Application of the morphometric maturity coefficient to determine terminal molt in the crab Chionoecetes angulatus from the Okhotsk Sea

Abstract

Results of studies on the relationship between the claw morphometric parameters and the carapace width (CW) of the triangle crab (Chionoecetes angulatus) crab from the Sea of Okhotsk presented. For the operational screening and separation of males into morphometrically mature (ММ – large-clawed) and immature (MI – small-clawed) species, it is proposed to use the coefficient of morphometric maturity (K%). This coefficient can be defined as the ratio of claw height to carapace width (KH%) or as the ratio of claw diagonal to carapace width (KD%), expressed as a percentage. When assessing the coefficient of morphometric maturity (K%), the boundary value for KH% is 16, and for KD% it is 35, which allows reliable identification of large-clawed (MM) males at K% values above the boundary values, and small-clawed (MI) males at K% values below the boundary values. Four functional groups were distinguished in males of C. angulatus: 1) MI physiologically immature — CW ≤90 mm, KH% <13.5, and KD% ≤29; 2) MI physiologically mature — CW 90.1–120 mm, KH% 12–16 and KD% 25–35; 3) MI large-sized physiologically sexually mature — CW >120 mm, KH% 13–16 and KD% 29–35; 4) MM morphometrically and functionally mature — CW 74–167 mm, KH% >16 and KD% >35. The correlation of the onset of morphometric maturity with biochemical parameters of hemolymph and with the development of muscle tissue is discussed. For various functional groups of males C. angulatus, an abundance estimate was implemented taking into account the K% coefficient.