Homarus Americanus Milne-Edwards Research Articles

Evidence for the decline and possible extinction of a marine parasite species caused by intensive fishing

Abstract The first good evidence of the role of intensive commercial fishing in the decline and possible extinction of a marine parasite is presented. The larva of Stichocotyle nephropis Cunningham, 1887 (Aspidogastrea: Digenea) was described in 1887 from the outside of the intestine of the decapod crustacean Nephrops norvegicus (L., 1758) in the North Sea. Similar larvae were found outside the intestine of the American lobster Homarus americanus (Milne-Edwards, 1837) caught off New England in 1895. The adult form was first found in 1898 in the bile ducts of the thornback ray Raja clavata (L., 1758) from the North Sea, then in the barndoor skate Dipturus laevis (Mitchill, 1818) caught off Nantucket. There have been few records of its occurrence since then, with the last records from the northeast and northwest Atlantic published in 1972 and 1986 respectively, despite the recent attempts reported herein to find larvae and adult parasites. Both the elasmobranch final hosts are listed as “near threatened” or “ endangered” and the latest evidence on their population sizes suggests that they may have been fished to below the thresholds required for successful transmission of the parasite.

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

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.

Naturally occurring bacteraemia in American lobsters, Homarus americanus Milne‐Edwards, in Long Island Sound

The health status of the American lobster, Homarus americanus Milne-Edwards, in Long Island Sound (LIS) has been in decline, with seasonal mortality events occurring since 1998. In order to assess the potential effects of environmental conditions on lobster health via haemolymph analysis, lobsters collected from various sites in LIS were examined and sampled while concurrent environmental data (water temperature, salinity and dissolved oxygen) were recorded. The pH of the haemolymph of each lobster was tested, followed by a collection of haemolymph for serum biochemistry analysis and bacterial culture. This report focuses on the results of the bacterial sampling. The majority of bacteria cultured were opportunistic pathogens commonly found in the environment, including some that are associated with sewage and pollution. The prevalence of bacteraemia was correlated with the site of collection, the month in which the lobsters were sampled, and water temperature.

Spatio‐temporal variation in serum chemistry of the lobster, Homarus americanus Milne‐Edwards

Monthly variations in serum chemistry of the American lobster, Homarus americanus Milne-Edwards, were investigated at one location in Long Island Sound (LIS). Comparisons between three locations within and outside LIS were also made for a single time point. Most serum analytes displayed significant fluctuation over the study period and between locations. Temporal patterns could be classified as: low in cool months/high in warm months, i.e. Na, Cl, Na:K ratio, Ca, albumin:globulin ratio, percentage Fe saturation; high in cool months/low in warm months, i.e. pH, K, urea, total protein, albumin, globulin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), lipaemia; June spike, i.e. glucose, cholesterol, creatine kinase, iron, transferrin iron-binding capacity; other less obvious fluctuations, i.e. Mg, PO4; and no apparent fluctuation, i.e. HCO3, alkaline phosphatase. The proportion of samples correctly classified into month of collection by a subset of 13 analytes using discriminant analysis improved as the months progressed from May (0.75) to October (>0.95). Discriminant analysis also resolved 96.5% of samples by location. The significant depression of serum calcium at the eastern LIS site correlates with excretory calcinosis, a calcium storage disease described from lobsters at this site, but contrasts with a seasonal elevation in serum calcium recorded in the temporal component of the study. Serum proteins, the electrolytes Ca and K and the enzymes ALT and AST proved to have the strongest spatio-temporal patterns of variation. Serum chemistry is a useful research tool for lobster populations, but the dearth of information on the homology of analyte functions in this species with those in vertebrate species makes interpretation of the results challenging. Late summer/autumn water conditions appear to cause stress for lobsters in LIS.

Astaxanthin deposition in the cuticle of juvenile American lobster (Homarus americanus): implications for phenotypic and genotypic coloration

