Mature Lobsters Research Articles

Movements of Tagged American Lobsters, Homarus americanus, off Southwestern Nova Scotia

A total of 4304 American lobsters (Homarus americanus) were tagged and released in inshore areas off southwestern Nova Scotia and on northwest Browns Bank during June–August 1975. Of the 424 lobsters recaptured within 5.4 yr of release, 385 had known recapture locations. For all release areas the average straight-line distance traveled by mature ([Formula: see text]carapace length) lobsters (15.6 km) was significantly greater than for immature (59–94 mm carapace length) lobsters (4.7 km). Most (69.3%) of the immature lobsters (N = 212) were recaptured less than 18.5 km (10 naut mi) from the release sites; for mature lobsters (N = 173) this percentage was 40.5%. Previous tagging studies off southwestern Nova Scotia revealed little evidence of long-distance movement; our study, however, shows that mature lobsters can move long distances. Many (19.7%) of the mature lobsters were recaptured more than 92.6 km (50 naut mi) from the release sites. The overall direction of travel was south, in both an east and west direction, with many lobsters moving greater than 50 km from coastal Nova Scotia and Browns Bank into the Gulf of Maine and to the slopes of the continental shelf. Thirteen lobsters moved from Browns Bank to inshore areas of southwestern Nova Scotia. The evidence of the long-distance interchange of a portion of the mature adults between southwestern Nova Scotia and the adjoining continental shelf suggests that lobsters in these areas could belong to a single stock.

Growth of Tagged American Lobsters, Homarus americanus, in the Bay of Fundy

Sphyrion-tagged lobsters recaptured in the Bay of Fundy during 1977–80 yielded mean annual molt increment and molt probability data for male and female lobsters of 60–171 mm carapace length from which growth curves were calculated. In addition, a multiple regression model was used to generate growth curves from premolt size, number of molt periods lobsters were exposed to, and growth increment data for 850 tagged lobsters at liberty for 1–5 yr. Von Bertalanffy parameters were calculated from these empirical growth curves, which suggest that lobsters take 20–35 yr from time of hatching to reach 200 mm carapace length in the Bay of Fundy. Analysis of pleopods indicated that the majority of lobsters molt during August–October each year. Growth per molt of immature (60–94 mm carapace length) and mature (95–170 mm carapace length) male and immature female lobsters was arithmetic (regression slope 1.04) but was regressive for mature females (slope 0.95). Mature lobsters molted less frequently than immature lobsters, but mature males grew more rapidly than mature females. Most mature females in the Bay of Fundy are on a 2-yr molt–reproductive cycle. About 20% of ovigerous females recaptured within 2 yr after release had extruded eggs a second time without molting, confirming that multiple egg extrusions between molts do occur naturally.

Differentiation of identifiable lobster neuromuscular synapses during development.

The ultrastructure of physiologically identified low and high release synapses arising from a single axon on fibres of the distal accessory flexor muscle (DAFM) in a mature lobster was examined by serial section electron microscopy. Low release neuromuscular terminals located only on the proximal fibre were characterized by large synapses (mean area 2.084 micron2), small presynaptic dense bars (mean are 0.021 micron2) and hence a low (2.3%) ratio of dense bar area to synaptic area. In contrast high output terminals located only on the distal fibre had smaller synapses (mean area 0.625 micron2), large dense bars (mean area 0.066 micron2) and a high (23.9%) ratio of bar area to synaptic area. A similar ratio was consistently found for each synaptic type in several other examples of mature lobsters. Hence it was used as a criterion for determining the point at which differentiation occurs during development. In the first larval stage (24 h old) the innervation was localized and undifferentiated. In the fourth (2 week old) and twelfth (1 y old) stage lobsters, the innervation had proliferated to small bundles of proximal and distal fibres. During development synapses increase in their mean surface area in the proximal fibre while remaining constant in the distal fibre. The mean surface area of the dense bars is similar in all stages except for the proximal fibres of the twelfth stage where it is smaller by 50%. Similarly the ratio fo dense bar area to synaptic area is not significantly different for all stages except for the twelfth stage proximal fibres where it is half the value. Consequently differentiation of low and high release neuromuscular terminals occurs by the twelfth stage with an increase in the mean surface area of synapses and a decrease in the mean surface area of dense bars. This morphological differentiation is enhanced in the mature lobster.

