Lobster Population Research Articles

Can scientific observations of early life stages be scaled up to the level of a fished population? A case study using Homarus americanus

Ecological studies of the early life stages of benthic crustaceans are typically conducted at small scale to measure processes such as settlement and survival and the factors that affect them. A test of the measurements is whether or not the results of such studies can be extrapolated successfully to the level of a population. Do the data and inferences fit within the geographic space and the relatively few, available population reference points? We address this question for the lobster fishery for Homarus americanus in Lincoln County, Maine, USA, by constructing a life table linking all stages from egg production to the fishery using an age-structured model. We used early life history data (postlarvae and early benthic stages) from 1989 to 1995 and fisheries data from 1995 to 2001, a time lag that is appropriate for newly settled lobsters to enter the fishery. We used inverse methods to estimate the total number of settlers (Young-of-Year) needed to maintain the population and harvest of the late 1990s at steady state; we then estimated the amount of habitat needed to accommodate those settlers based on observed settlement densities. This was compared to the available space identified using a geographic information system (GIS). We predict that the population of lobsters from which the fishery is extracted can be supported by YOY settlement in 7–16% of the sublittoral area shallower than 20 m, a proportion that surveys confirm is available. We obtained an average larval mortality rate of ≤0.07 per day and we estimated that ∼2.5% of planktonic postlarvae settle successfully. The amount of egg production inferred by the model is easily accounted for by the abundance of sexually mature females in a recent survey.

Incorporating ecological process and environmental change into spiny lobster population models using a spatially-explicit, individual-based approach

Marine fisheries and the ecosystems that sustain them are increasingly beset by environmental deterioration, yet traditional fishery models used for stock prediction typically handle these dynamics poorly if at all. To do so requires the integration of spatio-temporal change in environmental quality and its subsequent effects on habitat suitability and life history dynamics. Spatially-explicit, individual-based simulation models are particularly well suited to this task and, although they are seeing increased use in fisheries ecology and management, this approach has seen limited application in crustacean fisheries. In 1993, we began development of a spatially-explicit individual-based model (IBM) describing the recruitment of Caribbean spiny lobster ( Panulirus argus) in the Florida Keys, Florida (USA) to investigate the impact of regional changes in environmental quality, habitat structure and postlarval supply on lobster recruitment. The shallow coastal waters of the Florida Keys ecosystem have experienced an unprecedented series of environmental perturbations over the past decade. Seagrass die-offs, cyanobacteria blooms, sponge die-offs and dramatic changes in salinity have occurred and these potentially impact the recruitment of spiny lobsters in the region via both direct and indirect means. Here I provide an overview of the unique approach that we have used to examine these dynamics, an approach that links environmental events that occur on large scales (e.g. changes in habitat structure and salinity) with their population-level consequences for lobsters via impacts that operate on the individual-level. Although not applicable in all situations, spatially-explicit IBMs should see wider use in crustacean fishery applications because of both the ecological insight they yield and their ability to integrate data across hierarchical scales of organization.

The performance of a size-structured stock assessment method in the face of spatial heterogeneity in growth

Monte Carlo simulation is used to assess the performance of a size-structured stock assessment method of the type commonly employed to assess rock lobster populations in Australia and New Zealand. The simulations consider the impact of measurement error and process error in catchability and the length at 50% selectivity, as well as the implications of pooling data across populations that differ in terms of growth rate. The ability to estimate the virgin biomass depends critically on having catch-rate or size-composition data for earliest years of exploitation; in the absence of such data the estimates can be highly biased and imprecise. Several of the reference points commonly reported for assessment purposes (e.g. the biomass at which maximum sustainable yield is achieved) are, however, based on the estimate of the virgin biomass. Estimation performance (bias and precision of estimated quantities) deteriorates with increasing process error. For most of the scenarios examined, the expected benefits of increased precision arising from pooling data across spatial zones are not realized and better performance can be achieved by conducting assessments at the level of population and subsequently aggregating results spatially.

