Table 1. — Prevalence of American lobsters infected with 

 nematodes, Ascarophis sp., in the Mid-Atlantic Bight, August 1975- 

 March 1977. 



1 III. Norfolk Canyon and adjacent slope 



IV. Between Norfolk and Washington Canyons 



V. Washington Canyon 



VIM. Between Wilmington and Hudson Canyons. 

 2 One 86 mm female contained 33 acanthocephalan cysts, Corynosoma sp. 



from Northumberland Strait, southern Gulf of St. 

 Lawrence That higher proportion of infection was 

 highly significantly different from that reported off 

 southern New England and in the Mid-Atlantic 

 Bight. 



Mid-Atlantic Bight lobsters examined for parasites 

 ranged from 49 to 179 mm carapace length (CL) 

 (Table 2). Larval Ascarophis sp. were found in 13 

 (14.3%) of 91 male lobsters and in 26 (20.5%) of 127 

 female lobsters. No significant difference in preva- 

 lence of infection between males and females, when 

 size was ignored, could be demonstrated with a 2 

 x 2 contingency table analysis. This agrees with the 

 absence of sex specificity in the canyon lobsters 



Table 2.— Numbers of American lobsters examined and prevalence 

 of infection by the larvae of the nematode Ascarophis sp. in the 

 Mid-Atlantic Bight. 



reported by Uzmann (1967b) and also reported from 

 Northumberland Strait by Boghen (1978). 



Almost one-half (46.3%) of all infections occurred 

 in the 60-79 mm size classes; intensity of infection 

 ranged from 1 to 13 (mean 3.0) (Table 2). None of 

 the 11 lobsters >110 mm CL contained parasites. 

 Boghen (1978) reported 51.3% infection in the 

 60-69.9 mm range When the occurrences of para- 

 sites in males and females are arranged in three size 

 groups, 40-59, 60-79 and 80-109 mm, and statistically 

 examined with a 2 x 3 contingency table, no depar- 

 ture from the expected 1:1 ratio was observed. 



A single specimen of the commensal polychaete, 

 Histriobdella homari, was obtained from the gills 

 of a female lobster, 82 mm CL, caught in Norfolk 

 Canyon in June 1974. Gills of four other lobsters 

 were excised, placed in dilute seawater in specimen 

 bowls, and refrigerated overnight. The polychaete 

 was found in the sediment collected from one gill. 

 Because of the small number of lobster gills ex- 

 amined, an estimate of prevalence is inappropriate 

 Previously, Histriobdella was reported by Uzmann 

 (1967a) in the gills and by Simon (1968) in the gills 

 and bodies of New England lobsters, and by Boghen 

 (1978) in the branchial chamber and gills of lobsters 

 from Northumberland Straits. 



One female lobster, 86 mm CL, caught in Norfolk 

 Canyon in August 1975, was infected with cysts of 

 an acanthocephalan, Corynosoma sp. Thirty-three 

 cysts were found in the intestinal wall and in the 

 mesenteries along the outside of the intestine Adult 

 Corynosoma sp. are parasites of mammals and 

 aquatic birds; crustaceans are first intermediate 

 hosts and fishes are second intermediate hosts 

 (Yamaguti 1963). 



According to Uzmann (1970), Corynosoma sp. is 

 a discriminator of coastal lobster stocks. Therefore 

 its presence in a lobster taken in Norfolk Canyon 

 indicates that migration from inshore to offshore 

 waters occurs. Montreuil (1954) reported that the 

 acanthocephalan infections in lobsters from the 

 Magdalen Islands, Gulf of St. Lawrence, varied with 

 the sex of the lobster and by season: 20% of females 

 and 20% of males had cysts seemingly acquired 

 towards the end of summer and early fall. Boghen 

 (1978) attributed the absence of cysts in his North- 

 umberland Strait samples to the fact that the lob- 

 sters were collected before the end of summer. 



Discussion 



The variety of animal parasites and their inten- 

 sity of infection are small in the Mid-Atlantic Bight 

 lobsters. Differences in the occurrence and rates of 



199 



