Pacific sand lance spend much of their lives either hiding in the sandy substrate of shallow marine areas or swimming in the water column feeding. In the spring the sand lance’s main food source, zooplankton, become highly abundant. During this time sand lance eat a lot and are able to build up their energy reserves (see energy density in top graph for the months of June and July). Soon after this sand lance begin developing gonads in preparation for spawning. We can detect this growth by comparing the size of their gonads with the rest of their body (GSI; bottom graph). Their gonads continue to grow steadily until October when they spawn, but at the same time the fish’s energy density (their energy reserves) are being depleted as the season progresses and there is less and less food available. After the spawn in October, sand lance are dormant through the winter until the zooplankton return in the spring.

Because of this life-cycle marine predators, including seabirds, gain maximum benefit from eating sand lance in early summer rather than during the winter. We have found that seabirds do tend to eat high quantities of Pacific sand lance in the summer and that this could potentially benefit their reproductive success in a positive way.

Energy Density* and GSI* of Pacific Sand lance for One Calendar Year.