Comparisons of size at maturity and fecundity of two Scottish populations of the European lobster, Homarus gammarus

Sampling of Homarus gammarus on commercial boats and regular visits to local ports were carried out during 1999–2001 for the Firth of Forth and Hebrides fisheries. Biological data on size, sex, morphometric measurements and egg samples were collected. Size at the onset of sexual maturity (SOM), fecundity and egg development were compared between populations. Techniques that require transformed (Logarithm base e) or untransformed morphometric data, were applied to the data. Lobsters from the Firth of Forth had smaller SOM ( ♂=80 mm carapace length (CL) and ♀=79 mm CL) than those from the Hebrides ( ♂=98 and ♀=110 mm CL). Fecundity ( x ̄ =8154 eggs) for the Firth of Forth was lower than for the Hebrides ( x ̄ =14 238 eggs). ANCOVA showed no significant differences in the size–fecundity relationship between locations ( F 1,1=2.62, P>0.05) for lobsters with eggs in which the eye spot index (ESI) was between 0.29 and 0.54, using CL and ESI as co-variates. The reliability of the methods and the resulting estimates are discussed.

Recent settlement trends in Panulirus argius (Decapoda: Palinuridae) pueruli around St. Thomas, U.S. Virgin Islands.

Puerulus settlement of the western Atlantic spiny lobster, Panulirus argus, was monitored using modified Witham collectors from December 1996 to March 1998 at seven sites around St. Thomas, U.S. Virgin Islands. A total of 605 pueruli were collected from 553 samples for a catch per unit effort (CPUE) for all sites of 1.09 pueruli. The greatest settlement occurred on sites within a recently declared marine reserve, which had an overall CPUE of 1.77 pueruli. Settlement in non-reserve sites was much lower with an overall CPUE of 0.31 pueruli. Pueruli recruitment declined 67% at inshore sites and 53% at offshore sites between July 1992 - April 1994 and February 1997 - March 1998. Also, only 10% of months sampled in 1997-98 had a CPUE > 0.5 compared to 55% in a previous study in 1992 - 1993. Despite the decline in pueruli CPUE in 1997-98 compared to 1992-94, the commercial lobster catch in the 2000-01 fishing season, and by inference the adult lobster population (legal lobster size in the US Virgin Islands is > or = 3.5 cm carapace length), remained stable.

Size at maturity, fecundity and reproductive potential of a protected population of the spiny lobster Palinurus elephas (Fabricius, 1787) from the western Mediterranean

Protected lobster populations are expected to contribute to the replenishment of fished populations through increased egg production. We studied the reproductive biology and egg production potential of a population of the spiny lobster Palinurus elephas protected from fishing since 1990 in the Columbretes Islands Marine Reserve (western Mediterranean). An index of spawning potential was derived to compare egg production potential in the Reserve and in western Mediterranean exploited populations. Females' physiological maturity (ability to reproduce) and functional maturity (ability to mate and bear eggs) occurred at a carapace length (CL) of 76–77 mm. Males' physiological maturity occurred at a slightly larger size, 82.5 mm CL. In the Reserve, P. elephas' individual fecundity increases linearly with body size up to the females' maximum size, although maximum reproductive yield (eggs per body gram) was reached at intermediate sizes. Size-specific fecundity in the protected population was similar to that of lightly fished populations off Ireland and greater than that of western Mediterranean exploited populations. The female size class of 105–110 mm CL contributed most to egg production in the protected population and is well above the minimum landing size (MLS) for western Mediterranean fisheries. Newly mature females (below MLS) generate a very small fraction (1%) of the egg production from the Reserve. Given the pattern of exploitation in western Mediterranean fisheries, egg production potential depends more on the quantity than on the mean size and fecundity of the available females. The role of the greater availability of large males for mating in unfished populations is discussed in terms of the females' individual fecundity and mating success.

Movement patterns of mature spiny lobsters, Jasus edwardsii, from a marine reserve

