Michel Comeau

The geography and bathymetry of American lobster benthic recruitment as measured by diver-based suction sampling and passive collectors

Abstract We present results of an international collaboration to survey American lobster Homarus americanus Milne-Edwards, 1837 nurseries in Atlantic Canada and the northeast United States from 2007 to 2009 under a standardized protocol involving two sampling methods, diver-based suction sampling and passive collectors. We surveyed young-of-year and older juveniles at 191 sampling sites over 39 sampling areas considerably expanding the known depth range and geographic limits of benthic recruitment. Young-of-year densities were strongly correlated in space with the abundance of older juveniles, signifying consistently strong settlement in the Gulf of Maine, lower Bay of Fundy, southwestern Nova Scotia and southern Gulf of St. Lawrence, and relatively weak settlement in southern New England, eastern coastal Nova Scotia and Newfoundland, a pattern consistent with commercial lobster harvests. Passive collectors elucidated bathymetric patterns of young-of-year recruitment in oceanographically contrasting regions. Although we observed young-of-year lobsters as deep as 80 m, they were most abundant above the thermocline in summer-stratified regions, such as the western Gulf of Maine and southern New England, and depth-wise differences were less extreme in thermally mixed waters of the eastern Gulf of Maine–Fundy region, a finding consistent with previous observations that postlarvae concentrate above the thermocline. Between the two samplers, we detected no sampling bias for young-of-year lobsters, although collectors may slightly under-represent older juveniles entering from the surrounding sea bed. Finally, we found that interactions between juvenile lobsters and suspected predators or competitors in collectors, such as crabs and fishes, are weak and unlikely to bias collector results.

Mating of Snow Crab Chionoecetes Opilio (Ο. Fabricius, 1788) (Decapoda, Majidae) in the Fjord of Bonne Bay, Newfoundland

Pairs of male and female snow crabs, Chionoecetes opilio, in mating courtship embrace were collected by SCUBA diving between 1984 and 1991, and with tangle nets between 1987 and 1993 in the Bonne Bay fjord, Newfoundland. A Nephrops trawl was also used to study the snow crab population size structure between 1988 and 1993. Males in mating courtship embrace were all identified as hard-shell morphometrically mature. Although large hard-shell juvenile males were present in the population, they did not participate in the reproduction. Comparison of the size structure of males in mating pairs and in the population also show that small mature male crabs can be excluded from mating by larger dominant mature males. The size structure between females in mating pairs and in the population was not significantly different. A depth segregation by size on the very steep slope of the fjord was observed for male snow crabs in mating pairs, as smaller males were found above 50 m. There was no correlation between male and female size in mating couples, but males were always larger than females. We conclude that there is a strong intra-specific competition between males during mating in nature.

Variation in the size and composition of ejaculates produced by male American lobsters, Homarus americanusH. Milne Edwards, 1837 (Decapoda: Nephropidae)

Variation in the quality of ejaculate produced by male American lobsters, Homarus americanusMilne Edwards, 1837, has been previously described, but never quantified. This study examined the size and composition of ejaculates produced by 111 males ranging from 60 to 108 mm in carapace length (CL). Ejaculates were obtained via electrical stimulation, photographed and then processed for histology. Half of the males produced an ejaculate from each gonopore, 29% produced only one ejaculate, and the remainder (21%) produced none. Males as small as 64 mm CL produced an ejaculate containing sperm. Ejaculate weight increased with male size, but there was a negative relationship between ejaculate weight and the percent of the ejaculate that was composed of sperm mass. Variation observed in the size and composition of ejaculates produced by similarly-sized males indicates that not all males invest equally in reproduction. Additionally, larger males may invest disproportionately more in the sperm plug (acellular component), possibly as paternal assurance.

Occurrence of Pseudohermaphroditism in the Rock Crab, Cancer Irroratus Say, 1817, in the Southern Gulf of St. Lawrence, Canada (Decapoda, Brachyura)

Nine bisexual rock crabs (Cancer irroratus Say, 1817) were found in the southern Gulf of St. Lawrence. These individuals, externally male, were determined as pseudohermaphrodites (intersexes), because an incomplete female reproductive system (ovary without oviduct, seminal receptacle, and genital openings) was found among a complete male reproductive system. The cause of the occurrence of bisexuality in this crab is unknown. This is the first record of the occurrence of pseudohermaphroditism in this species.

