SEPA's Sea Lice Regulatory Framework

Annex D: an example of fragmentation and ambiguity in the Sea Lice Regulatory Framework documentation

242. The set of documents released through the consultation process for managing sea lice interactions provides an example of the challenge in regulatory transparency: the absence of a single, definitive reference source, resulting in potential ambiguity in a clear understanding of the SLRF.

243. To highlight one example of determining the final and definitive final value used, a single parameter description of the sea lice exposure threshold is given here, the value of which varies between consultation documents, referenced reports and papers, and the regulator’s website. Although this example is not a unique case in finding information in a dispersed set of documentation. Obtaining a definitive description of parameters and principles applied in the SLRF should be easily obtainable, described and a detailed rationale for its set value described.

244. When considering reference to the exposure threshold, within the December 2021 consultation^[88] document there are the following inclusions:

P21

“We are proposing to apply an exposure threshold of 0.7 infective-stage sea lice-days m² integrated over the upper 2m of the sea for this purpose (e.g. exposure for one day to a concentration of 0.7 infective-stage sea lice per m²; or exposure to 0.3 infective-stage sea lice per m² on the first day of migration and to 0.4 infective-stage sea lice per m² on the second day).”

“Our proposed exposure threshold is derived from scientific studies in Norway in which sea lice numbers found on salmon post-smolts held in sentinel cages were compared with the corresponding environmental concentrations of infective-stage sea lice. The sea lice concentrations were estimated from sea lice dispersion modelling. The proposed threshold of 0.7 sea lice-days m² is the exposure level up to which sea lice infection levels found on sentinel caged fish are indicative of sea areas where infestation pressure on wild salmon post-smolts is low.”

P22

“First principles, biological models have been developed by scientists in Scotland incorporating realistic estimates of sea lice swimming velocities and attachment success as well as salmon post-smolt swimming speeds. The findings of these models are consistent with a sea lice exposure of around 0.7 sea lice-days m² being capable of producing infestation levels of close to 0.1 mobile sea lice per gram of a wild salmon post-smolt”

245. When considering reference to the exposure threshold, within the May 2023 consultation document^[89] there are the following inclusions:

P24

“ For example, 1 day exposed to a concentration of 0.75 lice per m² or 2 days exposed to a concentration of 0.375 lice per m² would be produce exposures at the exposure threshold, which is 0.75 sea lice per m² days.”

“Based on the review, we are satisfied that the proposed threshold of 0.75 infective-stage sea lice per m² days is suitable for assessing whether a significant impact on salmon post-smolts is likely.”

P27

“This capacity can be represented in terms of how far the 95th percentile of exposures is from the exposure threshold (0.75 infective-stage sea lice per m² days).”

P42

“Apply a sea lice exposure threshold of 0.75 lice per m² days.”

P103

“The proposed sea lice exposure threshold (0.75 infective-stage sea lice per m² days) is based on the findings of two different research approaches; one led by Norwegian scientists and the other led by Scottish scientists. “

P104

“The latest Scottish and Norwegian research suggest that the threshold is less than 0.8 infective-stage sea lice per m². When we consulted in 2021, we proposed a sea lice exposure threshold of 0.7 lice per m² days. In this consultation, we are proposing to express the exposure threshold to 2 decimal places as 0.75 infective-stage sea lice per m² days. The evidence from all studies suggests that exposures higher than this are likely to result in significant impact.

The proposed threshold will be exceeded at any value greater than 0.75. However, it would not be exceeded at values within 50 hundredths of 0.7 infective-stage sea lice per m² days.”

P106

“The results for Spring 2021 indicate that up to around 20 % of the virtual post-smolts accumulated exposures greater than the sea lice exposure threshold (0.75 lice per m² days)”

246. Two years later in the December 2023 Response^[90] to the consultation reference to the exposure parameter value is included:

P26

“….Fisheries Management Scotland:

We do not have the capacity to fully assess the screening models in detail, but we understand the basis behind them and support their use until such time as refined modelling is available for all WSPZs on a consistent, agreed basis”. “We seek clarification from SEPA that the proposed threshold of 0.75 infective-stage sea lice per m² days is suitably protective of wild fish”.

P27

“For assessing risk, the 95th percentile of modelled exposures of the relevant population of virtual salmon post-smolts will be rounded to one decimal place and compared with the infective stage sea lice exposure threshold of 0.7 infective-stage sea lice per m² days.”

247. There is no reference to the exposure threshold value in the December 2023 Implications assessment^[91], nor in the September 2024 Performance Standard relating to Sea lice surveillance^[92], 2025 SLRF Overview^[93] , and 2025 Position statement^[94]

248. This 0.75 or 0.7 sea lice per m² day illustrates the challenge of determining the documented processes applied to the SLRF.

249. The first consultation references 0.7 (as well as 0.3 and 0.4 for different temporal exposures), whilst the second consultation document acknowledges the 2021 documented value and proposes to define the threshold based on scientific modelling as 0.75. This figure represents the empirical foundation, it appears backed up with scientific reference, that this is the determined stipulated threshold.

250. Given that FMS also refer to the threshold as 0.75 in their consultation response which SEPA include in their response document, this ambiguity is picked up by other readers.

251. The SEPA response document in 2023 re-introduces the figure of 0.7, stating that the modelled exposure will be "rounded to one decimal place and compared with the infective stage sea lice exposure threshold of 0.7..." There is no discussion or reference to 0.7 elsewhere in the 2023 consultation (other than reference to modification compared to the 2021 consultation).

252. A confusing situation is created by embedding an act of rounding, which changes the regulatory threshold, within a sentence in a response document (and then an absence of a statement in the more recent publications). The new, final, administrative threshold should be declared in a dedicated, prominent section of a description of the SLRF. A regulated industry or concerned stakeholder must sift through multiple documents to deduce that the scientific basis for components of the SLRF, in this case that the threshold is 0.75, but the regulatory comparison is made against 0.7.

Other Changes Indicating Fragmentation

253. There are two other instances where information evolves across different documents, reinforcing the need for consolidation:

254. The consultation process involved detailed discussions on which specific models (Screening vs. Refined) would be required for new or expanding salmon farms. The criteria and triggers for moving from the simpler screening model to a more complex, costly refined model evolved between the early proposals and the final response.

255. The status and relative risk characterisation of Wild Salmon Protection Zones (WSPZs) were subject to refinement. While the framework is inherently adaptive, the process of documenting the final, ratified boundaries and risk classifications often requires cross-referencing maps and tables across several PDFs to establish the current operating criteria. This deficiency has been amended with a publication in September 2025 (after this review was commissioned and commenced).

256. A core weakness in the documentation process is the reliance on a collection of documents such as "consultation proposals," "responses," and "implications assessments." Without a final, consolidated Regulatory Rulebook or Technical Guidance Document that supersedes all previous drafts and explicitly states the final methodology, assessment and implementation requirements, stakeholders can be left trying to assemble the currently operative framework from a complex regulatory development history.

257. Whilst the consultation process demonstrates a commitment to transparency, a consolidated final document outlining the processes of the SLRF is essential for effective regulation and its communication.