Does Maternal Size Affect Red King Crab Recruitment Potential Due to Embryo
or Larval Production?
Figure 8. Female red king crab brooding eggs. Photo by Katherine Swiney.
Figure 9. Scatterplot of Bristol Bay red king fecundity by
maternal size summer 2008.
Figure 10. Seasonal comparison of large (≥ 105 mm carapace length) Bristol Bay red king crab fecundity by maternal size summer and fall 2008.
A priority for fishery managers is to develop biological reference points based on monitored characteristics of a population, such as reproductive potential, which reflect population status. Stock assessment and management of Alaskan red king crab, Paralithodes camtschaticus, (Fig. 8) does not currently incorporate recruitment potential based on embryo or larval production. To improve upon this, data on fecundity, embryo quality, and larval quality variability due to maternal size is needed.
Red king crab fecundity increases with maternal size (Fig. 9). Egg loss may occur over the 10- to 12-month brooding period, so fecundity data should ideally be collected close to hatching. In Bristol Bay, however, red king crab fecundity is typically estimated shortly after extrusion; therefore, an understanding of egg loss during brooding is necessary.
Between 2007 and 2009, fecundity from small (<105 mm carapace length (CL)) and large females (≥ 105 mm CL) early in the brooding period (summer) was compared to later (fall) fecundity. There was no clear pattern for small females, with results among years ranging from 16.7% lower fall fecundity, to no seasonal difference, to 11.8% higher fall fecundity. Large females were 4.8%-8.2% less fecund in the fall than summer (Fig. 10), suggesting embryo loss during brooding which should be accounted for in stock assessment and management.
Maternal size influences embryo quality, larval quality, and recruitment potential in some, but not all, crustacean species. For example, American lobster, Homarus americanus, fecundity and embryo quality both increase with increasing maternal size resulting in larger females having a higher recruitment potential.
In 2008, larval quality based on dry mass, carbon (C) and nitrogen (N) content, and time to 50% mortality (LT50) under starvation conditions was assessed as a function of maternal size from crab 93-135 mm CL. Maternal size did not affect any of the measured parameters. In 2009, embryo quality based on dry mass, and C and N content was assessed from red king crab females 86-145 mm CL. Among these measures of quality only N content significantly increased with maternal size although maternal size explained very little of the variance (r 2 = 0.16). To determine if maternal size effects on embryo N levels persist inter-annually, samples are being collected in 2010.
Larger females likely have a higher recruitment potential due to higher fecundity even if larval quality does not vary with maternal size. Maternal size effects on fecundity and embryo loss must be considered in order to incorporate recruitment potential into stock assessment and management of red king crab.
