Papers by Ching Villanueva
Interim Report of the Working Group on Multispecies Assessment Methods (WGSAM)
Design processes and analytical modeling are presented showing creation of a low-cost concentrati... more Design processes and analytical modeling are presented showing creation of a low-cost concentrating photovoltaicthermoelectric (PV/TE) hybrid power system for research and laboratory teaching built using a small upcycled satellite dish. Today, concentrated solar hybrid PV/TE systems are drawing significant research attention and funding investment. However, the literature lacks examples of how this cutting-edge energy technology can be made accessible at low cost for STEAEM education at universities, vocational institutions, and high schools. By applying Energy Engineering Laboratory Module (EELMTM) design principles and pedagogy, a process is presented to make this technology easily accessible at low cost. The concentrating solar hybrid PV/TE system presented here is divided into four subsystems: 1) a concentrator, 2) a PV/TE generator, 3) data acquisition, and 4) a cooling system. The key engineering decisions governing the design for each sub-system are described. In addition, a ...
Landings in 2015 from the five FUs combined were 274 t. The TAC set for the whole Division 9.a wa... more Landings in 2015 from the five FUs combined were 274 t. The TAC set for the whole Division 9.a was t and 320 t for 2015 and 2016. A recovery plan for southern hake and Iberian Nephrops stocks has been in force since 2006. The aim of the recovery plan is to rebuild the stocks within 10 years, with a reduction of 10% in F relatively to the previous year and the TAC set accordingly (Council Regulation (EC) No. 2166/2005). FU 26+27 (West Galicia and North Portugal): The fishery shares the same characteristics of that in Division 8.c, described above. Landings are reported by Spain and minor quantities by Portugal. Spanish fleets fish in FU 26 and FU 27, whereas Portuguese artisanal fleets fish with traps in FU 27. Two periods can be distinguished in the time-series of landings available 1975-2014. During 1975-1989, the mean landing was 680 t, fluctuating between 575 and 800 t approximately. Since 1990 onwards there has been a marked downward trend in landings, being below 50 t from 2005 to 2011. In the last four years, landings continued to decrease and were below 10 t. Discards rates are negligible. According to the ICES data-limited approach, this stock is considered as category 3.1.4. These FU 26-27 are assessed by the analysis of the LPUE series trend, as was done in 2012. The perception of the stocks is the same as last year indicating an extremely low abundance level. FU 28+29 (SW and S Portugal): Nephrops is taken by a multispecies and mixed bottomtrawl fishery. The trawl fleet comprises two components, one targeting fish operating along the entire coast, and another one targeting crustaceans, operating mainly in the southwest and south, in deep waters. There are two main target species in the crustacean fishery, Norway lobster and deep-water rose shrimp, with different but overlapping depth distributions. In years of high rose shrimp abundance, the fleet directs its effort preferably to this species. Additional details can be found in Section 14. European Sea bass in Division 8.c, 9.a Spanish and Portuguese vessels represent almost of the total annual landings in divisions 8.c and 9.a. Commercial landings represent 821 t in 2015, a slight decline on the previous year. A peak of landings is observed in the early 90's and in 2013, reaching more than 1 000 t, and lowest landings have been observed in 1980 and 1981 and more recently in 2003 (466 t). No discards have been observed for this stock by the observer program. No stock assessment is carried out as the stock is considered as category 5.2.0. Information on abundance or exploitation is not yet available and this year, there are no new data available that change the perception of the stock. Additional details can be found in Section 15.
Asian Fisheries Science, 2004
The diet composition and feeding habits have been investigated for several economically important... more The diet composition and feeding habits have been investigated for several economically important indigenous species based on diel surveys collected from the Ubolratana reservoir (Thailand). For some of these populations the daily food ration, feeding periods, ingestion and evacuation rates were determined using MAXIMS, an iterative computer software utilizing 24hour series of stomach content data obtained in natural populations. The results obtained provide useful information for studies of the trophic relationship in the reservoir
Water Science and Technology, 2017
The Houjing River has long been an environmental victim of economic development. Industries that ... more The Houjing River has long been an environmental victim of economic development. Industries that have settled along the bank of this river may have largely contributed to severe organic wastes pollution. This study collected water and sediment samples at various points along the river and measured concentrations of 61 volatile organic compounds (VOCs) and 128 semi-volatile organic compounds (SVOCs) for a period of 16 months (Feb 2014–June 2015). Our analyses show that elevated levels of VOCs were observed near two industrial areas, Dashe and Renwu industrial parks. High SVOC concentrations were found in the vicinities of the Nanzih Export Processing Zone (NEPZ) and CingPu station, possibly due to considerable effluent discharges of adjacent industrial and residential areas. Comparing this study's findings with the standard values of different governmental agencies and studies similar to this one, the ecosystem of the Houjing River was seriously contaminated. This study could be ...
