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The analysis of concentration and crowding in shellfish research
... Concentration profile, calculated as the product among the density and its frequency, represents all the population and the real density experimented by its individuals, and is linked with the fishing process (Prince & Hilborn, 1998). While the allocation of fishing effort in space can be best analyzed in connection to a map of density of the exploited population, the resulting level of depletion is a function of concentration profile (Orensanz et al, 1998). ...
... As consequence, the fishing effort tends to concentrate on the areas with highest abundance, depleting them gradually (Caddy, 1975(Caddy, , 1979. In these cases, the CPUE can remain stable in high values while the depletion takes place, or (if the densest patches are few and small) it can drops quickly without reflecting a equivalent change in the abundance (Orensanz et al., 1998). These reasons reduce the use of the CPUE as index of abundance for these cases, limiting their application to small spatial scales to which assumptions of homogeneity can be made (Caddy, 1989;Prince & Hilborn, 1998). ...
... In PO, fishermen operated allocating their effort on the dense patch described in Figure 9. This relationship type has been described as "hyperdepletion", in opposition to the "hyperstability" that occurs when the CPUE drops at a much slower rate than absolute abundance (Orensanz et al., 1998). ...
Mussels were fished in San Matías Gulf (Argentine Patagonia) during three decades using dredges and performing a small-scale fishery. This fishery was characterized by pulses of productivity (1988-1992; 2002-2008) determined by the spasmodic nature of recruitment. Annual landings ranged among 200 – 2100 t. During the first pulse, the exploitation was done mainly by the industrial fleet, with vessels that operated on several fishing grounds, switching among them in response to abundance. The state of fishing grounds was assessed based in surveys conducted between 1987 and 1997, following the same methodology (vessel, dredge and sampling design) to estimate abundance of mussels and other epifaunal components using catch and swept-area data. A research program conducted during this period was addressed to collect data about population dynamics and harvesting. After nine years without successful recruitments, in early 2001 new settlements was detected and the fishery was reopened to exploitation. In this second pulse the reduction of the fishery scale (only artisanal fishing was allowed) was established by Administration. More than 30 artisanal boats (less than 10 m length) operated with two modalities: diving and small-sized dredges. fishing pulses, (2) to analyze management constrains of both types of fisheries, including social and economics implications and, (3) to propose a management scheme with operative short term actions and strategic long term component to mitigate the effects of biological uncertainty (recruitment, spatial-temporal variability of abundance) and control difficulties.
... The two methods are conceptually different, the former being an area-based while the latter being a distance-based method (Gatrell et al., 1996). The advantage provided by the quadrat method is that it allows application at different sampling scales, hence it provides indications about space stationarity of the epidemic statistics, while the advantage of the nearest-neighbor method is that a greater number of statistical quantities can be retrieved and that these are scaleindependent as long as the punctual density of infected plants is not exceedingly high (Orensanz et al., 1998). ...
Analyses of space-time statistical features of a flavescence dorée (FD) epidemic in Vitis vinifera plants are presented. FD spread was surveyed from 2011 to 2015 in a vineyard of 17,500 m² surface area in the Piemonte region, Italy; count and position of symptomatic plants were used to test the hypothesis of epidemic Complete Spatial Randomness and isotropicity in the space-time static (year-by-year) point pattern measure. Space-time dynamic (year-to-year) point pattern analyses were applied to newly infected and recovered plants to highlight statistics of FD progression and regression over time. Results highlighted point patterns ranging from disperse (at small scales) to aggregated (at large scales) over the years, suggesting that the FD epidemic is characterized by multiscale properties that may depend on infection incidence, vector population, and flight behavior. Dynamic analyses showed moderate preferential progression and regression along rows. Nearly uniform distributions of direction and negative exponential distributions of distance of newly symptomatic and recovered plants relative to existing symptomatic plants highlighted features of vector mobility similar to Brownian motion. These evidences indicate that space-time epidemics modeling should include environmental setting (e.g., vineyard geometry and topography) to capture anisotropicity as well as statistical features of vector flight behavior, plant recovery and susceptibility, and plant mortality.
... The estimation of benthic biomass and production is thus of basic importance to the rational management of natural resources (Tumbiolo & Downing 1994). The scale of analysis chosen for a given study may have profound effects on the spatial patterns found (Wiens 1989; Bellehumeur & Legendre 1998), and the information gathered from these patterns becomes essential for understanding ecological processes (Thrush et al. 1989; Orensanz et al. 1998). In the marine environment, the spatial distribution pattern of benthic biomass is not random. ...