The phenotypic brownish-green color of an American lobster (Homarus americanus Milne-Edwards, 1837) is determined by genetic and dietary mechanisms. Diet influences color through the carotenoid astaxanthin. This pigment can appear red or blue depending if it is bound to protein, and the relative amounts of each form influence lobster color. Carotenoprotein formation was examined in sibling American lobsters rendered white by a diet low in astaxanthin, by feeding a diet containing 0, 55, 110, or 220 μg astaxanthin g−1 for 110 days beginning on 7 February 2004. The relative levels of red and blue in these lobsters were assessed through the analysis of digital photographs of the lobsters, which were taken monthly. The red/blue ratio was used to assess if free (red) or protein-bound astaxanthin (blue) was the dominant form in the lobsters, or if the two forms occurred in ratios allowing for natural coloration. Naturally colored lobsters developed only in the highest astaxanthin diet group, while lobsters fed the 55-μg diet were blue. Differences were observed among different parts of the body, and were presumed to be a function of cuticle thickness. However, within each diet treatment, some lobsters initially became red, suggesting an accumulation of free astaxanthin, while other lobsters initially became blue, suggesting an accumulation of protein-bound astaxanthin. This variation may be a result of differences in the uptake of astaxanthin, the rate of carotenoid-protein complexing, or in the total amount of protein available for binding. This variability is likely to be the key to understanding the underlying basis of genetically determined color in American lobsters.

Sex differences and prior residence effects in shelter competition in juvenile lobsters, Homarus americanus Milne-Edwards

Using a resident–intruder paradigm, a four-experiment study of competition for a single shelter between same- and mixed-sex dyads of juvenile lobsters, Homarus americanus Milne-Edwards, revealed a significantly greater advantage for male residents than female residents against intruders of either sex. However, there was no significant direct competitive advantage for residents of one sex over intruders of the other, as occurs for adult males over females in this species. There was a prior residence effect only in the male–male dyad condition. Unexpectedly, there was a reliable intruder advantage in female–female dyads. The methods employed showed that the shelter-seeking response of the juvenile lobster is a phylogenetic adaptation and that juvenile aggressive behavior differs little in form from that of adult lobsters but appears to be more intense.

Pre- and post-settlement processes in recruitment of the American lobster

In censuses conducted between 1989 and 1993 the cause of consistent local differences in benthic recruitment of the American lobster ( Homarus americanus Milne-Edwards) to coastal sites in Maine was unclear. Field experiments were conducted to assess the role of pre- and post-settlement processes in causing high and low extremes in recruitment on opposite sides of an outer coastal island in our study area. The west side of the island has some of the highest population densities measured in New England. Our results indicate that postlarval supply determines these differences in recruitment between the two sites. Standardized replicate cobble plots deployed on each side of the island ruled out habitat differences as an explanation for these differences, because they exhibited the same east-west difference in recruitment as the natural habitat. We also ruled out differing rates of post-settlement loss because we recovered previously marked and released settlers in equal numbers in similar plots from both sites. The distribution of neustonic postlarvae and hydrographic evidence indicate that wind-driven surface transport produces an asymmetric postlarval supply to the two sides of the island during the settlement season. Differences in the degree of asymmetry from year to year correspond to differences in the magnitude of eastward transport. We also conducted experiments at the site receiving high recruitment to assess whether new recruits or older year classes were near the saturation of cobble habitat for these animals. The combination of saturation seeding trials, using hatchery-reared lobsters, and weekly counts of natural recruits and immigrants suggests that lobsters may become increasingly subject to crowding as they grow. Movements away from the initial settlement site, probably in part caused by crowding, tend to smooth the inequality in population density which is set initially by postlarval supply.

The effects of reduced salinity on lobster ( Homarus americanus Milne-Edwards) metabolism: implications for estuarine populations

During periods of substantial freshwater runoff, lobsters that inhabit estuaries, such as the Great Bay Estuary in NH, are exposed for several days to weeks to seawater that is diluted as low as 10 ppt. To assess the physiological stress imposed by these conditions, we measured the oxygen consumption, heart rate, ventilation rate and hemolymph osmolarity of lobsters while sequentially exposing them, for 24-h periods, to seawater of 20, 15, and 10 ppt. Measurements of hemolymph osmolarity confirmed previous results which demonstrated that at salinties below 20 ppt lobsters are limited osmoregulators; allowing their hemolymph osmolarity to drop as the environmental salinity is reduced, but always maintaining it higher than the ambient osmolarity. All animals exposed to 10 ppt, at 15 °C, were capable of surviving for at least 72 h. There was a nearly linear increase in oxygen consumption, heart and scaphognathite rates in animals exposed to dilute seawater, with almost a twofold increase in metabolic rate when animals were moved from 20 to 15 to 10 ppt. At the lowest salinity tested (10 ppt) the average oxygen consumption was higher for females than for males. We conclude that at low salinities the energetic demands of osmoregulation are greater for females than males, and for both sexes the physiological stress imposed may determine, in part, their distribution and/or movements in estuarine habitats.

