Summary
Integrin Advanced Biosystems Ltd
Mckenzie, J ; McIntyre, C
Data from the FSAS offshore and inshore monitoring programmes were examined to determine seasonal and long term trends in domoic acid levels over different spatial scales to see if there is a case for changing the sampling regimes.
Mean domoic acid concentrations in scallops from Scotland show a year on year increase. It is not clear if this represents a genuine rise in domoic acid production in the environment or is a characteristic of the slow growth and long detoxification times that are peculiar to King Scallops. Areas that were associated with low domoic acid levels at the beginning of monitoring are now showing elevated levels.
The concept of using Zones of Significant Equivalence to justify using larger box sizes was explored. Arguments can be made for treating some groupings of boxes as equivalent in terms of the regulatory state that scallops will be in at any time either in terms of whole animal concentrations or gonad concentrations but not both at the same time.
Because of the general rise in domoic acid concentrations, there is a tendency for all scallops in Scottish waters to exceed 20 mg/kg. This means that they can be treated as a unified regulatory state with regard to whole animal concentrations and monitoring effort switched to improved definition of long term trends. Conversely, gonad concentrations are increasingly fluctuating between state 1 (< 20 mg/kg) and state 2 (> 20 mg/kg) in all areas.
Mean data from the gross data set and from other species shows that domoic acid production is confined to the months between May and November with a peak in September. Bi-modal production may be occurring in some areas with two high periods of production.
There is no evidence that domoic acid production is constant in all areas during the domoic acid season. This makes it difficult to predict in which areas domoic acid will rise each month except at very large scales. Detoxification in gonads does, however, occur relatively quickly out of season and is usually below the regulatory level in January for all areas.
Detoxification rates are approximately 30% per month but there are huge differences between boxes and between different months. This is probably largely due to intrabox variation in domoic acid levels. This makes it impossible to accurately predict what the domoic acid concentration will be in a sample from what it was in the previous sample from the same box.
It is recommended that the sampling regime be altered so as to collect better data (i.e. more duplicate samples) from fewer areas and to improve the sampling frequency in these “Monitoring Boxes”. Other resources should be switched to supporting industry in developing and improving shucking standards so that consumer protection is achieved through improved HACCP and end product testing.
Project Code: S02020
