44
G. J. Pierce and J. Portela
However, cephalopods also show some life history characteristics that may be
thought of as ‘k-selected’ and are normally associated with ‘higher’ animals such
as large fish, birds and mammals: many cephalopods, including familiar coastal
species of squid, cuttlefish and octopus lay relatively few eggs (compared to, say,
a cod: a few thousands as opposed to hundreds of thousands). Furthermore, they
show complex behaviour patterns (leading to suggestions of high intelligence, especially in octopus) and mating strategies (e.g. in loliginid squids, large males guard
the females on the spawning grounds while small ‘sneakers’ attempt to mate with
the females when the larger animals are distracted—and genetic evidence suggests
they often succeed; Hanlon and Messenger 1998; Shaw and Sauer 2004). Eggs from
a single female Loligo forbesii may be fertilized by two or more different males
(Shaw and Boyle 1997). Signal transmission in nerves is rapid (hence, squid giant
axons are used in medical research) and the squid eye appears quite similar to the
vertebrate eye in terms of general morphology. Curiously, many cephalopod species
engage in highly colourful visual displays even though most cephalopods are apparently colour blind (Hanlon and Messenger 1998; Wood and Jackson 2004). The
answer to this apparent contradiction may lie in the possession of high-resolution
polarisation vision, as found in cuttlefish by Temple et al. (2012). Octopuses even
show parental care, with the females of many species protecting their eggs (Rocha
et al. 2001).
A key aspect of their ecology is the trophic role of cephalopods. Several studies on ecosystem structure have highlighted cephalopods as keystone species (e.g.
Gasalla et al. 2010). Cephalopods are both active predators and important sources
of prey for species ranging from fish to seabirds and marine mammals. Their fast
metabolism and rapid growth result in a high ratio of production to biomass so that
the amount of energy flowing through the cephalopod component of marine ecosystems is high relative to the biomass present at any one time. It should be noted,
however, that energy flow is likely to show seasonal peaks, especially at higher
latitudes, reflecting the seasonality of cephalopod life cycles. Ommastrephid squids
such as Illex argentinus are major nutrient vectors and play a key role as transient
‘biological pumps’ linking spatially distinct marine ecosystems (Arkhipkin, 2013).
Cephalopods are a major prey source for commercially important fishes (e.g. hakes,
tunas and salmon), marine mammals and seabirds in ecosystems worldwide (Hunsicker et al. 2010). Two species of hake in the Benguela system are estimated to take
between 565,000 and 988,000 t of cephalopods annually (Punt et al. 1992; Smale
1996). Sperm whales may eat 213 to 320 million t of cephalopods per year (Clarke
1996).
What are the implications of these life cycle and ecological characteristics for
fisheries? The rapid growth rate and high productivity, coupled with relative ease of
capture, good nutritional quality and acceptable taste (at least to the southern European, southern American and Asian palates), make them attractive fishery resources. Experience in many fishing grounds seems to suggest that they are relatively
resilient stocks. Cephalopods contribute to fisheries in many marine ecosystems,
both directly as a commodity (harvest and sale of cephalopods) and through providing an ecological support service (the portion of the landings and landed value of
other species that rely on cephalopods for their production; Hunsicker et al. 2010).
G. J. Pierce and J. Portela
However, cephalopods also show some life history characteristics that may be
thought of as ‘k-selected’ and are normally associated with ‘higher’ animals such
as large fish, birds and mammals: many cephalopods, including familiar coastal
species of squid, cuttlefish and octopus lay relatively few eggs (compared to, say,
a cod: a few thousands as opposed to hundreds of thousands). Furthermore, they
show complex behaviour patterns (leading to suggestions of high intelligence, especially in octopus) and mating strategies (e.g. in loliginid squids, large males guard
the females on the spawning grounds while small ‘sneakers’ attempt to mate with
the females when the larger animals are distracted—and genetic evidence suggests
they often succeed; Hanlon and Messenger 1998; Shaw and Sauer 2004). Eggs from
a single female Loligo forbesii may be fertilized by two or more different males
(Shaw and Boyle 1997). Signal transmission in nerves is rapid (hence, squid giant
axons are used in medical research) and the squid eye appears quite similar to the
vertebrate eye in terms of general morphology. Curiously, many cephalopod species
engage in highly colourful visual displays even though most cephalopods are apparently colour blind (Hanlon and Messenger 1998; Wood and Jackson 2004). The
answer to this apparent contradiction may lie in the possession of high-resolution
polarisation vision, as found in cuttlefish by Temple et al. (2012). Octopuses even
show parental care, with the females of many species protecting their eggs (Rocha
et al. 2001).
A key aspect of their ecology is the trophic role of cephalopods. Several studies on ecosystem structure have highlighted cephalopods as keystone species (e.g.
Gasalla et al. 2010). Cephalopods are both active predators and important sources
of prey for species ranging from fish to seabirds and marine mammals. Their fast
metabolism and rapid growth result in a high ratio of production to biomass so that
the amount of energy flowing through the cephalopod component of marine ecosystems is high relative to the biomass present at any one time. It should be noted,
however, that energy flow is likely to show seasonal peaks, especially at higher
latitudes, reflecting the seasonality of cephalopod life cycles. Ommastrephid squids
such as Illex argentinus are major nutrient vectors and play a key role as transient
‘biological pumps’ linking spatially distinct marine ecosystems (Arkhipkin, 2013).
Cephalopods are a major prey source for commercially important fishes (e.g. hakes,
tunas and salmon), marine mammals and seabirds in ecosystems worldwide (Hunsicker et al. 2010). Two species of hake in the Benguela system are estimated to take
between 565,000 and 988,000 t of cephalopods annually (Punt et al. 1992; Smale
1996). Sperm whales may eat 213 to 320 million t of cephalopods per year (Clarke
1996).
What are the implications of these life cycle and ecological characteristics for
fisheries? The rapid growth rate and high productivity, coupled with relative ease of
capture, good nutritional quality and acceptable taste (at least to the southern European, southern American and Asian palates), make them attractive fishery resources. Experience in many fishing grounds seems to suggest that they are relatively
resilient stocks. Cephalopods contribute to fisheries in many marine ecosystems,
both directly as a commodity (harvest and sale of cephalopods) and through providing an ecological support service (the portion of the landings and landed value of
other species that rely on cephalopods for their production; Hunsicker et al. 2010).