Influence of a thermocline on vertical distribution and settlement of post-larvae of the American lobster Homarus americanus Milne-Edwards

The hypothesis that the presence of a strong thermal gradient in the water column acts as a negative physical cue for settling lobster post-larvae ( Homarus americanus, Milne-Edwards) (Thermally-Mediated Settlement Success hypothesis, TMSS) was tested in the laboratory. Our approach was to compare the relative distribution of competent post-larvae (mid-stage IV) in a thermally stratified water column and in a control, unstratified, water column. The proportion of post-larvae settled after 24 h was significantly lower in the presence of a thermocline than in the corresponding control situations (≤25% vs. ≥50%, respectively). Gradients from 18.5 to 13.5 °C and from 16.5 to 12 °C were sufficient to significantly reduce the proportion of settled post-larvae, even though these temperatures were well within the range encountered in nature. The proportion of post-larvae crossing the thermocline increased with a decrease in stratification, going from 13% for a thermocline of 6 °C, to 15 and 28% for gradients of 4.5 and 2.5 °C, respectively. Conversely, settled post-larvae left the bottom when the ambient temperature was reduced. The vertical distribution and settlement of post-larvae were unaffected by the day/night regime. The role of the thermocline as a mediator of settlement success is discussed.

Habitat selection and predator avoidance: ontogenetic shifts in habitat use by the Jonah crab Cancer borealis (Stimpson)

Ontogenetic changes in behaviour and habitat use of Jonah crabs Cancer borealis Stimpson were examined as part of a study on habitat competition between Jonah crabs and American lobsters Homarus americanus Milne-Edwards. Crabs, lobsters and predatory fish ( Tautoga onitis Linnaeus) were placed in large circular tanks, each containing three “habitats”: cobble, featureless sand, and sand with shelter boxes. Two treatments of shelter availability were used: one shelter for every two decapods (limited) or two shelters per decapod (excess). Three size-classes of crabs (encompassing 65–158 mm carapace width) were tested with lobsters 49–59 mm carapace length. When excess shelter was available, crabs and lobsters occupied shelters significantly more frequently than the other habitats. When shelter availability was limited, crabs were displaced to other areas. The alternative habitat selected by crabs and the way in which they used it depended on crab size. Most small and medium crabs chose cobble, while large crabs were found equally in cobble and sand. Small crabs burrowed more deeply than large crabs, and burrowed more deeply in sand than in cobble. Interspecific aggressive interactions increased in intensity with crab size. T. onitis readily kill and consume Jonah crabs in tanks with no substratum or shelter. Based on the literature and my qualitative observations, I predicted that smaller crabs would be more vulnerable to predation than large crabs. However in my habitat choice experiments, crab mortality due to predation was low and was not related to crab size or habitat type. I hypothesize that size-dependent patterns of crab habitat use and behavior compensated for the greater vulnerability of smaller crabs.

Feeding ecology of benthic mobile predators: experimental analyses of their influence in rocky subtidal communities of the Gulf of Maine

The feeding ecology of mobile predators and their impact on benthic organisms inhabiting the rocky shallow subtidal zone off the coast of Maine, USA, was investigated. To determine diets and degree of prey selection we analyzed gut contents of lobsters ( Homarus americanus Milne-Edwards), two species of crabs ( Cancer irroratus Say and C. borealis Stimpson) and 13 fish species of which pollock ( Pollachius virens (Linnaeus)), cunners ( Tautogolabrus adspersus (Walbaum)), and sculpins (several species) were the most conspicuous species of this assemblage. Dietary data were compared with those on benthic prey availability. In the laboratory, we conducted experiments to test whether there is prey selection in relation to their energetic value. In the field, we conducted two experiments: (1) to test whether fish predators move into the intertidal zone during high tide for feeding purposes; and (2) to test the impact of increased predator abundance in these communities using artificial reefs made of concrete blocks. Large fish and crustacean predators foraged both benthic (mainly invertebrates) and pelagic (mostly fishes) prey. Juveniles or small individuals of crustaceans, mollusks and fish were the most heavily preyed, crabs ( Cancer spp.), mussels ( Mytilus edulis Linnaeus), and herring ( Clupea harengus Linnaeus) being the most common items. Juvenile sea urchins ( Stronglocentrotus droebachiensis (Muller)) were important prey of cunners. In the laboratory, lobsters, cunners and sculpins exhibited strong preference for small crabs and mussels but not for echinoderms. These results were consistent with those obtained with a prey selection index, and were closely related to the energy value of prey, suggesting that these predators behave as energy maximizers. 13 pollock and four cunners were caught in the mid-intertidal zone. These specimens contained a variety of undigested benthic intertidal organisms indicating that they utilize intertidal zones as feeding grounds. These results suggest that fishes may play an important role on the structure and organization of intertidal sessile communities. A significant number of predators colonized the artificial reefs, indicating that the availability of living space is an important factor affecting the distribution and abundance of large mobile predators. These predators reduced the abundance of juvenile or small benthic species, particularly of green sea urchins, in the area surrounding the reefs, suggesting that size-selective predation is presumably the mechanism by which predators influence the structure and organization of benthic communities in these environments.