Bioaccumulation and potential sources of heavy metal contamination in fish species in Taiwan: assessment and possible human health implications
Environmental science and pollution research international, Jan 4, 2017
In this study, tissues of five fish species prevalent in the Houjing River were analyzed for heav... more In this study, tissues of five fish species prevalent in the Houjing River were analyzed for heavy metal concentrations. Results show concentrations of such metals to be much higher than internationally recommended standard limits (as determined by the WHO and FAO) and other similar studies. Heavy metal contamination of fish in the Houjing River is hence significant. High hazard and carcinogenic risk related to the Houjing River's fish was proven based on target hazard quotient (THQ) and target cancer risk (TR) estimations. In fact, four of the five species studied present THQ levels higher than 1, and seven TRs of zinc (Zn) and arsenic (As) are higher than 10(-4). Despite lower estimated daily intake (EDI) of fish in the area (per recommended daily allowance guidelines), possible heavy metal bioaccumulations in fish stock pose a high health risk for human consumption. From our analyses, the highest bioaccumulation factor (BAF) estimated above 1000 was of Zn. Among the fish spec...
A preliminary model of coastal resources of the Pantagonian marine ecosystem
Sagittal otolith morphogenesis asymmetry in marine fishes
Journal of Fish Biology, 2015
This study investigated and compared asymmetry in sagittal otolith shape and length between left ... more This study investigated and compared asymmetry in sagittal otolith shape and length between left and right inner ears in four roundfish and four flatfish species of commercial interest. For each species, the effects of ontogenetic changes (individual age and total body length), sexual dimorphism (individual sex) and the otolith's location on the right or left side of the head, on the shape and length of paired otoliths (between 143 and 702 pairs according to species) were evaluated. Ontogenetic changes in otolith shape and length were observed for all species. Sexual dimorphism, either in otolith shape and length or in their ontogenetic changes, was detected for half of the species, be they round or flat. Significant directional asymmetry in otolith shape and length was detected in one roundfish species each, but its inconsistency across species and its small average amplitude (6·17% for shape and 1·99% for length) suggested that it has barely any biological relevance. Significant directional asymmetry in otolith shape and length was found for all flatfish species except otolith length for one species. Its average amplitude varied between 2·06 and 17·50% for shape and between 0·00 and 11·83% for length and increased significantly throughout ontogeny for two species, one dextral and one sinistral. The longer (length) and rounder otolith (shape) appeared to be always on the blind side whatever the species. These results suggest differential biomineralization between the blind and ocular inner ears in flatfish species that could result from perturbations of the proximal-distal gradient of otolith precursors in the endolymph and the otolith position relative to the geometry of the saccular epithelium due to body morphology asymmetry and lateralized behaviour. The fact that asymmetry never exceeded 18% even at the individual level suggests an evolutionary canalization of otolith shape symmetry to avoid negative effects on fish hearing and balance. Technically, asymmetry should be accounted for in future studies based on otolith shape.
A review of the aquatic living resources in Gulf of Guinea lagoons, with particular emphasis on fisheries management issues
ABSTRACT
PLOS ONE, 2015
Identifying the various drivers of marine ecosystem regime shifts and disentangling their respect... more Identifying the various drivers of marine ecosystem regime shifts and disentangling their respective influence are critical tasks for understanding biodiversity dynamics and properly managing exploited living resources such as marine fish communities. Unfortunately, the mechanisms and forcing factors underlying regime shifts in marine fish communities are still largely unknown although climate forcing and anthropogenic pressures such as fishing have been suggested as key determinants. Based on a 24-year-long time-series of scientific surveys monitoring 55 fish and cephalopods species, we report here a rapid and persistent structural change in the exploited fish community of the eastern English Channel from strong to moderate dominance of small-bodied forage fish species with low temperature preferendum that occurred in the mid-1990s. This shift was related to a concomitant warming of the North Atlantic Ocean as attested by a switch of the Atlantic Multidecadal Oscillation from a cold to a warm phase. Interestingly, observed changes in the fish community structure were opposite to those classically induced by exploitation as larger fish species of higher trophic level increased in abundance. Despite not playing a direct role in the regime shift, fishing still appeared as a forcing factor affecting community structure. Moreover, although related to climate, the regime shift may have been facilitated by strong historic exploitation that certainly primed the system by favoring the large dominance of small-bodied fish species that are particularly sensitive to climatic variations. These results emphasize that particular attention should be paid to multidecadal natural climate variability and its interactions with both fishing and climate warming when aiming at sustainable exploitation and ecosystem conservation.
