218 
Influence of soak time and fish accumulation 
on catches of reef fishes in a multispecies 
trap survey 
Email address for contact author: nate.bacheler@noaa.gov 
Abstract— Catch rates from fishery- 
independent surveys often are as- 
sumed to vary in proportion to the 
actual abundance of a population, 
but this approach assumes that 
the catchability coefficient (g) is 
constant. When fish accumulate in 
a gear, the rate at which the gear 
catches fish can decline, and, as a 
result, catch asymptotes and q de- 
clines with longer fishing times. 
We used data from long-term trap 
surveys (1990-2011) in the south- 
eastern U.S. Atlantic to determine 
whether traps saturated for 8 reef 
fish species because of the amount 
of time traps soaked or the level of 
fish accumulation (the total num- 
ber of individuals of all fish species 
caught in a trap). We used a delta- 
generalized-additive model to relate 
the catch of each species to a variety 
of predictor variables to determine 
how catch was influenced by soak 
time and fish accumulation after 
accounting for variability in catch 
due to the other predictor variables 
in the model. We found evidence of 
trap saturation for all 8 reef fish 
species examined. Traps became sat- 
urated for most species across the 
range of soak times examined, but 
trap saturation occurred for 3 fish 
species because of fish accumula- 
tion levels in the trap. Our results 
indicate that, to infer relative abun- 
dance levels from catch data, future 
studies should standardize catch or 
catch rates with nonlinear regres- 
sion models that incorporate soak 
time, fish accumulation, and any 
other predictor variable that may 
ultimately influence catch. Determi- 
nation of the exact mechanisms that 
cause trap saturation is a critical 
need for accurate stock assessment, 
and our results indicate that these 
mechanisms may vary considerably 
among species. 
Manuscript submitted 27 September 2012. 
Manuscript accepted 6 May 2013. 
Fish. Bull. 111:218-232 (2013). 
doi 10.7755/FB.111.3.2 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necesarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Nathan M. Bacheler (contact author ) 1 
Valerio Bartolino 2 ' 3 
Marcel J. M. Reichert 4 
1 Beaufort Laboratory 
Southeast Fisheries Science Center 
National Marine Fisheries Service, NOAA 
101 Pivers Island Road 
Beaufort, North Carolina 28516 
2 Swedish University of Agricultural Sciences 
Department of Aquatic Resources 
Lysekil, 45330, Sweden 
3 Department of Earth Sciences 
University of Gothenburg 
Gothenburg, 40530, Sweden 
4 Marine Resources Research Institute 
South Carolina Department of Natural Resources 
217 Fort lohnson Road 
P.O. Box 12559 
Charleston, South Carolina 29412 
Robust fishery-independent survey 
data are a critical component of mod- 
ern fisheries stock assessments (Pen- 
nington and Stromme, 1998). Catch 
rates from fishery-independent sur- 
veys often are assumed to vary in 
proportion to the actual abundance 
of a fish population and, therefore, 
provide a relative measure of an- 
nual changes in abundance that can 
be used as a tuning index in a stock 
assessment (Kimura and Somerton, 
2006). The basic assumption of this 
approach is that the catchability 
coefficient (q), or the efficiency of a 
fishery or survey gear, is constant 
over space, time, and over the range 
of environmental conditions encoun- 
tered in a survey (Hilborn and Wal- 
ters, 1992). 
It is also typically assumed that 
q is not influenced by the amount 
of time a particular fishing gear is 
fished (Hamley, 1975). When the 
rate at which a fishing gear catches 
fish declines as fish accumulate in 
it, the fishing gear becomes satu- 
rated and q declines as fishing times 
increase (Miller, 1979; Olin et al., 
2004). Therefore, catch rates tend to 
increase asymptotically rather than 
proportionally with fish abundance, 
and at high levels of abundance, 
catch rates are an insensitive indica- 
tor of change (Ricker, 1975). Numer- 
ous mechanisms have been shown to 
cause gear saturation, which can be 
broadly categorized as space limita- 
tion of gear, increased gear avoid- 
ance, interspecific competition, bait 
degradation or consumption of bait, 
or fishing gear that causes local de- 
pletion of fish (Kennedy, 1951; Rich- 
ards et al., 1983; Olin et al., 2004). 
Depending on the exact mechanism 
that causes gear saturation, the 
catch at which a fishing gear be- 
comes saturated may or may not re- 
flect actual abundance (Beverton and 
Holt, 1954). 
Although saturation in gill nets, 
longlines, and trawl nets has been 
well studied (Ragonese et al., 2001; 
Olin et al., 2004; Rodgveller et al., 
2008), there has been a paucity of 
empirical research on the presence 
of trap saturation. Traps are widely 
used, especially in sensitive habi- 
