Lobster Population Research Articles

Recovery of the eastern rock lobster Sagmariasus verreauxi off New South Wales, Australia

Catch per unit effort in the fishery for eastern rock lobsters peaked in 1971–72 and then declined until 1992–93. In response to this pattern, a management package consisting of individual catch quotas, restricted entry and a legal maximum length was imposed upon the fishery. The effectiveness of these management measures to rebuild the eastern rock lobster population has been monitored annually through data collected from surveys of puerulus larvae abundance, fishery independent surveys, a compulsory logbook, observer surveys and biological studies. The total allowable commercial catch (TACC) is set annually by the TAC Committee after considering submissions from the public and industry and an annual report for the lobster fishery. The annual report prepared by government consists of an appraisal of the performance of the fishery against the objectives of the share management plan and goals of the fishery management strategy for the rock lobster fishery and includes a formal stock assessment. The trigger points behind the objectives and goals relating to the status of the stock have not been activated in the 2010–11 year. Total biomass and exploitable biomass have increased, spawner biomass has increased to now be above 25% of the pre-exploited biomass and the relative abundance of recruits (puerulus larvae) to the population is increasing. The stock is considered to be rebuilding and the resource now supports a viable fishery with an increasing share price.

The Geography and Body-Size Dependence of Top-Down Forcing in New England's Lobster-Groundfish Interaction

We examined changes in the body-size dependence of the groundfish-American lobster interaction across the steep environmental and biogeographic gradient from the Gulf of Maine to southern New England, USA. Lobster (Homarus americanus H. Milne-Edwards, 1837) abundance has increased dramatically in the Gulf of Maine since the 1980s. A parallel upsurge in southern New England ended in 1997 with the onset of a disease epizootic. To characterize the geography and body-size scaling of the predator-prey interaction, and to determine whether changes in the predator assemblage could explain the increases in lobster abundance, we drew on field predation experiments and surveys on nurseries where lobsters first settle, as well as trawl-survey time series of fish and lobster abundance on habitats exploited by older lobsters. Our results suggested that the fish predators frequenting lobster nurseries in the Gulf of Maine are less diverse or abundant than those in southern New England and that predation risk in the Gulf of Maine is correspondingly lower. Trawl-survey time series suggested that the expansion of the lobster population was more strongly correlated with declines in average body mass of fish predators in the Gulf of Maine than in southern New England. The resultant relaxation of predation pressure on the American lobster in the Gulf of Maine reflects a functional change in a key link of the food web induced by a change in predator body size. A closer examination of size-specific interactions of individual species and functional groups in the groundfish assemblage is therefore warranted.

Increased Disease Calls for a Cost-Benefits Review of Marine Reserves

Marine reserves (or No-Take Zones) are implemented to protect species and habitats, with the aim of restoring a balanced ecosystem. Although the benefits of marine reserves are commonly monitored, there is a lack of insight into the potential detriments of such highly protected waters. High population densities attained within reserves may induce negative impacts such as unfavourable trophic cascades and disease outbreaks. Hence, we investigated the health of lobster populations in the UK’s Marine Conservation Zone (MCZ) at Lundy Island. Comparisons were made between the fished, Refuge Zone (RZ) and the un-fished, No-Take Zone (NTZ; marine reserve). We show ostensibly positive effects such as increased lobster abundance and size within the NTZ; however, we also demonstrate apparent negative effects such as increased injury and shell disease. Our findings suggest that robust cost-benefit analyses of marine reserves could improve marine reserve efficacy and subsequent management strategies.

Detecting immigrants in a highly genetically homogeneous spiny lobster population (Palinurus elephas) in the northwest Mediterranean Sea

We investigated the genetic structure of early benthic juveniles of the spiny lobster Palinurus elephas in the northwest Mediterranean Sea by means of ten polymorphic microsatellite markers. Non-metric Multidimensional Scaling coupled with assignment tests were used as a new approach to further delimit a reference population inside a genetically homogeneous pool of individuals and test for the presence of long distance immigrants. From this approach, we found that most early benthic juveniles collected while settling in the northwest Mediterranean Sea originated from a common larval pool. However, 4.2% of the individuals were classified as immigrants from other genetically differentiated populations, with more immigrants in the south than in the north of the sampled basin. Given currents in the northwest Mediterranean Sea and the long pelagic larval phase of P. elephas that lasts several months, this result suggest a restricted homogenized zone in the studied basin with some individuals probably coming from more differentiated populations through the Almeria-Oran Front or the Strait of Sicily.

