Clark et al.: Underwater video surveillance of catch saturation in lobster traps 
169 
escape vents in standard traps (Nulk, 1978; Saila 
et al., 2002; Courchene and Stokesbury, 2011), 
and some of them likely remained in the vicinity 
of the traps. 
Entry and escape rates 
The rate of American lobster entries and escapes 
varied between the 2 types of traps. For stan¬ 
dard traps, lobsters entered and escaped at ap¬ 
proximately the same rates each day (Figs. 5 and 
6), resulting in an overall low catch when traps 
were hauled on day 2. In standard traps, when a 
lobster entered through the kitchen entrance, it 
would either escape through the entrance or move 
into the parlor (Fig. 2). As observed by Karnofsky 
and Price (1989), lobsters often escaped the par¬ 
lor shortly after entering it (<2 min). Similarly, 
in our study, standard traps did not saturate be¬ 
cause, once a lobster entered the trap, that same 
lobster, or one of the other lobsters already in the 
trap, left shortly thereafter. 
Ventless traps filled with lobsters at a rate of 
~7 individuals/h on day 1, but the rate of entry 
by day 2 slowed to about 12% of the rate of day 
1. Because very few lobsters escaped from the 
ventless traps, a relatively high number of lob¬ 
sters accumulated in ventless traps on day 1 and 
an average of 23 individuals (SD 7.8) remained 
in the trap until the end of the 2-d soak (Table 
1, Figs. 5-7). The mean density of lobsters dur¬ 
ing trap deployment was 0.1 individuals/m 2 (SD 
0.02). Assuming that a typical effective fishing 
area around a trap is deployed for a 24-h soak is 
2600 m 2 (Watson et ah, 2009), there would be a 
pool of 260 lobsters (0.1 individuals/m 2 x2600 m 2 ) 
that might approach or encounter a trap in day 1. 
Fewer than 260 lobsters approached the ventless 
trap in each trial of this study; therefore, it is unlikely 
that ventless traps saturated from catching all of the 
available lobsters. Our data do not support the hy¬ 
pothesis that depletion, or reduction, in the number of 
lobsters within the effective fishing area is a primary 
cause of trap saturation. 
Approximately 40-50% of the bait, determined 
by weight, remained in ventless traps after having 
soaked for 24-48 h (Clark, 2012). Interestingly, vent¬ 
less traps retained more bait by weight than standard 
traps after 48 h, possibly because lobsters repeatedly 
escaped and re-entered the standard traps to con¬ 
sume the remaining bait (Clark, 2012; Clark et al., 
2015). However, even though bait remained, the olfac¬ 
tory attractiveness of the bait likely declined after a 
24-h soak, as a result of the leaching of attractants 
(W. Watson, unpubl. data). We hypothesize that be¬ 
cause typical lobster bait releases more odorants early 
in the soak time (i.e., <24 h), the rate of entry into 
traps eventually declines and an equilibrium between 
entries and escapes is reached, leading to a plateau in 
catch level and trap saturation. 
120 
100 
80 
60 
CO 
3 40 
CO 
n 
O on 
Ventless 
Catch: 23 + 7.8 lobsters 
Half-entries 
Entries 
Escapes 
Standard 
Catch: 1.3 ± 1.5 lobsters 
. 1 
Day 1 
Day 2 
Figure 7 
Number of half-entries, entries, and escapes of American 
lobsters (Homarus americanus ) in ventless traps («=3) and 
standard traps {n= 3) during the first 3-h period on day 1 and 
day 2 of deployments off New Hampshire (Wallis Sands) dur¬ 
ing 2010-2012. Catch values represent the mean number of 
lobsters caught in ventless traps and standard traps after 
each trial, determined by cumulative number of entries and 
escapes (Table 1, Fig. 6). A half-entry is an instance when a 
lobster makes contact with the mesh funnel of a kitchen en¬ 
trance in a trap but does not fully enter the kitchen. 
Acknowledgments 
We recognize the support of the state fisheries agen¬ 
cies and the University of New Hampshire (UNH). We 
thank R. Glenn and T. Pugh from the Massachusetts 
Division of Marine Fisheries for supplying lobster 
traps, D. Shay and the late N. Carlson of the UNH Ma¬ 
rine Program for their time and field assistance, UNH 
students K. Jenks, E. Dubofsky, H. Cheng, E. Mor¬ 
rissey, A. Campbell, S. LaChance, and C. Chambers for 
their help, and 3 anonymous reviewers for their feed¬ 
back. New Hampshire Sea Grant provided funding for 
this research (R/CFR-15). 
Literature cited 
Addison, J. T. 
1995. Influence of behavioural interactions on lobster 
distribution and abundance as inferred from pot-caught 
samples. ICES Mar. Sci. Symp. 199:294-300. 
