SARF 054
CONTAINMENT SPECIAL
The main causes of escapes
HOLES IN NETS ARE RESPONSIBLE FOR MORE FISH ESCAPES IN SCOTLAND THAN ANY OTHER IMMEDIATE CAUSE: MOST OF THESE ARE CAUSED BY PREDATORS
Predator attack A
THERE ARE APPROACHES THAT CAN
HELP REDUCE ATTACKS
20
ddressing predation is a particularly difficult issue, due to the unpredictability of otter and mink in freshwater incidents and the persistent nature of seal attacks in sea water. Research during the study revealed that, while some farmers think that the threat of predation has remained constant, others con- sider that it has greatly increased, particularly from seal attacks. Predation also varies on a site-by-site basis, and with time. Nevertheless, some companies have not reported an escape incident caused by predators, including some with sites in areas of considerable predator ac- tivity, which suggests that there are approaches that may help to reduce the likelihood of an incident.
Materials
The traditional material used for cage nets is nylon, which is supplied across a range of breaking strengths and different construction
techniques. However, there appears to be little information available about whether increas- ing the net specification could help reduce the number of incidents – this would benefit from more research.
In recent years there has been interest in nets made from materials other than nylon, including high modulus polyethylene (HMPE) such as Dyneema®
by DSM Dyneema. The potential advantages of Dyneema®
– an HMPE material made are known to include increased
strength and lightness. However, it is typically considered to have less flexibility or abrasion resistance and greater financial cost compared to traditional net materials. During the study period, two companies trialled Dyneema® based nets in a study facilitated by the SSPO, although the trials had not been completed by the end of the SARF project). One company also expressed interest in the use of Dyneema® chafe panels at the waterline or base of the
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