Pleuroncodes Monodon Research Articles

Cohorts in space:geostatistical mapping of the age structure of the squat lobster Pleuroncodes monodon population off central Chile

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 196:239-251 (2000) - doi:10.3354/meps196239 Cohorts in space: geostatistical mapping of the age structure of the squat lobster Pleuroncodes monodon population off central Chile Rubén Roa*, Fabián Tapia** Departamento de Oceanografía, Universidad de Concepción, Casilla 160-C, Concepción, Chile *E-mail: rroa@udec.cl **Present address: Biology Department, MS#34, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA ABSTRACT: Animal populations are spatial objects in the sense that their structure and functioning depend on the spatial context they inhabit. However, most population dynamics models ignore the spatial context and set populations Œin the air¹. This paper is focused on the squat lobster Pleuroncodes monodon population inhabiting the narrow continental shelf off central Chile, and encompassing 3 degrees of latitude. We tested the hypothesis that the spatial functioning of this population is driven by annual cohorts that enter the population through a nursery ground, and then radiate away from the nursery to the north and south by individual dispersal, thus creating a spatial pattern where age and distance from the nursery are correlated. To test the hypothesis we performed an extensive survey from 34 to 37°S along the continental shelf, collecting data on individual mean size by sex and spatial location. The data gathered was analysed using a combination of mixture distribution analysis on size frequency data and geostatistical mapping on size and location data. Isotropic and anisotropic variogram models were fitted to size data for both sexes. Selection of the appropriate models and kriging parameters was done by cross validation. The hypothesis posed was fully corroborated by the data and the analysis, with 6 adult cohorts identified for both sexes radiating away from the nursery ground in waves at an average distance of one fifth the latitudinal range of the population. Geostatistical mapping of size data for juveniles in the nursery ground, collected with a higher resolution in previous years, showed that recruitment can occur as several relatively small patches interspersed through the nursery area or as a large patch in the middle of the nursery. The corroborated model of spatial population functioning explains the history of commercial over-exploitation and recolonisation of this population. It also suggest that this 350 km long population is renewed by recruits from nearby cohorts, both to the south and north of the nursery area, while cohorts farther north can be exporting recruits to prime nursery habitat. These insights into the functioning of this large population could only be gained by a fully spatially explicit analysis. KEY WORDS: Population dynamics · Cohort dispersal · Geostatistical mapping · Spatially explicit · Habitat features · Crustacean biology · Chile Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 196. Publication date: April 18, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.

New regulations in Chilean Fisheries and Aquaculture: ITQ’s and Territorial Users Rights

The large industrial fishery development that turn Chile into the third fishing nation in the world is described, and recent regulatory innovations introduced by new Fishery and Aquaculture legislation are reviewed. In addition to classical Fishery management tools, different types of limited entry systems are now defined in the law and applicable to Chilean fisherie. These for the first time include allocation of resources in the form of Individual Fishing Quotas and Individual Transferable Quotas (IFQs and ITQs). Territorial User’s Rights in Fisheries (TURF’s) were incorporated in the law to enhance self-regulatory practices among artisanal fishermen. Among them, the Areas for Management and Exploitation for Benthic Resources (AME) represent an associative assignment of TURFs. Large-scale zoning is used to re-define Aquaculture Grants and to ritualise the conflicts between Artisanal and Industrial fishermen by establishing the Artisanal Reserve in which small-scale coastal fishermen have Priority Access. Performance of the new management instruments are documented with case studies, for the following fisheries: the loco ( Concholepas concholepas) a carnivorous snail, keyhole limpets (Fissurella spp.), langostino or squat lobster ( Cervimunida johni), Black hake ( Dissostichus eleginoides) and the Yellow prawn ( Pleuroncodes monodon).

Spatial differences in growth and sexual maturity between branches of a large population of the squat lobster Pleuroncodes monodon

A large population of the squat lobster Pleuroncodes monodon inhabits the narrow continental shelf off central Chile From a single nursery ground, 2 adult branches extend In a N-S onentation over 3 of latitude, wlth the northern branch being much larger than the southern one Squat lobsters from the southern branch are smaller on average than ind~viduals from the northern branch Two hypotheses were tested (1) southern squat lobsters are smaller than northern ones because they grow to smdller sizes, and (2) southern squat lobsters a l e sexually mature at smaller slzes and earlier ages than northern squat lobsters U s ~ n g data from 6 reseaich surveys done on the southern branch of the population we estimated growth functions for male and female squat lobsteis and compared them with previous lesults fiom the northern branch Furthermole using data from 1 survey we estimated a matunty function for southern females and colnpaled it with a previous estimation for northern females Southern squat lobsters grow faster and to smaller asymptotic sizes than northern ones reaching sexual marunty at smaller sizes and earlier ages hioreover individuals Iron1 the southern branch appear to live less (5 age classes) than individuals from the northern branch (8 to 9 age classes) These results imply that physiolog~cal processes are significantly faster in the southern branch Previous cases of the same phenomenon In benthic crustaceans occurred in spatially discontinuous populations, while in thls case it occurs between branches connected through a common nursery ground and separated by a relatively short distance In thls population, spatial heterogene~ty in population functioning anses without physical discontinuities, but in the context of a branched population Alternative hypotheses, based on features of the hab~ ta t , are posed to exp la~n the difference Finally, it was found that the ratio between size at 50% matunty and asymptotic size does not differ between branches, in agreement with the hypothesis that this ratio is a constant for a wide spectrum of phyla in the animal kingdom

Demersal crustacean assemblages along the Pacific coast of Costa Rica: a quantitative and multivariate assessment based on the Victor Hensen Costa Rica expedition (1993/1994).