Neilonella sulculata is a dominant bivalve on muddy bottoms of the continental shelf and gulfs off Argentina (Southwest Atlantic). Two benthic surveys performed in 2007 and 2009 in San Jorge Gulf, a depositional area characterized by silt/clay sediments, gave us the opportunity to test whether the population of this clam displays a significant spatial structure and to analyse if there is an inverse relationship between size and density. Density, biomass and size–frequency distribution displayed significant spatial structure, being positively autocorrelated at the smallest spatial scales (c. 1.7–14/17 km). Biomass also showed spatial contagion at scales of 25–33 km. A substantial increase in density and biomass occurred between 2007 and 2009. Empty valves in the sediment showed that the maximum size attained by the species may exhibit considerable variation at relatively short temporal scales. Regardless of temporal changes in density and biomass, the spatial structure of these variables remained stable. In densely populated areas, shell size decreased with increasing density, suggesting a density-dependent control of growth. A clear north–south increase in density and biomass was detected, which might be related to a gradient in food availability caused by a thermohaline frontal system associated with wind-related upwelling.
... Gardant à l'esprit ce qu'est un paysage, nous estimons que cette démarche peut offrir de larges possibilités d'analyse. Ain de vériier la régularité spatiale des lieux de vente, un indice de concentration employé notamment en écologie est utilisé (Orensanz et al., 1998) par la méthode des « quadrats » 8 (Getis, 1964 ;Krause et Gagnon, 2006). Lorsque l'indice de concentration est inférieur à 1, la distribution des points est régulière. ...
The usual little holiday ritual, landscape postcards have for first purpose to maintain the social link between people going on holiday and people staying at home. But, by giving a view of a certain area from a different place, those postcards represent an original manner to apprehend touristic places and to answer a seemingly simple question: Why this landscape would be sold on that particular spot ? This theoretical question leads to other questions: Is there a hierarchy among those touristic sites? Would the lack of attractivity of several territories cause their eviction? Would the media coverage of sites have effects upon the destruction of territories ? To answer all those questions, we conducted a survey in two departments of the French Alps: Savoie and Haute-Savoie. Eight thousand postcards have yet been listed, described, analyzed then georeferenced, giving us an exceptional landscape corpus. Methods of spatial and statistical analysis allowed us to focus on a sequence of factors involved in the media coverage of landscapes and to bring a particular look on the ways territories are visualized.
... Our third and final hypothesis concerned whether density-dependent factors were important. Crowding clearly emerged as having a strong link to intensity of competition (Fig. 2), but the importance of crowding is already well known for shellfish rearing (see Orensanz et al. 1998) and even encrusting organisms elsewhere (Barnes and Clarke 1998). What we have shown is that competition intensity was only significantly different with changing percent cover, not density of individuals (Tables 2, 3, 4). ...
Variability in interference competition was studied in benthic marine communities of the arctic and subarctic Atlantic intertidal and shallow subtidal zones. We sampled multiple square-metre quadrats at distances of 101, 103, and 105 m apart around the high polar island of Spitsbergen (Svalbard Archipelago). We also took some similar samples in Iceland and in the Faeroe Islands (106 m apart from Spitsbergen samples). Encrusting fauna were present on high arctic intertidal rocks but we only found competitive interactions on subtidal substrata. On subarctic Icelandic and Faeroese shores, in contrast, spatial competition was common even in the intertidal zone. Analysis of variance of competition intensity data (numbers of interactions per area) revealed multiple factors to be significant influences explaining variability. Amongst the 101-, 103-, and 105-m spatial scales, only the largest emerged as a significant term. Whether intra- or interspecific competition dominated the types of interactions varied greatly between sites: 21–97% of competition was intraspecific. The proportion of competitive encounters resulting in a decided outcome (i.e. a win for one competitor and a loss for the other, rather than a tie or standoff between them) showed little variability at any scale. All the values of competition transitivity (how hierarchical a pecking order is) were very high compared to values reported in the literature from any other (polar or non-polar) locality. Variability in this measure was generally 5-m scale but different aspects of competition varied at different scales and by hugely different amounts.
... Es considerada criptogénica en Australia , pues se sospecha que sea un complejo de especies (Hutchings y Turvey, 1984), aunque otros autores piensan que puede ser de origen australiano (Pollard y Hutchings, 1990; Wilson, 1999). Se ha utilizado como modelo para análisis espacial en sustratos blandos inter y submareales (Orensanz et al., 1998; Yokoyama e Ishihi, 2007). Se ha registrado para la costa occidental de Estados Unidos, donde pudo ser introducida alrededor de la década de 1920 en el estado de California, como parte de la epibiota del ostión japonés Crassostrea gigas, y posteriormente introducida de manera similar en Oregón y Washington (Molnar et al., 2008). ...
In this contribution we include 32 species of exotic marine and coastal invertebrates, from Mexican coasts, these are all benthic species, i.e. living in the marine floor as adults. Twelve of them are sponges, nine to polychaetes, and 11 ascidians. Additionally, nine species of polychaetes and four of ascidians are considered potential alien species for Mexico.
