Reproductive capacity morphometrically assessed in Cancer pagurus from the Shetland Islands

Reproductive capacity morphometrically assessed in Cancer pagurus from the Shetland Islands

S.M.L. Tallack

Reproductive capacity morphometrically assessed in Cancer pagurus from the Shetland IslandsThis is part of Crabs in Cold Water Regions: Biology, Management, and Economics
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Description

Reproductive capacity and size at maturity were investigated in the edible crab, Cancer pagurus, using both conventional and novel morphometric measurements. Measurements of cheliped length and height (males) and abdomen width (females) were analyzed and verified against biological findings of maturity (ovigerous, hatched, or "plugged" status in females; mature testes in males). The sizes at maturity derived through Hiatt straightline analysis were lower than anticipated: 102-105 mm CW in males and 90 mm CW in females. This result may indicate a prepubertal molt in C. pagurus. Alternatively, the Hiatt straight line analysis may identify the onset of behavioral rather than functional maturity.

Female C. pagurus typically show increased fecundity with increasing crab size, though little explanation is offered in the literature. This study investigated four morphological features likely to assist in realizing this trend: abdomen width, pleopod capacity, sperm plug weights, and spermathecae weights. These were chosen for their role in brood protection,egg attachment, and egg fertilization through sperm retention. The positive relationship found between crab size and each feature suggests that these reproductive accessories assist larger females to produce larger broods, thereby increasing their reproductive capacity. Allometric analysis of female pleopod capacity indicated a size at maturity of 138 mm,which is in line with recordings of ovigerous females around Shetland.

Despite the lack of morphometric attention paid to this species to date, it was concluded that both conventional and novel morphometric measurements represent useful tools for estimating the size at maturity C. pagurus, though calibration against other biological indicators of maturity remains advisable.

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