Erimacrus

Lore & Background

Erimacrus isenbeckii has a hard shell covered with soft spines. It is commonly found on sandy benthic environments from shallow water to depths of up to 350 meters. The species feeds three to four times in a ten- to twelve-hour period, and cannibalism is common in the spring. The carapace of adults can reach 100 to 120 mm in length, and individuals can weigh over 1 kg. Like the two other species in the same family, the gonophores of females are exposed.

The embryonic development of the species is divided into nine stages, defined by cleavage and formation of distinct appendages. After spawning, females attach the eggs to their pleopods for incubation, which is estimated to last over a year, with the growth rate controlled by water temperature. Young hatch between March and May and remain as zooplankton until they reach the sea bottom by July. The hatching process occurs during the spring phytoplankton bloom in the Sea of Okhotsk. The zoea lack carapace spines and have shorter lateral spines on the fork of the telson, distinguishing them from the two other species in the same family.

Reader's Guide

Erimacrus isenbeckii, the sole species of the genus, holds significant economic and cultural value in Japanese cuisine, where it is known as kegani. The fishery for this crab reached a peak of 27,000 tons in the 1950s, but catches declined to 2,000 tons by 2003, prompting stock enhancement programs to sustain the fishery. Despite its commercial importance, biological studies of the species are specialized and limited. The crab's life cycle, including a lengthy incubation period of over a year and a spring hatching synchronized with the phytoplankton bloom, reflects its adaptation to the cold waters of the Northwest Pacific. The species' distribution spans the Hokkaido coast, the Sea of Okhotsk, and the western Bering Sea, with males and females occupying slightly different temperature and depth ranges. The distinct morphology of its zoea, lacking carapace spines and having shorter lateral spines on the telson fork, aids in identification among related species. The ongoing management efforts highlight the balance between exploitation and conservation for this important crustacean.

Did You Know?

• The horsehair crab is also known by its Japanese name, kegani, meaning 'hairy crab'.
• Catch for the species peaked at 27,000 tons in the 1950s and fell to 2,000 tons by 2003.
• Females incubate eggs attached to their pleopods for over a year.
• The zoea of Erimacrus isenbeckii lack carapace spines, unlike two other species in the same family.