The ovary of the lobster, Homarus americanus: I. Architecture of the mature ovary

We have examined the architecture of the mature lobster ( Homarus americanus ) ovary using microscopical techniques. The ovary is comprised of five tubular lobes which are organized in an H-shaped pattern. Each lobe contains four morphological components which are: (i) the ovarian wall, (ii) the epithelium, (iii) the follicles, and (iv) the extensions of the ovarian wall. The wall is made up of blood vessels and sinuses, blood cells, and nonstriated muscle cells which may undergo spontaneous contraction when the ovary is cut. The epithelial cells are flat and rest on a thick basal lamina. They form a thin seet on the luminal surface of the ovary. Portions of this sheet fold outward toward the ovarian wall. Epithelial cells are continuous with and may give rise to follicle cells around oocytes. The mature ovary contains large (mature, 1.2–1.6 mm)-, intermediate (0.1–0.4 mm)-, and small (0.07–0.1 mm)-sized follicles. Small follicles and some intermediate follicles are found embedded in the epithelium lining the lumen. Most intermediate follicles form chains linking the luminal epithelium to mature follicles. The mature follicles are stacked in tiers three to five follicle layers deep between the ovarian wall and the lumen. The extensions of the ovarian wall consist of both blood vessels and muscle cells; these project into the follicular region and insert on follicle walls and on the epithelium. This description of the mature lobster ovary extends our knowledge on the organization of the decapod ovary and provides a basis for future detailed structural and physiological analyses of this organ.

Collagenase solutions induce in vitro ovulation in lobsters (Homarus americanus)

AbstractThe effect of several hydrolytic enzymes on ovulation of lobster (Homarus americanus) oocytes was studied in vitro using strips of ovarian tissue. Only ovaries which were judged by candling and microscopic examination to be close to natural ovulation were used. Ovaries were removed and cut into small, flat strips (1 cm2) and placed in either seawater (SW) or SW containing an enzyme. The number of oocytes ovulated from these strips was determined periodically over a 3–6‐hour period. Of the enzymes tested, only crude collagenase treatment produced ovulation. Highly purified collagenase was tested subsequently and found effective. Moreover, when cysteine, a collagenase inhibitor, was added to crude collagenase preparations, ovulation did not occur. These results (1) show that mature lobster ovaries will undergo in vitro ovulation in SW solutions containing collagenase, and (2) are the first demonstration that a hydrolytic enzyme may be directly involved in invertebrate ovulation. It is suggested that collagenase disrupts the thick basement membrane surrounding each follicle, thus initiating follicular rupture and subsequent extrusion of the oocyte. This technique provides a useful method for in vitro studies of lobster ovulation.

North Cape — a ‘nursery area’ for the packhorse rock lobster,Jasus verreauxi(Deeapoda: Palinuridae)

In the North Cape area (34°26'S, 173°07'E) there appears to be a concentration of late juvenile packhorse rock lobsters, Jasus verreauxi (H. Milne Edwards'), which subsequently contributes significantly to the nearby fishery for adult J. verreauxi off Cape Reinga. Evidence for this is based on the overall smaller size and fewer mature rock lobsters at North Cape compared to areas nearby, and on the results of tagging experiments carried out during 1976–77. Rock lobsters tagged at North Cape moved 21–514 km, mainly west and south, before recapture at minimum rates of 0.03–2.00 krn.d‐1. For females at least, the movement away from North Cape usually occurs at about the time that sexual maturity is attained. Rock lobsters tagged near Cape Reinga moved 3–34 km west at minimum rates of 0.04–0.35 km.d‐1. Although the closure of the North Cape grounds to rock lobster fishing restricts the taking of the small number of legal‐sized fish available in the area, the restriction ensures less mortality and damage to th...

Minimum Size of Mature Spiny Lobsters, Panulirus argus, at Dry Tortugas, Florida

Abstract Of 1,594 female lobsters examined during April 1973-1975, 55% were bearing eggs (berried). The specimens ranged in carapace length from 39 mm to 140 min. No berried females were found with carapace lengths less than 78 min. Maturity was reached by one half of the females in the 86-95 mm size class. The current minimum legal size for sport and commercial lobster fishing in Florida is 76-mm carapace length.

Effects of Several Factors on the Growth of the American Lobster (Homarus americanus) in Captivity

With existing methods, there is little possibility of growing lobsters economically through a moult in captivity.In initial experiments on effects of temperature, feeding rate, diet, and sex on growth of spring-caught lobsters of 0.6–1.0 lb (0.28–0.45 kg) in captivity, gross weight of all 19 groups decreased by an average of 36% by 6 or 8 months (McLeese 1972).In these experiments on effects of maturity and storage density, lobsters of 1.0 lb (0.45 kg), maintained at four storage densities at 15 C, were fed fish, squid, and beef liver at 6% of their weight per week. Moulting occurred mainly from early July to late October with only a few others moulting by March (10 months). There was no difference in weight increment for mature and immature lobsters. Mean increments in length and weight were inversely related to storage density. Heavy mortality in one group was caused in part by lobster blood disease, gross weight in the remaining six decreased by an average of 2.5% by 6 months, and 19% by 10 months, corresponding with mortality of 17.5 and 29.4%.