The maintenance of long‐term associations with particular reef sites is likely to have contributed to the rebuilding of the spiny lobster population (Jasus edwardsii (Hutton) (Decapoda: Palinuridae)) in the Leigh Marine Reserve, in northeast New Zealand. Between 1983 and 1985, 429 lobsters were tagged underwater with western rock lobster tags and antennae tags. Underwater tagging and commercial traps were used to tag a further 737 lobsters with T‐bar tags and antennae tags between 1994 and 1996. Twenty‐one percent of lobsters resighted (n = 323) between 1983 and 1985 maintained their association with a 15 ha reef inside the reserve for 1–8 years. Site association tended to increase with female size, whereas site association in males was relatively constant until 130 mm carapace length, and then markedly increased. Legal‐sized lobster abundance fluctuated seasonally, suggesting that a proportion of the population undertook larger‐scale movements beyond the reef. This was confirmed during a second tagging programme conducted between 1994 and 1996. About 30% of resighted lobsters (n = 212) moved 0.25–6 km from their tagging site and 20% crossed the boundary, either moving into or out of the reserve. These results indicate that although the Leigh Marine Reserve reduces spatial access to fishing grounds, a proportion of the lobster population moves out of the protected area and becomes susceptible to capture in the adjacent fishery.

Scaling restoration of American lobsters: combined demographic and discounting model for an exploited species

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 264:177-196 (2003) - doi:10.3354/meps264177 Scaling restoration of American lobsters: combined demographic and discounting model for an exploited species Deborah P. French McCay1,*, Mark Gibson2, J. Stanley Cobb3 1Applied Science Associates, 70 Dean Knauss Drive, Narragansett, Rhode Island 02882, USA 2Division of Fish and Wildlife, Rhode Island Department of Environmental Management, 3 Fort Wetherill Rd., Jamestown, Rhode Island 02835, USA 3Department of Biological Sciences, University of Rhode Island, Kingston, Rhode Island 02881, USA *Email: dfrench@appsci.com ABSTRACT: Ecological theory does not currently allow precise predictions of the consequences of ecological restoration. Ecological restoration and species enhancement projects could be profitably used to test theoretically based predictions, but only if theory were first applied to develop quantitative predictions suitable for testing. Here, we review what is known about factors limiting population size and production of the American lobster Homarus americanus, and use that information to construct a demographic life-table model of population dynamics. We then use the model to evaluate alternative options for enhancing lobster population size and production. Because this species represents an example of a population subjected to intense human exploitation as a target of commercial fisheries, which has stimulated much research on its biology, demographic modeling is facilitated. Furthermore, intervention into the fishery provides a viable restoration option available only to exploited species. We apply the economic concept of discounting (of future pay-back in the form of restoration, analogous to being paid interest on a loan) to allow quantification of the scale of restoration needed to compensate for both the magnitude of the estimated loss of American lobsters and the time lags between loss and restoration following a major oil spill. Quantification of benefits is rarely performed for restoration projects to guide compensation for natural resource damages caused by environmental incidents. The methods and approach developed here can help address this past failure in order to provide compensating ecological and human services equal to those lost. The approach represents a significant step forward in conceptually and quantitatively addressing restoration needs. The methods may be applied to other species, especially those that are exploited by humans, but also others that can feasibly be restored to mitigate impacts of adverse environmental events. KEY WORDS: Restoration · American lobster · Population model · Limiting factor · North Cape oil spill · Fishery · Natural resource damage assessment · Interim loss Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 264. Online publication date: December 15, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

Intense removal and non-saturating functional responses by recreational divers on spiny lobster Panulirus argus

The effects of recreational fishing often go undetected, yet can lead to the collapse of fishery populations. Fishery managers must understand the dynamics of recreational fishers and their prey to successfully predict the outcome of management actions. We measured the impact of a 2 d exclusively recreational fishery on the Caribbean spiny lobster Panulirus argus in the Florida Keys, USA, and used a theoretical, predator-prey functional response approach to identify whether or not sport diver catch rates were density-independent or -dependent (Types I, II or III functional response), and if catch rates were saturated (i.e. reached an asymptote) at relatively high lobster densities. Herein, we describe how this predator-prey framework could be applied to fisheries management for the spiny lobster. Our approach consisted of SCUBA diver surveys of lobster distribution and abundance patterns immediately before and after the 2 d recreational 'mini-season' coupled with counts of recreational boats and divers to assess the aggregative response of divers to lobster density. During the mini-season, the density of boats along coral patch reefs and patch heads was over 900 × higher than during the regular fishing season ~3 wk later. Overall, there was a 95 and 79% decline in mean lobster densities in the patch reef and patch head habitats, respectively. Fishing effort was 10 × greater on patch heads than on reefs, prob- ably due to ~100-fold higher lobster densities in patch-head habitats. In both patch reefs and heads, the proportion of lobsters removed by divers was density-independent (Type I functional response). Diver catch never reached saturation at natural lobster densities. Thus, recreational divers have a relatively simple predatory response to spiny lobsters, whereby catch rates increase linearly with lobster density such that catch is a reliable indicator of abundance. A major concern is that the current levels of lobster exploitation by sport divers are extremely high (~90%); however, diver predation pressure is not expected to increase proportionally with a decline in lobster density, which could exacerbate local extinction. Management actions that reduce diver effort should have a concomitant reduction in catch. The recreational diver-lobster predator-prey construct in this study provides a useful predictive frame- work on which to build as the spatiotemporal scales of measurements expand, management actions are implemented, and the lobster population varies.

