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Fishery Bulletin 96(3), 1998 
The condition of most reef fish stocks is unknown 
because of the large number of species in the fishery, 
a lack of fishery-effort and landings data, and the 
quantity of population dynamics data needed to do 
traditional stock assessments. The goal of this pa- 
per is to develop a technically sound quantitative 
method for multispecies management assessments. 
For this purpose, we present an integrated baseline 
assessment to reference the status of the multispecies 
fishery so that the effects of management changes 
in the FKNMS may be accurately evaluated in the 
future (U.S. Dep. Commerce, 1996). Using fishery- 
independent data, we conducted an 18-year retro- 
spective, analytical yield assessment of economically 
important Florida Keys reef fish stocks to elucidate 
the effects of fishing and to help define an effective 
fishery management strategy. 
Hypothesis 
A key to our ability to assess reef fish stocks was the 
use of “average size” (in length) of fish in the exploit- 
able phase of the population ( L ) as an indicator of 
stock status. Average size of fish was derived from 
visual survey data or headboat landings data. 
Headboats are party boats that carry more than 15 
anglers per fishing trip (Dixon and Huntsman 1 ). The 
use of L in stock assessment has deep roots in tra- 
ditional fisheries management (Beverton and Holt, 
1956, 1957; Ricker, 1975). The statistic provides a 
population level metric that integrates individual 
metabolic variables such as interdependent_growth, 
mortality, and reproductive processes. The L statis- 
tic also is an important index of fishing effects be- 
cause persistent heavy fishing reduces the average 
size of the population over time, making the stock 
younger through a process known as “juvenescence” 
which successively eliminates older, more fecund size 
classes (Ricker, 1963). This is extremely important 
in the context of stock and recruitment because the 
fecundity potential of individuals increases exponen- 
tially with size. In general, the average length of fish 
in the exploitable phase (i.e. between the size at first 
capture, L', and the maximum size, L x ) is highly corre- 
lated with average population size and thus reflects 
the rate of fishing mortality operating in the fishery. 
Theoretically, the average size of fish landed for 
any given species should be equal to the average size 
in the exploited phase of the remaining population 
1 Dixon, R. L., and G. R. Huntsman. 1992. Estimating catches 
and Fishing effort of the southeast United States headboat fleet, 
1972-1982. Beaufort Laboratory, Southeast Fisheries Science 
Center, Natl. Mar. Fish. Serv., NOAA, Beaufort, NC 28516. Draft 
report. 
just after fishing. In other words, we hypothesize that 
fishery-independent survey estimates of average 
length derived from visual data reported by divers 
should equal fishery-dependent estimates derived 
from catch data reported by headboat anglers. The 
greater the correlation between the two independent 
estimates of L , the more robust “average length” ( 
should be as an indicator of stock status subject to 
exploitation. 
Methods and materials 
Study area 
The Florida Keys coral reef ecosystem is a unique 
tropical coastal marine environment stretching about 
370 km from Key Biscayne southwest to the Dry 
Tortugas (Fig. 1). Situated parallel to the Florida 
current and Florida Bay, the coastal ecosystem en- 
compasses many varied habitats comprising fresh- 
to saltwater marshes, estuaries, lagoons, mangrove 
stands, coral islands, sea grass beds, and coral reefs. 
Florida Bay and adjacent coastal estuaries serve as 
nursery areas for spiny lobster and many juvenile 
fishes that occupy reefs as adults. The clear water 
and high diversity of reef fish in the Florida Keys 
coral reef tract provide a unique environment to as- 
sess multispecies fisheries. Here we use a “systems 
approach” to facilitate effective decision making and 
to improve fishery management performance (Ault 
and Fox, 1989; Rothschild et al., 1996). 
Reef fish surveys 
Fishery-independent visual estimates of the abun- 
dance and size distributions of multispecies reef fish 
populations were taken along the Florida Keys reef 
track continuously from 1979 to 1996 (Table 1) by 12 
highly trained and experienced divers using the sta- 
tionary visual survey method of Bohnsack and 
Bannerot (1986). This nondestructive method pro- 
vides reliable quantitative estimates of species abun- 
dance, frequency-of-occurrence, and size structure for 
the reef fish community. Divers recorded the abun- 
dance as well as the minimum, mean, and maximum 
lengths of each species seen during 5 minutes within 
randomly selected 7.5-m radius circular quadrats. 
Underwater visual estimates of reef fish size and 
abundance have frequently been made (Bellwood and 
Alcala, 1988; Harvey and Shortis, 1996); however, 
accurate and precise visual estimates of fish length 
require well-trained and experienced observers be- 
cause objects in water appear magnified and closer 
than their actual range (Bell et al., 1985; Harvey and 
