Washed up - euphausiid shrimp on area beach

Observation by Richard Hocking

The Stranded Marine Animal hotline received a call at Alaska SeaLife Center reporting the following:

A caller reported that a tremendous number of shrimp were washed into the intertidal zone and on the beach near Whittier, as far as we could tell, on the beach near the tunnel portal.

I have seen a similar wash-up of thousands of euphausiid shrimp, the species identified here in Resurrection Bay as Thysanoessa spinifera. That species is what our caller seems to have captured in images she shared.

The reason these animals are washing up has been coalescing around the observation that coastal euphausiids may be in a reproductive phase in the spring when they are especially numerous in shoals and there is a temperature inversion or some other oceanographic condition that traps them in a water layer where conditions are not ideal and they die and wash ashore. This is what I've been told by UAF researchers who worked for some years in Resurrection Bay and are familiar with the plankton and nekton in our waters. The contact I have at UAS, Juneau, suggested it be studied further from a euphausiid population expansion or from a ocean temperature/water mass stratification standpoint.

This sighting on April 24 also got some airing in the media for a day or two.

Comments by LEO Editors

Thysanoessa Spinifera are a genus of krill which occupy the habitat from the southeastern Bering Sea to mid-Baja California in depths usually less than 100 meters. They play an important ecological role as they feed on microplankton and phytoplankton, and fish, birds, and whales feed on them. The spawning season of Antarctic Krill is from January to March, above the continental shelf. Female krill lay up to 10,000 eggs at a time, sometimes several times a season. The eggs are spawned close to the surface and start sinking. The reproductive stage of krill supports the explanation of the UAF researchers statements above. The Sea temperatures of the Gulf of Alaska near Whittier match are near normal and do not indicate marine heatwave. The Sea Temperatures of the Gulf of Alaska near Whittier are attached below.

LEO Network has three other observations from Alaska of die-off events with krill and shrimp species. The first report was November 1, 2013 in Metlakatla. The die-off was attributed to bubble net feeding of humpback whales and overflow from straining washing up on the beach. On July 22, 2019 krill were found washed up along the beach in Dutch Harbor. Here again the die-off may have been related to the large number of humpback whales feeding in the vicinity. On June 25, 2019, observers found dead krill, fish, and sea birds along the coast of Shishmaref. No specific cause was attributed to this event but ocean and air temperatures at the time were far above normal. Chyna Perez-Williams