FISHERY BULLETIN: VOL. 72. NO. 1 



larger individuals. In order to place more males 

 on the mating grounds and to stabilize annual 

 harvests, a quota system was initiated in 1970. 



It is important to know whether that segment 

 of the male population harvested by the commer- 

 cial fishery, i.e., large males and old-shell males 

 (Nickerson, Ossiander, and Powell. 1966) pos- 

 sess greater mating capabilities than smaller 

 protected males which molt during the mating 

 season. Also of significance is the question of 

 whether undersized males would be adequate in 

 numbers and ability to mate all females if larger 

 males were removed by the fishery. Recent in- 

 creases in the numbers of adult females with 

 broods of reduced size appear related to simul- 

 taneous increased exploitation rates and may 

 result from matings with males which had 

 mated several times previously. Our experiment 

 was designed to gain insight into these phenom- 

 ena and to obtain more complete data for 

 individual males, especially comparative data 

 on mating ability for old-shell males and recently 

 molted new-shell males. 



In this paper, mating refers to the actual fer- 

 tilization of the eggs. Hence, the term "mating 

 capability" refers to the ability of the male to 

 fertilize the eggs of the females to which he is 

 exposed. 



METHODS AND MATERIALS 



Experimental Equipment and Location 



The experiment was conducted in undersea 

 l^ens, the sides and top of which were covered 

 with nylon mesh; the bottoms were open to 

 allow crabs to dig in the substrate as they would 

 do in nature. Each pen was 8' X 8' X 4' and each 

 divided into four equal sized compartments. 

 Compartments were numbered 1 through 28 and 

 situated in 40 ft of water on a level stretch of 

 muddy-sand bottom east of Near Island adjacent 

 to an area where king crabs normally mate. The 

 study location is one mile from the city of 

 Kodiak, Alaska. Pens were designed and located 

 to simulate natural conditions. Environmental 

 factors such as daily tidal currents, pressures, 

 light intensities, temperatures, and salinities 

 were considered important in that they might in- 

 fluence mating. For this reason, undersea pens 

 were considered superior to aquaria. 



The mating study was conducted in compart- 

 ments 1 through 24 while 25 through 28 were 



used to store crabs. Females were held in storage 

 prior to and after the completion of mating. 



Fishery biologists and trained technicians 

 utilizing scuba observed the crabs underwater 

 every day. Individual crabs were identified by 

 tagging with permanent "isthmus" loop tags 

 (Gray, 1965) prior to being placed in the pens. 



Experimental Procedures 



The experiment was designed to compare 

 mating capabilities of four size shell-age classes 

 of male king crabs (small new-shell, small old- 

 shell, large new-shell, and large old-shell) by 

 studying the effects of repeated matings on the 

 ability of these males to mate successfully with 

 additional females. A 5-mm range, 145-149, was 

 used as a dividing ])oint between small and 

 large males at the juncture of legal and under- 

 size crabs. Those 144 mm or less (commercially 

 undersize males) were classified as small while 

 those 150 mm or larger were classified as large 

 (Table 1). Small males averaged 140 mm, large 

 males 167. 



Most males used in the experiment were 

 captured by scuba divers. A few of the males of 

 required size, however, were not available by 

 diving (the preferred method of collecting) and 

 therefore were taken from the catches of com- 

 mercial pots and trawls. 



All females used in the study were in premolt 

 condition and were in the pre-copulatory em- 

 brace (Powell and Nickerson, 1965): i.e., they 

 had already been selected for mating by males 

 in the natural environment. The use of these 

 females (called "graspees") was our method of 

 insuring that females were ready to mate with 

 males when introduced into the ])ens. Females 

 from natural mating areas near the pens were 

 captured by scuba divers a day or two before 

 they were needed and ranged in length from 104 

 to 181 mm, with an average size of 134 mm. 



Table 1. — Size relationships of experimental crabs. 



No. of 



Coropoce length (mm) 



Three extra males replaced three original males which died. 



172 