Ecological Modelling, 2015
Ecological network analysis was applied in the Seine estuary ecosystem, northern France, integrat... more Ecological network analysis was applied in the Seine estuary ecosystem, northern France, integrating ecological data from the years 1996 to 2002. The Ecopath with Ecosim (EwE) approach was used to model the trophic flows in 6 spatial compartments leading to 6 distinct EwE models: the navigation channel and the two channel flanks in the estuary proper, and 3 marine habitats in the eastern Seine Bay. Each model included 12 consumer groups, 2 primary producers, and one detritus group. Ecological network analysis was performed, including a set of indices, keystoneness, and trophic spectrum analysis to describe the contribution of the 6 habitats to the Seine estuary ecosystem functioning. Results showed that the two habitats with a functioning most related to a stressed state were the northern and central navigation channels, where building works and constant maritime traffic are considered major anthropogenic stressors. The strong top-down control highlighted in the other 4 habitats was not present in the central channel, showing instead (i) a change in keystone roles in the ecosystem towards sediment-based, lower trophic levels, and (ii) a higher system omnivory. The southern channel evidenced the highest system activity (total system throughput), the higher trophic specialisation (low system omnivory), and the lowest indication of stress (low cycling and relative redundancy). Marine habitats showed higher fish biomass proportions and higher transfer efficiencies per trophic levels than the estuarine habitats, with a transition area between the two that presented intermediate ecosystem structure. The modelling of separate habitats permitted disclosing each one's response to the different pressures, based on their a priori knowledge. Network indices, although nonmonotonously, responded to these differences and seem a promising operational tool to define the ecological status of transitional water ecosystems. Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. ► Six food web models of the Seine estuary, 15 groups each, for the years 1996-2002. ► Network and keystone analysis performed by functional habitats. ► Construction works and maritime traffic identified by network stress levels. ► Structural and functional differences along the salinity gradient. ► Subdivision in habitats improves interpretation in ecological network analysis.
Journal of Applied Ecology, 2015
1. Well-designed marine protected area (MPA) networks can deliver a range of ecological, economic... more 1. Well-designed marine protected area (MPA) networks can deliver a range of ecological, economic and social benefits, and so a great deal of research has focused on developing spatial conservation prioritization tools to help identify important areas. 2. However, whilst these software tools are designed to identify MPA networks that both represent biodiversity and minimize impacts on stakeholders, they do not consider complex ecological processes. Thus, it is difficult to determine the impacts that proposed MPAs could have on marine ecosystem health, fisheries and fisheries sustainability. 3. Using the eastern English Channel as a case study, this paper explores an approach to address these issues by identifying a series of MPA networks using the Marxan and Marxan with Zones conservation planning software and linking them with a spatially explicit ecosystem model developed in Ecopath with Ecosim. We then use these to investigate potential trade-offs associated with adopting different MPA management strategies. 4. Limited-take MPAs, which restrict the use of some fishing gears, could have positive benefits for conservation and fisheries in the eastern English Channel, even though they generally receive far less attention in research on MPA network design. 5. Our findings, however, also clearly indicate that no-take MPAs should form an integral component of proposed MPA networks in the eastern English Channel, as they not only result in substantial increases Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. in ecosystem biomass, fisheries catches and the biomass of commercially valuable target species, but are fundamental to maintaining the sustainability of the fisheries. 6. Synthesis and applications. Using the existing software tools Marxan with Zones and Ecopath with Ecosim in combination provides a powerful policy-screening approach. This could help inform marine spatial planning by identifying potential conflicts and by designing new regulations that better balance conservation objectives and stakeholder interests. In addition, it highlights that appropriate combinations of no-take and limited-take marine protected areas might be the most effective when making trade-offs between long-term ecological benefits and short-term political acceptability.
New developments in Ecosim, which is part of the well known Ecopath software have allowed the use... more New developments in Ecosim, which is part of the well known Ecopath software have allowed the user to evaluate the effects of a range of possible fisheries management strategies for the Lake Victoria fisheries. The software is also used in this report to explore the fisheries and fish community of Lake Victoria. In particular, management strategies are explored aimed at achieving specified socioeconomic objectives, including maximising the economic value of the ecosystem and maximising employment by altering the pattern of fishing effort by the fishing fleets comprising the Lake Victoria fishery. Further, the same approach was used to consider optimal management strategies from an ecological perspective.
