168 
Fishery Bulletin 11 6(2) 
Ventless 
° Accumulated entries 
° Accumulated escapes 
■ Catch 
Day 1 Day 2 
Figure 6 
Rates at which entries, escapes, and catch of American lob¬ 
sters (Homarus americanus > accumulated in ventless traps 
(n=3) and standard traps (n=3) over the first 3-h period on 
day 1 and day 2 of deployments off New Hampshire (Wallis 
Sands) during 2010-2012. Rates were calculated by using the 
slopes of the regression lines fitted to each segment of data 
points. 
Agonistic encounters 
Behavioral interactions between American lobsters and 
their conspecifics in proximity of the traps are closely 
linked to a reduction in overall trap catch (Richards 
et al., 1983; Miller, 1990; Frusher and Hoenig, 2001; 
Barber and Cobb, 2009). Similar interactions were ob¬ 
served in our study. Many experiments have confirmed 
that American lobsters are aggressive in their inter- 
and intraspecific interactions (Tamm and Cobb, 1978; 
Rutishauser et al., 2004; Steneck, 2006; Williams et 
al., 2006; Williams et al., 2009); therefore, agonistic 
behavior is common among American lobsters congre¬ 
gating in and near lobster traps (Jury et al., 2001), 
as is the case with other decapods, including the rock 
lobster (Jasus edwardsii ; Ihde et al., 2006), and the gi¬ 
ant mud crab {Scylla serrata; Robertson, 1989), and the 
European green crab (Carcinus maenas ; Bergshoeff et 
al., 2018). In all of these studies, agonistic encounters 
contributed to reduced trap entry, a factor believed to 
cause trap saturation (Miller, 1979). 
“Prestocking” traps with lobsters is one way to de¬ 
termine whether lobsters inside traps reduce catch of 
their conspecifics. Richards et al. (1983) showed that 
prestocking traps inhibits the catch of additional lob¬ 
sters and some crab species (e.g., Cancer spp.). 
A more recent study has provided evidence that 
prestocking reduces the rate of entry, but it does 
not reduce the total catch in standard traps if the 
total catch includes the stocked lobsters (Watson 
and Jury, 2013). However, it should also be noted 
that, in general, traps in most of the previous 
studies were stocked with adult, legal-size lob¬ 
sters, but in this study, many of the lobsters ob¬ 
served in and around the traps were of sublegal 
size. Interestingly, in our study, interactions with 
lobsters inside the traps did not appear to be the 
dominant cause of half-entries. Rather, distur¬ 
bance by lobsters outside of the traps accounted 
for almost 30% of half-entries for each trap type. 
When the lobsters approached the traps, other 
encroaching lobsters outside of the traps often 
deterred their conspecifics from entering by lung¬ 
ing at them or chasing them away from the trap 
entrances. This type of behavior was observed 
around both standard and ventless traps and lim¬ 
ited the frequency of successful entries into each 
trap type. Even when there were lobsters inside 
the kitchen, entry rates were influenced more by 
interactions outside of the traps and, therefore, 
by the density of lobsters around the traps. 
Most lobsters in ventless traps accumulated in 
the parlor area of traps, rather than the kitchen, 
and it is unlikely that they directly influenced 
subsequent trap entries unless there were other 
deterrent cues provided by trapped lobsters (e.g., 
olfactory cues, auditory cues). Importantly, with 
regard to the mechanisms that lead to catch lev¬ 
eling off at some value, there were fewer half¬ 
entries on day 2, for both trap types, than on day 
1 (Fig. 7); therefore, agonistic interactions between 
lobsters inside and outside of the traps may have con¬ 
tributed to the reduction in trap entries, as observed 
in previous studies, but they were likely not the reason 
entries and catch leveled off on day 2. 
The decline in lobsters outside of the ventless traps 
on day 1 was negatively correlated with the number 
of lobsters inside the traps. However, because the lob¬ 
sters were not tagged, it was not possible to track the 
movement of individuals; therefore, we cannot conclude 
that lobsters in the surrounding field of view at the 
point of trap deployment were, in fact, the same lob¬ 
sters that were caught later in the trial. Nonetheless, 
the relationship between increasing catch by ventless 
traps and decreasing number of surrounding lobsters 
(observed) indicates that these lobsters are partially 
removed from the fishable area of the trap. On the 
other hand, the number of lobsters that surrounded 
standard traps did not significantly differ between day 
1 and day 2. This difference between trap types may 
have been a result of the size-frequency distribution of 
lobsters in this area—a distribution over which most 
of the lobsters (>99%) were below legal size (as deter¬ 
mined by using data from dive surveys). Because of 
their size, many lobsters were able to exit through the 
