438
12 Species Case Studies
MPA design would need to take into account these ontogenetic movements, the
importance of non-reproductive residential areas, spawning aggregation sites and
the migration routes to and from those sites.
Monitoring of Nassau populations and their aggregations is crucial. Where they
are monitored, continued monitoring should be required. Where Nassau grouper
populations are not monitored, monitoring plans should be initiated. Monitoring
metrics should include an assessment of total population size if possible, but aggregation size, spawning frequency, recruitment of new adults to the spawning stock,
overall harvest rates, and mortality rate estimates should be included at a minimum.
A Caribbean-wide genetic assessment should be conducted to assess overall population structure and connectivity.
Given the diffi culties of monitoring the numbers of Nassau groupers in large
spawning aggregations, especially in three dimensional balls up in the water column just prior to spawning, hydroacoustic surveys are occasionally used to document fi sh numbers. Such techniques hold great promise, but are only meaningful
where careful ground-truthing and independent evaluation (usually by divers) are
carried out concurrent with hydroacoustic work (Taylor et al. 2006 ) . Acoustic surveys that lack controls, and fail to consider the known parameters of spawning
aggregations have not yet proven reliable and may signifi cantly overestimate the
numbers of fi sh present (Ehrhardt and Deleveaux 2007 ) . Given the multi-species
nature of nearly all Nassau grouper aggregations (Whaylen et al. 2004 ) , the presence of many other (non-aggregating) reef fi shes in their normal populations, and
other unknowns, considerable caution is required in interpreting hydroacoustic
results. They cannot, at this stage of understanding, be used for assessing fi sh numbers for stock assessments.
In-water assessments, while challenging, may prove to be the most feasible and
reliable method for assessing aggregation size. Visual assessment can have broad
confi dence intervals, but may be used for tracking of trends. Various methods have
been suggested for counting fi sh numbers just prior to spawning when in a large ball
up in the water column, a particularly challenging task (Fig. 12.10b ) (Sala et al.
2001 ; Whaylen et al. 2007 ) . Mark-recapture techniques can allow for additional
estimates of population size through simple Lincoln-Peterson estimates or more
complex techniques. Acoustic telemetry (Starr et al. 2007 , Semmens et al. 2006,
2009 ) can be used to evaluate spawning aggregation visit frequency by individual
fi sh, and possibly also mortality rates. The REEF database can be used to track
general trends, through underwater visual census surveys, in Nassau grouper abundance in non-aggregation times (e.g. Stallings 2009 ) on islands where dive tourism
is popular. SAH and coworkers (unpublished data) have developed a technique to
use size distribution data from video-based laser length measurements as a means to
quantify population recovery in a protected aggregation and identify new recruitment to the adult spawning population.
Although the species can be spawned and raised in hatcheries (e.g. Watanabe
et al. 1995 ) , the use of such cultured fi sh to restore populations is currently unrealistic due to limited understanding of survival rates on release, the factors involved
in spawning aggregation formation and expense. In an experimental release of
12 Species Case Studies
MPA design would need to take into account these ontogenetic movements, the
importance of non-reproductive residential areas, spawning aggregation sites and
the migration routes to and from those sites.
Monitoring of Nassau populations and their aggregations is crucial. Where they
are monitored, continued monitoring should be required. Where Nassau grouper
populations are not monitored, monitoring plans should be initiated. Monitoring
metrics should include an assessment of total population size if possible, but aggregation size, spawning frequency, recruitment of new adults to the spawning stock,
overall harvest rates, and mortality rate estimates should be included at a minimum.
A Caribbean-wide genetic assessment should be conducted to assess overall population structure and connectivity.
Given the diffi culties of monitoring the numbers of Nassau groupers in large
spawning aggregations, especially in three dimensional balls up in the water column just prior to spawning, hydroacoustic surveys are occasionally used to document fi sh numbers. Such techniques hold great promise, but are only meaningful
where careful ground-truthing and independent evaluation (usually by divers) are
carried out concurrent with hydroacoustic work (Taylor et al. 2006 ) . Acoustic surveys that lack controls, and fail to consider the known parameters of spawning
aggregations have not yet proven reliable and may signifi cantly overestimate the
numbers of fi sh present (Ehrhardt and Deleveaux 2007 ) . Given the multi-species
nature of nearly all Nassau grouper aggregations (Whaylen et al. 2004 ) , the presence of many other (non-aggregating) reef fi shes in their normal populations, and
other unknowns, considerable caution is required in interpreting hydroacoustic
results. They cannot, at this stage of understanding, be used for assessing fi sh numbers for stock assessments.
In-water assessments, while challenging, may prove to be the most feasible and
reliable method for assessing aggregation size. Visual assessment can have broad
confi dence intervals, but may be used for tracking of trends. Various methods have
been suggested for counting fi sh numbers just prior to spawning when in a large ball
up in the water column, a particularly challenging task (Fig. 12.10b ) (Sala et al.
2001 ; Whaylen et al. 2007 ) . Mark-recapture techniques can allow for additional
estimates of population size through simple Lincoln-Peterson estimates or more
complex techniques. Acoustic telemetry (Starr et al. 2007 , Semmens et al. 2006,
2009 ) can be used to evaluate spawning aggregation visit frequency by individual
fi sh, and possibly also mortality rates. The REEF database can be used to track
general trends, through underwater visual census surveys, in Nassau grouper abundance in non-aggregation times (e.g. Stallings 2009 ) on islands where dive tourism
is popular. SAH and coworkers (unpublished data) have developed a technique to
use size distribution data from video-based laser length measurements as a means to
quantify population recovery in a protected aggregation and identify new recruitment to the adult spawning population.
Although the species can be spawned and raised in hatcheries (e.g. Watanabe
et al. 1995 ) , the use of such cultured fi sh to restore populations is currently unrealistic due to limited understanding of survival rates on release, the factors involved
in spawning aggregation formation and expense. In an experimental release of