Canadian Journal of Fisheries and Aquatic Sciences, Feb 1, 2005
Snow crab (Chionoecetes opilio) migrations in the eastern Bering Sea have long been ignored. Base... more Snow crab (Chionoecetes opilio) migrations in the eastern Bering Sea have long been ignored. Based on preliminary information, we hypothesized that females undergo an extensive ontogenetic migration, tracking down environmental gradients. We analyzed a 25-year time series of survey data and defined ontogenetic stages in terms of a "shell condition index" calibrated with radiochemical methods. "Pseudo-cohorts" of mature females (groups of females that undergo puberty molt in a given year) "recruit" to the mature female pool in the Middle Domain (50-100 m) of the intermediate shelf. Females undergo puberty molt and primiparous mating in winter. Over the next year, they migrate an average net distance of 73.5 nautical miles towards the shelf edge following a predominantly northeastsouthwest direction. Maximum post-terminal molt life span is 6-7 years. Results support the hypothesis that the variable tracked is near-bottom temperature. Although near-bottom temperature fields vary from year to year, the corresponding vector field is a conservative template, which explains the consistency observed in the pattern of migration. Elucidation of the life history schedule of mature female snow crabs in the eastern Bering Sea revealed that it is very similar to that reported for eastern Canada, although patterns of migration may differ substantially between the two systems. Résumé : L'étude des migrations du crabe des neiges (Chionoecetes opilio) dans l'est de la mer de Béring a longtemps été négligée. Sur la base de données préliminaires, nous posons l'hypothèse selon laquelle les femelles complètent une importante migration ontogénique, en suivant des gradients environnementaux. Nous avons analysé une série temporelle de 25 années de données d'inventaire et nous avons défini les stades ontogéniques d'après un « indice de condition de la carapace » calibré au moyen de méthodes radiochimiques. Des « pseudo-cohortes » de femelles matures (des groupes de femelles qui subissent la mue de puberté dans une même année) s'incorporent comme « recrues » dans le pool de femelles adultes dans le domaine central (50-100 m) de la plate-forme intermédiaire. Les femelles complètent leur mue de puberté et leur accouplement de primipare au cours de l'hiver. Dans l'année qui suit, elles migrent sur une distance moyenne nette de 73,5 milles marins vers la marge de la plate-forme, en s'orientant dans une direction surtout nord-est et sud-est. La longévité maximale après la mue terminale est de 6-7 ans. Nos résultats appuient l'hypothèse qui veut que la variable qui est suivie soit la température près du fond (NBT). Bien que les champs de NBT varient d'une année à l'autre, le champ vectoriel qui en résulte a une structure relativement stable, ce qui explique la constance qui existe dans les patrons de migration. L'élucidation du calendrier du cycle biologique des crabes des neiges femelles matures dans l'est de la mer de Béring montre qu'il est très semblable à celui qui a été signalé dans l'est du Canada, bien que les patrons de migration puissent différer considérablement entre les deux systèmes. [Traduit par la Rédaction] Ernst et al. 268
The tsunami that hit the Juan Fernández islands of Chile has tested the resilience of the traditi... more The tsunami that hit the Juan Fernández islands of Chile has tested the resilience of the traditional tenure system of the fishing community of the area.Fil: Ernst, Billy. Departamento de Oceanografía, Universidad de Concepción; ChileFil: Chamorro, Julio. Sindicato de Trabajadores Independientes Pescadores Artesanales, Juan Fernández; ChileFil: Manríquez, Pablo. Sindicato de Trabajadores Independientes Pescadores Artesanales, Juan Fernández; ChileFil: Orensanz, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin
... Billy Ernst, Pablo Manríquez, JM (Lobo) Orensanz, Rubén Roa, Julio Chamorro, and Carolina Par... more ... Billy Ernst, Pablo Manríquez, JM (Lobo) Orensanz, Rubén Roa, Julio Chamorro, and Carolina Parada ... The authority refers to SERNAPESCA, the Chilean Servicio Nacional de Pesca. Seasons Source of data Percentage of trips sampled Documented by 197071, 197172 ...
