INSTAR IDENTIFICATION AND LIFE HISTORY ASPECTS OF 



JUVENILE DEEPWATER SPIDER CRABS, 



CHIONOECETES TANNERI RATHBUN 



Patricia A. Tester 1 and Andrew G. Carey, Jr. 2 



ABSTRACT 



For the deepwater spider crab, Chionoecetes tanneri, seven instars from first crab stage (3.8 mm carapace 

 width (CW)) to instar VII (26.8 mm CW) are identified from size-frequency histograms. The average 

 growth per molt for the first seven instars is 39% and the time from egg to instar VII is estimated to 

 be 20 months. 



Measurements of chela length, abdomen width and carapace width were used to define two growth 

 phases for C. tanneri and to determine size at maturity for males (142.7 mm CW) and females (102.3 

 mm CW). The unequal sex ratio of adults (29% males) and presence of chitinoclastic lesions on 76% of 

 the adult females as compared with only 29% of the adult males suggest that adult females are anecdysic. 



In this study of material collected off the southern Oregon coast, the mean adult carapace widths 

 for males and females is very close to the sizes reported for adult males and females (148.9 and 102.5 

 mm CW respectively) from the northern Oregon coast. The similarity in size extends to the material 

 collected from near the type location (Gulf of the Farallons) where instars VI and VII are 19.4 and 27.3 

 mm CW compared with 19.8 and 26.7 mm CW for the same instars from the southern Oregon coast. 

 The biotic stability at depths of maximum abundance (500-775 m) contributes to this uniformity. 



The spider (or tanner) crab, Chionoecetes tanneri 

 Rathbun, is similar in size and morphology to the 

 better known and commercially harvested species 

 C. bairdi and C. opilio. Unlike C. bairdi and C. opilio 

 which are typically encountered in shallow waters 

 and are not reported deeper than 400 m in the 

 eastern Pacific, C. tanneri is a deep-water species 

 which ranges to 1,925 m and has its maximum abun- 

 dance at 500-775 m (Pereyra 1972). 



Although C. tanneri is not likely to be fished 

 commercially because of its deep-water habitat and 

 certain aspects of its biology, Somerton (1981) sug- 

 gested that fluctuating supplies of Alaskan crab 

 species might promote more economical methods for 

 fishing in deep water. Red crab, Geryon quin- 

 quedens, taken from depths of 257-1,000 m between 

 Georges Bank and Cape Hatteras are landed com- 

 mercially in limited numbers on the eastern sea- 

 board (Lux et al. 1982; U.S. National Marine 

 Fisheries Service Fisheries Statistics 1985). 



In part, because of its deep-water habitat, certain 

 life history aspects of C. tanneri are not well known. 

 Pereyra (1966, 1968) determined size at maturity 



1 College of Oceanography, Oregon State University, Corvallis 

 OR 97331; present address: Southeast Fisheries Center Beaufort 

 Laboratory, National Marine Fisheries Service, NOAA, Beaufort, 

 NC 28516-9722. 



2 College of Oceanography, Oregon State University, Corvallis 

 OR 97331. 



and described the seasonal distribution of adult and 

 late juvenile crabs. Egg development follows a year- 

 ly cycle with release of matured eggs and ovulation 

 of new eggs during the winter (Pereyra 1966). After 

 hatching, the total larval (pelagic) phase (prezoea, 

 zoea I, II and megalopa) is estimated to be 80 d 

 (Lough 1974). Samples collected mainly from a 

 series of cruises off the Oregon coast from 1972 to 

 1975 have provided us with C. tanneri specimens 

 from the first crab stage to adult. These specimens 

 have made it possible to identify a series of early 

 instars and to determine juvenile growth rates; they 

 also provided life history information on size at 

 maturity and adult and juvenile sex ratios for 

 comparison with earlier work. In addition, observa- 

 tions of the carapace condition of adults helped to 

 substantiate the anecdysic condition of adult 

 females. 



METHODS 



Sampling 



Samples of C. tanneri were collected off the con- 

 tinental shelf and slope areas adjacent to Coos Bay, 

 OR (lat. 42°25'N, long. 124°50'W) in depths rang- 

 ing from 300 to 1,200 m during 10 cruises between 

 April 1973 and March 1975. A total of 1,625 crabs 



Manuscript accepted February 1986. 

 FISHERY BULLETIN: VOL. 84, NO. 4, 1986. 



973 



