BIODIVERSITY FISHES DFO-CAPELIN BIOLOGY

Mode of reproduction

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As the spawning season approaches, capelin begin an intensive migration to the coast to spawn on sandy or fine gravel beaches or on the seabed, at depths of 30 to 280 m. When capelin spawn on beaches, this is called “rolling” or “landing.” In the Estuary and Gulf of St. Lawrence, capelin “roll” on the shores between mid-April and July, depending on the area, when water temperatures are between 6 and 10 °C. Spawning usually occurs at night.

At the start of the spawning season, male and female capelin form two separate shoals. The males move inshore first and wait for the females, which stay farther offshore until ready to spawn. When the females arrive, spawning begins. The males push on the sides of the females to expel the eggs. Using sweeping movements with their caudal fin, they deposit the fertilized eggs in the sand or gravel. The eggs are enveloped by a sticky substance, which holds them in place and protects them from tidal action and predation.

After spawning, it is not unusual to see large numbers of dead capelin on the beach or in the water, particularly males that are injured during repeated mating. ¹

The duration of the incubation period depends on the ambient water temperature. On average, it lasts two weeks. After hatching, the larvae feed on animal plankton, composed of tiny crustaceans. The juveniles will grow to a length of 2 to 4 cm before their first winter.

Capelin Spawning Habits

The Network has collected 1,713 observations since its founding. Of these, 913 observations involved spawning activity, 390 observations were of signs of capelin presence and 383 other observations did not indicate clearly whether spawning or some other type of activity was taking place. The information gathered, including the date and time of each observation, tidal conditions and the type of spawning site, is helping to reveal trends that can assist in answering questions such as:

• Do capelin spawn more frequently at night?
• Do they prefer high tide?
• What type of substrate do they prefer?

Time of Day

Capelin appear to spawn more frequently in the darkness, at least when this activity takes place along the shoreline. According to Network data, spawning is observed five times more often at night, namely between 6:00 p.m. and 6:00 a.m., than at other times of day.

Percentage of capelin spawning observations by time of day

(Number of spawning observations between 2002 and 2013 with information on the substrate type = 778)

Tides

Comparing spawning observations against tidal information reveals that capelin are 14% more likely to spawn during the rising tide than the falling tide. (Figure below).

Percentage (%) of capelin spawning observations by tidal cycle

¹ DFO: 2004. Capelin of the Estuary and Gulf of St. Lawrence (4RST) in 2003. Canadian Science Advisory Secretariat, Stock Status Report 2004/001.

Capelin Observers Network-Distribution

Capelin is a small cold-water fish of the Northern Hemisphere. It is found in the Atlantic, Pacific and Arctic oceans, from northern Europe to northern Japan, including Russia. In Canada, it occurs on both the west and east coasts. In the Northwest Atlantic, it is found along the shores of Newfoundland and Labrador, on the Grand Banks and in the Estuary and Gulf of St. Lawrence.

Interestingly, the range of capelin can vary locally from year to year depending on the ocean temperature. Indeed, it is considered an indicator species for temperature. During years when the water is colder, its range extends a little further south, sometimes as far as the Gulf of Maine.

Global distribution of capelin ¹

A recent study ² revealed considerable genetic diversity in capelin. The DNA (mitochondrial) analysis of capelin from the three oceans revealed the existence of four distinct major groups, distributed as follows:

• Northwest Atlantic, including Hudson Bay
• From west Greenland to the Barents Sea (northern Norway and Russia)
• Arctic Ocean
• Northeast Pacific

1. Source : Froese, R. and D. Pauly. Editors. 2009. FishBase. www.fishbase.org, version (10/2009).
2. Dodson, J.J. et al. Blackwell Publishing Ltd Trans-Arctic dispersals and the evolution of a circumpolar marine fish species complex, the capelin (Mallotus villosus). Molecular Ecology (2007) 16, 5030–5043.

Habitat

During the breeding season, capelin begin an intensive migration to the coast and spawn on beaches or in deep water (up to depths of 280 metres).

Spawning Site Type

According to the great majority of observations, spawning occurs on sandy beaches (79%). However, the data collected do not specify the substrate diameter. Spawning also takes place on gravel beaches slightly more than 10% of the time.

When capelin reproduce on the shore, this is called “rolling” or “landing,” literally on sandy or fine gravel beaches. Spawning occurs mainly when the water temperature is between 6° and 10oC and is most commonly observed at night. In the estuary and Gulf of St. Lawrence, the capelin “roll” on the shores between mid-April and July. They rely on the tides to carry them to the beach.

Percentage of capelin spawning observations by substrate type

During spawning, capelin give off a very characteristic cucumber odour. For local residents, this odour is a tell-tale sign that the capelin are spawning.

Capelin carried by the waves (Photo: Louise Proulx)

Fish eggs of the Capelin

Deepwater Spawning
Deepwater spawning grounds also have substrates composed of gravel and sand and must be located in an area that provides good oxygenation of the eggs. Spawning grounds may be found at depths ranging from several metres to 280 metres.

Capelins on different types of substrate used for spawning (clockwise: sand, gravel, bedrock et pebbles)