Progress in Oceanography, 2015
Recent theoretical considerations have highlighted the importance of the pelagic-benthic coupling... more Recent theoretical considerations have highlighted the importance of the pelagic-benthic coupling in marine food webs. In continental shelf seas, it was hypothesized that the trophic network structure may change along an inshore-offshore gradient due to weakening of the pelagic-benthic coupling from coastal to offshore areas. We tested this assumption empirically using the eastern English Channel (EEC) as a case study. We sampled organisms from particulate organic matter to predatory fishes and used baseline-corrected carbon and nitrogen stable isotope ratios (δ13C and δ15N) to determine their trophic position. First, hierarchical clustering on δ13C and δ15N coupled to bootstrapping and estimates of the relative contribution of pelagic and benthic carbon sources to consumers' diet showed that, at mesoscale, the EEC food web forms a continuum of four trophic levels with trophic groups spread across a pelagic and a benthic trophic pathway. Second, based on the same methods, a discrete approach examined changes in the local food web structure across three depth strata in order to investigate the inshore-offshore gradient. It showed stronger pelagic-benthic coupling in shallow coastal areas mostly due to a reorganization of the upper consumers relative to the two trophic pathways, benthic carbon sources being available to pelagic consumers and, reciprocally, pelagic sources becoming accessible to benthic species. Third a continuous approach examined changes in the mean and variance of upper consumers' δ13C and δ15N with depth. It detected a significant decrease in δ13C variance and a significant increase in δ15N variance as depth increases. A theoretical two-source mixing model showed that an inshore-offshore decrease in the pelagic-benthic coupling was a sufficient Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. condition to produce the δ13C variance pattern, thus supporting the conclusions of the discrete approach. These results suggest that environmental gradients such as the inshore-offshore one should be accounted for to better understand marine food webs dynamics. ► Marine food web is reorganized along a seaward gradient in the English Channel. ►Stronger coupling of the pelagic and benthic pathways from offshore to the coast. ►Shift of pelagic predators to the benthic pathway in shallow areas. ►Adaptive foraging of pelagic predators may explain food web reorganization.
Recent Trends in the Lake Victoria Fisheries Assessed by Ecopath
Cowx/Management, 2007
The Ecopath IV software with Ecosim, was used to describe te exploited fish community of the Wina... more The Ecopath IV software with Ecosim, was used to describe te exploited fish community of the Winam Gulf in the Kenyan sector of Lake Victoria, Africa. Developments in the ecosystem structure that can provide possible explanations for recent trends of evolution of the lake following preliminary assessments made on the trophic relationships in the fish community during the mid-1980s using Ecopath II were demonstrated. Further studies on system dynamics are made using the Ecosim simulation program that can describe the effects of some fisheries management schema during the past 10 years and for the future
Coastal Ecosystems of …, 2005
An Ecopath model of the Sine Saloum estuary (Senegal) with a total of 37 functional groups is use... more An Ecopath model of the Sine Saloum estuary (Senegal) with a total of 37 functional groups is used in this study to determine the key features of this aquatic system. The high fish species biodiversity in the ecosystem may play a role of ensuring its integrity, especially in the presence of stress, though it was observed that this is not entirely the case. Results show that another mitigating factor is the level of interaction strengths between functional groups. Stability is improved by weaker connectance as well as shorter and fatter pyramids. Though differing issues arise with respect to questions driving a system's stability, methods and approaches should consider placing results in the context of a broader ecological theory. RÉSUMÉ. -Un modèle Ecopath de l'estuaire du Sine-Saloum (Sénégal) comportant au total 37 groupes fonctionnels a été appliqué dans la présente étude en vue de déterminer les faits essentiels de ce système aquatique. La grande biodiversité spécifique des poissons de l'écosystème peut y jouer un rôle en assurant son intégrité, spécialement en présence de facteurs de stress, bien qu'il Coastal Ecosystems of West-Africa Biological Diversity-Resources-Conservation (Edited by J.-J. SYMOENS) Brussels (2005) pp. 15-26 Les écosystèmes côtiers de l'Afrique de l'Ouest Diversité biologique-Ressources-Conservation (Edit. : J.-J. SYMOENS) Bruxelles (2005) pp. 15-26 16 M.C. VILLANUEVA ET AL. ait été observé que ce n'est pas entièrement le cas. Les résultats montrent qu'un autre facteur de mitigation est le niveau des forces d'interaction entre les groupes fonctionnels. La stabilité est accrue par des relations plus faibles et des pyramides plus courtes et plus larges. Bien que différentes questions se posent concernant les facteurs conduisant à la stabilité d'un système, les méthodes et les façons de les approcher devraient envisager d'en situer les résultats dans le contexte d'une théorie écologique plus large.
