shell blue crabs, but more recently the harvests have fluctuated both here and in other regions. There have been
a number of attempts to understand the relationships
between production and environmental variables, river
discharges, wind, temperature, salinity, rainfall, and hurricane events, but few patterns have emerged (Fogarty and
Lipcius, 2007). Modelling studies by Mistiaen et al. (2003),
however, have confirmed that productivity would be negatively impacted by poor water quality, suggesting that
a decline in the oxygen content of the water to 4 mg l
À1
could lead to a 48 % decline in the harvest with the same
level of fishing effort.
Populations of the Dungeness crab S. magister, in the
Northeast Pacific, have large amplitudes with a 9–10-year
cyclic periodicity. The adults breed offshore, but, like
some other decapod crustaceans, rely upon nursery
grounds to produce the adult stocks which are captured
in other locations. Larvae of the Dungeness crabs enter
estuaries where they grow faster than their cohorts,
occupying other nearshore habitats (Armstrong et al.,
2003). These juveniles, especially those from the large
estuary zones close to the ports, are important because
mortality is low and abundances are high. There is therefore a high economic value of the estuarine zone in stabilizing coastal landings.
Found in most of the Indo-Pacific, the mud crab Scylla
serrata is a short-lived species, commonly collected for
food and more recently cultured in some countries including the Philippines. Associated with mangroves it survives
in low salinities down to 20 psu in estuaries. In subtropical
and tropical Australia, S. magister is highly sought after,
but there are size restrictions and no female crabs are taken
from Moreton Bay, allowing females to reproduce. Over
the years the commercial catch has increased (113.3 t in
2003), but there is a high recreational catch which exceeds
the commercial harvest. It is also suggested that the formation of marine reserves provides the potential for allowing
exploited species to recover from the effects of fishing
(Pillans et al., 2005). Culture techniques have been tried
using pens within mangrove areas in the Philippines and
sourced with juveniles from the natural habitat
(Trino and Rodriguez, 2002). This study found that mixed
sex monoculture in the mangroves was feasible and that
production was acceptable at stocking densities in the
range 0.5–1.5 crabs m
À2
. It was concluded that this aquaculture venture is possible without the need to remove
mangroves to build aquaculture ponds.
Echinoderm (sea cucumber) production
Following worldwide trends for shellfish production, sea
cucumbers, which belong to the class Holothuroidea, are
highly prized in Asia, where they are sold as trepan or
beche-de-mer and have a variety of food and medicinal
uses. They occur in nearshore habitats, including muddy
shores close to estuaries, sea grass beds, and rocky and
coral reefs. Sea cucumber fishing is important to the livelihoods of coastal communities, especially in developing
countries. In Japan for hundreds of years, the people of
Oki Island used loose stone piles to encourage the sea
cucumbers to aggregate, aestivate, and protect juveniles
and young (Choo, 2008). In tropical and subtropical
waters in Asia, the fisheries are multispecies, whereas in
temperate areas there may be a single species such as the
Apostichopus japonicus. Indonesia is the largest capture
fishery for holothuroids and, together with the Philippines,
comprises about 47 % of the world landings, averaging
2,572 t wet weight per annum between 2000 and 2005
(Choo, 2008). It is uncertain what proportion of this catch
is collected from estuarine regions and compared with
fish, crustaceans, and molluscs. These landings represent
only a small percentage (less than 0.25 %) of the total
landings. Many boom-and-bust sea cucumber fisheries
have occurred since the 1950s as markets rapidly
expanded, and regional assessments now suggest that
81 % of the sea cucumber stocks have declined due to
overfishing, and the average size reduced by as much as
a third. In addition the harvesters have moved from nearshore habitats to offshore habitats and into less valuable
species (Anderson et al., 2011). These fisheries are likely
to be difficult to manage because of incomplete knowledge about their life cycle, aging, and reproductive cycles.
Also, while some countries lack regulations (Indonesia
and the Philippines), other populations such as those in
Japan and Alaska are well managed (Clark et al., 2009).
In the last 20 years, there have been advances in farming
practices for sea cucumbers, especially in China, Ecuador,
Indonesia, Japan, Malaysia, and the Philippines. China is
the largest producer of sea cucumbers; farming and ranching
in the Liaoning and Shandong Provinces, landings have
exceeded 10,000 t (dry weight) per annum. Pond culture is
the preferred method of farming, sometimes employing
unused shrimp ponds containing shelters to protect the
animals (Chen, 2004). Sea ranching is a less expensive
option for some species, such as Apostichopus japonicus
the prickly sea cucumber, where the temperature, salinity
range (28–31 psu), and sufficient natural food are good.
In a sea ranch experiment, Zhang and Liu (1998) report
a mean output for this species of 273 kg (dry weight) per
hectare, at a density of 12.9 individuals m
À2
.
Management of shellfish production
For both wild populations and aquaculture, there are management techniques aimed at increasing shellfish production. For oysters on the Atlantic and Gulf coasts of North
America, the increased shelling of beds and the removal
of gastropod and starfish resulted in a 45-fold increase in
the production in Long Island Sound Connecticut in the
1990s (Dumbauld et al., 2009). Management is also
required for the oyster industry to minimize the effects
of shellfish disease and polluting effects of land runoff
and urban development. Other improvements have been
achieved through transplants, seeding, silt removal, and
reef construction to protect brood stock. Over the past
10 years, there has been increasing interest in developing
576
SHELLFISH PRODUCTION
a number of attempts to understand the relationships
between production and environmental variables, river
discharges, wind, temperature, salinity, rainfall, and hurricane events, but few patterns have emerged (Fogarty and
Lipcius, 2007). Modelling studies by Mistiaen et al. (2003),
however, have confirmed that productivity would be negatively impacted by poor water quality, suggesting that
a decline in the oxygen content of the water to 4 mg l
À1
could lead to a 48 % decline in the harvest with the same
level of fishing effort.