The Juan Fernández Ridge (JFR) is a chain of topographical elevations in the eastern South Pacifi... more The Juan Fernández Ridge (JFR) is a chain of topographical elevations in the eastern South Pacific (~33-35°S, 76-81.5°W). Rich in endemic marine species, this ridge is frequently affected by the arrival of mesoscale eddies originating in the coastal upwelling zone off central-southern Chile. The impacts of these interactions on the structure and dynamics of the JFR pelagic system have, however, not been addressed yet. The present model-based study is focused on the coupled influence of mesoscale-submesoscale processes and biological behavior (i.e., diel vertical migration) on the horizontal distribution of planktonic larvae of the spiny lobster (Jasus frontalis) around the JFR waters. Two case studies were selected from a hydrodynamic Regional Ocean Modeling System to characterize mesoscale and submesoscales structures and an Individual-based model (IBM) to simulate diel vertical migration (DVM) and its impact on the horizontal distribution and the patchiness level. DVM behavior of these larvae has not been clearly characterized, therefore, three types of vertical mechanisms were assessed on the IBM: (1) no migration (LG), (2) a short migration (0-50 m depth, DVM1), and (3) a long migration (10-200 m depth, DVM2). The influence of physical properties (eddy kinetic energy, stretching deformation and divergence) on larval aggregation within meso and submesoscale features was quantified. The patchiness index assessed for mesoscale and submesoscale structures showed higher values in the mesoscale than in the submesoscale. However, submesoscale structures revealed a higher accumulation of particles by unit of area. Both migrational vertical mechanisms produced larger patchiness indices compared to the no migration experiment. DVM2 was the one that showed by far the largest aggregation of almost all the aggregations zones. Larval concentrations were highest in the submesoscale structures; these zones were characterized by low eddy kinetic energy, negative stretching deformation, and slight convergence.-Stretching deformation flow appeared to be triggered by the eddies-eddies interactions and the Robinson Island barrier effect, which likely promotes the aggregation of the spiny lobster larvae in the Juan Fernández system. These results highlighted the importance of the coupled effect of physical (meso and submesoscales oceanographic features) and biological processes (DVM) in the generation of larval patchiness and concentration of spiny lobster larvae around the JFR, which could be key for their survival and retention in those waters.
Protecting the ecological health of rivers relies on maintaining intact flows from source areas t... more Protecting the ecological health of rivers relies on maintaining intact flows from source areas to downstream navigable waters (1). Yet the U.S. Environmental Protection Agency (EPA) intends to rescind legal protection of tributary rivers, streams, and wetlands that do not have year-round flows (temporary waterways) and whose surface waters contribute flow to permanent navigable waters (2). This decision would severely damage the condition and uses of many U.S. waters, both temporary and navigable. Temporary waterways provide many ecosystem services, including water provision and purification, that contribute substantially to securing water quantity and quality (3–5). Fifty-eight percent of all waterways that provide drinking water to the continental United States are temporary or headwater streams, which support more than one-third of the United States’s population (6). Furthermore, temporary waterways harbor important biodiversity (5) and imperiled species (7) and underpin global carbon and nutrient cycles (8). Even when dry, they provide ecosystem services such as providing groundwater, attenuating toxicants, buffering floods, and providing habitat for unique biodiversity (5, 9). A comprehensive scientific review (10) of all the services provided by temporary waterways led to the decision in 2015 Edited by Jennifer Sills to recodify the definition of “waters of the United States” to include temporary waters hydrologically connected to navigable waters. This provided protection to many temporary waterways under the U.S. Clean Water Act and was hailed as a wise, well-informed decision (4). However, the recodification has not yet been implemented because the legal process is incomplete, and now reversal of the decision is expected (2). We urge the EPA to uphold its 2015 decision and to ratify the legal status and protection of temporary waterways. This would provide U.S. temporary waterways with a level of protection similar to that in other countries, such as Australia (5). Failure to do so sets a poor global precedent and, more importantly, risks costly (11) and potentially irreversible harm to the ecosystem services supported by temporary waterways in the United States, including the provision of secure potable water.
