26
such as a sheltering home (Cigliano 1993). This lack of defence is accompanied by
frequent moves from one to another small home range (Mather and O’Dor 1991).
The exception may be Abdopus aculeatus (Huffard et al. 2008) which is known
to gather at high densities in sea grass beds during reproduction. However, it is
not known whether the animals are permanent or temporary occupants of these
restricted areas. In the laboratory, octopuses may maintain dominance hierarchies
based on size (Mather 1980). Cigliano’s (1993) observations that with time, interactions may decrease, suggest recognition of this hierarchy. Tricario et al. (2011)
have demonstrated the possibility of familiarity in O� vulgaris, but the flaws in the
statistical analyses make it difficult to confirm.
The general lack of sociality in cephalopods may be one factor contributing to
the frequency of cannibalism in the group. In their review of 34 species, Ibáñez
and Keyl (2009) report cannibalism was common in 59 % of species reported and
high in 24 %. The combination of little sociality with short lifespan, semelparous
reproduction, and high metabolic rate may favour cannibalism. In the wild, it may
contribute to population limitation, although for culture in the laboratory it is a
major problem. In I� illecebrosus squid, cannibalism is found during high densities
(O’Dor and Dawe 1998), and this is also true for O� briareus (Aronson 1983). It
may be a response to a limited food supply, as in squid during migration (O’Dor
and Dawe 1998), and some reports of cannibalism may be distorted due to stress
during capture in fisheries. It is also size based, and where males and females are
dimorphic in size, the larger sex may consume the smaller one.
Regardless of circumstances, cannibalism is a major problem for anyone keeping
cephalopods in captivity. By definition, culturing animals means keeping them at
high densities, which not only is stressful for them (Boal et al. 1999) but also creates
a situation for consumption of animals by each other. To some extent, cannibalism
can be avoided by keeping animals of the same size together, and since cannibalism
is also partly dependent on food supply, it is useful to have a good supply of preferred food—which may be expensive and hard to procure (see discussion of food
and feeding). Giving cephalopods a complex environment in captivity may maximize their ability to escape from conspecifics who would consume them, as well as
increasing their growth and learning capacity (Dickel et al. 2000). Yet enrichment
(Anderson and Wood 2001; Mather in press) is only a partial solution to the expression of normal behaviour in an unnatural environment.
2.5 Reproduction and Lifespan
2.5.1 Life History
Shallow-water coleoid cephalopods grow rapidly, mature at an early age, and are
typically semelparous (but see below), dying shortly after laying eggs. Most cephalopods live only for 1–2 years (Boletzky 2003b; e.g. for O� vulgaris, Katsanevakis
J. Mather and D. Scheel
such as a sheltering home (Cigliano 1993). This lack of defence is accompanied by
frequent moves from one to another small home range (Mather and O’Dor 1991).
The exception may be Abdopus aculeatus (Huffard et al. 2008) which is known
to gather at high densities in sea grass beds during reproduction. However, it is
not known whether the animals are permanent or temporary occupants of these
restricted areas. In the laboratory, octopuses may maintain dominance hierarchies
based on size (Mather 1980). Cigliano’s (1993) observations that with time, interactions may decrease, suggest recognition of this hierarchy. Tricario et al. (2011)
have demonstrated the possibility of familiarity in O� vulgaris, but the flaws in the
statistical analyses make it difficult to confirm.
The general lack of sociality in cephalopods may be one factor contributing to
the frequency of cannibalism in the group. In their review of 34 species, Ibáñez
and Keyl (2009) report cannibalism was common in 59 % of species reported and
high in 24 %. The combination of little sociality with short lifespan, semelparous
reproduction, and high metabolic rate may favour cannibalism. In the wild, it may
contribute to population limitation, although for culture in the laboratory it is a
major problem. In I� illecebrosus squid, cannibalism is found during high densities
(O’Dor and Dawe 1998), and this is also true for O� briareus (Aronson 1983). It
may be a response to a limited food supply, as in squid during migration (O’Dor
and Dawe 1998), and some reports of cannibalism may be distorted due to stress
during capture in fisheries. It is also size based, and where males and females are
dimorphic in size, the larger sex may consume the smaller one.
Regardless of circumstances, cannibalism is a major problem for anyone keeping
cephalopods in captivity. By definition, culturing animals means keeping them at
high densities, which not only is stressful for them (Boal et al. 1999) but also creates
a situation for consumption of animals by each other. To some extent, cannibalism
can be avoided by keeping animals of the same size together, and since cannibalism
is also partly dependent on food supply, it is useful to have a good supply of preferred food—which may be expensive and hard to procure (see discussion of food
and feeding). Giving cephalopods a complex environment in captivity may maximize their ability to escape from conspecifics who would consume them, as well as
increasing their growth and learning capacity (Dickel et al. 2000). Yet enrichment
(Anderson and Wood 2001; Mather in press) is only a partial solution to the expression of normal behaviour in an unnatural environment.
2.5 Reproduction and Lifespan
2.5.1 Life History
Shallow-water coleoid cephalopods grow rapidly, mature at an early age, and are
typically semelparous (but see below), dying shortly after laying eggs. Most cephalopods live only for 1–2 years (Boletzky 2003b; e.g. for O� vulgaris, Katsanevakis
J. Mather and D. Scheel