The effects of sediment deposits from Namibian diamond mines on intertidal and subtidal reefs and rock lobster populations

Abstract Extensive diamond mining occurs on land and in the sea on the west coasts of South Africa and Namibia, raising fears that diamond‐mining activities may impact commercial rock‐lobster fisheries and benthic communities. To explore this possibility, the effects of the diamond‐mining fines‐discharge on intertidal and subtidal rocky‐shore communities and on the population structure of the rock lobster Jasus lalandii were assessed at Elizabeth Bay. Sampling over six years at sites covering a range of wave exposures compared impacted sites with comparable reference sites never exposed to the fines. Percentage cover and densities of benthic organisms were recorded on both intertidal and subtidal reefs. Rock‐lobster abundance was estimated from counts and catch‐per‐unit‐effort, and their length frequencies and sex ratios compared in impacted and reference areas. The deposition of fines had no effect at wave‐exposed sites, but did impact intertidal and subtidal communities at sheltered localities where fines accumulated because wave action was insufficient to disperse them. Reductions of grazers, proliferation of algae and increased dominance by filter‐feeders were recorded at the impacted sites and persisted throughout the monitoring programme. Differences in community structure associated with different levels of wave exposure were, however, greater than those produced by depositing fines. The detected effects of fines‐deposits on the benthos were local and likely to be reversible after cessation of mining. The fines‐deposit had no detectable effects on the sex‐ratio, size or abundance of rock lobsters, indicating that there is no conflict between the deposition of fines and the fishery for rock lobsters, although substantial inter‐site variability makes it difficult to regard the results as definitive. Copyright © 2002 John Wiley & Sons, Ltd.

Larval transport and retention of the spiny lobster, Panulirus argus, in the coastal zone of the Florida Keys, USA

AbstractThe spiny lobster Panulirus argus is of ecological and commercial importance in the South Florida coast of the continental USA and throughout the Intra‐Americas Sea. Essential spiny lobster habitat in South Florida is primarily located in the Florida Keys coastal zone (including the Dry Tortugas), where the dynamic regional circulation coupled with the long planktonic larval duration (6–12 months) of P. argus raises questions of larval retention and recruitment. Locally spawned phyllosomata entrained in the Florida Current are likely to be expatriated out of the Straits of Florida, which implies that the local spiny lobster population is sustained by the transport of larval recruits from upstream locations. We examined the physical processes that may influence recruitment. Transport processes in the Keys coastal zone are spatially variable. Observed and modelled data suggest that the upper Keys is a point of onshore larval transport via the inshore meandering of the Florida Current, and the lower Keys to Dry Tortugas region apoint of retention through wind‐driven onshore/countercurrents and eddy recirculation. Eddies that propagate between the Dry Tortugas and the lower Keys facilitate the exchange of larvae between the Florida Current and the coastal zone. Northerly wind events associated with cold fronts can enhance recirculation of larvae in the upper Keys. The association of older larvae with the Florida Current front supports the hypothesis that spiny lobster larval recruits come from upstream sources in the Caribbean.