Large‐scale coherence in New England lobster (Homarus americanus), settlement and associations with regional atmospheric conditions

AbstractTime series of American lobster (Homarus americanus) postlarval settlement from southern New England to Atlantic Canada exhibit many common features, and a cluster analysis indicates a block of regions extending from Massachusetts to Maine that have coherent interannual variations. The spatial scale of this block suggests that variability in settlement is related to large‐scale, rather than local, processes. We examined the association between settlement at six reference regions and monthly mean atmospheric conditions (temperature, geopotential height, westerly and southerly wind components, and wind curl) from the North American Regional Reanalysis. We first extracted the dominant modes of variability in monthly averaged geopotential height, temperature, and wind curl. The leading mode from September, which represents high geopotential height, warm temperatures, and negative wind curl throughout the study area, was strongly correlated with settlement at most of the regions. The third mode from August, which represents enhanced southwesterly winds, was correlated with settlement in Rhode Island. Correlations between local atmospheric conditions and lobster settlement confirm the principal component results. Settlement was correlated to varying degrees with geopotential height (positive), temperature (positive) and wind curl (negative) with lobster settlement at the northern sites, with temperature being a stronger indicator in the north and curl a stronger indicator in the south. Rhode Island settlement was strongly correlated with August westerly winds. The correlation between settlement and atmospheric conditions could improve our understanding of stock‐recruit relationships for lobster populations and provides one mechanism for how climate change could impact lobsters.

Cryptic species within the commercially most important lobster in the tropical Atlantic, the spiny lobster Panulirus argus

Panulirus argus (Latreille in Ann Mus Hist Nat Paris 3:388–395, 1804) is the lobster of greatest economic importance throughout its distribution. In this study, mitochondrial (Cytochrome Oxidase I and 16S ribosomal genes) and nuclear (Adenine Nucleotide Transporter gene) sequences were used to evaluate the taxonomic status of P. argus sampled from five sites in the Caribbean Sea and nine sites in the Southwest Atlantic. Phylogenetic analyses indicate that lobsters from the two regions form two monophyletic groups with a molecular divergence similar to that observed between distinct congeneric lobster species and much larger than that found between conspecific lobster populations. Therefore, the Caribbean and the Southwest Atlantic lobster populations originally attributed to P. argus belong to different species, with an estimated time of isolation of around 16 Million years. An important consequence of these findings is that the fisheries of spiny lobsters from the Caribbean and the Southwest Atlantic species must be managed separately.

Shell Disease in the American Lobster,Homarus americanus: A Synthesis of Research from the New England Lobster Research Initiative: Lobster Shell Disease

The goal of this synthesis is to highlight some of the major findings of the New England Lobster Research Initiative (NELRI), provide a context for these findings based on previous research, discuss the potential impacts of this important emerging disease on the dwindling lobster populations in southern New England (SNE), and provide suggestions on avenues for future research. Most of the research funded in this initiative focused on epizootic shell disease (ESD), the emerging syndrome severely impacting lobster populations primarily in coastal waters in Rhode Island, southern Massachusetts, and eastern Long Island Sound (ELIS), but some new information about other forms of shell disease in lobsters is included. We also discuss how these novel findings on lobster shell disease should be used to inform management of lobster populations.

Endocrine-Disrupting Alkylphenols are Widespread in the Blood of Lobsters from Southern New England and Adjacent Offshore Areas

