Tuesday, April 17, 2012

Birds and mammals and fish and things

The complex rising and falling of the birds and mammals of the Salish Sea:


For other waterbirds, the March herring spawn is a time of plenty, particularly between Nanaimo and Comox. “There is an exodus from this side of the strait,” Bird Studies’ Davidson said.

Species such as gulls and harlequins gorge on the roe. Others such as Pacific loons and western grebes target the actual herring. “The cycle is so dynamic in the Salish Sea, so many different types of bait fish, birds and marine mammals that are all part of this complicated food chain,” he said.

Almost on cue, Davidson spots the slick dark-grey backs of two harbour porpoises farther offshore.

As perplexing as coastal birds, this marine mammal is listed as a species of special concern in our waters with information lacking on their overall numbers and population trends.

A PhD thesis by Anna Hall at the University of B.C. found that harbour porpoises seek out strong tidal areas for foraging during the reproductive season, from April to October, in the Salish Sea.

In April they will gather by the dozens off Point Roberts, another mystery of a coastal ecosystem dominated by strong tides and currents and the brutish muscle of the Fraser River.
“It’s a very complicated puzzle,” Davidson said. “Everything affects each other, probably in different ways.”