Fluctuations in abundance of commercially valuable crustacean stocks in sub-Arctic ecosystems hav... more Fluctuations in abundance of commercially valuable crustacean stocks in sub-Arctic ecosystems have been variously attributed to the effects of climatic forcing, fishing pressure, and predation, mostly by gadoid fishes. Landings of snow crab, Chionoecetes opilio (J. C. Fabricius, 1788), from the eastern Bering Sea declined after the early 1990s, reaching historical lows a decade later. At the same time, two phenomena became apparent in the dynamics of the primiparae (first-time female breeders): their geographic range contracted to the northwest along the middle shelf (50-100 m depth), and the contraction was punctuated by periodic recruitment to the mature female pool, with a period of approximately 7 yrs and declining amplitude. The first phenomenon has been addressed by the environmental ratchet hypothesis, which attributes the contraction to a combination of an ontogenetic female migration, circulation patterns, the spatial dynamics of benthic stages in relation to near-bottom temperature, and predation by Pacific cod, Gadus macrocephalus Tilesius, 1810. Mortality due to cod predation in the Middle Domain, apparently related to near-bottom temperature, increased after 1995, contributing to the ratchet effect and the disappearance of periodic pulses of primipara abundance. Cod predation does not, however, appear to have controlled the frequency of periodic recruitment fluctuations. On the other hand, amplitude of fluctuations of primipara abundance in the Middle Domain, purportedly the "engine" of renewal of this stock, do appear to be affected by both predation and climate, whose interaction is complex but perhaps interpretable. Top-down control of commercially valuable crustacean stocks from subarctic ecosystems, mostly with regard to predation by cod (Gadus spp.), has been the subject of much attention in recent years (Frank et al. 2005, Link et al. 2009). Those interactions are significant because of their role in the functioning of shelf ecosystems, their large spatial scale, and the economic significance of the species involved, both predators and prey (Worm and Myers 2003). Snow crab, Chionoecetes opilio (J. C. Fabricius, 1788), for example, is preyed upon by Atlantic cod, Gadus morhua Linnaeus, 1758, in eastern Canada (Chabot et al. 2008) and by Pacific cod, Gadus macrocephalus Tilesius, 1810, in the Bering Sea (Livingston 1989, Orensanz et al. 2004). Over the last two decades landings of snow crab have declined dramatically in the eastern Bering Sea (EBS; Fig. 1A), from a maximum of nearly 150,000 t in 1991 to historical lows on the order of 12,000 t during the early 2000s (NPFMC 2010). The stock, declared "overfished" in 1999, has recently been considered to be rebuilt. These fluctuations of abundance, variously attributed to climate, fishing, and predation, have MOTE SYMPOSIUM INVITED PAPER
Age structure, annual growth, and variance of size-at-age of the shrimp Heterocarpus reedi Ruben ... more Age structure, annual growth, and variance of size-at-age of the shrimp Heterocarpus reedi Ruben ~o a '~~~' , Billy ~r n s t~ '~nstituto de Fomento Pesquero. Sede Zonal V-IX Regiones. Casilla 347,
Alaska Sea Grant, University of Alaska Fairbanks eBooks, 2005
Male-only crab fi sheries often are assumed to be relatively well protected from recruitment over... more Male-only crab fi sheries often are assumed to be relatively well protected from recruitment overfi shing by virtue of male polygyny and female sperm retention. These fi sheries also off er the opportunity to directly assess the per capita female reproductive contribution. If the latter does not dwindle when a stock declines, then the decline cannot be attributed to overfi shing. We explored expedient ways to assess per capita female reproductive contribution of snow crab (Chionoecetes opilio) and Tanner crab (C. bairdi) of the Eastern Bering Sea (EBS) by measuring clutch volume and estimating an objective “clutch fullness index” (CFI) based on modeling the “maximum boundary line” (MBL) of scatterplots of clutch volume vs. body size. We investigated three estimation methods, selected quantile regression for further analysis, and examined the distribution of the CFI in extensive samples collected during trawl surveys conducted in 1992 and 1993. An objective protocol for the visual assessment of clutch size (based on an estimated MBL) was introduced in 1994, with a dramatic eff ect on estimated CFI. CFI distributions proved very useful for
