racycline. [In Engl, and Span.] Inter.-Am. Trop. Tuna 

 Comm. Bull. 17:509-560. 

 Wilson, K. H., and P. A. Larkin. 



1980. Daily growth rings in the otoliths of juvenile sockeye 

 salmon (Onchorhynchus nerka). Can. J. Fish. Aquat. Sci. 

 37:1495-1498. 



P. D. SCHMITT 



School of Biological Sciences, University of Sydney 



Sydney, N.S.W. 2006, Australia 



Present address: 



Southwest Fisheries Center La Jolla Laboratory 



National Marine Fisheries Service, NOAA 



P.O. Box 277, La Jolla, CA 92038 



TAG-RECAPTURE VALIDATION OF 



MOLT AND EGG EXTRUSION PREDICTIONS 



BASED UPON PLEOPOD EXAMINATION IN 



THE AMERICAN LOBSTER, 



HOMARUS AMERICANUS 



Techniques for molt prediction based upon epider- 

 mal and setal development in pleopods (Aiken 1973) 

 and for egg extrusion prediction based upon pleopod 

 cement gland development (Waddy and Aiken 1980; 

 Aiken and Waddy 1982) provide opportunities for 

 more comprehensive studies of growth and re- 

 productive potential in natural American lobster, 

 Homarus americanus, populations than have pre- 

 viously been possible. These laboratory-developed 

 techniques have only recently been applied to field 

 samples from a number of areas of Atlantic Canada 

 (Robinson 1979; Campbell and Robinson 1983; 

 Ennis 1984). Although the methodologies are fairly 

 straightforward and may be applied in field studies 

 quite readily, in practice the investigator will some- 

 times be faced with specimens for which predictions 

 can only be made with some degree of uncertainty. A 

 study of Newfoundland lobsters using these tech- 

 niques has included the tagging of animals from 

 which pleopods were obtained. This paper presents 

 results from observations on recaptured lobsters 

 which validate the predictions that were made at the 

 time of tagging that molting or egg extrusion would or 

 would not occur during the current molting/spawning 

 period. 



Materials and Methods 



Pleopods were obtained from American lobsters 

 (ranging from 33 mm to 130 mm CL (carapace 

 length)) caught in traps and by scuba divers near 

 Arnold's Cove, Placentia Bay, Newfoundland, be- 

 tween 24 June and 17 July 1981. These were 



examined for molt and cement gland stages accord- 

 ing to the methodologies of Aiken (1973), Waddy and 

 Aiken (1980), and Aiken and Waddy (1982). 



It is clear from Aiken (1973) that one can predict 

 with considerable confidence that lobsters with 

 pleopod stages 3.0 and higher just prior to or early in 

 the molting season will molt that year. It is also clear, 

 however, that for animals with pleopod stages 1.0-2.5 

 one cannot predict with confidence that molting will 

 or will not occur. Molt prediction for these stages is 

 not reliable because of development plateaus that 

 occur during D (i.e., molt stages 1.0-2.5). However, 

 most such plateaus occur at stages 1.5-2.0, and a 

 lobster will rarely remain at stage 2.5 for more than 2 

 wk. Once an animal has passed beyond stage 2.5, 

 there will be no further plateaus, and proecdysis will 

 proceed at a rate that is regulated by temperature 

 (Aiken 1973). Aiken (1980) also stated that at stage 

 2.5, the epidermis in the general integument begins 

 to show signs of activity, indicating imminent transi- 

 tion from indecisive D„ into the irreversible premolt 

 development of D,. Considering that animals with 

 stage 2.5 pleopods should molt in 48-52 d at 10°C 

 (Aiken 1973) plus the fact that at Arnold's Cove the 

 July-August temperatures on the lobster grounds 

 average in excess of 10°C (mean daily temperatures 

 from 24 June to 31 August averaged 12. 1°C in 1981), 

 it appeared more likely that lobsters with stage 2.5 

 pleopods during the 24 June-17 July sampling at 

 Arnold's Cove would molt. As a working hypothesis, 

 it was decided to predict that lobsters with pleopod 

 stages 2.5 and higher would molt during the 1981 

 molting season at Arnold's Cove and that those with 

 pleopod stages 0-2.0 would not molt. 



Cement glands were initially staged according to 

 the classification scheme of Waddy and Aiken 

 (1980). These stages were subsequently converted to 

 their more recent scheme (Aiken and Waddy 1982). 

 It is clear from these papers that for lobsters with 

 stage or stage 1 cement glands just prior to or early 

 in the spawning season one can confidently predict 

 that egg extrusion will not occur that year, whereas 

 for those with stage 2 or higher cement glands one can 

 confidently predict that egg extrusion will occur. 



During the sampling at Arnold's Cove, 356 of the 

 lobsters from which pleopods were removed for molt 

 and cement gland staging were tagged with 

 "sphyrion" tags, which are designed to remain 

 attached through ecdysis (Scarratt and Elson 1965), 

 and released within a few minutes of being taken from 

 the water very close to where they were captured. 

 Observations on 171 of these lobsters recaptured 

 subsequent to the molting/spawning period (mainly 

 during the 1982 fishing season, 20 April-30 June) 



242 



FISHERY lU'LLETIN: VOL. 82, NO. 1, 1984 



