Report of the Workshop on Age Determination of Salmon (WKADS)

A Workshop on Age Determination of Salmon (WKADS) was held in Galway, Ireland from January 18th to 20th,  2011.  The  meeting  was  chaired  by  Jonathan  White,  Ireland,  attended by 26 people from six countries representing eight laboratories, with one participant through correspondence. The objectives of the meeting were to review, assess, document and make recommendations on current methods of aging salmon Salmo salar. This primarily focused on digital scale reading, to measure age and growth, with a view to standardisation.
Recommendations included standardising digital scale reading, compilation of a digital image  reference  collection,  detailing  of  characteristics  and  reference  points,  itemising  scale marks and issues in their separation. Approaches to future sample and data collection to address questions of changing life histories and proposals for future data analyses were also made.   
The meeting began with presentations detailing reasons for scale reading and the procedures of different laboratories, a theoretical review and practical demonstrations. No‐table  variation  was  found in  the approaches  taken by  different  laboratories. The  most prevalent issues were presented and discussed in working sessions to reach consensus on how they should be addressed and the necessary steps to provide further information about them.
The  ICES  report  “No.  188  Atlantic  Salmon  Scale  Reading  Guidelines”  (Shearer,  1992)  was found to still be a primary reference point. As such its definitions were adopted, though technology has moved forward enabling greater detailing in measurements and image storage. Groups in the working session detailed:

• The procedure of digital scale reading being adopted by the Celtic Sea Trout Project was credible for reading salmon scales and should be adopted.
• A digital image reference collection was compiled to include recognised scale features and age groups.
• Scale spawning marks and erosion marks, commonly recognised as being difficult to recognise, were detailed.
• Scales from farm escapees and wild salmon were noted as being more complex  to  differentiate  between  than  in  the  past.  Informative  marks  on  scales useful in identify fish origins and were listed and supporting data should include comment on fish morphology.
• Reference  points  on  scales  that  are  important  for  accurate  calculation  of growth periods with digital apparatus were listed.
• Approaches to data analyses being used on the more detailed data sets being collated from digital scale reading were presented and discussed.
• Means of determining changes in growth and life histories from scales were addressed  and  recommendations  for  the  necessary  data  collection  to  determine these were made.
• Sampling scales from a position below the adipose fin and above the lateral line was suggested as providing better quality scales than the previously recommended (Shearer, 1992) sampling site. The impact of recommending collection from this revised position for future scale collections requires detailed consideration and study, owing to the consistency of previous collections and the potential to undermine the existing scale time‐series.