Geoscience Reference
In-Depth Information
action of the fish in the tiny puddle of water thus formed can be distinctly heard. After separating the
capelin lie still on the sand for a second as if exhausted before starting to paddle furiously in an attempt to
regain the water, for by this time another wave has rolled up the beach. The writer [G.W. Jeffers] has tried
to pick up a pair that was still in contact but found it impossible. Timing the spawning act with a stop-
watch shows that it is over in less than five seconds.
Most capelin spawn at three to four years of age and then die, though some females may survive. Inshore
spawning spans a four to six-week period during June and July. Most spawning occurs on the beach, but if wa-
ter temperatures on the beach become too high, some capelin will spawn in the shallows rather than coming
ashore. Capelin prefer water temperatures of 5.5° to 8.5°C (42°C to 47°F), and spawning usually occurs at
night or on dull, cloudy days. An offshore stock spawns on the southern Grand Banks, underwater. This popu-
lation is probably a holdover from the last glaciation, when the Grand Banks were emergent and the fish
spawned there on the ice-free beaches—and when sea level rose, they continued to use these relict beaches.
Beach spawning seems like a bizarre and risky behavior, but it may be a safer strategy to leave your eggs to
develop on the beach than in the water, where predators can get at them. Capelin prefer beaches with fine
gravel to which the sticky eggs adhere. The eggs themselves are relatively big, providing the larval fish with a
“large box lunch” during their stay in the beach gravel. Depending on the temperature on the beach, the eggs
take two to three weeks to hatch, and then the embryonic fish have three to eight days of yolk-sac reserve be-
fore they must begin to feed on their own.
The critical event in a capelin larva's life is whether or not an onshore wind blows a warm mass of water in-
to the capelin coves. If so, the rise in temperature triggers its emergence, and the warm water provides an ideal
environment for its growth. The water contains a large biomass of small plankton in the edible size range for
the still-translucent little fish and contains relatively few predators compared with the deep upwelling water,
where the larvae are transported by offshore winds. If no onshore winds occur, the larvae deplete their box
lunch of egg sacs and starve; or they emerge into a relative biological desert, where predators such as jellyfish
are numerous. More than half of the difference in production from any given year to the next—which can be
great, as much as thirty times—can be accounted for by meteorological variations: wind direction, air and wa-
ter temperature, and hours of sunlight.
Capelin are high in oil and therefore are the main source of fat—read energy—for many marine predators. It
would not have been possible for the large populations of cod to develop before the capelin entered the North
Atlantic ecosystem. Capelin are also largely responsible for the huge seabird colonies that rim the coast of
Newfoundland and Labrador, which boasts among the largest seabird populations in the world. An estimated
10 million seabirds breed here, and some 35 to 45 million use the offshore waters as feeding grounds.
Moreover, the distributions of the principal colonies of puffins and other seabirds coincide with those of
spawning capelin. In winter, the 4 million thick-billed murres from Greenland and the Canadian Arctic, and
many of the estimated 1 million common murres that breed in Newfoundland and Labrador, feed on capelin in
offshore waters. Together, breeding and wintering seabirds are thought to consume 250,000 tonnes of capelin
each year, the same order of magnitude as consumption by harp seals and fin and minke whales, but only one-
tenth of what cod consumed when they were at their peak populations.
The Sound and Fury
All major seabird colonies in Newfoundland and Labrador are found on islands, except the one on Cape St.
Mary's, at the southwestern tip of the H-shaped Avalon Peninsula. Its near-vertical 125-meter (400-foot) cliffs
provide the nations of seabirds gathered here with ample protection from terrestrial predators. It is the world's
southernmost gannetry, the southernmost major breeding site for common murres in the western Atlantic, and
the most southerly breeding area for thick-billed murres in the world.
