292 
Abstract — Commercial fisheries 
that are managed with minimum 
size limits protect small fish of all 
ages and may affect size-selective 
mortality by the differential removal 
of fast growing fish. This differential 
removal may decrease the average 
size at age, maturation, or sexual 
transition of the exploited population. 
When fishery-independent data are 
not available, a comparison of life his- 
tory parameters of landed with those 
of discarded fish (by regulation) will 
indicate if differential mortality is 
occurring with the capture of young 
but large fish (fast growing pheno- 
types). Indications of this differential 
size-selective mortality would include 
the following: the discarded portion 
of the target fish would have similar 
age ranges but smaller sizes at age, 
maturation, and sexual transition 
as that of landed fish. We examined 
three species with minimum size 
limits but different exploitation his- 
tories. The known heavily exploited 
species (Rhomboplites aurorubens 
[vermilion snapper] and Pagrus 
pagrus [red porgy]) show signs of this 
differential mortality. Their landed 
catch includes many young, large 
fish, whereas discarded fish had a 
similar age range and mean ages but 
smaller sizes at age than the landed 
fish. The unknown exploited species, 
Mycteroperca phenax (scamp), showed 
no signs of differential mortality due 
to size-selective fishing. Landed catch 
consisted of old, large fish and dis- 
carded scamp had little overlap in 
age ranges, had significantly different 
mean ages, and only small differences 
in size at age when compared to com- 
parable data for landed fish. 
Manuscript submitted 25 June 2010. 
Manuscript accepted 13 April 2011. 
Fish. Bull. 109:292-304(2011). 
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. 
Comparison of life history parameters 
for landed and discarded fish captured 
off the southeastern United States 
l 
Jessica A. Stephen 1 
Patrick J. Harris 2 
Marcel J. M. Reichert 1 
I 
Email address for contact author: Jessica.Stephen@noaa.gov 
1 Marine Resources Research Institute 
South Carolina Department of Natural Resources 
217 Fort Johnson Road 
P.O. Box 12559 
Charleston, South Carolina 29412 
2 Department of Biology 
East Carolina University 
Greenville, North Carolina 27858 
Size limits are commonly used to 
manage commercial and recreational 
fisheries. Minimum size limits, which 
are relatively easy to enforce, have 
been used to restrict total harvest, 
prevent growth overfishing (where 
fish are harvested at an average size 
smaller than the size needed to pro- 
duce maximum yield per recruit), and 
allow individuals at least one spawn- 
ing event before removal from the 
fishery (Pitcher and Hart, 1982; Roth- 
schild, 1986). One widely acknowl- 
edged disadvantage of size limits is 
the mortality immediately at release 
(release mortality) for under-size fish, 
but another emerging concern is that 
size-selective fisheries drive a pheno- 
typic change in the life history traits 
of a population (Stokes and Law, 
2000; Hutchings, 2005; Williams and 
Shertzer, 2005; Swain et al., 2007). 
Observed phenotypic changes can be 
driven by genetic and environmental 
influences. If the observed phenotypic 
change is mostly influenced by envi- 
ronmental changes (e.g., fishing pres- 
sure), then the observed phenotype 
may easily be reversed by adjusting 
the environmental influence, whereas 
if the change is largely influenced by 
genetic changes, it may not be read- 
ily reversed. 1 Recent studies have 
1 Law, R. 2002. Selective fishing and 
phenotypic evolution: past, present, and 
future. ICES CM 2002/Y:ll, 9 p. 
shown that high levels of fishing pres- 
sure can create changes in size at 
age, age at maturation, and size at 
maturation (Law, 2000; Heino and 
Godp, 2002; Grift et al., 2003; Olsen 
et al., 2005; Kuparinen and Merila, 
2007; Mollet et al., 2007; Sharpe and 
Hendry, 2009). In long-lived species, 
the decrease in individual growth 
rates, caused by early maturation in 
response to size-selective mortality, 
may have a severe effect on the stock. 
High levels of fishing pressure can 
not only decrease size at maturation, I 
which results in an overall decrease 
in size at age, but because fecundity 
is correlated with size (Buckley et al., 
1991; Hutchings and Meyers, 1993; 
Kjesbu et al., 1996; Trippel et al., 
1997), high fishing pressure can also 
decrease reproductive potential of a 
population (Ratner and Lande, 2001). 
That these phenotypic shifts not only 
occur, but occur within several gen- 
erations has been documented in sev- 
eral experimental studies (Reznick et 
al., 1990; Conover and Munch, 2002; 
Conover et al., 2005; Reznick and 
Ghalambor, 2005; Walsh et al., 2006). 
Size limits are intended to pro- 
tect fished populations by allowing 
young, small fish to grow larger and 
spawn at least once before capture, 
and thereby increase long-term yield 
(Ricker, 1945; Goodyear, 1996; Cole- 
man et al., 2000). However, minimum 
size limits can increase fishing mor- 
