443
12 Species Case Studies
exceeded the landed catch, even when based on a relatively conservative release
mortality rate estimate of 20%. This problem is not limited to the recreational
fi shery as during seasonal closures of the gag fi shery, gag are still present in the
commercial bycatch when other reef fi shes are targeted.
Overfi shing has the propensity to skew size and age ratios affecting reproductive
capacity of the population. It can also alter normal sex ratios, as has been clearly
seen for gag, with the percentage of males declining by over an order of magnitude
between the 1970s and 1990s in both the Gulf of Mexico and the Atlantic populations (Coleman et al. 1996 ; McGovern et al. 1998a ; Chap. 8 , Fig. 8.12). Declining
male sex ratios on spawning sites occur due to male removal as males are present on
aggregation sites year-round (Coleman et al. 2010 ). The decline in the proportion of
males may be related to more aggressive feeding by males on spawning aggregations, causing them to be caught preferentially to females (Gilmore and Jones 1992 ) .
An alternative explanation is that males are more vulnerable to capture after the
spawning season when females are dispersed and fi shermen continue to fi sh spawning sites. Evidence for this hypothesis comes from the data of Collins et al. ( 1998 )
which show that the catch of males is highest within several months after the spawning season. If the second hypothesis explains most of the loss of males, then yearround closures of the spawning sites would be necessary to ensure the historical sex
ratio in the gag population. The removal of males and presumptive (transitional)
males through fi shing could feed back to disrupt the social system responsible for
sex change, reducing the social interactions that occur during aggregations triggering the production of transitionals, the percentage of which is highest during the
post-aggregation period. The potential fi shery consequences of male loss are: (1)
reduced spawning opportunities for females, and (2) lowered fertilization rates
through sperm limitation.
The overwhelming evidence for gag stocks, and for many other species, has been
that: (1) loss of the largest reproductive individuals because they are targeted by
fi sheries and the largest fi sh tend to occur on spawning sites; (2) recruitment is now
highly variable, and (3) there has been a decline in the number of historical aggregation sites. Once sites are fi shed out, they tend not to recover or reappear. Individually,
any of these effects can have devastating repercussions on a population and they can
interact to put groupers at particularly high risk of economic extinction and raise the
spectre of becoming evolutionarily threatened.
The gag population was considered stable in 1994 (Schirripa and Goodyear
1994 ) , “experiencing overfi shing” in 1997 (Schirripa and Legault 1997 ) , then both
“overfi shed” and “experiencing overfi shing” in 2001 (Turner et al. 2001 ) when
increased discard mortality (undersize fi sh that are released, but die due to barotraumas or hooking mortality), attributed to increased size limits (particularly in the
recreational fi shery), represented 40–50% of the entire number of fi sh killed in
recent years. Despite the “overfi shed” status, landings by both commercial and recreational sectors increased sharply. The gag populations are now considered to
be “experiencing overfi shing“ and “approaching an overfi shed condition” along the
Atlantic coast of the SE US and Gulf of Mexico gag are currently ‘overfi shed’ and
‘undergoing overfi shing’ (SEDAR 2009 ) . GMFMC must develop a plan to end
12 Species Case Studies
exceeded the landed catch, even when based on a relatively conservative release
mortality rate estimate of 20%. This problem is not limited to the recreational
fi shery as during seasonal closures of the gag fi shery, gag are still present in the
commercial bycatch when other reef fi shes are targeted.
Overfi shing has the propensity to skew size and age ratios affecting reproductive
capacity of the population. It can also alter normal sex ratios, as has been clearly
seen for gag, with the percentage of males declining by over an order of magnitude
between the 1970s and 1990s in both the Gulf of Mexico and the Atlantic populations (Coleman et al. 1996 ; McGovern et al. 1998a ; Chap. 8 , Fig. 8.12). Declining
male sex ratios on spawning sites occur due to male removal as males are present on
aggregation sites year-round (Coleman et al. 2010 ). The decline in the proportion of
males may be related to more aggressive feeding by males on spawning aggregations, causing them to be caught preferentially to females (Gilmore and Jones 1992 ) .
An alternative explanation is that males are more vulnerable to capture after the
spawning season when females are dispersed and fi shermen continue to fi sh spawning sites. Evidence for this hypothesis comes from the data of Collins et al. ( 1998 )
which show that the catch of males is highest within several months after the spawning season. If the second hypothesis explains most of the loss of males, then yearround closures of the spawning sites would be necessary to ensure the historical sex
ratio in the gag population. The removal of males and presumptive (transitional)
males through fi shing could feed back to disrupt the social system responsible for
sex change, reducing the social interactions that occur during aggregations triggering the production of transitionals, the percentage of which is highest during the
post-aggregation period. The potential fi shery consequences of male loss are: (1)
reduced spawning opportunities for females, and (2) lowered fertilization rates
through sperm limitation.
The overwhelming evidence for gag stocks, and for many other species, has been
that: (1) loss of the largest reproductive individuals because they are targeted by
fi sheries and the largest fi sh tend to occur on spawning sites; (2) recruitment is now
highly variable, and (3) there has been a decline in the number of historical aggregation sites. Once sites are fi shed out, they tend not to recover or reappear. Individually,
any of these effects can have devastating repercussions on a population and they can
interact to put groupers at particularly high risk of economic extinction and raise the
spectre of becoming evolutionarily threatened.
The gag population was considered stable in 1994 (Schirripa and Goodyear
1994 ) , “experiencing overfi shing” in 1997 (Schirripa and Legault 1997 ) , then both
“overfi shed” and “experiencing overfi shing” in 2001 (Turner et al. 2001 ) when
increased discard mortality (undersize fi sh that are released, but die due to barotraumas or hooking mortality), attributed to increased size limits (particularly in the
recreational fi shery), represented 40–50% of the entire number of fi sh killed in
recent years. Despite the “overfi shed” status, landings by both commercial and recreational sectors increased sharply. The gag populations are now considered to
be “experiencing overfi shing“ and “approaching an overfi shed condition” along the
Atlantic coast of the SE US and Gulf of Mexico gag are currently ‘overfi shed’ and
‘undergoing overfi shing’ (SEDAR 2009 ) . GMFMC must develop a plan to end