Analysis · AIS data up to 12 Sep 2026

Wellboats and the spread of disease

Name: Wellboats and the spread of disease
Creator: The Salmon Ledger
License: https://creativecommons.org/licenses/by/4.0/

Wellboats move fish and water between farms. We have linked AIS tracks from the Norwegian Coastal Administration with disease cases from the Food Safety Authority to see how often an ISA or PD outbreak was preceded by a visit from a boat that had recently been at a farm with the same disease, compared with ordinary farm-weeks.

Get alerts Read the methodology

106ISA and PD outbreaks in the period (35 ISA, 71 PD)Norwegian Food Safety Authority · 29 Dec 2024–10 Sep 2026
60 of 106Had wellboat visits up to 28 days beforeComputed by The Salmon Ledger · AIS to 12 Sep 2026
14 of 106Were visited by a boat recently at a farm with the same diseaseWithin 14 days before the visit · The Salmon Ledger
37Vessels that visited up to 28 days before these outbreaksCoastal Administration (AIS) · 01 Oct 2026
unknownDisinfection between visitsNot publicly recorded

Did boats from infected sites come more often before an outbreak?

The dot shows the share, the line the 95% confidence interval. Dashed line: the share in ordinary farm-weeks for the same disease. Overlapping intervals mean the difference may be down to chance.

ISA: share with a visit from a farm with ISA in the 28 days before

Show as table

Group	Share	95% CI, lower	95% CI, upper
ISA outbreaks2 of 35	5.7%	1.6%	18.6%
Ordinary farm-weeks623 of 51,442	1.2%	1.1%	1.3%
Ordinary farm-weeks (ISA)	1.2%	–	–

ISA: 2 of 35 outbreaks (5.7%, 95% CI 1.6%–18.6%) had such a visit in the 28 days before, against 1.2% of ordinary farm-weeks (1.1%–1.3%). That is 4.7 times as common, but the interval for the outbreaks is wide.

PD: share with a visit from a farm with PD in the 28 days before

Show as table

Group	Share	95% CI, lower	95% CI, upper
PD outbreaks12 of 71	16.9%	9.9%	27.3%
Ordinary farm-weeks3,039 of 49,526	6.1%	5.9%	6.4%
Ordinary farm-weeks (PD)	6.1%	–	–

PD: 12 of 71 outbreaks (16.9%, 95% CI 9.9%–27.3%) had such a visit in the 28 days before, against 6.1% of ordinary farm-weeks (5.9%–6.4%). That is 2.8 times as common, but the interval for the outbreaks is wide.

Period 29 Dec 2024–10 Sep 2026 · Sources: Coastal Administration (AIS), Food Safety Authority (cases, and zones via BarentsWatch) · Grey hatching: too few outbreaks to estimate a share (under 5) · Wilson interval

Vessels and visits

Recorded farm visits in 2025, sorted by number. "After infected site": visits where the boat had, in the previous 14 days, been at another farm with active ISA or PD or in a protection zone, and the farm itself was not infected. A visit is not proof of infection.

Vessels and visits
Vessel	Visits 2025	Farms	After infected site	Share of visits	2026 to date
Steinar Olaisen 79.8 m	438	61	24	5%	291
Ronja Explorer 70.0 m	376	30	35	9%	343
Ronja Princess 77.0 m	343	49	81	24%	144
Rostein 43.9 m	334	85	169	51%	289
Faeroeysund 77.0 m	321	60	0	0%	280
Grotanger 77.0 m	320	55	0	0%	259
Kristoffer Tronds 90.7 m	319	24	40	13%	251
Froy Odin 85.4 m	312	50	72	23%	290
Robris 46.5 m	305	52	90	30%	164
Ro Sailor 78.8 m	305	78	42	14%	152
Ro Senja 84.2 m	302	58	26	9%	296
Ro Fjord 72.2 m	296	45	113	38%	167
Caspian 79.3 m	285	49	15	5%	214
Ro Fortune 82.1 m	278	93	16	6%	151
Seigrunn 110.0 m	276	30	82	30%	202
Bjorg Pauline 84.3 m	274	38	16	6%	246
Steigen 84.8 m	271	48	0	0%	164
Robas 46.5 m	265	64	170	64%	197
Inter Fjord 70.0 m	264	29	0	0%	333
Ronja Azul 77.0 m	264	33	0	0%	266