Embryonic Development of the American Lobster (Homarus americanus): Quantitative Staging and Characterization of an Embryonic Molt Cycle.

The growth of a single brood of lobsters (Homarus americanus Milne-Edwards 1837) maintained at constant temperature is studied from the naupliar stage to hatching, and the sequence of appearance of morphological, anatomical, and behavioral characteristics observed. A percent-staging system based upon Perkins' eye index (1972) is presented, and ten equally spaced embryonic stages are illustrated and characterized at different levels of resolution: whole eggs, dissected embryos, antennulae and telsons. The tegumentary and setal changes in the telson show that a complete molt cycle takes place in the egg starting at about 12% embryonic development (E12%) with the molt of the nauplius into the metanauplius and ending just after hatching when the metanauplius molts into a first stage larva (L1, first zoea). At E30%, the cuticle begins to separate from the setae in the telson; this signals the start of Drach's (1939) stage D0 of the metanaupliar embryonic molt cycle. At that time, the first sign of organogenesis of the L1, the formation of the endopod of the antennulae, becomes visible; presumed sensory neurons and their axons are observed at the tip of the exopod of the antennulae where a giant sensillum is differentiating. During D0 the setae of the first larval stage are forming proximally and medially in the bilobed telson under the metanaupliar cuticle. At E90%, these setae are retracting, and the embryo has entered stage D1. After hatching (E100%), the telson of the free metanauplius (prelarva) shows the characteristics of stage D2-3 and ecdysis soon follows. The arrested development observed at constant temperature in the experimental brood occurred at stage D0 of the metanaupliar molt cycle, whereas development was resumed as the embryos entered stage D1. These changes in developmental pace from D0 to D1 in the embryonic molt cycle are parallel to those occurring in older lobsters (Aiken, 1973). The quantitative staging of lobster development from extrusion to hatching, and the description of the embryonic molt cycle will facilitate future investigations on particular aspects of the embryogenesis of Homarus such as neural differentiation.

Influence of Some External Factors on the Acrosome Reaction in the Spermatozoa of Homarus americanus Milne-Edwards, 1837

ABSTRACT Four experiments were performed to determine the effects of external Ca++, L-cysteine, ammonia, and contact with glass surfaces on the acrosome reaction of spermatozoa of Homarus americanus. Few of the spermatozoa incubated in Ca++-free sea water or in sea water containing L-cysteine showed an acrosome reaction. Many acrosome reactions were observed among spermatozoa incubated in sea water containing Ca++ or ammonia and also when Ca++ was added to spermatozoa suspended in Ca++-free sea water. It is concluded that Ca++ plays an important role in this lobster's acrosome reaction. Incidences of acrosome reactions were higher in suspensions of spermatozoa in Ca+ +-free sea water that were agitated than in those that were not agitated.

Effects of starvation on moult cycle and hepatopancreas of Stage I lobster(Homarus americanus) larvae

Effects of feeding and starvation on the moult cycle and on the ultrastructure of hepatopancreas cells were studied in Stage I lobster larvae (Homarus americanus Milne-Edwards). The relative significance of yolk and first food was quite different in larvae originating from two females. This difference was evident also in the amounts of stored lipid in the R-cells of the larval hepatopancreas. Most larvae from one hatch were, in principle, able to develop exclusively with yolk reserves (without food) to the second instar. The larvae from the second hatch showed lecithotrophic development only to the transition between late intermoult and early premoult (Stages C/D0 of Drachs's moult cycle) of the first larval instar. When initial starvation in this group lasted for 3 days or more, the point of no return (PNR) was exceeded. After the PNR, consumption of food was still possible, but development ceased in the transition C/D0 or in late premoult (D3–4). It is suggested that these stages of the moult cycle are critical points were cessation of development and increased mortality are particularly likely in early larval lobsters under nutritional stress. Examination of hepatopancreas R-cells suggested that the PNR is caused by an irreversible loss of the ability to restore lipid reserves depleted during initial starvation. Initial periods of starvation ending before the PNR prolonged mainly Stage D0 of the same instar (I). During this delay, structural changes in the R-cells caused by the preceding period of starvation were reversed: reduced lipid inclusions, swollen mitochondria, an increased number of residual bodies indicating autolysis, and a reduction of the microvillous processes. Continually starved larvae which showed lecithotrophic development throughout the first instar and were then re-fed after moulting successfully, had later a prolonged intermoult (Stage C) period in the second instar. This shows that, despite occasional lecithotrophy, food is an important factor in early larval development of the lobster.