Endocrine-disrupting pollutants in rivers and oceans represent a poorly understood but potentially serious threat to the integrity of aquatic and coastal ecosystems. We surveyed the hemolymph of lobsters from across southern New England and adjacent offshore areas for 3 endocrine-disrupting alkylphenols. We found all 3 compounds in hemolymph from every year and almost every region sampled. Prevalence of contamination varied significantly between regions, ranging from 45% of lobsters from southern Massachusetts to 17% of lobsters from central Long Island Sound. Mean contamination levels varied significantly as a function of region, year sampled, and collection trip, and were highest overall in lobsters from western Long Island Sound and lowest in lobsters from central Long Island Sound. Surprisingly, lobsters from offshore areas were not less contaminated than lobsters from inshore areas. Contamination levels also did not vary as a function of lobster size or shell disease signs. Contaminated lobsters held in the laboratory did not retain alkylphenols, suggesting that hemolymph contamination levels represent recent, rather than long-term, exposure. Our data set is the first, to our knowledge, to survey endocrine-disrupting contaminants in a population across such a broad temporal and spatial scale. We show that alkylphenol contamination is a persistent, widespread, but environmentally heterogeneous problem in lobster populations in southern New England and adjacent offshore areas. Our work raises serious questions about the prevalence and accumulation of these endocrine-disrupting pollutants in an important fishery species.

Relationship between Temperature and Shell Disease in Laboratory Populations of Juvenile American Lobsters (Homarus americanus)

Epizootic shell disease is affecting American lobster (Homarus americanus) populations and the associated fisheries significantly. Historical movement of the disease suggests that temperature has been a critical factor in driving the susceptibility of lobsters to this disease. Here, juvenile lobsters were held in the laboratory at 10°C, 15°C, or 20°C for up to 1,021 days. Survival, growth, and shell disease were tracked throughout, and a separate experiment was conducted to assess the rate at which dietary white lobsters deposited pigment to the cuticle at the different temperatures. In the laboratory, shell disease was tracked as an initial “spot,” the melanization of the cuticle in response to the bacterial ingress, or, as it progressed, a lesion, which was a visible erosion of the shell. The length of the molt cycle (number of days from one molt to the next consecutive molt) was inversely associated with temperature. Average growth (increase in weight and carapace length per molt) at 10°C and 15°C was equivalent and higher than at 20°C, whereas shell disease was greatest at the intermediate temperature. The amount of initial melanization responses to bacteria (spots) was similar across temperatures, but the number of lesions was greatest at 15°C. This is likely a result of the conditions that allow for a combination of longer molt cycles and active bacterial growth, which allowed the disease to progress to the more advanced lesioned state. At the highest temperature, lobsters molted the compromised shell before severe lesion formation could occur. No gross differences in shell structure were observed at the different temperatures. The lack of a linear relationship between shell disease and temperature does not discount temperature as a critical factor in the onset of this disease in lobsters, but signifies that additional factors are important and the disease is complicated and multifactorial in nature. The continued use of a laboratory model system to study this disease further is important to be able to control the multitude of complicating factors appropriately.

Dysbiosis in Epizootic Shell Disease of the American Lobster (Homarus americanus)

Epizootic shell disease (ESD) in the American lobster (Homarus americanus) is continuing to affect the southern New England lobster population, and the etiology of the disease has not been well defined. We hypothesized that a dysbiotic shift in the shell microbial biofilm played a key part in the etiology of the disease. We analyzed the community structure of the surface microflora of apparently healthy and diseased lobsters using multitag pyrosequencing to correlate the abundance of key taxa within the lesions. Discriminant analysis (DA) was used to identify taxa in the microbial community that were associated with diseased and healthy states. Among the 170 bacterial taxa that were identified, 58 were helpful in determining the diseased and healthy states. The remaining 112 were not significantly different between the 2 states. The genus Aquimarina was present in high abundance in both healthy and diseased lobsters, but had a significantly higher abundance on animals in the diseased state. However, DA demonstrated that this genus does not strongly discriminate between the diseased and healthy state. Phylogenetic analysis indicated that there was significant strain diversity of this genus in all the samples analyzed. Our results indicate that the lesions seen in ESD may be viewed as being correlated with a polymicrobial component rather than being caused by a discrete pathogen.

