# One hundred fifty-seven Faroese fishers wore sleep trackers at sea and on land and life offshore split sleep into shorter fragments, pushed end-of-trip sleepiness higher and left more major reaction-time lapses before the voyage was over

> Why can a crew finish a trip feeling worn down even when a simple median reaction-time number barely moves? A 2022 study in Nature and Science of Sleep followed 157 Faroese fishers across real voyages and found a clearer answer in the...

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Byline: ARGO.net Editorial Team
Published: 2026-08-11T10:35:02+00:00
Categories: Humans, Statistics

![Black and white photo of a boat crew onboard a fishing vessel titled 'El Principe Azul.'](https://www.argo.net/wp-content/uploads/2026/08/fishing_vessel_crew.jpg)

Why can a crew finish a trip feeling worn down even when a simple median reaction-time number barely moves? A 2022 [study](https://pmc.ncbi.nlm.nih.gov/articles/PMC8899098) in **Nature and Science of Sleep** followed **157 Faroese fishers** across real voyages and found a clearer answer in the pattern around the average: sleep at sea became shorter, more broken and less efficient, while sleepiness climbed by the end of the trip and **major lapses** became more common.

The researchers did not rely on a single diary or one laboratory test. They sent crews out on **18 trips** across four vessel groups, used **wrist actigraphs** at sea and during a week on land, logged ship movement and noise and matched those records with repeated ratings on the Karolinska Sleepiness Scale plus a three-minute simple reaction-time task. A matching [PubMed record](https://pubmed.ncbi.nlm.nih.gov/35264889) confirms the publication details and the core abstract claims.

The stakes were not abstract. The paper opens with a blunt maritime safety fact: Faroese fishers have an accident rate four times higher than workers on land. Seen from that angle, the study is about far more than tired mornings. It is about what happens to attention, recovery and safe work when the same place is workplace, bunk room and moving platform for days or weeks at a time.

## How the study followed crews

The sample covered 176 invited full-time fishers and 157 agreed to take part, an 89 percent participation rate. Almost all were men, their mean age was 42 and the crews were spread across netting vessels, longliners without freezers, trawlers and longliners with freezers. Those groups mattered because they were living under different work-rest systems rather than one shared schedule.

Field studies at sea are messy in a way lab studies are not, which is one reason this one is useful. The researchers collected data aboard working vessels instead of asking crews to remember a rough trip weeks later. Their table of vessel characteristics shows longliner freezer crews on trips averaging 39 days, fresh-fish longliners near 14 days, netting vessels around 3.4 days and trawlers about 5.2 days.

The design also let the authors compare the same kinds of people in two very different conditions. On land, fishers could usually sleep in one main stretch. Offshore, rest had to fit around catches, watches, equipment, weather and the physical motion of the vessel. That contrast made it easier to see whether the problem sat mainly inside the workers or inside the shipboard routine surrounding them.

## Sea sleep was shorter and more broken

The clearest numbers come from the actigraphy table. Across all ships, fishers averaged **272.3 minutes of sleep per day** at sea, about 4 hours and 32 minutes. On land the same overall sample averaged 418.8 minutes, just under 7 hours. Their sleep was also split more often offshore, rising from 1.1 sleep periods per day on land to **1.8 sleep periods per day** at sea.

Rest quality dropped at the same time. Overall **sleep efficiency** fell from 83.3 percent on land to 65.4 percent at sea, while the sleep fragmentation index rose from 33.6 to 72.6. It also took much longer to fall asleep offshore. Mean sleep latency climbed from 1.7 minutes on land to 7.8 minutes at sea and time spent in bed without actually sleeping expanded from 85.3 minutes to 146.3 minutes.

Those figures fit older maritime sleep research rather than standing alone. A 2008 paper on [fishermen on rotating schedules](https://doi.org/10.1080/07420520802106728) also linked work timing at sea with restricted and disrupted rest. The Faroese study strengthens that picture because it used a much larger field sample and placed sea data directly beside land data from the same occupational group.