Spatially explicit dispersal dynamics and equilibrium population sizes in marine harvest refuges

For marine reserves to function as effective harvest refuges for exploited species, the reserve must protect a substantial proportion of the population for an indefinite period of time. Because most marine reserves are space-limited, the buildup and equilibrium population sizes of mobile species will be influenced by the size and boundary conditions of the refuge. A logistic rate model was used to predict equilibrium population sizes in a marine harvest refuge, based on species-specific dispersal dynamics and the spatial configuration of the refuge. The model parameters were derived for Caribbean spiny lobsters and queen conch in an isolated marine reserve at Glover's Reef, Belize, and were compared to observed population change over a 5-yr period. Spiny lobsters and queen conch, the two most heavily exploited species in the Caribbean, differ in larval recruitment rates (immigration) and mobility of adults (emigration). The expected increase in the population size of spiny lobsters in this refuge was 250% and queen conch was 420% over that of the initial fished population. The observed densities of lobsters and conch in the refuge approached the predicted estimates within three years. To further explore the impact of alternative spatial configurations on refuge populations, the model was run on the same populations in two hypothetical refuges. In a refuge of the same area but 50% less absorbing boundary (adjacent to intensively fished areas), the spiny lobster population was expected to be 30% larger than the equilibrium population size in the original refuge, whereas the queen conch population was not expected to change from that in the original refuge. In a refuge that was 50% larger and with 50% less absorbing boundary, the spiny lobster population was expected to increase 110% and the queen conch population was expected to increase 50% over the equilibrium population size in the original refuge. Relatively minor changes in refuge area and boundary conditions may thus result in major population-level responses by exploited species, depending on dispersal dynamics and habitat availability. This simple model may be applicable for rapid assessment of the potential efficacy of proposed harvest refuges. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved .

Population parameters of American lobster inside and outside no-take reserves in Bonavista Bay, Newfoundland

Marine no-take reserves are being used increasingly to conserve exploited populations and fisheries, but there have been few studies of whether they achieve the goals for which they were created. To determine the potential effectiveness of no-take reserves as a fisheries conservation tool for American lobster ( Homarus americanus), I quantified the consequences to population structures of two small, no-take reserves (Round Island and Duck Islands) in Bonavista Bay, Newfoundland, during 1997–1999. Although this study concerned only the first 3 years following reserve establishment, there were obvious differences in lobster population parameters inside and outside no-take reserves. At the Round Island reserve, population density was high and stable over time, and female and male size increased, as did the proportion of ovigerous females. However, at the Duck Islands reserve, population density increased dramatically between 1997 and 1998, and male size increased over time, but there was no change in female size or in the proportion of ovigerous females. Lobster density, female and male size, and the proportion of ovigerous females were greater within the Round Island reserve compared to an adjacent harvested area. At the Duck Islands, females and males were larger in size within the reserve, but I found no difference in lobster density or the proportion of females that were ovigerous between the reserve and an adjacent harvested area. Taken together, these data suggest that no-take reserves offered increased survival to lobsters (particularly at the Round Island site) and thereby may, over time, provide benefits to the local fishery.

Effects of marine reserve protection on spiny lobster (Jasus edwardsii) abundance and size at Tonga Island Marine Reserve, New Zealand

1. Diving surveys were undertaken to investigate the effects of marine reserve protection on spiny lobster (Jasus edwardsii) populations at Tonga Island Marine Reserve, northern South Island, New Zealand over a 2 year period from December 1998 to December 2000. 2. Spiny lobsters were 2.8 times more abundant overall, and mean size was 19 mm carapace length larger in shallow transects and 28 mm carapace length larger in deep transects, in the marine reserve than at adjacent fished sites. That pattern was evident despite very high variability within sites, and among sites within reserve and fished areas. 3. Large reproductive males were 10 times more abundant within the reserve compared to adjacent fished areas, suggesting that more eggs would be fertilized in the reserve than on the adjacent fished coast. 4. Estimates of size-specific fecundity, combined with abundances of females, suggested that almost nine times more eggs would be produced in the reserve than in fished areas. 6. We estimate that the mean abundance of spiny lobster in the reserve has increased by 22%, 5 years after its establishment, indicating an annual population increase of 4.4%. Over the same period, abundance of spiny lobster outside the reserve has declined by 2.9% per annum. 7. Based on known spiny lobster movements, we suggest that marine reserves of more than 10 km length should be given priority over smaller reserves. Smaller reserves will, however, protect part of the population for at least a portion of their lifespan. 8. Previous studies of movement of J. edwardsii suggest that spillover from the reserve should occur, and as population density increases we predict that more spiny lobsters will move out from the reserve. Copyright © 2002 John Wiley & Sons, Ltd.