Functional anatomy of the male reproductive system of the American lobster (Homarus americanus)

Despite supporting a valuable fishery, the reproductive system of the male American lobster (Homarus americanus) is poorly understood. The elongated H‐shaped testis is responsible for spermatogenesis and is composed of follicles, a common collecting duct with interlaced scattered striated muscles, and a serosa as an external wall. Sertoli cells are associated with the spermatogenesis that produces spermatozoa, which are transferred to the collecting duct through a temporary passageway. Spermatogenesis is asynchronous between follicles and occurs on a continuous basis. The anterior and posterior lobes of the testes are independent and connect to the vasa deferentia through the Y‐shaped collecting tubules that have a different cell anatomy and function than the two organs they connect. The vas deferens is divided into four regions. Spermatophores, produced in the proximal vas deferens, are packets of spermatozoa encapsulated in a single layer—the spermatophoric wall, which is composed of mucopolysaccharide acid. Large dense ovoid granules and the seminal fluid, composed of acidic sulfated mucosubstances, are secreted in the median vas deferens. Spermatophores within these secreted substances (i.e., semen) are stored in the distal vas deferens that, with the spermiduct (last region of the vas deferens), is responsible for the extrusion of the semen by striated muscle contractions. Smooth muscles suggest a peristaltic movement of the spermatophores within the vas deferens. Finally, the gonopores and the first pair of pleopods (i.e., gonopod) move the semen to the female seminal receptacle during copulation.

Spatio-temporal patterns and reproductive costs of abnormal clutches of female American lobster, Homarus americanus, in eastern Canada

Spatio-temporal patterns and reproductive costs of abnormal clutches of female American lobster, Homarus americanus, in eastern Canada Feng Tang*, Marthe Larsen Haarr, Bernard Sainte-Marie, Michel Comeau, M. John Tremblay, Julien Gaudette, and Rémy Rochette Department of Biology, University of New Brunswick Saint John, P.O. Box 5050, Saint John, NB E2L 4L5, Canada Institut Maurice-Lamontagne, Pêches et Océans Canada, 850 Route de la Mer, Mont-Joli, QC G5H 3Z4, Canada Centre des Pêches du Golfe, Pêches et Océans Canada 343 Avenue Université, Moncton, NB C.P. 5030, Canada Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, P.O. Box 1006, Dartmouth, NS, Canada Department of Fisheries and Oceans, Saint Andrews Biological Station, 531 Brandy Cove Road, Saint Andrews, NB E5B 2L9, Canada *Corresponding author: tel: þ 44 793 452 2869; e-mail: ft290@cam.ac.uk.

Spatial patterns of richness and abundance of benthic decapod crustaceans and fishes in the North-west Atlantic as measured by cobble-filled bio-collectors

ABSTRACT Examination of spatial patterns of organisms in the rocky subtidal zone is logistically challenging, particularly over large geographic distances. In the present study, we describe patterns of richness and abundance of decapod crustaceans and small demersal fishes colonizing cobble-filled bio-collectors in 2008 and 2009 at nearshore sites across an important oceanographic and biogeographic gradient in the North-west Atlantic from Rhode Island, USA to Newfoundland, Canada. At least 17 decapod and 24 fish genera were caught, including cryptic fish taxa not readily sampled with other gear. Species richness and abundance of decapods and fishes in collectors at shallow sites (5–10 m) was similar among nearby sites and was greatest in the southernmost region, but did not follow a simple latitudinal cline. The lack of clear latitudinal patterns is likely to be a result of the complex geography of summer temperatures along this coast, with the lowest temperatures at the mouth of the Bay of Fundy, the centre of the study domain. In 2008, the abundance of crabs was positively related to temperature while that of shrimp was negatively related. There was also a significant interaction between depth and study area, with greater similarity among areas at greater depths (up to 76 m), and greater similarity among depths in areas with little temperature stratification. Our results indicate that bio-collectors are a powerful tool for sampling decapod crustaceans and small demersal fishes in nearshore rocky habitats. Given the anthropogenic impacts in coastal habitats, this information is likely to prove useful for detecting changes in rocky subtidal habitats.