406 
Fishery Bulletin 96(3), 1998 
c 
Yellowtail snapper 
— i — • — i — i — 1 — i — i — i — i — 1 — 
“ t 1 1 1 1 1 1 1 1 1 1 1 h— 
u t — i— i — i — i — i — i — i — i — i— i — i — i — i i i — i — i — i — i — i — i — i — i— 
1975 1980 1985 1990 1995 2000 
Figure 4 
Average length (cm) in the exploitable phase of the stock estimated from headboat (•) and visual survey (0) data for several reef 
fish stocks during the period 1979 to 1996: (A) red grouper, (B) black grouper, (C) yellowtail snapper, (D) gray snapper, (E) white 
grunt, (F) bluestriped grunt, (G) hogfish, and (H) great barracuda. Bars around visual survey estimates are 95% confidence intervals 
of the mean. Horizontal dotted lines show the minimum size at first capture L' regulated by regional fishery management. 
two decades. Total fishing effort has increased sub- 
stantially because of greater average fishing power 
per vessel and a much larger recreational fishery. 
Mace (1997) estimated that the average “fishing 
power” per vessel (i.e. the average proportion of the 
stock removed per unit of fishing effort) has increased 
4-fold over the previous 25 years mainly because of 
improved technology involving better vessel designs, 
hydroacoustics, hydraulics, and navigation (GPS, 
Loran C, charts). The arithmetic increase of recre- 
ational fishing vessels is an important factor also, 
although its absolute effect on reef fish stocks is un- 
known because the recreational fleet is distributed 
diffusely and heterogeneously and has not been well 
sampled to date. 
Stock assessment indicator variable 
The estimated average lengths (size) of reef fish in 
the exploitable phase, determined from statistically 
independent visual and headboat data, were highly 
comparable for groupers, snappers, and grunts, sup- 
porting their use in the multispecies assessment. 
Average sizes of hogfish and barracuda, however, 
differed between the two data sets. The larger aver- 
age hogfish size in headboat samples appears to be 
the result of life history patterns and different re- 
sponses to fishing gears with depth. Hogfish tend to 
move from shallow to deeper water with age (Davis, 
1976) and are more vulnerable to spearfishing than 
hook-and-line gear. Divers, however, are effectively 
