encountered, one or two anchors are placed at the end of headlines. At exposed
sites, a mid-anchor may be needed to control movement and stretch; screw anchors
may also be used to maintain the position of the longline. Continuous seeding of
entire loops of culture rope over 200 m long—rather than 5 m lengths—is now
common and was invented in New Zealand. Harvesting has also become mechanized: one machine lifts and strips the ropes, washes, separates and packs the
mussels into bags. Longlines may be sunk to greater depths to reduce aesthetic
objections. The aquaculture area can then be shared with recreational fishing and
pleasure boats. Raft culture is similar in many respects to longline culture, except
that the raft commonly swings on a single mooring. As with longline culture, ropes
are suspended from the raft. Most harvesting is done by hand since this technique
has far less scope for mechanization, but over the last decade, mechanization also
started. Raft culture in Europe is typically found in Spain. The operations generally
are smaller in scale compared to longlining ones. However, the raft does provide a
valuable depot structure.
Mussel spat is rarely produced in hatcheries because the production cost relative
to the market value of the commercial product doesn’t justify the effort. There are
exception though along the West coast of USA and Canada (British Columbia)
where the introduced blue mussels Mytilus edulis and M. galloprovincialis are
being produced in hatcheries. Currently, the largest larval production takes place in
Nelson (New Zealand) for New Zealand green-lipped mussels, Perna canaliculus.
2.5.3.2 Oysters
Oysters can also be cultured on- and off-bottom. Off-bottom cultivation strategies
include (1) lantern nets, where oysters are placed in little bags suspended in the
water column, or (2) poche culture, where the oysters are stuffed in bags, which are
put on metal frames along the beach at low tide, and finally (3) in trays (Buck et al.
2006a). These systems are places on the seafloor or are deployed in a suspended
manner below longline or other floating carrying devices as mentioned in the
previous paragraph.
2.6 Current Status of Offshore Seaweed and Bivalve
Production and Their Potential for Multi-Use
When looking at the offshore production of extractive species in a multi-use concept, it can be concluded that most projects were conducted in Europe and some
others in Asia and the USA. In this section we provide a review on the potential and
constraints of offshore seaweed and bivalve research and production in terms of
biology, technology, and system design, as reported for different countries.
34
B.H. Buck et al.
sites, a mid-anchor may be needed to control movement and stretch; screw anchors
may also be used to maintain the position of the longline. Continuous seeding of
entire loops of culture rope over 200 m long—rather than 5 m lengths—is now
common and was invented in New Zealand. Harvesting has also become mechanized: one machine lifts and strips the ropes, washes, separates and packs the
mussels into bags. Longlines may be sunk to greater depths to reduce aesthetic
objections. The aquaculture area can then be shared with recreational fishing and
pleasure boats. Raft culture is similar in many respects to longline culture, except
that the raft commonly swings on a single mooring. As with longline culture, ropes
are suspended from the raft. Most harvesting is done by hand since this technique
has far less scope for mechanization, but over the last decade, mechanization also
started. Raft culture in Europe is typically found in Spain. The operations generally
are smaller in scale compared to longlining ones. However, the raft does provide a
valuable depot structure.
Mussel spat is rarely produced in hatcheries because the production cost relative
to the market value of the commercial product doesn’t justify the effort. There are
exception though along the West coast of USA and Canada (British Columbia)
where the introduced blue mussels Mytilus edulis and M. galloprovincialis are
being produced in hatcheries. Currently, the largest larval production takes place in
Nelson (New Zealand) for New Zealand green-lipped mussels, Perna canaliculus.
2.5.3.2 Oysters
Oysters can also be cultured on- and off-bottom. Off-bottom cultivation strategies
include (1) lantern nets, where oysters are placed in little bags suspended in the
water column, or (2) poche culture, where the oysters are stuffed in bags, which are
put on metal frames along the beach at low tide, and finally (3) in trays (Buck et al.
2006a). These systems are places on the seafloor or are deployed in a suspended
manner below longline or other floating carrying devices as mentioned in the
previous paragraph.
2.6 Current Status of Offshore Seaweed and Bivalve
Production and Their Potential for Multi-Use
When looking at the offshore production of extractive species in a multi-use concept, it can be concluded that most projects were conducted in Europe and some
others in Asia and the USA. In this section we provide a review on the potential and
constraints of offshore seaweed and bivalve research and production in terms of
biology, technology, and system design, as reported for different countries.
34
B.H. Buck et al.