During the first cruise leg with the RV Victor Hensen to the Pacific coast of Costa Rica in December 1993 (end of the rainy season) the crustacean fauna found in the demersal collections revealed an unexpected species richness and biomass. The Crustacea collections were analyzed qualitatively and quantitatively during the fourth leg (February 1994, dry season) in the three study areas Golfo Dulce (GD), Bahía Coronado in the Sierpe-Térraba-estuary (ST) and Golfo de Nicoya (GN). Qualitative data were available for comparison from the first leg in december 1993. A total of 24 beamtrawl and ten ottertrawl sample collections were done on an area of 860.000 m2 yielding a total of 119 species with a biomass of 37.8 kg (10275 specimens). Despite the smaller area covered by the beamtrawl, it collected a higher number of species and more biomass than the ottertrawl due to the smaller mesh size (0.8 cm). Judging from the shape of the species -per-area-curves, the crustacean fauna appeared as representatively sampled for the study area. As compared with the GN (biomass 0.36 g +/- 0.26, SR = 97) and the ST (0.41 g +/- 0.27, SR = 59) and according to the results of the log-series-plots constructed from the abundance data, the GD seems to be a depauperated area with significantly lower biomass (0.05 g +/- 0.07) and species richness (45 sp.). No crustaceans were found in the center of the deep basin of the GD put parts of the interior gulf with adjacent mangrove areas seem to be important as nursery area for some commercially important penaeid shrimp species. The ST-estuary revealed the highest mean species number per station in the whole study area, but the GN had the highest total number of species. Biomass seems to be regularly distributed and not depth-depending within the GN, while species abundance varies clearly, confirming previous results. In contrast, abundance and biomass correlated well in the ST. Based on the results of the multivariate analysis, seven station groups of particular species assemblages can be distinguished in the study areas. Despite a high variability between stations in abundance and biomass, the following four areas of characteristic species assemblages can be identified which are also confirmed by an independent study on demersal fishes: (1) the interior part of the GN, characterized by juvenile shrimps (Sicyonia disdorsalis, Trachypenaeus fuscina), several patchily distributed anomurans, brachyurans and other predator species like portunids (especially Portunus asper) and pre-adult stomatopods (Squilla spp.); (2) the exterior part of the GN with high amounts of caridean (Pantomus affins, Plesionika spp.) and penaeid shrimps (Sicyonia picta, Solenocera mutator), the highly abundant Iliacantha hancocki and some specimens of the stomatopod Hemisquilla stylifera and the deep water portunid Portunus iridescens; (3) a transition zone between 60 and 120 m water depth with a heterogeneous faunal composition, located in the ST and east of Isla Tortugas in the GN, and (4) the oxygen-depleted shelf edge area, dominated by the galatheid Pleuroncodes monodon. Mass occurrence of this species takes place off the GD and to a lesser extent off the ST-estuary, associated with high numbers of Solenocera spp. There seems to be a general trend of species groupings along abiotic gradients (depth, temperature, oxygen saturation) interrupted by small-scale variations in habitat type, current regime, food availability and other factors not identified in this study. Neither total abundance and biomass nor biotic summary parameters like diversity, dominance or species richness correlated well with the abiotic factors measured during this survey.

Nursery ground, age structure and abundance of juvenile squat lobster Pleuroncodes monodon on the continental shelf off central Chile

Newly settled individuals and juveniles of several benthic decapod crustaceans spend their first months or years in nursery habitats different from those of the adult population. It was unknown if this was the case for the squat lobster Pleuroncodes monodon, an exploited crustacean which inhabits the continental shelf off central Chile, and of which 2 adult populations exist, the larger Achira (35' 10' S to 36' 15' S) and the smaller Biobio (36' 35' S to 36' 50' S). We report here the presence of a large nursery area of the species, connecting both adult populations; the habitat is dominated by extensive sulphide microbial communities which fluorish at very low oxygen concentrations. We inferred the existence of northerly and southerly migration routes from the nursery ground to the adult populations, with juvenile year classes migrating as they advance through age classes. The juvenile population was composed of 2 year classes: 0 yr old (newly settled mdividuals) and 1 yr old juveniles; thus juveniles seemed to spend their first year of life in the nursery area. Total abundance was estimated as 3290 x lo6 individuals (asymmetric 95 % confidence interval: 2153 to 7039 x lo6), although the above figure is a lower bound because the sampling did not cover the whole nursery area. We hypothesize that the Biobio adult population is not self-sustaining, but depends on a surplus production of juveniles from the Achira population.

