Aggregative Mating of Tanner Crabs,Chionoecetes bairdi

Abstract

In April 1991, a high-density mating aggregation of Tanner crabs, Chionoecetes bairdi, was discovered at 150 m depth near Kodiak, Alaska, with the research submersible DSRV Delta. The aggregation consisted primarily of oldshell, multiparous female crabs which formed mounds 1–2 m in diameter, 0.5–1.0 m high, and spaced at intervals of 1–2 m. Mounds contained hundreds of crabs each at densities > 100∙m−2. Male crabs were found mating with females at the periphery of the aggregation, with sex ratios (male to female) varying from 1:10 to 1:100. The entire aggregation covered an area of about 2.2 ha and included approximately 100 000 crabs. No mounds were observed in May 1992, but recently spawned female crabs were found buried in the sediment at high densities (up to 2.2∙m−2) over an area of about 25 ha, suggesting that aggregation had reoccurred at the same location. Newly ovigerous females exhibited a cycle of nocturnal activity and diurnal burial whereas unmated crabs remained exposed on the sediment surface. Many body parts and presumably dead crabs were observed. We conclude that aggregative mating is a major mode of reproduction in the family Majidae.

Distribution and habitat selection of early benthic stages of snow crab Chionoecetes opilio

“…The observed burrowing behaviour in mud might serve to reduce predation, as suggested by Stevens et al (1994) for tanner crabs Chionoecetes bairdi. This burrowing behaviour was also observed for juvenile snow crabs in the field (Conan et al 1996) and for other species of crabs (Richards 1992, Zhou & Shirley 1998).…”

Distribution of red king crabs and Tanner crabs in the summer by habitat and depth in an Alaskan fjord

“…Because Tanner crabs have a behavior of burying in the sediment (Stevens et al 1994a) and red king crabs do not, a sand-mud habitat may be more important for Tanner crabs. Unlike the red king crab, the Tanner crab did not have a high density in the debris habitat.…”

“…Aggregation and podding behavior has been reported for both red king crabs and Tanner (Dew, 1990;Dew et al, 1992;Stevens et al, 1993Stevens et al, , 1994aStone et al, 1993). Stone et al referred to structurally dense and socially organized groups of adults as aggregations, and referred to them as pods when the majority of individuals were in physical contact with each other and stacked atop one another.…”

“…First, we may have simply missed the aggregations; second, mature crabs might not aggregate during summer. Dense aggregations of red king crabs and Tanner crabs have only been reported during late winter and spring (Stevens et al, 1993(Stevens et al, , 1994aStone et al, 1993). This behavior is thought to be related to molting and mating (Powell and Nickerson, 1965;Stevens et al, 1994).…”

Podding of juvenile king crabs Lithodes santolla (Molina, 1782) (Crustacea) in association with holdfasts of Macrocystis pyrifera (Linnaeus) C. Agardh, 1980

“…This behavior has also been well documented for the Majidae, including Chionoecetes bairdi (Zhou & Shirley, 1997), Chionoecetes opilio (Comeau et al, 1998), Hyas lyratus (Stevens et al, 1992b), and Maja squinado (Sampedro & González-Gurriarán, 2004). Various reasons were proposed for the aggregation behaviour in the majids, including protection during moulting, location of mates, aid in food capture, and protection from predation (Powell & Nickerson, 1965;Stevens et al, 1994;Zhou & Shirley 1997;Gardner, 1999). Observations of M. squinado by Sampedro & González-Gurriarán (2004) suggested that this behaviour was based on protection from predation.…”