Effects of environmental manipulation on the locomotor activity and agonistic behavior of cultured juvenile American lobsters, Homarus americanus

The locomotor activity patterns and agonistic encounters of cultured juvenile (IX–XIII stage) American lobsters, Homarus americanus (Milne-Edwards) held in 8 experimental environments were investigated to examine their relative contribution to aggressive level. Three variables: (1) lobsters individually or communally maintained, (2) shelters present or absent, and (3) open or closed seawater system were tested in a set of factorial experiments. Locomotor activity of lobsters held in a 12 h: 12 h light: dark regime was recorded for individually separated lobsters for the first 5 days and for communally held lobsters for the next 5 days of a 10-day experimental period. All lobsters maintained individually had similar levels of activity. When the same individuals were communally maintained, there appeared to be social inhibition of activity. In addition, communally held lobsters without shelter were twice as active as those provided with shelter. The activity levels of groups of communally held lobsters with shelter progressively decreased over the experimental period. All lobsters became somewhat entrained to the light: dark cycle and were nocturnally active. However, the degree of entrainment was strongly influenced (P<0.001) by the presence or absence of shelter and other lobsters. Individually maintained lobsters all showed good entrainment, although those provided with shelter were slightly better entrained. The presence of conspecifics desynchronized activity patterns when shelter was not provided. Aggressive level, as measured by the frequency of agonistic encounters per 15-min observation period and the number and types of displays per encounter, decreased over an 8-day period for groups of 3 lobsters in all experimental environments. Lobsters maintained in a closed system initially showed higher frequencies of agonistic encounters than those held in an open system. The observed decrease in aggressive level with time primarily resulted from decreased activity levels. When two lobsters met, the probability of an agonistic encounter was about 0.8 throughout the experimental period, but decreasing activity levels resulted in progressively fewer encounters. The results suggest several approaches for limiting aggression among communally maintained lobsters in culture systems by environmental manipulation.

A laboratory energy balance for the larvae and juveniles of the American lobster Homarus americanus

A laboratory energy budget was constructed for the larvae and juveniles of the American lobster Homarus americanus Milne-Edwards fed brine shrimp, Artemia saline L. Measured energy flows included ingestion, egestion, excretion of ammonia, routine and fed metabolism, growth, and production of exuvia. Digestion and assimilation were calculated and minimum ration of protein necessary to sustain larval lobsters was estimated. No change associated with metamorphosis was observed in rates of excretion, fed metabolism, and production of exuvia. Routine metabolism is not significantly higher for larvae than for juveniles. Growth changes from exponential in larvae to a slower increase in post-larvae. Consumption reflects changes in other variables. Changes in energy partitioning and energetic efficiencies associated with metamorphosis are largely due to change in rate of growth.

Survival of communally reared larval and juvenile lobsters, Homarus americanus

Survival of individually reared larval and juvenile stage lobsters, Homarus americanus (Milne-Edwards), was significantly higher than in corresponding groups of communally reared individuals. Among communally reared lobsters, the mortality rate was highest in the second-stage larvae and then progressively decreased in the later stages. The relationship between survival and duration of molt period of each life-cycle stage indicates that asynchronous molting in the groups of communally reared lobsters is a contributing factor to the higher mortality rate. The molting and mortality curves of communally held lobsters reared from the first larval to first or second juvenile stage showed best cross correlation at 0- or 1-day time lag. The decreased mortality rate observed in the later larval and juvenile stages appears to have resulted from the establishment of new behavior patterns. Group interactions which are influenced by numerous extrinsic and intrinsic factors lead to higher mortality rate (“cannibalism”) among communally reared lobsters.

