Watson et al.: Experimental analyses of the mechanisms leading to lobster ventless trap saturation 
217 
<20% of its initial concentration of potential attractants. 
In the field, the decrease in attractiveness would likely be 
even greater because feeding on the bait would reduce its 
quantity and increase the rate of leaching. These data add 
further support to the hypothesis that even though loss of 
bait attractiveness is not the only factor influencing vent¬ 
less trap saturation, it is a key factor 
leading to a decrease in the rate of lobster 
entries into a trap even after a soak of 
just 24 h. 
Time-lapse video observations of ventless 
traps For insight into the behavioral 
mechanisms underlying the effect of 
new versus old bait, time-lapse videos 
of ventless traps (n=7) were obtained 
before and after the addition of fresh 
bait (Fig. 6). Data from analysis of these 
videos indicate that the entry of lobsters 
typically leveled off on day 2 of a soak, 
but when fresh bait was added by div¬ 
ers on day 2 there was an immediate 
increase in the entry of lobsters into the 
trap (Fig. 6). As a result, while the entry 
rate of lobsters in control traps dropped 
77% between day 1 and 2 (from 1.7 to 0.4 
entries/h), it only dropped 38%, from 1.6 
to 1.0 entries/h, for experimental traps 
with fresh bait added. 
Discussion 
Although the mechanisms underlying 
trap saturation in standard lobster 
traps have been addressed in a number 
of previous studies (Miller, 1979; Rich¬ 
ards et al., 1983; Fogarty and Addison, 
1997; Jury et al., 2001), the focus of this 
study was the testing of specific hypoth¬ 
eses concerning the potential causes of 
ventless trap saturation. Our results 
indicate that catch typically reaches a 
plateau after ~24 h for 2 main reasons: 
1) a loss of bait attractiveness, which 
leads to a decrease in the rate of entries; 
and 2) behavioral interactions between 
American lobsters, which become more 
prevalent as traps fill and cause both 
a decrease in the entry of new lobsters 
and an increase in the rate of escapes. 
These conclusions are supported by data 
showing that, if fresh bait was added, or 
lobsters in a trap were removed, catch 
was higher than in control traps, and 
if old bait was used, or lobsters were 
pre-stocked in traps, catch declined rel¬ 
ative to catch in control traps (Fig. 7). 
These same mechanisms are likely to 
come into play with standard traps as well, but the rela¬ 
tive rates of entry and escape differ, leading to different 
behavioral dynamics. 
In a previous study, Clark et al. (2015) demonstrated 
that ventless traps saturate before they reach capacity 
(i.e., they reach the maximum biomass they can hold) and 
Figure 6 
The effect of fresh bait on the entry rate of American lobsters (Homarus amer- 
icanus ) into traps deployed off New Hampshire in 2013, based on video obser¬ 
vations. The accumulated rates of entry (black squares), catch (white circles), 
and escapes (white triangles) are shown for one representative 72-h soak of 
a ventless trap. Lines that best fit the data are overlaid on each segment of 
data points. Note that on day 2 (after traps already had been fished for 24 h), 
rates of entry and catch reached a plateau. Then scuba divers added fresh 
bait to the trap (vertical line labelled Day 2 rebait ), which led to an immediate 
increase in entries and catch. Also note that, when escapes were equivalent 
to entries, catch reached a plateau. Missing data are the result of night hours 
when observations were not possible because lights were not used on traps. 
30 
25 
UJ 20 
3 
Q, 15 
° 10 
5 
0 
J 24-h soak 
L 
I l 
Control 
Old bait 
Experiment 
Pre-stock 
45 
40 
35 
LU 30 
Z> 25 
n 20 
u 15 
10 
5 
0 
48-h soak 
I I I 
Control 
Rebait 
Experiment 
Remove 
Figure 7 
Summary overview of the effects of various experiments on the catch per 
unit of effort (CPUE) of American lobsters (Homarus americanus) in vent¬ 
less traps. These data are presented in summary for comparison; there¬ 
fore, error bars have been omitted. Note that pre-stocking traps and using 
1-day-old bait reduces catch, compared with catch of control traps (24-h 
soak), and that removing the lobsters captured on day 1, or adding fresh 
bait after 24 h, led to an increase in catch. The CPUE data for the “remove 
experiment” includes the lobsters that were removed on day 1 and the new 
lobsters captured on day 2. 