Recruitment of the Squat Lobster Pleuroncodes monodon on the Continental Shelf off Central Chile

A benthic megafaunal study off Concepcion Bay, central Chile (36°32'S, 73°W), provided abundance and bathymetric distribution data of the newly recruited squat lobster Pteuroncodes monodon (Decapoda, Galatheidae). The megafauna was surveyed 8 times between July 1991 and April 1992, with an Agassiz trawl at depths of 40, 64, and 96 m along a transect across the continental shelf. Recruits of P. monodon (carapace length (CL) 3-10 mm) were first sampled in all depth strata in early March, and then in April. April density (1 ind/m 2) and mean size (6.1 mm CL) were significantly higher than March density (0.07 ind/m2) and mean size (S.3 mm CL). Depth did not affect abundance and its significant effect on mean size was conditional on month effect. We interpret these results as evidence that the main pulse of recruitment occurred simultaneously across the continental shelf transect in April, and that larvae settling in April have a larger size than larvae settling in March. Recruitment appears to be associated with late summer development of the giant sulfur bacteria Thioploca spp., suggesting an eco­ logical relationship. Moreover, the observed recruitment occurred in late summer to early fall when the oceanographic regime in the area shifls to a postupwelling regime.

Growth and expansion of an exploited population of the squat lobster ( Pleuroncodes monodon) after 3 years without harvesting

In 1991, after 3 years of fishery prohibition, the most important surviving population of squat lobster ( Pleuroncodes monodon, Galatheidae, Decapoda) on the continental shelf of central Chile, the Achira population (36 °S, 73 °W), reached the highest biomass recorded since the start of population assessments in 1979 (34 084–43 910 t, 95% confidence interval), and expanded its distribution by 56 km to the north. The age composition of the population was characterised by two strong year-classes (1988 and 1989, born at the end of the previous fishing period and at the start of the prohibition respectively) and a mixture of older year-classes, less important in terms of numerical abundance. Population expansion had a clear spatial structure. The 1989 year class (mean size 23.5 mm carapace length) populated the traditional southern population area, while the 1988 and older year-classes (mean carapace length 33.5 mm and 39.5 mm, respectively) populated the areas to the north which were vacant prior to the fishery closure in 1989. We interpret this spatial structure as the result of size-dependent dispersal capacity, with recruitment of the 1989 year-class providing the impetus for expansion of the individuals of the 1988 and older year-classes. Using the simple age structure of the Achira population, we estimated an average rate of population increase of 10 323 t year −1 during the period without harvesting, and a rate of expansion of 20 km year −1. Most of the reproductive potential (eggs km −2) was transported into the expansion zone, which may create new nursery grounds towards the north. This in turn may alter the spatial distribution of size, if recruitment is successful in the northern areas, with a potential effect on expansion dynamics.

Annual growth and maturity function of the squat lobster Pleuroncodes monodon in central Chile

Length-frequency data (LFD) for the squat lobster Pleuroncodes rnonodon (Decapoda, Galatheidae) from 5 research surveys carried out in central Chlle (3520'S to 36'20's) between 1982 and 1991 were analysed to model male and female growth. The 1991 data were further used to model female maturity. From the 5 yr of LFD, 17 year classes were identified in males and 19 in females. To classlfy those year classes into age classes, a simple statistical procedure based on a stochastic dependency of growth on age was developed. The procedure classified male and female year classes into 6 and 7 age classes, respectively. Size variances due to within-year-class (indvidual) variability and among-year-classes (temporal) variability were estimated. The ratio between temporal and individual size variance did not increase with age. This indicates that size variation of individuals reaching a given age is mainly determined by the inherent variability of their year class rather than by environmental changes encountered across ages. A von Bertalanffy growth function provided a good description of both male and female growth. There were significant differences in the parameterization of the growth function between males and females: females were smaller than males for every age class. Logistic regression on female maturity data from 1991 shows that female squat lobsters reach maturity, as a population average, at intermediate sizes (ages). The 5 % plausibility regions and 95 % confidence intervals, as measures of uncertainty in maturity estimation, showed very s w a r interval estimates. The shape of the maturity curve corresponded to a stable population in terms of age structure.

Larval development of the red crab Pleuroncodes monodon (Decapoda Anomura: Galatheidae) under laboratory conditions

Larvae of Pleuroncodes monodon (Milne-Edwards, 1837), a red crab of commercial importance in South America, were reared in the laboratory at 2 different temperatures (15° and 20°C), from hatching up to the last larval stage. The 5 typical stages, with their corresponding functional appendages, are described and figured. The main characteristics useful in differentiating larvae of P. monodon from those of the other Chilean species of Galatheidae and its northern congener P. planipes are discussed. Data on duration of each larval stage, length of moulting intervals and mortality at the 2 test temperatures are also given.