Brief description
Fecundity and egg size of giant crabs (Pseudocarcinus gigas) were determined from egg masses of 162 crabs sampled from three sites in south-eastern Australia: western Victoria, western Tasmania and eastern Tasmania. Crabs ranged in carapace length from 126 to 220 mm and egg number ranged from 830000 to 2500000.
Lineage
Maintenance and Update Frequency: notPlanned
Statement: Ovigerous female crabs (n=166) were collected in traps by commercial fishers during the period 10 August to 15 September 1995 from eastern Tasmania (n=30), western Tasmania (n=121) and western Victoria (n=11).
The following measures were recorded: whole weight (with egg mass removed), carapace length (CL, mm), abdomen width, chela length and chela height. The sample included 21 crabs missing one leg and 2 crabs missing two legs; the whole weight (W, g) of these individuals was adjusted by correcting for missing limbs with a regression formula, W = -4076.3 + 37.35[CL] + 0.0325[CL]2. It was considered that fecundity might change between successive clutches, so a measure of shell wear was used to quantify time since the previous moult. Shell wear, or 'carapace condition', was classified as follows.
Carapace condition 1: shell clean, bright; little to no fouling. If gooseneck barnacles present, then < 5 mm across longest axis, little to no wear apparent on the dactylus of pereiopods.
Carapace condition 2: shell bright; fouling often heavy but composed almost entirely of gooseneck barnacles; wear apparent on the dactylus of pereiopods, with the bristles being completely removed in places.
Carapace condition 3: shell often faded; fouling heavy and composed of many organisms besides gooseneck barnacles, especially colonial scidians and bryozoans; dactylus of pereiopods heavily worn with abrasion on the shell surface.
Derivation of egg counts
Half of each egg mass was removed from the crabs by severing four of the eight pleopods at their base in an alternate fashion, to avoid possible
bias from uneven distribution of eggs between pleopods. Eggs were removed from the pleopods by severing setae at the point of junction with
the pleopods.
Mean dry weight of the individual egg was calculated from the weight of two subsamples of at least 250 eggs, counted and then weighed collectively. Samples were dried at 80°C for 24 h, followed by a 1-h period in a vacuum. Dry weight of the whole egg mass was estimated by weighing the blotted egg mass and then calculating mean moisture content from two subsamples of 1.5 g. Total number of eggs per female was estimated from the mean egg dry weight and the dry weight of the whole egg mass.
Egg diameter
Subsamples were taken from each abdominal egg mass and teased apart in sea water. The diameters of 50 eggs were recorded by image analysis using NIH-Image 1.60 software. Only those eggs that were round and appeared normal were measured. Egg volume was calculated from egg diameter.
Notes
Credit
Australian Postgraduate Award
Credit
University of Tasmania
Credit
Tasmanian DPIF
Credit
Victorian DCNR
Purpose
Assess the effect of the following factors on fecundity and on egg size: (1) size of the female, (2) regional variation between three widespread sites around south-eastern Australia representative of the major fishing areas, and (3) successive broods produced between moults.