KREKORIAN, SOMMERVILLE, and FORD: LOBSTER BEHAVIORAL INTERACTIONS 



H. americanus between Monterey Bay and British 

 Columbia (Ghelardi and Shoop, 1968). The exact 

 reasons for the failure of these introductions are 

 unknown. However, three possible causes were: 

 1) low stocking density, 2) unsuitability of the 

 locations used for introductions, and 3) possible 

 injuring or weakening of lobsters through mis- 

 handling or disease before the introductions 

 (Ghelardi and Shoop, 1968). In the lobster trans- 

 plants, as in virtually all other attempts to trans- 

 plant species, there has been little or no effort 

 to evaluate the impact the exotic would have on 

 native species or to control pathogens and other 

 potentially harmful organisms associated with it. 

 Only the recent pilot introduction in British 

 Columbia by Ghelardi and Shoop (Ghelardi, 1967; 

 Ghelardi and Shoop, 1972) considered potential 

 detrimental effects and was conducted on a truly 

 scientific basis. 



While it might be argued that one can never 

 determine what the effects of an exotic intro- 

 duction will be until it takes place, we feel 

 that a serious attempt must be made to evaluate 

 potential adverse effects by laboratory studies 

 before even a small-scale pilot transplant is 

 attempted. During the period 1970-73 we, and 

 others of our group, have conducted a series of 

 studies on the social interactions of H. ameri- 

 canus with ecologically similar decapod crusta- 

 ceans from southern California waters. This paper 

 describes the results of one of our studies con- 

 cerning interactions between H. americanus and 

 P. interruptus with comparative observations on 

 P. interruptus and the rock crab, Cancer anten- 

 narius. In it, we have primarily considered 

 agonistic interactions. Other studies have shown 

 that interspecific aggression can be important 

 in regulating the lives of sympatric species 

 (see Aspey, 1971; also Myreberg, 1972a). 



METHODS AND MATERIALS 



American lobsters were purchased in San 

 Diego from the Gulf of Maine Lobster Corpora- 

 tion. They were quarantined 2 wk in a large 

 holding tank (0.5 x 1.2 x 2.3 m) for effects of 

 gaffkemia or other diseases before being intro- 

 duced to experimental tanks. California spiny 

 lobsters and rock crabs were trapped in shallow 

 water off the San Diego coast and were 

 either introduced directly into experimental 

 tanks or maintained for short periods in holding 

 tanks of the same size employed for//, americanus. 



Holding tanks were supplied with fresh run- 

 ning seawater from the Scripps Institution sys- 

 tem. The temperature of the water in tanks 

 varied throughout the year in close correspon- 

 dence with ambient ocean temperatures, from a 

 minimum of 14°C in January to a maximum of 

 23°C in August. The study began in July 1972 

 and ended in April 1973. Lobsters and crabs 

 in holding tanks were fed frozen squid, Loligo 

 opalescens, and northern anchovy, Engraulis 

 mordax, twice a week. No attempt was made to 

 control the photoperiod for these individuals while 

 in the holding tanks. However, they were exposed 

 to the normal day-night cycle during this period 

 from light entering through the walls, roof, and 

 building openings. 



Three experimental tanks were used, each 3.04 

 m in diameter and 1.22 m in height, with a 

 capacity of approximately 9,000 liters. Each tank 

 had four observation windows 68.5 x 48.0 cm 

 positioned equidistant around the perimeter. 

 The tanks were enclosed in lightproof tents made 

 of black Mobil Kordite^ polyethylene sheeting of 

 6-mil thickness. Lobsters in the experimental 

 tanks received 11 h of light daily from 0400 

 to 1500 P.s.t. (Pacific standard time), supplied 

 by two 75-W General Electric floodlights. The 

 experimental subjects were not fed while in the 

 experimental tanks so as to eliminate the variable 

 of interactions for food. 



Three experimental conditions were studied. 

 These were: 1) social interaction between P. 

 interruptus and H. americanus in the absence of 

 shelter, 2) social interaction between P. inter- 

 ruptus and //. americanus with more shelters 

 than lobsters, and 3) social interaction between 

 P. interruptus andC. antennarius without shelter. 

 Seven shelters were provided for the experimental 

 condition involving interaction between P. inter- 

 ruptus and //. americanus with shelter. The 

 shelters, which measured 25 cm in width, 38 cm 

 in length, and 14 cm in height, were made by 

 cutting 76-cm sections of concrete conduit length- 

 wise and then into 38-cm lengths. 



In each experimental condition, five California 

 spiny lobsters and either one American lobster or 

 one rock crab were employed. Five replicates of 

 each experimental condition were made using 

 naive animals for each replicate. The 5:1 ratio 

 used for the P. interruptus and //. americanus 



^Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



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