Capelin fish actively feed during their winter spawning migration north of Iceland, with about 62 to 64 percent of fish containing prey in their stomachs during January and February. According to Gram Research analysis, this contradicts the common assumption that spawning fish stop eating, though winter feeding intensity is lower than autumn levels. The fish primarily eat copepods and small krill, with more feeding occurring during daylight hours.
Scientists studying capelin fish north of Iceland discovered something surprising: these fish continue to eat during their winter spawning migration, even though they’re focused on reproduction. Gram Research analysis of stomach samples from 2018 and 2019 found that about 6 out of 10 fish had food in their stomachs during January and February. The fish were eating tiny ocean creatures called copepods and krill, with more feeding happening during the day than at night. While winter feeding was less intense than in autumn, the discovery challenges the common belief that spawning fish stop eating entirely.
Key Statistics
A 2026 study of 423 capelin fish stomachs collected north of Iceland in January-February 2018 and 2019 found that 64 percent and 62 percent of fish, respectively, contained prey during the winter spawning migration.
Copepods and euphausiids dominated the diet of capelin during winter spawning migration, with mean feeding intensity observed to be higher during daylight hours than at night according to the 2026 research.
Winter feeding intensity in capelin was lower than autumn values measured using the same methodology, yet feeding remained present in the majority of fish examined during spawning season.
The Quick Take
- What they studied: Whether capelin fish eat food while migrating to spawn during winter months in the cold waters north of Iceland
- Who participated: 423 capelin fish stomachs were examined during January and February surveys in 2018 and 2019 in waters north of Iceland
- Key finding: About 62 to 64 percent of the fish had food in their stomachs during winter spawning season, showing they actively feed despite being focused on reproduction
- What it means for you: This research helps scientists better understand fish behavior and energy use during breeding season, which could improve fishery management and predictions about fish populations
The Research Details
Researchers collected capelin fish during winter months (January and February) in 2018 and 2019 from waters north of Iceland. They examined the stomachs of 423 individual fish to see what they had eaten and how much food was present. They also noted whether the fish were caught during daytime or nighttime to see if feeding patterns changed throughout the day. This direct stomach examination method, called stomach content analysis, is a straightforward way to see exactly what fish are eating in their natural environment.
The researchers compared their winter findings to autumn feeding data they had collected using the same methods. This allowed them to see how feeding intensity changed between seasons. They identified the specific types of prey, focusing on copepods (tiny crustaceans) and euphausiids (small shrimp-like creatures), which are common food sources for capelin in the North Atlantic.
Understanding what fish eat during spawning season is important because scientists previously thought capelin stopped eating almost completely during winter migration. If fish are actually feeding during this time, it changes how we calculate their energy budgets and survival rates. This information helps fishery managers make better decisions about sustainable fishing and predict how fish populations will respond to environmental changes.
The study examined a substantial sample size of 423 fish stomachs across two years, which provides reliable data. The researchers used consistent methods across both years and compared seasons using the same approach, making the comparison valid. However, the study focused on a specific geographic region (north of Iceland) and specific time period (January-February), so results may not apply to capelin in other locations or seasons.
What the Results Show
In both years studied, the majority of capelin had food in their stomachs during the winter spawning migration. Specifically, 64 percent of fish examined in January-February 2018 contained prey, and 62 percent in 2019 contained prey. This consistency across two years suggests the pattern is reliable and not due to chance.
The diet consisted mainly of two types of small ocean animals: copepods (particularly Calanus species) and euphausiids (small krill-like creatures). These are nutritious, energy-rich foods that help sustain the fish during their demanding spawning migration.
The researchers also found that feeding activity varied by time of day. Fish caught during daylight hours showed higher feeding intensity compared to those caught at night, suggesting capelin feed more actively during the day. This pattern is common in many fish species that rely on sight to find food.
While winter feeding was clearly present, the intensity of feeding was noticeably lower in winter compared to autumn months. This makes biological sense because the fish are allocating significant energy to reproduction rather than growth. The fish were still eating enough to maintain themselves during the migration, but not at the high rates seen during the pre-spawning autumn period.
The prevailing scientific assumption had been that capelin minimize or stop feeding during winter spawning migration to redirect all energy toward reproduction. This study provides direct evidence that contradicts that assumption. The findings align with emerging research showing that many fish species maintain some feeding activity even during reproductive periods, though at reduced levels compared to other seasons.
The study examined fish only from waters north of Iceland during January and February, so the results may not apply to capelin populations in other geographic regions or during other winter months. The research did not measure the exact amount of energy the fish gained from feeding or how this feeding contributes to reproductive success. Additionally, the study did not examine whether feeding patterns differ based on fish size, age, or sex, which could provide more detailed insights into capelin biology.
The Bottom Line
Based on this research, fishery managers should revise models of capelin energy use to account for winter feeding activity. The evidence is strong (consistent across two years with a large sample size) that capelin feed during spawning migration, even if at reduced intensity. This finding should be incorporated into population management strategies and ecosystem models.
Fishery scientists and managers who work with capelin or similar fish species should pay attention to these findings. Researchers studying fish reproduction and energy allocation will find this relevant. Environmental agencies managing North Atlantic fisheries should consider this when making policy decisions. The general public should care because capelin is an important food source for larger commercial fish species and marine mammals.
This is observational research showing what happens naturally, not an intervention study. The findings apply immediately to how scientists should think about capelin biology, but there is no timeline for personal benefits since this is not a human health study.
Frequently Asked Questions
Do fish eat while they are spawning?
Yes, capelin fish continue eating during winter spawning migration, though at reduced levels. A 2026 study found 62 to 64 percent of spawning capelin contained food in their stomachs, primarily copepods and krill.
What do capelin fish eat in winter?
Capelin primarily eat copepods (tiny crustaceans) and euphausiids (small krill-like creatures) during winter. These small prey provide energy for the demanding spawning migration in cold North Atlantic waters.
How does winter feeding affect fish reproduction?
Capelin maintain some feeding during spawning to sustain energy levels, though they allocate most resources to reproduction. This balance allows them to complete spawning migration while staying nourished, though feeding intensity is lower than in autumn.
Do fish feed more at certain times of day during spawning?
Research shows capelin feed more intensively during daylight hours than at night during spawning season. This suggests they rely on sight to locate food, even while focused on reproduction.
Want to Apply This Research?
- Track seasonal feeding patterns of local fish species in your area by recording stomach content observations if you fish or participate in citizen science programs. Note the percentage of fish with food present and the types of prey found during different seasons.
- If you’re interested in sustainable fishing, use this research to understand that fish may need to feed during spawning seasons. Support fishing regulations that allow fish adequate access to food during migration periods, and choose seafood from fisheries that account for seasonal fish behavior.
- Follow updates from fishery research organizations about how capelin and similar species are managed. Monitor whether fishing regulations in your region incorporate findings about winter feeding behavior. Track population health indicators for capelin and species that depend on them as food.
This research describes natural fish behavior and does not apply to human health or medical conditions. The findings are specific to capelin populations north of Iceland and may not generalize to other fish species or geographic regions. This information is intended for educational purposes and to inform fishery management decisions, not to provide medical or nutritional advice for humans.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.