Alkylphenols affect lobster (Homarus americanus) larval survival, molting and metamorphosis

Alkylphenols are widely distributed in the marine environment and we have found them to be widely dispersed in New England lobster populations. In vertebrates, these compounds act as estrogenic endocrine disruptors. Here, we tested two alkylphenols, bisphenol A and 2,4-bis-(dimethylbenzyl)phenol for their effects on lobster larvae. In particular, we examined their toxicity and their effects on molting and metamorphosis. Lobsters were raised to stage 2 and were then isolated individually in ice cube trays with nylon mesh netting on the bottom giving access to flow through cooled seawater. The experimental larvae were fed with 5 or 10 ng alkylphenol per day in their diet. Controls were fed the same diet minus the test chemicals. The alkylphenols were toxic to second and third stage larvae, and fourth stage post-larvae, with 13–21% surviving to 25 days compared to 69% of controls. The compounds significantly delayed each molt by 2–3.5 days, and the surviving treated larvae were predominantly larval–juvenile intermediates at metamorphosis (62%). The differences between treatments and controls in all cases were highly significant using survival analysis based on the Weibull distribution. We conclude that alkylphenols are endocrine disruptors to lobster larvae at metamorphosis because they possess juvenile hormone activity. They also delay molting, reduce growth, and are toxic at relatively low concentrations.

Demography, fishery yield and potential management strategies of painted spiny lobster (Panulirus versicolor) at Northwest Island, Great Barrier Reef, Australia

Quantification of demographic parameters is important for understanding how populations interact with their environment and for developing sustainable harvest strategies. Our aims were to quantify demographic parameters and yield of painted spiny lobster (Panulirus versicolor) at Northwest Island, Great Barrier Reef and review fishery management regulations in view of the findings. Using catch-curve analysis and an intensive mark–recapture program, the local lobster population was found to be sparsely distributed (~1.3 ha–1), with low rates of natural mortality (0.25–0.28 year–1) and immigration (0.05 ha–1 year–1). Under current management regulations (no minimum size limit; MSL), yield-per-recruit peaked at 0.38 kg when fishing mortality was 0.4 year–1. Implementation of a 100-mm (carapace length) MSL is recommended because it provides the best compromise between yield and stock size and has minimal impact on existing fishing practices. Revocation of the prohibition on possessing egg-bearing females is also recommended because it would reduce wastage of lobsters that are inadvertently killed by spear-fishers and because there appears to be little chance of localised recruitment overfishing. This study provides the first estimate of mortality rate for P. versicolor and highlights the importance of this parameter for understanding demographic processes and optimising management regulations.

Collaborative assessment of California spiny lobster population and fishery responses to a marine reserve network

Assessments of the conservation and fisheries effects of marine reserves typically focus on single reserves where sampling occurs over narrow spatiotemporal scales. A strategy for broadening the collection and interpretation of data is collaborative fisheries research (CFR). Here we report results of a CFR program formed in part to test whether reserves at the Santa Barbara Channel Islands, USA, influenced lobster size and trap yield, and whether abundance changes in reserves led to spillover that influenced trap yield and effort distribution near reserve borders. Industry training of scientists allowed us to sample reserves with fishery relevant metrics that we compared with pre-reserve fishing records, a concurrent port sampling program, fishery effort patterns, the local ecological knowledge (LEK) of fishermen, and fishery-independent visual surveys of lobster abundance. After six years of reserve protection, there was a four- to eightfold increase in trap yield, a 5-10% increase in the mean size (carapace length) of legal sized lobsters, and larger size structure of lobsters trapped inside vs. outside of three replicate reserves. Patterns in trap data were corroborated by visual scuba surveys that indicated a four- to sixfold increase in lobster density inside reserves. Population increases within reserves did not lead to increased trap yields or effort concentrations (fishing the line) immediately outside reserve borders. The absence of these catch and effort trends, which are indicative of spillover, may be due to moderate total mortality (Z = 0.59 for legal sized lobsters outside reserves), which was estimated from analysis of growth and length frequency data collected as part of our CFR program. Spillover at the Channel Islands reserves may be occurring but at levels that are insufficient to influence the fishery dynamics that we measured. Future increases in fishing effort (outside reserves) and lobster biomass (inside reserves) are likely and may lead to increased spillover, and CFR provides an ideal platform for continued assessment of fishery-reserve interactions.