Social Science Information, 2007
English It is becoming increasingly clear that humans impact marine ecosystems and their biodiver... more English It is becoming increasingly clear that humans impact marine ecosystems and their biodiversity to a very considerate degree, and evidence of the scale of impact is growing. An enabling factor for this has been a change in focus from local-level studies to increased emphasis on meta-analysis of global or regional-level analysis of fisheries' impact. Results include the facts that the world's total fish catches have been decreasing over the last decade or more; that larger, predatory fishes (table fish) are becoming increasingly scarcer; and that we are appropriating the ocean shelves' primary productivity to the same level as we are for terrestrial ecosystems. Ecosystems are being eroded in countries throughout the world, and though one might get the impression from the IUCN Red List that it is mainly a developed-country problem, it is alarming that the impact of severe overfishing may be on an even larger scale for developing countries. We describe aspects of the ...
Estuarine, Coastal and Shelf Science, 2008
This study attempts to assemble and summarize existing information in order to build a general re... more This study attempts to assemble and summarize existing information in order to build a general representation of the trophic interactions within the shallow coastal ecosystem of Sri Lanka. A multispecific ecosystem-based approach on trophic relationships and their possible variations was performed using ECOPATH. Thirty-nine functional groups were considered representing all trophic levels in the food web. Time-dynamic simulation was carried out using the ECOSIM routine to evaluate the impact of the 1998 El Niño event on key functional groups. Results show that the time needed for any impacted functional group to recover to its initial abundance increased with the trophic level. Two time-series data sets derived from commercial catch and effort statistics were used for validation of ECOSIM results. The El Niño simulation results validated by the time-series data confirmed the ability of the proposed multispecies model to describe the sudden environmental changes. Possible impacts due to increase of fishing effort were also simulated by separately considering frequently used fishing gears. The analysis revealed that small-mesh gillnet fishery operates independently from the other existing developing fisheries in the same area and can be managed accordingly. Fishing-effort simulations suggest that the increase of fishing intensity by small-mesh gillnets would contribute to the decline of small pelagic catch. This was also found to influence the overall catch. The present level of exploitation of small pelagic fishery resources does not seem sustainable.
Ecological Modelling, 2008
An Ecopath model of the southern part of Lake Kivu, a deep African equatorial lake was constructe... more An Ecopath model of the southern part of Lake Kivu, a deep African equatorial lake was constructed to quantitatively describe the possible impact of fish introductions in this ecosystem. This study is considered as an initial step in summarizing ecological and biological information, under a coherent framework, on this ecosystem. Fourteen compartments were considered. As a phytoplankton-based food web, it is observed that key food sources are not fully utilized as transfer efficiencies per trophic levels (TL) varies between 4.5 and 9.4%. Zooplankton plays a major role in transferring organic matter from TL1 to higher TLs due to the abundance of zooplanktivores. Shifts in food preferences and distribution of some of the fish functional groups were observed as a response to competition. The majority of fish biomass concentration is in TL3 (55%). The fishery is concentrated at TL3 and can, therefore, be consider as "immature", sensu Odum. The direct and indirect effects of predation between system components (i.e. fish, invertebrates, phytoplankton and detritus) are quantitatively described and the possible influence and role in the ecosystem's functioning of introduced fish species are discussed.
Ecological Modelling, 2006
The trophic dynamics of Bagré reservoir which has been recently impounded in Burkina Faso was bas... more The trophic dynamics of Bagré reservoir which has been recently impounded in Burkina Faso was based on the data collected during 1997-1998 period using the Ecopath model and software. Total fish biomass is 22.63 t km -2 and mainly represents trophic levels (TLs) 2 and 3. The trophic food chain is relatively long and the overall transfer efficiency is quite low. Grazing foodweb based on primary producers is prominent in the reservoir ecosystem and detritus plays a less significant role. Seasonal and long-term variations in water quality have significant influences on the lower TLs clearly showing a bottom-up functioning of the ecosystem. Environmental degradations, such as siltation occurring in the lake, suggest possible risks in limiting ecosystem productivity.
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Papers by Ching Villanueva