Show all 86 vessels

More vessels
Vessel	Visits 2025	Farms	After infected site	Share of visits	2026 to date
Ronja Ocean 79.9 m	262	39	19	7%	193
Ro Master 72.1 m	262	86	86	33%	192
Ro Vision 84.2 m	260	47	8	3%	152
Ro Server 82.1 m	260	65	169	65%	145
Ronja Vest 87.1 m	258	31	0	0%	178
Ro Venture 84.2 m	257	82	28	11%	183
Ronja Heroy 92.7 m	255	44	0	0%	162
Ronja Naeroeysund 87.1 m	254	36	0	0%	196
Ronja Queen 77.0 m	252	39	0	0%	226
Namsos 84.8 m	251	37	38	15%	200
Ro Arctic 75.5 m	247	97	11	4%	174
Ronja Ode 41.0 m	247	6	0	0%	120
Hordagut 88.9 m	245	55	116	47%	130
Ro North 82.1 m	244	54	0	0%	212
Ro West 82.1 m	243	40	18	7%	152
Seihav 78.8 m	242	29	103	43%	185
Ronja Maloy 83.6 m	242	30	0	0%	150
Harald Martin 84.3 m	239	32	28	12%	22
Horda Pioneer 77.0 m	233	65	117	50%	145
Veidnes 112.1 m	231	40	0	0%	252
Aasvaerfjord 84.8 m	231	49	60	26%	221
Ronja Skilsoy 84.4 m	231	29	8	3%	44
Freyja 84.6 m	226	39	39	17%	151
Ro Fjell 87.5 m	225	56	28	12%	180
Ro Spirit 79.3 m	222	74	0	0%	102
Langsund 43.9 m	221	87	91	41%	119
Reisa 84.8 m	215	32	13	6%	191
Skrova 63.9 m	214	32	0	0%	149
Ronja Havsoy 84.4 m	213	44	0	0%	190
Oddoey 32.7 m	207	27	0	0%	201
Ro Sunrise 79.3 m	203	35	0	0%	217
Froy Hovding 83.7 m	200	23	0	0%	195
Ronja Boroy 92.7 m	194	55	4	2%	151
Kristiansund 84.8 m	182	28	5	3%	157
Ronja Silver 92.5 m	176	32	0	0%	201
Doennland 62.9 m	175	52	0	0%	141
Froy Jarl 84.6 m	175	44	9	5%	125
Navoey 17.1 m · probably not a wellboat	168	38	0	0%	48
Seifjell 69.9 m	163	59	0	0%	153
Viknatrans 62.1 m	159	44	19	12%	84
Njord Kya 79.3 m	156	28	9	6%	163
Rohav 57.9 m	155	65	48	31%	192
Ronja Evolution 77.0 m	148	43	0	0%	82
Ronja Mistral 77.0 m	147	34	0	0%	95
Froy Saga 85.4 m	142	22	21	15%	130
Hauglaks 26.8 m	136	14	21	15%	163
Firda Savior 15.0 m · probably not a wellboat	126	10	30	24%	81
Tonny 47.5 m	121	70	15	12%	–
Ronja Merdoe 59.2 m	118	27	0	0%	83
Froey Viking 78.0 m	116	28	0	0%	95
Mowi Star 26.8 m	114	52	0	0%	116
Ronja Aurora 77.0 m	106	42	6	6%	108
Ronja Vita 77.0 m	102	50	0	0%	200
Ro Chief 53.3 m	100	46	2	2%	95
Firda Eir 83.7 m	92	9	13	14%	30
Tauranga 46.5 m	89	24	0	0%	73
Korsholmen 40.4 m	88	8	0	0%	45
Ronja Superior 57.1 m	82	26	41	50%	125
Smola Vag 33.0 m	66	21	0	0%	83
Krabat 15.0 m · probably not a wellboat	54	4	0	0%	70
Havoern 31.6 m	54	11	0	0%	19
Norwegian Gannet 94.0 m	43	24	6	14%	–
Neptun 14.8 m · probably not a wellboat	13	10	0	0%	15
Ronja Spirit 92.5 m	12	4	0	0%	167
Ronja Follafoss 92.5 m	–	–	–	–	51
Ronja Viking 77.0 m	–	–	–	–	14

Sources: Norwegian Coastal Administration (AIS), Food Safety Authority (disease) · visits derived by The Salmon Ledger · AIS data up to 12 Sep 2026 · updated 01 Oct 2026 · – = no recorded visits

Good to know

A visit is not proof of infection. We show when a vessel was at a farm, not what it had on board. Whether the boat was disinfected between visits is not publicly recorded and is shown as unknown. The figures show association, not cause.

What we do not adjust for: farms near other infected farms get more visits from boats working in the area, large farms get more visits, and treatment trips increase when a farm already has problems.

How we link AIS and outbreaks

How we define a visit

Vessels: Everything registered as "Fish Carrier" in the Coastal Administration's data. Includes some harvest and transport boats; boats under 25 m are flagged.
Visit: Stationary (average speed under 0.4 knots) with its centre within 500 m of the farm's registered position for at least 30 minutes (AIS).
From an infected site: The same boat was at another farm with an active ISA or PD case, or in an active protection zone, in the previous 14 days.
Exposed outbreak: The farm had such a visit (same disease) in the 28 days before the case started.

Times are approximate (about an hour). The AIS archive lags about 17 days and has occasional gaps. AIS data from 01 Jan 2024.

Recent outbreaks with visits

Date = suspicion or first notification · Food Safety Authority