Sleep, Sleepiness, and Fatigue on Board Faroese Fishing Vessels

Abstract

Purpose: Faroese fishers have four times more accidents than workers on land. The aim was to understand fishers' fatigue better and how their work and sleep patterns influenced their sleepiness levels and cognitive performance.

Materials and methods: A total of 157 Faroese fishers wore wrist-worn actigraphs at sea and one week on land and filled in sleep and sleepiness diaries during the trip. Furthermore, a 3-minute simple reaction time (SRT) test was completed at the beginning and end of the trip. The ship's movement and noise were also logged. The actiwatch results were analysed with mixed methods repeated measures. The sleepiness registrations and performance on the SRT-test were analysed with paired t-test. The ship movements (Pitch and roll) were divided into approximately three same-sized groups (lowest 1/3, medium 1/3, and highest 1/3) and compared against the Karolinska Sleepiness Scores (KSS ranging from 1-9) ≥7 and physical tiredness (ranging from 1-9) scores ≥7. Chi-square tests were used to determine the significance of these differences. Mean sleepiness scores at sea, and the proportion of sleepiness scores ≥7 were calculated, as well as sleepiness scores as a function of the time of day.

Results: While at sea, fishers had more split sleep, slept less, and had lower sleep efficiency than onshore. Sleepiness was higher at the end of the trip, and cognitive decline was found. The number of major lapses was higher at the end of the trip, but with no significant difference between the median reaction times.

Conclusion: The crew on-board the freezer longliner, who worked 8-8 shifts, slept the most, had the longest continuous sleep periods, the highest sleep efficiency, the lowest sleepiness levels, and the highest noise exposure during their time off.

Keywords: actigraph; fisher; fishing; shift work; tired.

Figure 1

Actigraphy recordings of one representative fisher for each vessel group, during five days at sea, or the length of the trip, if shorter than five days, and five days at home. The recordings show the fishers rest/activity cycles and was used to study sleep/wake patterns. The pink and green bars indicate the periods when he first fell asleep and woke up, as determined by the algorithm. The blue colour indicates activity in awakened state. The actigraph was worn on the non-dominant wrist and continually recorded movement.

Figure 2

Mean for all fishers and occurrence of severe sleepiness (% KKS ≥ 7) as a function of time of day.

Figure 3

Sleepiness on board all ship groups.