Spot shrimp are the largest wild species of shrimp found in Alaska, with females reaching more than 12 inches (30 cm) in length. Because of their large size, marketers often refer to them as “spot prawns,” but they are not prawns.
What is the difference between a prawn and a shrimp? They might look similar, but shrimp differ from prawns in many ways. Prawns and shrimp are both decapod crustaceans, but they belong to separate sub-orders. Shrimp have plate-like gills and a set of claws on their front two pairs of legs, while prawns have branching gills and claws on three sets of their legs. Shrimp have three body segments, with the middle segment overlapping the front and rear sections, causing their bodies to curve. Prawns, however, lack the body segmentation and have straighter bodies than shrimp. Shrimp and prawns vary in many other ways too, including their reproductive habits. Prawns release their progeny into the water to survive on their own, while a female shrimp carries her eggs on her abdomen for five months.
Spot shrimp range from Southern California to the Aleutian Islands to the Sea of Japan and the Korea Strait. They occupy a variety of habitats and water depths from very shallow to 1510 ft. (460 m), but they most commonly live at approximately 300 ft (90m.). They usually remain close to the bottom and stay near rock piles, crevices, under boulders, or in other areas where they can seek protection from predators. Juvenile spot shrimp remain in shallow, inshore areas and migrate offshore when they mature.
Spot shrimp appear reddish-brown to tan and have horizontal bars on the carapace. The distinctive white spots, from which they derive their common name, are located on the first and fifth abdominal segments. The slender body of a spot shrimp has five pairs of swimmerets on the underside of its abdomen. A spot shrimp repeatedly molts throughout its life and grows larger with each molt.
The most amazing fact about spot shrimp is, like some other shrimp species, spot shrimp are protandric hermaphrodites. They mature as males and later transform into females. They reach sexual maturity at age three when they can produce sperm and spawn as males. As they grow, they pass through a transitional stage and become females capable of producing eggs. Research indicates not all spot shrimp follow this pattern, though. Some skip the male-phase of the life cycle and develop directly into females.
Before mating, a female molts into a shell specialized for carrying eggs. Each egg attaches to her abdomen by a hair-sized structure called a seta, and she carries the eggs from October to March. Biologists believe each spot shrimp spawns once as a male and one or more times as a female. They spawn at depths of 500-700 ft. (152.4 m to 213.4 m).
Spot shrimp are bottom feeders, and they feed at night. They eat a wide variety of bottom organisms, including worms, diatoms, dead organic material, algae, mollusks, and even other shrimp. Fish such as halibut Pacific cod, pollock, flounders, and salmon pursue and eat spot shrimp. Spot shrimp can live seven to eleven years.
Due to destructive fishing methods used to catch shrimp in many areas of the world, biologists consider the commercial harvest of shrimp to be one of the most unsustainable of all global fisheries. Bottom trawls destroy everything in their path. In Alaska, the shrimp harvest is mainly restricted to pot fisheries in certain areas.
In Southeastern Alaska, the Alaska Department of Fish and Game closed the spot shrimp fishery to commercial and sport fishermen in 2013, but the spot shrimp population in the area has continued to decline. Biologists wonder if recent warmer, more-acidic ocean waters could be the cause for dwindling spot shrimp numbers, and they are beginning to research the issue. Shrimp remain most vulnerable to acidification during early life stages when they rely on calcification to build their exoskeletons.
Robin Barefield is the author of four Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter, and Karluk Bones. You are invited to watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska, and listen to her podcast, Murder and Mystery in the Last Frontier.
