43
3 Fisheries Production and Market Demand
growth of cephalopod landings could be achieved through exploitation of oceanic
resources of ommastrephid squid. Clarke (1987, 1996) estimated that sperm whales
alone could be consuming almost two orders of magnitude more cephalopods than
are presently taken by fisheries, although much of this amount would be oceanic
species, many inaccessible due to them living far from the coast and at depth and
being unpalatable to humans due to their high ammonia content.
In the European Union (EU), despite their importance in the southern European
diet, cephalopods have long been regarded as minor resource species. Under the
EU’s Common Fisheries Policy, it remains the case that there is little assessment or
regulation of cephalopod fisheries (ICES 2012).
3.2 Why are Cephalopods not Fish but Good Fishery
Resources?
While researchers working on cephalopods have tended to emphasise the differences between squid and fish, fishery biologists have pointed to parallels with, for
example, short-lived pelagic fish (e.g. Pauly 1998).
Firstly, to state the obvious, there are important differences between the various
groups of cephalopods. Although most species (excluding cuttlefish) have planktonic paralarvae, the juveniles and adults of octopus, cuttlefish and myopsid squid
are all generally benthic or demersal, and mature females lay eggs attached to the
seabed or other stationary structures (including fixed fishing gears). Octopuses are
more sedentary as adults than the other groups; both cuttlefish and myopsid squids
normally undertake ontogenetic migrations. The oegopsid squids extend into the
pelagic zone as juveniles and adults and may undertake long migrations to feeding
and spawning grounds. Their eggs are embedded in gelatinous, free-floating egg
masses.
Many of the shared characteristics of all coleoid cephalopods relate to being
‘r-selected’ or pioneer species, selected for their short life cycles with fast growth
and early breeding. Also consistent with the view that cephalopods are ‘r-selected’
is the high metabolic rate, which helps explain why both individual physiology
(metabolism, growth) and population growth parameters (juvenile survival, recruitment, migration patterns) appear to be very sensitive to environmental conditions.
This has been shown by experimental studies on juveniles which suggest that temperature conditions experienced around hatching can have profound (and sometimes unexpected) consequences for growth rate, age at maturity and final adult
size (e.g. Forsythe 1993; Forsythe et al. 2001; Wangvoralak 2011) and are backed
up by field observations (e.g. Jackson and Domeier 2003). Studies on larger squids
such as the jumbo squid Dosidicus gigas suggest that high temperatures can be also
problematic because they lead to elevated metabolic rates in water with low oxygen content, thus effectively excluding these squids from otherwise suitable habitat
(Rosa and Seibel 2008).
3 Fisheries Production and Market Demand
growth of cephalopod landings could be achieved through exploitation of oceanic
resources of ommastrephid squid. Clarke (1987, 1996) estimated that sperm whales
alone could be consuming almost two orders of magnitude more cephalopods than
are presently taken by fisheries, although much of this amount would be oceanic
species, many inaccessible due to them living far from the coast and at depth and
being unpalatable to humans due to their high ammonia content.
In the European Union (EU), despite their importance in the southern European
diet, cephalopods have long been regarded as minor resource species. Under the
EU’s Common Fisheries Policy, it remains the case that there is little assessment or
regulation of cephalopod fisheries (ICES 2012).
3.2 Why are Cephalopods not Fish but Good Fishery
Resources?
While researchers working on cephalopods have tended to emphasise the differences between squid and fish, fishery biologists have pointed to parallels with, for
example, short-lived pelagic fish (e.g. Pauly 1998).
Firstly, to state the obvious, there are important differences between the various
groups of cephalopods. Although most species (excluding cuttlefish) have planktonic paralarvae, the juveniles and adults of octopus, cuttlefish and myopsid squid
are all generally benthic or demersal, and mature females lay eggs attached to the
seabed or other stationary structures (including fixed fishing gears). Octopuses are
more sedentary as adults than the other groups; both cuttlefish and myopsid squids
normally undertake ontogenetic migrations. The oegopsid squids extend into the
pelagic zone as juveniles and adults and may undertake long migrations to feeding
and spawning grounds. Their eggs are embedded in gelatinous, free-floating egg
masses.
Many of the shared characteristics of all coleoid cephalopods relate to being
‘r-selected’ or pioneer species, selected for their short life cycles with fast growth
and early breeding. Also consistent with the view that cephalopods are ‘r-selected’
is the high metabolic rate, which helps explain why both individual physiology
(metabolism, growth) and population growth parameters (juvenile survival, recruitment, migration patterns) appear to be very sensitive to environmental conditions.
This has been shown by experimental studies on juveniles which suggest that temperature conditions experienced around hatching can have profound (and sometimes unexpected) consequences for growth rate, age at maturity and final adult
size (e.g. Forsythe 1993; Forsythe et al. 2001; Wangvoralak 2011) and are backed
up by field observations (e.g. Jackson and Domeier 2003). Studies on larger squids
such as the jumbo squid Dosidicus gigas suggest that high temperatures can be also
problematic because they lead to elevated metabolic rates in water with low oxygen content, thus effectively excluding these squids from otherwise suitable habitat
(Rosa and Seibel 2008).