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Papers by Catarina Vendrell
ICES Journal of Marine Science, 2009
We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likel... more We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likelihood estimates of the distribution of ages in fish egg samples. To compare this method with another one based on a non-linear regression of age as a function of development stage and water temperature, which is also suitable for asynchronous spawners, we applied both to simulated and real datasets. The estimates of egg abundance-at-age obtained with the traditional method were biased upwards, compared with estimates obtained with the proposed EM algorithm. The EM method also provided the most accurate and precise estimates, in terms of fitting an exponential-decay, egg-mortality model and the back-calculation of the time of spawning for two datasets used as examples. Besides the ageing of fish eggs, the method described here can be used for any analysis involving the fitting of multinomial models to age and stage classified data, such as the ageing of post-ovulatory follicles.
Journal of Plancton Research, 2003
We found 1049 of 2409 mackerel eggs (46%) from 59 samples in the north-east Atlantic to be parasi... more We found 1049 of 2409 mackerel eggs (46%) from 59 samples in the north-east Atlantic to be
parasitized by the dinoflagellate Ichthyodinium chabelardi. The endogenous life cycle of the parasite
is briefly described.
Scientific Reports, 2020
The displacement of species from equatorial latitudes to temperate locations following the increa... more The displacement of species from equatorial latitudes to temperate locations following the increase in sea surface temperatures is among the significant reported consequences of climate change. Shifts in the distributional ranges of species result in fish communities tropicalisation, i.e., high latitude colonisations by typically low latitude distribution species. These movements create new interactions between species and new trophic assemblages. The Senegal seabream, Diplodus bellottii, may be used as a model to understand the population genetics of these invasions. In the last decades, this species has undergone an outstanding range expansion from its African area of origin to the Atlantic coast of the Iberian Peninsula, where now occurs abundantly. Mitochondrial and nuclear markers revealed a striking high haplotypic nucleotide and genetic diversity values, along with significant population differentiation throughout the present-day geographical range of the Senegal seabream. Th...
Nature research Scientific Reports, 2020
the displacement of species from equatorial latitudes to temperate locations following the increa... more the displacement of species from equatorial latitudes to temperate locations following the increase in sea surface temperatures is among the significant reported consequences of climate change. Shifts in the distributional ranges of species result in fish communities tropicalisation, i.e., high latitude colonisations by typically low latitude distribution species. these movements create new interactions between species and new trophic assemblages. the Senegal seabream, Diplodus bellottii, may be used as a model to understand the population genetics of these invasions. in the last decades, this species has undergone an outstanding range expansion from its African area of origin to the Atlantic coast of the iberian peninsula, where now occurs abundantly. Mitochondrial and nuclear markers revealed a striking high haplotypic nucleotide and genetic diversity values, along with significant population differentiation throughout the present-day geographical range of the Senegal seabream. These results are not consistent with the central-marginal hypothesis, nor with the expectations of a leptokurtic distribution of individuals, as D. bellottii seems to be able to retain exceptional levels of diversity in marginal and recently colonised areas. We discuss possible causes for hyperdiversity and lack of geographical structure and subsequent implications for fisheries. Tropicalisation, the displacement of species from equatorial latitudes to temperate locations, is one of the major reported consequences of climate changes 1-3. The increase of sea surface temperatures (SSTs) in the last decades has promoted shifts in the distributional ranges of species (e.g., 4,5) with individuals moving into areas best corresponding to their physiological optimum. Additionally, the ability of a species to colonise new habitats is influenced by oceanographic currents, the existence of adequate resource availability (i.e., habitat and food) and life-history patterns (e.g., number of eggs produced, age or parental care). These movements lead to the colonization of more poleward habitats by low latitude species, and create new interactions between species and new trophic assemblages. In commercial species, these shifts due to climate change can be magnified by fishing pressures, as reported for the North Sea cod (e.g., 6). Poleward colonization by organisms with a typically equatorial distribution was described almost three decades ago for terrestrial organisms in association with postglacial recolonisation routes (e.g., 7-10). As a general rule, organisms follow a leptokurtic distribution type, in which the majority of individuals stay at or near the original area, and only a fraction disperse to longer distances. This range extension is usually done in a steppingstone manner, implying that each settlement has fewer individuals compared with the previous one. Theoretically, this process corresponds to multiple successive genetic founder events associated with the corresponding genetic implications of the downsize in the effective population numbers: the erosion of the genetic diversity by genetic drift induces allele loss, the "southern richness and northern purity" paradigm 11. Additionally, the "central-marginal hypothesis" 12 posits that populations at the centre of the distribution have higher population sizes and gene flow, and peripheral (leading edge) populations, are smaller in size, have lower genetic diversity and will be more genetically differentiated 12. Phylogeographic studies using mitochondrial and nuclear genes revealed that species with similar environmental requirements and life-history traits often present distinct genetic and demographic historical patterns 13,14 .