Growth rates of juvenile southern rock lobster (Jasus edwardsii) estimated through a diver-based tag - recapture program

Despite being one of the most economically important fisheries in south-eastern Australia, growth rates of juvenile southern rock lobster (Jasus edwardsii) have not previously been quantified in the wild. This study utilised a diver-based tag–recapture program to estimate growth rates of individuals between 40–80 mm carapace length (CL) in temperate reef sites across south-eastern Australia. Of the 7064 lobsters tagged and released, 978 (14%) were recaptured with recapture rates of 23, 5 and 7% in the States of Tasmania, South Australia and Victoria respectively. Although individual growth increments were similar between the sexes, differences in annual growth rates were evident at 50 mm CL, with males growing ~1.4 times faster than females. Increased levels of growth in males resulted from a higher moult frequency, which was found to significantly reduce in females as they reached sexual maturity at ~70–80 mm CL. No significant difference was found in growth rates of males or females between the States when all sites within each State were combined. The growth estimates from this work contribute to the understanding of juvenile lobster population dynamics and will improve current fishery models by confirming relationships between early juvenile, pre-recruit abundance and entry to the fishable biomass.

A review of burrow counting as an alternative to other typical methods of assessment of Norway lobster populations

The diurnal and seasonal regulation of the complex burrowing behavior of Nephrops norvegicus complicates population assessment for this species. Population assessment is traditionally carried out by Virtual Population Analysis (Length Cohort Analysis; LCA) and swept area density estimations from catch data. However, burrow counting from visual surveys has also acquired increasing importance in recent years as an alternative and apparently efficient method. All these approaches produced non-equivalent assessment results in the literature, and therefore, a comparison and critical discussion of these methods is warranted. In this review, we pursued this goal by using already published and unpublished fishery data for a commercially exploited western Mediterranean shelf (60–100 m) population as an example. The cross-assessment was carried out by LCA, the swept area method and burrow counting in different seasons (spring-summer and autumn–winter) to highlight biases in abundance estimations in relation to Nephrops behavior. We also used novel trawl density data for other fish and decapod species in the area because the burrowing behavior of these species may deeply bias Nephrops abundance in visual surveys. LCA provided intermediate assessment values when compared to the swept area and photographic estimates, which over- and underestimated the abundance, respectively. We reviewed the problems related to the peculiar burrowing behavior of the species that generate assessment estimations of such different magnitude.

Comparison of Vented and Ventless Trap Catches of American Lobster with Scuba Transect Surveys

ABSTRACT Ventless trap surveys are becoming an increasingly common method to estimate American lobster (Homarus americanus) population structure and abundance. These surveys typically consist of strings of conventional commercial vented traps set alternately with experimental ventless traps, which lack escape vents and, as a result, capture higher proportions of sublegal-size lobsters. To determine how accurately ventless trap surveys reflect lobster populations on the seafloor, lobster density, size distribution, and sex ratios observed from scuba transect and tagging surveys were compared with ventless trap survey catches at 17 locations that varied by average temperature and dominant substrate. Diver surveys indicated that higher lobster densities were associated with increasing substrate complexity and constant temperature. Trap catch per unit effort increased with substrate complexity and decreased with increasing water temperatures. Comparisons of survey methods suggest ventless trap surveys overest...

Bait and the susceptibility of American lobsters Homarus americanus to epizootic shell disease

Shell disease (SD) has been observed in lobster populations for almost a hundred years, but recently, rates of an epizootic form of shell disease (ESD) have increased in the southern New England (USA) area. A large proportion of fish in the diet of American lobsters Homarus americanus has been linked to increased rates of SD. Therefore, the use of fish as lobster bait may be linked to increased ESD rates in lobsters. Lobsters from the western portion of Martha's Vineyard, MA (41 degrees N, 71 degrees W), were randomly divided into 3 groups of 16 and exposed to dietary treatments (100% herring; 48% crab, 48% blue mussel and 4% plant matter; or 50% herring, 24% crab, 24% mussel, 2% plant matter) to determine if lobster tissue delta15N levels reflected diet. The results of the feeding experiment confirmed that differences in diet are observed in the delta15N levels of lobster muscle tissue. The delta15N levels of tissue samples from 175 wild lobsters with varying degrees of ESD were unrelated to ESD severity but did indicate lobsters were eating large amounts of fish (bait). This result does not support the speculation that fish used as bait is contributing to ESD outbreaks in portions of the southern New England area.