## Vessel schedules changed the picture

Offshore fatigue did not hit every crew in the same way. The most protected group in this study was the freezer longliner crew working an **8-on/8-off schedule**. They averaged 332.5 minutes of sleep per day at sea, the highest among the vessel types and they also had the longest continuous sleep periods, the best offshore sleep efficiency at 71.7 percent and the lowest frequency of severe sleepiness scores.

Longliners without freezers had a **6-on/6-off schedule** and looked worse on several sleep measures. Their average sleep duration at sea was 278.8 minutes per day and their sleep efficiency fell to 62.8 percent, the lowest of the four groups. Trawler crews had the shortest average sleep per sleep period at 117.7 minutes, which helps explain why repeated short rest windows can still leave a person under-recovered even when sleep happens more than once per day.

Netting vessels stood out for subjective strain. Severe sleepiness, defined as Karolinska scores of 7 or higher, reached 25.5 percent on netting vessels, compared with 18.5 percent on trawlers, 16.0 percent on longliners and 12.8 percent on freezer longliners. The paper's discussion links those differences to long consecutive work periods and to the way shipboard schedules force sleep into short blocks rather than one sustained recovery period.

## Sleepiness rose before reaction time collapsed

The end-of-trip ratings showed one of the paper's most useful distinctions. Across all vessels, mean sleepiness scores rose from 3.5 at the beginning of trips to 5.8 at the end. Median reaction time for the full group did not shift much, moving from 333.0 milliseconds to 334.5 milliseconds. A reader could stop there and assume performance barely changed. The rest of the analysis points elsewhere.

The more revealing signal was in the tail of the performance distribution. For the whole sample, the number of reaction-time responses slower than 1000 milliseconds increased significantly by trip end. Longliner crews went from 0.62 major lapses to 1.23 and trawler crews went from 0.56 to 1.33. That pattern lines up with a broader sleep-loss literature showing that a tired brain can keep an acceptable average for a while and still suffer sudden failures of sustained attention. A classic [Sleep study on chronic sleep restriction](https://doi.org/10.1093/sleep/26.2.117) found the same kind of accumulating performance cost when people kept missing sleep over repeated days.

Time of day added another layer. The Faroese crews reported higher sleepiness during late evening, night and early morning, which is the part of the day when human alertness already tends to dip. Offshore schedules pile work demands on top of that natural low point. The study therefore suggests that fatigue risk at sea is less about one dramatic collapse and more about repeated periods when attention becomes less stable and mistakes become easier to make.

## What the findings can and cannot prove

The paper is strongest when it describes the lived sleep pattern offshore. It logged more than four thousand sleep periods in a natural work environment and compared sea and land conditions with objective measures. The authors also checked other environmental pressures, including noise and ship motion and their discussion points to both as contributors to weaker recuperation. A 2016 study on [noise and sleep aboard Royal Norwegian Navy vessels](https://doi.org/10.4103/1463-1741.178481) gives useful outside context for why interrupted rest at sea should be taken seriously.

The paper is weaker, by design, when it tries to isolate one single cause. Different vessel groups had different trip lengths, workloads and work-rest systems. The researchers also note normal field-study limits: some missing diary data, some lost actigraphy files and the possibility that having a researcher on board changed behavior slightly. Even so, the direction of the results is unusually consistent. Sleep offshore was shorter and more fragmented across every vessel type.

The practical lesson is clear enough without overreaching. Life at sea did not merely trim a little rest from the edges. It cut daily sleep by roughly two and a half hours, lowered efficiency, lengthened the time needed to fall asleep, raised end-of-trip sleepiness and increased the kind of long reaction-time lapses that can matter during real work. Among the schedules studied here, the freezer longliners looked most resilient, while repeated split sleep and long work stretches looked hardest on the mind.