As Pål Mugaas Jensen, editor of Norsk Fiskeoppdrett, explains, while the overall quantity of delousing medicines did indeed increase tenfold, in terms of weight, this does not take into account the radical difference in strength between the chemicals used for bath treatments (Azamethiphos, cypermethrin and teflubenzuron) and in-feed treatments (emamectin and deltamethrin).
“If you have a back pain and one day take a pill containing 50mg of diclofenac and the next take a pill containing 500mg paracetamol it would be wring to say that you have increased your drug use by 10 times,” he observes.
The Scottish Environment Protection Agency (SEPA) statistics show that, in 2006, the Scottish industry used 38kg of in-feed treatments (emamectin-equivalents) and approximately 1kg of deltamethrin-equivalents (only cypermethrin) for bath treatments. Meanwhile, in 2016 the industry used 56kg of in-feed and 19kg of bath treatments.
However, when the relative strengths of the treatments are taken into account it paints a very different picture of the growth in the overall use.
“You need 50 times as much the bath treatment Azamethiphos in weight as the in-feed treatment deltamethrin in order to do the same amount of delousing; and you need 120 times as much teflubenzuron as in-feed emamectin to achieve the same effect,” Pål explains.
“For example, if one year you used 1kg emamectin and 1kg of deltamethrin, and the next year used 120kg teflubenxuron and 50kg Azamethiphos, you used a total of 2kg the first year and 170kg the next. While the activists and the regular media will tell you that you have used 85 times more, in reality you have in those two years done the same amount of delousing and also exposed the wild animals to the same amount of risk,” he points out.
As a result, the data should be presented very differently, according to Pål.
“When the authorities publish statistics for use of antibiotics in humans they always use the term DDD, meaning defined daily dose. By this they acknowledge the fact that for some drugs you need say 2 grams each day, but for others you need say 10 mg for the same effect,” he argues.
Such a method is not without its difficulties, but does present a more accurate picture.
As Pål continues: “It’s not straightforward to calculate bath and in-feed treatment drugs either, but if you apply this weighting to the Scottish statistics, one comes out with 39kg used in 2006 and 75kg in 2016 – a 92% increase.
“However, when the increase in salmon production [from 133,00 to 180,000 tonnes] is taken into account, it would be more accurate we can calculate that the industry used 0.29mg of active ingredient of delousing drugs per kg of salmon in 2006 and 0.42mg/kg in 2016 – roughly 1.4 times more active ingredient of delousing medicine per kilo of salmon produced."