We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likel... more We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likelihood estimates of the distribution of ages in fish egg samples. To compare this method with another one based on a non-linear regression of age as a function of development stage and water temperature, which is also suitable for asynchronous spawners, we applied both to simulated and real datasets. The estimates of egg abundance-at-age obtained with the traditional method were biased upwards, compared with estimates obtained with the proposed EM algorithm. The EM method also provided the most accurate and precise estimates, in terms of fitting an exponential-decay, egg-mortality model and the back-calculation of the time of spawning for two datasets used as examples. Besides the ageing of fish eggs, the method described here can be used for any analysis involving the fitting of multinomial models to age and stage classified data, such as the ageing of post-ovulatory follicles.
Ices Journal of Marine Science, 2009
We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likel... more We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likelihood estimates of the distribution of ages in fish egg samples. To compare this method with another one based on a non-linear regression of age as a function of development stage and water temperature, which is also suitable for asynchronous spawners, we applied both to simulated and real datasets. The estimates of egg abundance-at-age obtained with the traditional method were biased upwards, compared with estimates obtained with the proposed EM algorithm. The EM method also provided the most accurate and precise estimates, in terms of fitting an exponential-decay, egg-mortality model and the back-calculation of the time of spawning for two datasets used as examples. Besides the ageing of fish eggs, the method described here can be used for any analysis involving the fitting of multinomial models to age and stage classified data, such as the ageing of post-ovulatory follicles.
Journal of Plankton Research
ICES, 2000
Environ Biol Fish, 2014
ABSTRACT Behavioural observations of juvenile Diplodus sargus in natural habitats were conducted ... more ABSTRACT Behavioural observations of juvenile Diplodus sargus in natural habitats were conducted to test whether agonistic interactions occur in natural circumstances and, if they do, in which context they happen. The level of aggression and the shoals composition were also compared between distinct natural habitats. Behavioural observations were also conducted in captivity, and the level of aggression was compared with the level recorded in natural conditions to investigate which factors may promote aggressive behaviours. The observations were performed at two sites in the Atlantic Portuguese shore: São Pedro do Estoril (38°41′N, 9°22′W) and Cabo Raso (38°42′N, 9°29′W) from early July to late August 2010 and from late July to early October 2011, respectively. In nature agonistic behaviours do occur, with a higher frequency in pools than in open areas. However, even the highest values observed in nature are significantly lower than those reported for captive conditions. Shoal composition also changed in different habitats, with more members and aggregates more compact in open areas. We suggested that the high levels of aggression observed in captive groups may be an artefact caused by very high densities in confined spaces and eventually by the accumulation of chemicals that are known to be released by stressed fish and can be detected by other conspecifics. The confinement imposed in captivity may also affect shoal composition limiting the number of members and inter-individual distances in each group.
ICES Journal of …, 2008
To determine the effect of temperature on the development rates of artificially fertilized eggs o... more To determine the effect of temperature on the development rates of artificially fertilized eggs of Trachurus trachurus, experiments were carried out at temperatures ranging from 10.58C to 198C. Egg development through to hatching only took place at 11.7-198C. At lower temperature, eggs did not develop beyond the stage where the outline of the embryo was clearly discernible and a defined median line of the embryonic shield (stage 4 in this study) was apparent. Development time took from 46 h at 198C to 126 h at 128C. A generalized linear model of the stage-dependent development time (age) as a function of incubation temperature was developed. The data are also compared with those reported in the literature and related to sea temperature on the spawning grounds.
Cybium, 2014
Les ovaires de la saupe, Sarpa salpa (Linnaeus, 1758), présen- tent des structures dures et facil... more Les ovaires de la saupe, Sarpa salpa (Linnaeus, 1758), présen- tent des structures dures et facilement visibles macroscopiquement.
Leur analyse histologique montre que ce sont des masses d’ovo- cytes hydratés résultant d’un événement de ponte, incomplète ou non. Le modèle linéaire généralisé (MLG) montre que la présence
de kystes a été significativement affectée selon les mois. Le fait que ces structures apparaissent fréquemment avec une prévalence éle- vée peut suggérer la présence d’un lien, ou d’une association, avec la stratégie de reproduction chez cette espèce.