Settlement and juvenile habitat of the European spiny lobster <i>Palinurus elephas</i> (Crustacea: Decapoda: Palinuridae) in the western Mediterranean Sea

Settlement characteristics, like timing, depth, microhabitat and density of European spiny lobster Palinurus elephas are described for the very first time. Regular SCUBA-diving surveys were conducted from July 1998 to January 2000 on rocky bottoms of three different geologic origins to assess substratum-dependent differences in recruitment density. Settlement of pueruli took place in June-July, a few weeks after sea surface temperature started to rise. The highest density of juveniles was found at 10-15 m depth. Most spiny lobsters settled in limestone rocks, into empty holes of the date mussel Lithophaga lithophaga, which provided daytime refuge. As they grew, individuals were increasingly found in larger holes and crevices of the rock surface. Sizes were estimated from photographs taken at night when the animals were actively foraging. The smallest observed individuals measured 7.5-8 mm carapace length (CL), but they reached 15-18 mm CL at the end of October. The consequences of our results for the management of the spiny lobster populations in the northwestern Mediterranean are summarily discussed.

Morphometric variability in UK populations of the European lobster

European lobsters (Homarus gammarus) were sampled from nine sites around the UK coast to determine whether populations could be differentiated on the basis of morphometric variability, and to relate this to depth and indices of population size at each site. Discriminant analysis indicated that exoskeleton damage was the only characteristic that could distinguish males between sites. In contrast, females were distinguished between sites on the basis of variation in exoskeleton damage, claw spines and rostrum teeth, which tended to be positively correlated to indices of population density. This study suggests that female morphology may respond more strongly than male morphology to local selection pressures, albeit in a limited capacity.

Environmental impact of chemical wastes produced by the salmon aquaculture industry

The rapid expansion of the salmon aquaculture industry in the last decade and the intentional and unintentional use of many chemicals have resulted in wastes that may have a direct environmental impact. Thus, methods and criteria are required to assess the environmental impact of these chemicals, in particular to identify the hazards and assess the risks of their uses. We describe a project in progress that is aimed at identifying the source of chemical wastes of salmon aquaculture in the Bay of Fundy, the quantities released, their distribution, and environmental fate. The project is also concerned with the effects of chemical wastes on important fisheries resources. Laboratory studies indicated that chemicals used in the treatment of sea-lice infestations are lethal to shrimp and lobsters. Lobsters exposed to sublethal concentrations of one of these chemicals, azamethipohos, had decreased reproductive success compared to control lobsters. However, more information is required to estimate the associated risk to wild populations of lobster and shrimp.

Ecophysiological adaptation to salinity throughout a life cycle: a review in homarid lobsters.

Adaptations to salinity are reviewed throughout development in both species of the genus Homarus. Some populations of homarid lobsters are known to inhabit coastal and estuarine areas where salinity fluctuates. Salinity tolerance varies during development, with 50 % lethal salinities (LS(50)) ranging from approximately 15-17 in larvae to approximately 12 in postlarvae and 10 in adults. Larval and adult lobsters can avoid low-salinity areas using behavioural strategies. When exposed to low salinity, the capacity to osmoregulate varies with development. Embryos are osmoconformers and are osmotically protected by the egg membranes. Larvae are also osmoconformers, and the pattern of osmoregulation changes at metamorphosis to hyper-regulation, which is retained throughout the later stages up to the adult stage. Exposure to low salinity increases the activity of Na(+)/K(+)-ATPase in postlarvae and later stages. The level of osmoregulation evaluated through the osmoregulatory capacity (the difference between haemolymph and medium osmolalities) is negatively affected by low temperature (2 degrees C). The variations in haemolymph osmolality resulting from osmoconforming or partial osmoregulation are compensated by intracellular iso-osmotic regulation. Neuroendocrine control of osmoregulation appears in postlarvae and seems to involve the crustacean hyperglycaemic hormone. In adult lobsters, the gills appear to have a respiratory function only, and extracellular osmoregulation is effected by the epipodites, with the addition of the branchiostegites at low salinity. These organs are present at hatching. Transmission electron microscopy and immunolocalization of Na(+)/K(+)-ATPase reveal that the epipodites become functional in larvae and that the branchiostegites become functional in postlarvae. An integrated series of events links the appearance of osmoregulatory tissues, the increase in Na(+)/K(+)-ATPase activity, the occurrence in postlarvae of hyper-regulation at low salinity and the increase in salinity tolerance. Further ecological and physiological studies are proposed for a better understanding of the adaptive significance of the ontogeny of osmoregulation in lobsters.

