Gilmour Point, Montague Island

Gilmour Point, Montague Island

by | May 14, 2023

Gilmour Point is a headland that forms the northern shore of Port Chalmers on the northwest coast of Montague Island in Prince William Sound, and an area of extensive eelgrass beds, about 62 miles (100 km) southeast of Whittier and 54 miles (87 km) southwest of Cordova, Alaska. Port Chalmers was named Chalmers Harbour by Captain Nathaniel Portlock in 1787 where he anchored the King George while on a three-year voyage with George Dixon on the Queen Charlotte to explore fur trading opportunities. Portlock’s sketch map of the area also labelled Gilmour Point. Montague Island was named in 1778 by Captain James Cook for John Montagu, Earl of Sandwiche. Lieutenant Gavril Sarychev published the Chugach Sugpiaq name for the island as ‘Tsukli’. Gilmour Point and most of Montague Island is formed by rocks representing the Orca Group that developed during the late Paleocene to middle Eocene from turbiditic sedimentary rocks including greywacke sandstone, siltstone, mudstone, and local conglomerate deposited as a submarine fan. These rocks are part of the Chugach-Prince William composite terrane that subsequently was uplifted and accreted to North America and is now exposed along 1400 miles (2250 km) of the Gulf of Alaska coast from the Kodiak Archipelago to Southeast Alaska.

Many of the sheltered bays in Prince William Sound, such as those near Gilmour Point, have extensive seagrass beds. Seagrasses are the only flowering plants which grow in marine environments and evolved from terrestrial plants which recolonized the ocean 70 to 100 million years ago. There are about 60 species of marine seagrasses and only 3 in Alaska, the most abundant being the eelgrass Zostera marina. Eelgrass grows in the soft sediments of shallow, protected marine bays, inlets, and lagoons. The plant is absent from most of the inside waters of Alaska apparently due to the turbid effluent of glaciers. It is also excluded from large river deltas and arctic environments. The plant is predominantly subtidal, although it can be found in intertidal pools, and the horizontal distribution in Alaska is disjunct, a result of environmental restrictions rather than a lack of dispersion mechanisms. Prince William Sound contains many eelgrass beds, but their distribution was altered by the 1964 earthquake that caused significant uplift in the eastern portion of the sound, elevating the eelgrass beds into the intertidal where they perished. The eelgrass beds on the Alaska coast are important contributors to all levels of production in the food web and provide an important habitat for juvenile fishes and spawning herring.

Pacific herring are a cornerstone species in the marine ecosystem because of their vital role in the food web. These small silvery fish directly support predators such as salmon, marine mammals, and a large diversity of marine birds. Herring mass into immense schools that move along coastlines and migrate across open water. They also stage one of the natural world’s most spectacular events with their annual spawn. Each year, tens of thousands of tons of herring migrate from offshore waters to more sheltered nearshore bays and estuaries where they spawn. Male herring release milt which colors nearshore waters a chalky white, sometimes for many miles of coastline. In this opaque water, female herring lay eggs upon the intertidal and nearshore vegetation, which often includes eelgrass and kelp. The herring population in Prince William Sound declined drastically in 1993, just 4 years after the Exxon Valdez oil spill. The collapse put an end to the lucrative fishery and created a missing link in the marine food web. Scientists have spent years trying to understand if and how the oil spill played a role in the herring’s demise and the results have been controversial. Herring abundance can naturally fluctuate, but the reasons behind the fluctuations are poorly understood, therefore, precautionary management of the herring population will require conservative, ecosystem-based principles. Read more here and here. Explore Gilmour Point and Montague Island here:

About the background graphic

This ‘warming stripe’ graphic is a visual representation of the change in global temperature from 1850 (top) to 2022 (bottom). Each stripe represents the average global temperature for one year. The average temperature from 1971-2000 is set as the boundary between blue and red. The color scale goes from -0.7°C to +0.7°C. The data are from the UK Met Office HadCRUT4.6 dataset. 

Credit: Professor Ed Hawkins (University of Reading). Click here for more information about the #warmingstripes.

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