Populations of the Dungeness crab S. magister, in the
Northeast Pacific, have large amplitudes with a 9–10-year
cyclic periodicity. The adults breed offshore, but, like
some other decapod crustaceans, rely upon nursery
grounds to produce the adult stocks which are captured
in other locations. Larvae of the Dungeness crabs enter
estuaries where they grow faster than their cohorts,
occupying other nearshore habitats (Armstrong et al.,
2003). These juveniles, especially those from the large
estuary zones close to the ports, are important because
mortality is low and abundances are high. There is therefore a high economic value of the estuarine zone in stabilizing coastal landings.
Found in most of the Indo-Pacific, the mud crab Scylla
serrata is a short-lived species, commonly collected for
food and more recently cultured in some countries including the Philippines. Associated with mangroves it survives
in low salinities down to 20 psu in estuaries. In subtropical
and tropical Australia, S. magister is highly sought after,
but there are size restrictions and no female crabs are taken
from Moreton Bay, allowing females to reproduce. Over
the years the commercial catch has increased (113.3 t in
2003), but there is a high recreational catch which exceeds
the commercial harvest. It is also suggested that the formation of marine reserves provides the potential for allowing
exploited species to recover from the effects of fishing
(Pillans et al., 2005). Culture techniques have been tried
using pens within mangrove areas in the Philippines and
sourced with juveniles from the natural habitat
(Trino and Rodriguez, 2002). This study found that mixed
sex monoculture in the mangroves was feasible and that
production was acceptable at stocking densities in the
range 0.5–1.5 crabs m
À2
. It was concluded that this aquaculture venture is possible without the need to remove
mangroves to build aquaculture ponds.
Echinoderm (sea cucumber) production
Following worldwide trends for shellfish production, sea
cucumbers, which belong to the class Holothuroidea, are
highly prized in Asia, where they are sold as trepan or
beche-de-mer and have a variety of food and medicinal
uses. They occur in nearshore habitats, including muddy
shores close to estuaries, sea grass beds, and rocky and
coral reefs. Sea cucumber fishing is important to the livelihoods of coastal communities, especially in developing
countries. In Japan for hundreds of years, the people of
Oki Island used loose stone piles to encourage the sea
cucumbers to aggregate, aestivate, and protect juveniles
and young (Choo, 2008). In tropical and subtropical
waters in Asia, the fisheries are multispecies, whereas in
temperate areas there may be a single species such as the
Apostichopus japonicus. Indonesia is the largest capture
fishery for holothuroids and, together with the Philippines,
comprises about 47 % of the world landings, averaging
2,572 t wet weight per annum between 2000 and 2005
(Choo, 2008). It is uncertain what proportion of this catch
is collected from estuarine regions and compared with
fish, crustaceans, and molluscs. These landings represent
only a small percentage (less than 0.25 %) of the total
landings. Many boom-and-bust sea cucumber fisheries
have occurred since the 1950s as markets rapidly
expanded, and regional assessments now suggest that
81 % of the sea cucumber stocks have declined due to
overfishing, and the average size reduced by as much as
a third. In addition the harvesters have moved from nearshore habitats to offshore habitats and into less valuable
species (Anderson et al., 2011). These fisheries are likely
to be difficult to manage because of incomplete knowledge about their life cycle, aging, and reproductive cycles.
Also, while some countries lack regulations (Indonesia
and the Philippines), other populations such as those in
Japan and Alaska are well managed (Clark et al., 2009).
In the last 20 years, there have been advances in farming
practices for sea cucumbers, especially in China, Ecuador,
Indonesia, Japan, Malaysia, and the Philippines. China is
the largest producer of sea cucumbers; farming and ranching
in the Liaoning and Shandong Provinces, landings have
exceeded 10,000 t (dry weight) per annum. Pond culture is
the preferred method of farming, sometimes employing
unused shrimp ponds containing shelters to protect the
animals (Chen, 2004). Sea ranching is a less expensive
option for some species, such as Apostichopus japonicus
the prickly sea cucumber, where the temperature, salinity
range (28–31 psu), and sufficient natural food are good.
In a sea ranch experiment, Zhang and Liu (1998) report
a mean output for this species of 273 kg (dry weight) per
hectare, at a density of 12.9 individuals m
À2
.
Management of shellfish production
For both wild populations and aquaculture, there are management techniques aimed at increasing shellfish production. For oysters on the Atlantic and Gulf coasts of North
America, the increased shelling of beds and the removal
of gastropod and starfish resulted in a 45-fold increase in
the production in Long Island Sound Connecticut in the
1990s (Dumbauld et al., 2009). Management is also
required for the oyster industry to minimize the effects
of shellfish disease and polluting effects of land runoff
and urban development. Other improvements have been
achieved through transplants, seeding, silt removal, and
reef construction to protect brood stock. Over the past
10 years, there has been increasing interest in developing
576
SHELLFISH PRODUCTION