Stock protection: pushing the boundaries
required nets with such high strength, the project was truly revolutionary. By trialing different kinds of nets and pens Hvalpsund worked with HUON to determine the best system to keep seals and birds away from the fi sh and feed. The key to the design is the use of an extra-wide, triple-collar stanchion that has specialised outer sockets to accommodate a seal fence post and bird net pole. The seal fence post allows an outer seal fence net surrounding the entire pen to rise 2.8 metres above the surface of the water.
The idea of the extra wide pen is to maintain
a good degree of separation between the outer seal fence and the inner containment net. The outer seal fence net is made using 125mm black knotted Dyneema®
with a breaking strength
of over 1200 kg. It is also fi tted with strong Dyneema®
vertical ropes from which the sinker
ring is suspended – by hanging the heavy sinker rings directly from the seal net it is kept as tight as possible all the time, which makes it more diffi cult for the seals to push the net or bite it.
SAFETY
The inner containment net is made with light yet strong Dyneema®
which ensures good water fl ow through the
No other salmon farm in the world had required nets of such high strength
pen and reduces fouling. As the outer seal net is perma- nently in place, the pen is kept as a safe work environ- ment where daily operations or net changes can be done without the risk of seals attacking stock or personnel. The wide clearance between the outer seal net and inner containment net means that the nets can be cleaned us- ing in situ net washers. The system also includes an ultra- light bird net that is suspended high above the surface by light, fl exible poles. The specially-designed, injection-moulded HDPE stan- chions can be fi tted with walkway plates either between the inner collars or both collars. This design provides a safe working space for doing daily operations on the pens, even in bad weather. The advantage of using a pen made with only HDPE is that it requires far less mainte- nance than pens with steel components. HUON is also now investigating the potential for the pen stanchions to be constructed with injection-moulded nylon which, if successful, will make the stanchion even stronger. The original trial has proved to be so successful that HUON has now decided to replace all their existing pens with the new system. However, the real benefi t will not come into play until all the pens at the site are replaced – as long as some of the pens with the old design are still in use the seals will target these. FF
www.fishfarmer-magazine.com
Top: HDPE pens need little maintenance Above: Hvalpsund suggested using Dyneema nets
45
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68