 2018 totaling 
over 62,000 metric tons and having a 
wholesale value of over $193 million 
(NMFS!). Following their terminal 
molt, female blue crab mate and store 
the sperm necessary for their life-long 
reproductive output (Millikin and 
Williams, 1984). After mating, female 
blue crab forage for several weeks 
(Turner et al., 2003) before begin- 
ning a seaward spawning migration 
(Aguilar et al., 2005). This migration 
ensures that females reach spawning 
grounds of sufficiently high salinity 
(>20.1; Costlow and Bookhout, 1959) 
' NMFS (National Marine Fisheries Service). 
2020. Fisheries of the United States, 2018. 
NOAA, Natl. Mar. Fish. Serv., Curr. Fish. 
Stat. 2018, 140 p. [Available from website.] 