ICES Journal of Marine Science, 2009
We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likel... more We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likelihood estimates of the distribution of ages in fish egg samples. To compare this method with another one based on a non-linear regression of age as a function of development stage and water temperature, which is also suitable for asynchronous spawners, we applied both to simulated and real datasets. The estimates of egg abundance-at-age obtained with the traditional method were biased upwards, compared with estimates obtained with the proposed EM algorithm. The EM method also provided the most accurate and precise estimates, in terms of fitting an exponential-decay, egg-mortality model and the back-calculation of the time of spawning for two datasets used as examples. Besides the ageing of fish eggs, the method described here can be used for any analysis involving the fitting of multinomial models to age and stage classified data, such as the ageing of post-ovulatory follicles.
Journal of Plancton Research, 2003
We found 1049 of 2409 mackerel eggs (46%) from 59 samples in the north-east Atlantic to be parasi... more We found 1049 of 2409 mackerel eggs (46%) from 59 samples in the north-east Atlantic to be
parasitized by the dinoflagellate Ichthyodinium chabelardi. The endogenous life cycle of the parasite
is briefly described.
Scientific Reports, 2020
The displacement of species from equatorial latitudes to temperate locations following the increa... more The displacement of species from equatorial latitudes to temperate locations following the increase in sea surface temperatures is among the significant reported consequences of climate change. Shifts in the distributional ranges of species result in fish communities tropicalisation, i.e., high latitude colonisations by typically low latitude distribution species. These movements create new interactions between species and new trophic assemblages. The Senegal seabream, Diplodus bellottii, may be used as a model to understand the population genetics of these invasions. In the last decades, this species has undergone an outstanding range expansion from its African area of origin to the Atlantic coast of the Iberian Peninsula, where now occurs abundantly. Mitochondrial and nuclear markers revealed a striking high haplotypic nucleotide and genetic diversity values, along with significant population differentiation throughout the present-day geographical range of the Senegal seabream. Th...
Nature research Scientific Reports, 2020
the displacement of species from equatorial latitudes to temperate locations following the increa... more the displacement of species from equatorial latitudes to temperate locations following the increase in sea surface temperatures is among the significant reported consequences of climate change. Shifts in the distributional ranges of species result in fish communities tropicalisation, i.e., high latitude colonisations by typically low latitude distribution species. these movements create new interactions between species and new trophic assemblages. the Senegal seabream, Diplodus bellottii, may be used as a model to understand the population genetics of these invasions. in the last decades, this species has undergone an outstanding range expansion from its African area of origin to the Atlantic coast of the iberian peninsula, where now occurs abundantly. Mitochondrial and nuclear markers revealed a striking high haplotypic nucleotide and genetic diversity values, along with significant population differentiation throughout the present-day geographical range of the Senegal seabream. These results are not consistent with the central-marginal hypothesis, nor with the expectations of a leptokurtic distribution of individuals, as D. bellottii seems to be able to retain exceptional levels of diversity in marginal and recently colonised areas. We discuss possible causes for hyperdiversity and lack of geographical structure and subsequent implications for fisheries. Tropicalisation, the displacement of species from equatorial latitudes to temperate locations, is one of the major reported consequences of climate changes 1-3. The increase of sea surface temperatures (SSTs) in the last decades has promoted shifts in the distributional ranges of species (e.g., 4,5) with individuals moving into areas best corresponding to their physiological optimum. Additionally, the ability of a species to colonise new habitats is influenced by oceanographic currents, the existence of adequate resource availability (i.e., habitat and food) and life-history patterns (e.g., number of eggs produced, age or parental care). These movements lead to the colonization of more poleward habitats by low latitude species, and create new interactions between species and new trophic assemblages. In commercial species, these shifts due to climate change can be magnified by fishing pressures, as reported for the North Sea cod (e.g., 6). Poleward colonization by organisms with a typically equatorial distribution was described almost three decades ago for terrestrial organisms in association with postglacial recolonisation routes (e.g., 7-10). As a general rule, organisms follow a leptokurtic distribution type, in which the majority of individuals stay at or near the original area, and only a fraction disperse to longer distances. This range extension is usually done in a steppingstone manner, implying that each settlement has fewer individuals compared with the previous one. Theoretically, this process corresponds to multiple successive genetic founder events associated with the corresponding genetic implications of the downsize in the effective population numbers: the erosion of the genetic diversity by genetic drift induces allele loss, the "southern richness and northern purity" paradigm 11. Additionally, the "central-marginal hypothesis" 12 posits that populations at the centre of the distribution have higher population sizes and gene flow, and peripheral (leading edge) populations, are smaller in size, have lower genetic diversity and will be more genetically differentiated 12. Phylogeographic studies using mitochondrial and nuclear genes revealed that species with similar environmental requirements and life-history traits often present distinct genetic and demographic historical patterns 13,14 .
