Sculpins can also increase their access to sockeye eggs by
being in nests during spawning events, as this is when the eggs
are most available. At spawning, the eggs (about 500–1000 per
spawning) are exposed and the easiest to capture. We have
shown that sculpins can eat a large number of eggs within
minutes of their discovery, particularly if they are freshly
spawned (Fig. 4). However, shortly after spawning, the
number of eggs that can be consumed drops for two reasons.
First, a spawning act lasts only seconds, and over about the
next 10 min the female covers the eggs with gravel. Although
the eggs within the nest may remain accessible to the sculpins
buried with them, they may not be easily localized or accessible
to other sculpins. Second, the eggs immediately start to
swell and harden, with the process largely complete within an
hour of spawning. Consequently, the size range of sculpins that
can consume these eggs decreases due to gape limitations
(Fig. 6), and those still able can consume fewer of them
(Fig. 4). The digestion rate of these water-hardened eggs is
also slower than that of freshly spawned eggs (McLarney
1967), further limiting the number of eggs that can be consumed.
Gape limitation may account for the relatively low
proportion of small sculpins on the spawning grounds (Fig. 2)
and act to select for the large egg size of beach spawning
sockeye.