Dynamics of a protected Western Mediterranean population of the European spiny lobster Palinurus elephas (Fabricius, 1787) assessed by trap surveys

A protected population of the spiny lobster, Palinurus elephas, was studied eight years after establishment of the Columbretes Islands Marine Reserve (western Mediterranean). Experimental trap fishing in the reserve and at two unprotected sites revealed that cessation of fishing in the reserve is probably responsible for high catch rates observed there and that the annual fishing closure is effective in rebuilding populations in exploited areas. In the reserve, variations in abundance, sex ratio, and size of lobsters were conspicuous. Catch rates were always higher in deep (50–80 m) than in shallow areas (20–50 m). Bathymetric differences in abundance were smallest in early summer, possibly because of seasonal onshore movements associated with reproduction. Females were always more abundant than males and less variable in number and size. Ancillary data suggest that reproductive and moulting behaviour, particularly of males, influences population estimates of P. elephas from trap surveys. Presence of subadults in deeper waters of the reserve suggests that 2- to 3-year-old juveniles undergo ontogenetic migration from the shallow settlement habitats (<20 m) to deeper habitats (>50 m). The results highlight the effectiveness of fishing restrictions in rebuilding P. elephas populations and suggest that the lobster population in the reserve is not closed.

Effects of artificial shelters (Casitas) on the abundance and biomass of juvenile spiny lobsters Panulirus argus in a habitat-limited tropical reef lagoon

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 221:221-232 (2001) - doi:10.3354/meps221221 Effects of artificial shelters (Casitas) on the abundance and biomass of juvenile spiny lobsters Panulirus argus in a habitat-limited tropical reef lagoon Patricia Briones-Fourzán*, Enrique Lozano-Álvarez Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Unidad Académica Puerto Morelos, PO Box 1152 Cancún, Quintana Roo 77500, Mexico *E-mail: briones@mar.icmyl.unam.mx ABSTRACT: ŒCasitas¹ are artificial habitats that mimic large crevice-type shelters sought by juvenile Caribbean spiny lobsters Panulirus argus. Despite the widespread use of casitas for lobster fishing in the Caribbean, the ecological performance of casitas is not yet fully understood. We examined the mode of operation of casitas in a habitat-limited population of juvenile P. argus in the reef lagoon at Puerto Morelos, Mexico. The density of juveniles in the reef lagoon was estimated with transects as 11 ha-1. After the transect surveys, a year-long baseline study on the lobster population, consisting of 13 visual censuses, was conducted at 9 fixed sites, each of area 100 x 100 m (1 ha). All lobsters were juveniles (10.7 to 56.5 mm carapace length, CL), and only 12% measured >35 mm CL. No movement of tagged lobsters was recorded among sites. Overall density in the 9 sites was 5.0 ha-1, but density varied widely in space and time. Two groups of sites were evident: a group of 5 sites with virtually no lobsters (NL sites), and a group of 4 sites with lobsters (WL sites). Lobster density was related to the abundance and size of natural shelters in each site. Casitas were deployed in 2 of the 4 WL and 3 of the 5 NL sites (treatment sites), and further bimonthly censuses were conducted in all sites for an additional year. Despite temporal variations, lobster density in both WL and NL treatment sites increased significantly compared to control sites and to their respective baseline values. The mean size of lobsters and the biomass of all lobsters became gradually larger in treatment sites compared to control sites and to the baseline study, but both mean size and biomass fluctuated in time. These results support the hypothesis that artificial habitats increase the abundance and biomass of lobsters in habitat-limited environments, and the notion of an attraction-production continuum effect of casitas on lobsters. KEY WORDS: Artificial habitats · Casitas · Spiny lobsters · Panulirus argus · Habitat limitation · Attraction-production · Mexican Caribbean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 221. Online publication date: October 18, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.