The seasonal and inter-annual variability in abundance of the main “local tropical tuna resources” in the EEZ of Côte d'Ivoire was analysed with catch and effort data from French and Spanish purse seiners over the period 2000–2019. A seasonal spatio-temporal model developed by Thorson et al. (2020a) was used to estimate abundance indices for the main tropical tunas by commercial category (<10 kg and> = 10 kg, which correspond roughly to maturity stage: immature and mature respectively), and fishing mode (free school sets and FAD sets). Furthermore, we decomposed the abundance time series into intrinsic mode functions using the CEEMDAN algorithm. The decomposition procedure made it possible to filter out the noise in the signal and extract the seasonal and inter-annual components of the abundance indices. A generalized additive model (GAM) was applied to the abundance indices to reveal the influences of environmental factors on species abundance and spatio-temporal distribution. Biological interpretations of the seasonal and inter-annual variability in tropical tuna abundance were made and the possible effects of environmental variables on this abundance discussed. Our results suggest that there are two main fishing seasons in the EEZ of Côte d'Ivoire. It was also found that mature yellowfin tunas are abundant between the first and second quarter of the year while the best season for skipjack occurs between the third and fourth quarter. In addition, we observed a considerable change over time in the seasonal and inter-annual variability of tropical tunas in this area.
Spatial and temporal environmental heterogeneity influences biodiversity distribution patterns and dynamics on sandy beaches. In these ecosystems, the microscale vertical distribution adds a dimension to the analysis of biological and physical processes, whose ecological patterns have been rarely described. An intensive across-shore sampling in a dissipative beach was conducted, using a stratified corer to analyze small-scale vertical variations in macrofaunal and physical variables. Sediment temperature decreased towards the swash zone and at deeper sediments. Conversely, moisture, grain size and organic content increased seaward, concurrently with the highest vertical variability. Species richness and density increased from the dunes to the swash zone, being highest at the surface, whereas biomass was higher in sediments deeper than 15 cm as a consequence of larger individual sizes. Sediment moisture and temperature showed a consistent correlation with biological descriptors. Deconstructed by taxonomic group, a significant vertical segregation of body size was observed, suggesting different microhabitat preferences and burrowing abilities. Species spatial patterns varied according to life history traits and differential susceptibility to variations in environmental conditions. This study provides novel insights on vertical environmental and biological variations across the dune-shore axis in a dissipative beach. Expanding the findings of this research to larger spatio-temporal scales is a short-term need to decipher the processes underlying the community and population patterns outlined here.
Fernández-Boán, M., Freire, J., Parma, A. M., Fernández, L., and Orensanz, J. M. 2013. Monitoring the fishing process in the sea urchin diving fishery of Galicia – ICES Journal of Marine Science, 70: 604–617.
The assessment and management of small-scale benthic fisheries requires attention to the spatial structure of stocks and patterns of effort allocation. Spatial information helps in the interpretation of fisheries data, and is required for designing spatially explicit management strategies, often prescribed in the case of benthic fisheries. Monitoring of boats with GPS, combined with port interviews, was evaluated as an approach to investigate the spatial pattern of fishing intensity and catch per unit of effort (CPUE) in the sea urchin (Paracentrotus lividus) diving fishery from Galicia, Spain. Fishing opportunities (FOs), relatively small regions of high fishing intensity, were identified and mapped at a fine scale. New FOs were first visited at an approximately constant rate. Concentration analysis shows that effort intensity was not uniformly distributed within FOs. CPUE did not exhibit a significant trend throughout the season, either at the scale of the aggregated fishery or within individual FOs. Catch per area and area covered per unit of diving time were inversely related, indicating that fishers stay longer in high-density patches. While abundance is the primary driver of effort allocation, other factors contributing to suitability were identified. Based on these results, we discuss realistic options for the monitoring of this and comparable fisheries.
This chapter discusses the dynamics, assessment, and management of exploited natural populations. All scallop stocks are structured as “metapopulations” in which subpopulations of sedentary post-larval individuals are connected with each other through the dispersal of pelagic larvae. The metapopulation is a useful conceptual framework for the analysis and management of benthic fisheries. Emphasis on spatial structure brings with it, the need to identify appropriate spatial scales for the observation, analysis and management of exploited scallop stocks. The hierarchy of spatial scales presented by Orensanz and Jamieson is adopted in the chapter. The primary factors tuning year-class-strength are those that affect advection and survival of pelagic larvae. These factors pertain largely to oceanographic conditions. It is natural that research on modulation of year-class-strength and the search for signs of climatic forcing focus on abundance indices aggregated at relatively large spatial scales. The empirical evidence about the influence of climate on larval availability and recruitment is considered. The transition between the two stages—namely, pelagic larvae and recruits is modulated by factors other than larval availability. The elusive relationship between aggregate spawning stock and recruitment is also discussed.
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