Yolk utilization and hatching time in the Canadian lobster Homarus americanus

During the course of its embryonic development, the Canadian lobster Homarus americanusMilne-Edwards exhibits steady increases in water content (56.2 to 86.8%) and ash (5.8 to 21.2%), and a progressive decrease in energy content from 6636 to 4292 cal/g dry weight. Mean dry weight of a single egg is 965 μg, equivalent to 6.4 cal; a freshly hatched egg. The lobster hatches about 1,500 larvae per night over a period of 4 to 5 days. Dry weight, ash and calorific contents of larvae hatched on different days show considerable variations. After larvae hatch on the first day, continuous salt absorption by eggs to hatch on subsequent days leads to a steady increase in ash content from 143 μg/larva hatched on the first day to 255 μg/larva hatched on the fourth day, and consequently, to an increase in dry weight from 854 to 956 μg/larva. Metabolism of embryos (0.1 cal/day), which are yet to be hatched on subsequent days, depletes the calorific content per unit weight (from 4637 to 3837 cal/g dry weight) as well as per larva (from 3.98 to 3.67 cal).

Geographic Morphometric Variation in the American Lobster

Saila, S. B., and Flowers, J. M. (Marine Expt. Sta., U. Rhode Island, Kingston, R. I.) 1969. Geographic morphometric variation in the American lobster. Syst. Zool., 18:330-338. [Morphology; geographic variation; multivariate; lobster; Homarus americanws].-An analysis of morphologic measurements from geographically separated samples of the American lobster, Homarus americanus, was made. The centour concept, which involved inferring an individual's group membership from multivariate data, was used. The study involved identification of inshore and offshore groups of lobsters by means of small shape differences based on simultaneous consideration of linear measurements from 16 body parts. The results of the study showed that definite profile differences existed between inshore and offshore groups when matched by size and sex. The observed differences were greater between inshore and offshore groups than those occurring within geographically separated samples of both inshore and offshore lobsters. The results of the study suggested that relatively little overlap was discernible between the inshore and offshore areas in the characters measured. These studies support inferences made from tagging studies to date. Sokal and Sneath (1963) have clearly pointed out the importance of numerical methods for evaluating the extent of affinity or similarity between taxonomic units. The scope of their work has been restricted primarily to methods intended to demonstrate taxonomic relationships and to create taxonomic groupings. The present study is related in approach to that of Thomas (1963), who analyzed morphological characters of the rabbit tick Haemaphysalis leporispalustris, with a view towards obtaining clues, to the operation of evolutionary mechanisms. In attempting to understand and measure causes, of fluctuations in the abundance of a species, it is imperative that the number and identity of any subsets of the species be established. The reason for this is obvious to, any rational management plan inasmuch as each subset of the population (species) may have a characteristic distribution and characteristic vital statistics, such as mortality and growth rates. These considerations are especially relevant to the lobster, Homarus americanus Milne-Edwards, because the fishery for this species in the offshore waters of the western 1 This research study was financed by the Bureau of Commercial Fisheries under Contract No. 14-17-0003-152. North Atlantic has rapidly expanded in recent years, and some segments of the lobster industry have contended that the offshore lobsters contribute significantly to the inshore pot fishery. Reports of the results of exploratory fishing in offshore areas have been made by Schroeder (1955; 1959) who also described depth and latitudinal distribution of offshore lobsters. In general, the inshore pot fishery is restricted to shoal waters not in excess of 20 fathoms, whereas the offshore lobsters are taken in depths from 60-250 fathoms, along the edge of the continental slope. No assessment of the relationship between inshore and offshore lobsters has been made to date. However, several approaches to this problem have been undertaken, and the work described herein is one segment of a comprehensive study conducted by the U. S. Fish and Wildlife Service, Bureau of Commercial Fisheries, Biological Laboratory, West Boothbay, Maine. The objectives of this study were: (a) to establish whether identifiable subsets (groups) of the lobster could be established on the basis of distinctive morphoimetric characters, and (b) to assign individuals on a probabilistic basis to these groups if they were found. The use of the term group

Different toxic mechanisms in kraft pulp mill effluent for two aquatic animals

Bleached kraft mill effluent (BKME) seems to contain at least two different toxic mechanisms or materials which affect aquatic animals. BKME stored under clean and quiescent conditions, lost much of its toxicity for salmon parr ( Salmo salar L.) in 1 week, and all in 2 weeks. By contrast, it lost little toxicity to lobster larvae ( Homarus americanus Milne-Edwards) in 2 weeks. Bio-oxidation of BKME for 1 week eliminated toxicity for salmon parr, but did not greatly change toxicity for lobster larvae. Biooxidation for 2 weeks reduced but did not eliminate toxicity to lobster larvae. A waste treatment process which reduces toxicity of BKME for one species may not protect other species.