Dietary change of the rock lobster Jasus lalandii after an ‘invasive’ geographic shift: Effects of size, density and food availability

During the 1990s the rock lobster Jasus lalandii shifted its focus of distribution south-eastwards along the coast of South Africa, to establish a dense population in an area where it was previously rare. This coincided with a marked decrease in the sea urchin Parechinus angulosus, a preferred prey item of J. lalandii and a vital source of shelter for juveniles of the abalone Haliotis midae. The range expansion of lobsters has thus economic and ecological ripple effects. We determined the diets of small (50–65 mm carapace length) and large (>69 mm CL) rock lobsters from gut content analyses, and compared them between three ‘lobster invaded’ sites and three adjacent ‘non-invaded’ sites where densities are still low. At the non-invaded sites, diets were collectively heterogeneous but the dietary breadth of individual lobsters was narrow (in contradiction to generally accepted ecological theory), and the lobsters fed mainly on large, individual, mobile, high-energy prey such as sea urchins and large winkles. Conversely, at invaded sites where lobster densities were high, they consumed predominantly small, colonial or sessile low-energy prey such as sponges, barnacles and foliar algae, and the diet was significantly more uniform among individuals, but broader within individuals. This was a direct result of the contrasting benthic community structure of the two areas, and consequent prey availability – itself caused by differences in intensity of rock-lobster predation. Cannibalism was unexpectedly greater at non-invaded sites, possibly as a result of lobsters being larger there. The diet of small and large lobsters also differed significantly. Large rock lobsters predominantly consumed large individual prey such as lobsters, urchins and crabs, while small rock lobsters ate mainly colonial, sessile prey such as sponges and barnacles, and small prey such as tiny winkles and crustaceans. Dietary selectivity indices revealed that algae and sponges were negatively selected (avoided) in non-invaded areas but positively or neutrally selected in invaded areas. These dietary differences have important ramifications not only for the lobster populations but also for the structure and functioning of the radically different communities that have developed in invaded areas, reflecting a regime shift induced by lobster predation.

Spatiotemporal variation in the population ecology of scaly slipper lobsters Scyllarides squammosus in the Northwestern Hawaiian Islands

Scaly slipper lobster (Scyllarides squammosus) population ecology was examined using tag/recapture information at Necker Island (23°30′N; 164°35′W), Gardner Pinnacles (25°00′N; 168°50′W), Maro Reef (25°30′N; 170°45′W), and Laysan Island (25°48′N; 171°45′W) in the Northwestern Hawaiian Islands (NWHI) USA from 2002 to 2008. Although many aspects of S. squammosus life history and population dynamics were similar to those of other scyllarids, somatic growth differed from its congers. Scyllarides squammosus growth abruptly declined at maturity and, because of this, growth at length was better described using the Schnute as opposed to the more commonly von Bertalanffy growth model. Growth varied among locations, and survival varied among years; thereby being the first documentation of variability in the life history of a scyllarid. This study has expanded knowledge of scyllarid biology and documented that spatiotemporal variability in biological characteristics must be considered to understand and describe the population ecology of this species and probably of other scyllarids.

Energetics of swimming to shore in the puerulus stage of a spiny lobster: Can a postlarval lobster afford the cost of crossing the continental shelf?

Nonfeeding postlarval pueruli of spiny lobsters migrate tens of kilometers across the continental shelf to settle in coastal waters. A model that analyzes hydrodynamic forces during swimming in the puerulus of Jasus edwardsii is described. The model calculates the speed at which forward propulsion balances drag. Calculated speeds agree with observed puerulus behavior. The computed mechanical work is converted to metabolic energy consumption using an assumed efficiency. Values concur with reported estimates of the utilization of lipid energy reserves in pueruli. For biochemical energy reserves reported for pueruli collected 20 km off the east coast of New Zealand, the model suggests that this distance and durations of 5 days active swimming are the approximate limits to endurance. Sustained swimming exceeding 15 cm s− 1 will likely exhaust energy reserves before an animal can reach the coast, whereas swimming at less than 5–7 cm s− 1 is inefficient because of the overhead of nonswimming, inactive metabolism. Successful onshore migration of this species is potentially limited by the animals' energy reserves. Reduced energy reserves at the outset due to prior poor feeding, or delays encountered en route due to unfavorable currents, could lead to exceeding the stored reserves of the pueruli, and death. Potentially, relatively small shifts in coastal ocean climate conditions could generate marked changes in recruitment to important spiny lobster fisheries, as has recently been observed in many coastal populations of spiny lobsters.