We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likel... more We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likelihood estimates of the distribution of ages in fish egg samples. To compare this method with another one based on a non-linear regression of age as a function of development stage and water temperature, which is also suitable for asynchronous spawners, we applied both to simulated and real datasets. The estimates of egg abundance-at-age obtained with the traditional method were biased upwards, compared with estimates obtained with the proposed EM algorithm. The EM method also provided the most accurate and precise estimates, in terms of fitting an exponential-decay, egg-mortality model and the back-calculation of the time of spawning for two datasets used as examples. Besides the ageing of fish eggs, the method described here can be used for any analysis involving the fitting of multinomial models to age and stage classified data, such as the ageing of post-ovulatory follicles.
Ices Journal of Marine Science, 2009
We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likel... more We describe an application of the expectation-maximization (EM) algorithm to obtain maximum likelihood estimates of the distribution of ages in fish egg samples. To compare this method with another one based on a non-linear regression of age as a function of development stage and water temperature, which is also suitable for asynchronous spawners, we applied both to simulated and real datasets. The estimates of egg abundance-at-age obtained with the traditional method were biased upwards, compared with estimates obtained with the proposed EM algorithm. The EM method also provided the most accurate and precise estimates, in terms of fitting an exponential-decay, egg-mortality model and the back-calculation of the time of spawning for two datasets used as examples. Besides the ageing of fish eggs, the method described here can be used for any analysis involving the fitting of multinomial models to age and stage classified data, such as the ageing of post-ovulatory follicles.
Journal of Plankton Research
ICES, 2000
Environ Biol Fish, 2014
ABSTRACT Behavioural observations of juvenile Diplodus sargus in natural habitats were conducted ... more ABSTRACT Behavioural observations of juvenile Diplodus sargus in natural habitats were conducted to test whether agonistic interactions occur in natural circumstances and, if they do, in which context they happen. The level of aggression and the shoals composition were also compared between distinct natural habitats. Behavioural observations were also conducted in captivity, and the level of aggression was compared with the level recorded in natural conditions to investigate which factors may promote aggressive behaviours. The observations were performed at two sites in the Atlantic Portuguese shore: São Pedro do Estoril (38°41′N, 9°22′W) and Cabo Raso (38°42′N, 9°29′W) from early July to late August 2010 and from late July to early October 2011, respectively. In nature agonistic behaviours do occur, with a higher frequency in pools than in open areas. However, even the highest values observed in nature are significantly lower than those reported for captive conditions. Shoal composition also changed in different habitats, with more members and aggregates more compact in open areas. We suggested that the high levels of aggression observed in captive groups may be an artefact caused by very high densities in confined spaces and eventually by the accumulation of chemicals that are known to be released by stressed fish and can be detected by other conspecifics. The confinement imposed in captivity may also affect shoal composition limiting the number of members and inter-individual distances in each group.
ICES Journal of …, 2008
To determine the effect of temperature on the development rates of artificially fertilized eggs o... more To determine the effect of temperature on the development rates of artificially fertilized eggs of Trachurus trachurus, experiments were carried out at temperatures ranging from 10.58C to 198C. Egg development through to hatching only took place at 11.7-198C. At lower temperature, eggs did not develop beyond the stage where the outline of the embryo was clearly discernible and a defined median line of the embryonic shield (stage 4 in this study) was apparent. Development time took from 46 h at 198C to 126 h at 128C. A generalized linear model of the stage-dependent development time (age) as a function of incubation temperature was developed. The data are also compared with those reported in the literature and related to sea temperature on the spawning grounds.
Cybium, 2014
Les ovaires de la saupe, Sarpa salpa (Linnaeus, 1758), présen- tent des structures dures et facil... more Les ovaires de la saupe, Sarpa salpa (Linnaeus, 1758), présen- tent des structures dures et facilement visibles macroscopiquement.
Leur analyse histologique montre que ce sont des masses d’ovo- cytes hydratés résultant d’un événement de ponte, incomplète ou non. Le modèle linéaire généralisé (MLG) montre que la présence
de kystes a été significativement affectée selon les mois. Le fait que ces structures apparaissent fréquemment avec une prévalence éle- vée peut suggérer la présence d’un lien, ou d’une association, avec la stratégie de reproduction chez cette espèce.