INCIDENCE OF MOLTING AND SPAWNING 



IN THE SAME SEASON IN FEMALE 



LOBSTERS, HOMARUS AMERICANUS 



The reproductive cycle in female lobsters, Homa- 

 rus americanus, normally covers 2 yr. Molting 

 and mating occur first, primarily during the 

 summer months. Laying of eggs (spawning) takes 

 place about a year later. Hatching of eggs, fol- 

 lowed by molting and mating again, takes place 

 another year later (Aiken and Waddy 1980). 

 However, departures from the normal cycle occur. 

 One such departure is molting and egg laying in 

 the same year (Aiken and Waddy 1980; Ennis 

 1980). Ennis (1980) noted that new-shelled ovi- 

 gerous females obtained in fall sampling at vari- 

 ous Newfoundland localities ranged towards the 

 lower end of the size range of all ovigerous 

 specimens and suggested that those females that 

 molt and spawn in the same year are spawning 

 for the first time. Aiken and Waddy (1980) simi- 

 larly suggested that this phenomenon probably 

 occurs primarily in the Adult-I year (i.e., first 

 spawning). 



In this paper I present data on the incidence of 

 this phenomenon in a Newfoundland lobster pop- 

 ulation and illustrate its relationship to size 

 of lobster. 



Materials and Methods 



Annually since 1975, research fishing for lob- 

 sters has been carried out in autumn, following 

 the summer molting/spawning period, in the area 

 of Arnold's Cove, Placentia Bay, on the southeast 

 coast of Newfoundland. The main purpose of this 

 fishing is to tag legal lobsters to obtain estimates 

 of standing stock during the following spring 

 fishing season. All lobsters caught are measured, 

 sexed, and examined for shell condition to deter- 

 mine whether molting has occurred recently and 

 for the presence of external eggs. Since hatching 

 of eggs laid the previous year occurs during July- 

 August in this area, all ovigerous specimens 

 present in the autumn carry recently laid eggs. 



To determine the relationship between percent 

 molting and laying eggs in the same season, it 

 was necessary to convert the observed postmolt 

 carapace length (CD of new-shelled ovigerous 

 specimens to premolt carapace length. This was 

 done using a premolt-postmolt carapace length 

 relationship for Arnold's Cove lobsters (Ennis 

 1978). The data for all years were pooled. The 

 total number of ovigerous specimens examined 



FISHERY BULLETIN: VOL. 82, NO. 3. 1984. 



and the number which had molted prior to laying 

 eggs at each 1 mm CL interval (premolt carapace 

 length for new-shelled specimens) were subjected 

 to probit analysis. 



Results and Discussion 



All ovigerous lobsters ==70 mm CL (premolt) 

 molted prior to laying eggs. Beyond 70 mm, the 

 percentage of animals that molt and lay eggs in 

 the same season declined very rapidly to zero at 

 82 mm CL (Fig. 1). 



The lobsters in which Aiken and Waddy (1976, 

 1980) noted the occurrence of molting and egg 

 laying in the same individual during the same 

 molting/spawning season came from the southern 

 Gulf of St. Lawrence. They suggested that the 

 high summer water temperatures that prevail in 

 the area may be the cause of the phenomenon. 

 However, its occurrence in several Newfoundland 

 localities (Ennis 1980) indicates that the phe- 

 nomenon may be quite widespread. 



At Arnold's Cove the percentage of non-ovi- 

 gerous females that molt and lay eggs in the 

 same season declines to zero over the size range 

 (70-82 mm CL) where functional maturity in- 

 creases to 50% (Ennis 1984). This is consistent 

 with the suggestion that this phenomenon occurs 

 in animals laying eggs for the first time. If this is 

 so, the incidence of this phenomenon in a popula- 

 tion is likely to be related to the minimum legal 



60 



30 



PROBIT EQUATION 

 y= 27 75IO-0 3072 « 

 P > 99 



i i i i > f i i i 



75 80 85 



Premolt Coropoce Length 



IOO 



FIGURE 1. — Percentage of non-ovigerous female lobsters that 

 molt and lay eggs in the same season in relation to size at 

 Arnold's Cove, Newfoundland. 



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