Nursery ground, age structure and abundance of juvenile squat lobster Pleuroncodes monodon on the... more Nursery ground, age structure and abundance of juvenile squat lobster Pleuroncodes monodon on the continental shelf off central Chile Ruben ~o a \ Victor A. ~a l l a r d o~~~, Billy ~r n s t~
Knowledge about the spatial patterns and movements of crustaceans has gained importance since the... more Knowledge about the spatial patterns and movements of crustaceans has gained importance since the creation of marine protected areas and the development of spatial management for benthic ecosystems. The Juan Ferná ndez spiny lobster (Jasus frontalis) is an endemic marine species and most valuable resource that exhibits migratory dynamics in a highly spatially regulated fishery. To study movement patterns around Alexander Selkirk Island, a mark-recapture program was implemented in 2008, when approximately 7000 non-commercial (undersized) lobsters were tagged and followed for nearly 14 months. Using quantitative georeferenced data, this study revealed spatial structuring of Juan Ferná ndez spiny lobster and tested hypotheses about alongshore and inshore-offshore movements. Eight clusters were identified around Alexander Selkirk Island, with moderate timevarying connectivity between them. Seasonal inshore-offshore movements were detected all around the island, but more conspicuously to the north. Average travelling distance was 1.2 km (1.7 sd). Our results confirmed that towards the end of austral spring males and females embark in a seasonal offshore migration to deeper waters, returning to shallower waters only during winter. These findings quantitatively consolidate the conceptual migratory model that local fishermen had already inferred for this resource from about a century of sustainable fishing.
Landings of the snow crab Chionoecetes opilio (J. C. Fabricius, 1788), which supports a lucrative... more Landings of the snow crab Chionoecetes opilio (J. C. Fabricius, 1788), which supports a lucrative fishery in the eastern Bering Sea (EBS), dropped to historical lows by 2000, and the geographic range of reproductive females contracted to the northwest. Resilience of the mature female range through larval advection may be hampered because hatching now occurs downstream. These changes have been punctuated by four pulses of recruitment, with a remarkably regular period of 6-7 yrs. Major pulses of the fishery, during the 1990s, were sustained by recruitment pulses that originated in regions of the northwest section of the EBS shelf beyond the reach of the fishery. Here we present, for the first time, a conceptual model of snow-crab spatial dynamics that integrates empirical information with new results from modeling of circulation and larval transport. The geographic region of interest, defined by means of biophysical modeling and tracking ontogenetic migrations, consists of the middle and outer domains of the EBS shelf, bounded by the 50-and 200m isobaths. Connectivity analysis highlights the significance of subsystems in the southeast and northwest sections of the EBS's middle domain. Predicted settlement regions match historical regions of abundance of immature crabs and are consistent with observed fields of suitable near-bottom temperature. Our study, together with others, highlights the significance of climate change for the fate of important highlatitude fisheries. Scenarios of climate change have prompted concerns about the future of high-latitude fisheries (
<p>(A) Marked lobsters by sex for all tagging periods and (B) Size structure (sex combined)... more <p>(A) Marked lobsters by sex for all tagging periods and (B) Size structure (sex combined) from biological sampling during 2008/09 fishing season [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200146#pone.0200146.ref035" target="_blank">35</a>]. Vertical dashed lines correspond to size of 50% of maturity and minimum legal size.</p
Genetics data have provided unprecedented insights into evolutionary aspects of colonization by n... more Genetics data have provided unprecedented insights into evolutionary aspects of colonization by non-native populations. Yet, our understanding of how artificial (human-mediated) and natural dispersal pathways of non-native individuals influence genetic metrics, evolution of genetic structure, and admixture remains elusive. We capitalize on the widespread colonization of Chinook salmon Oncorhynchus tshawytscha in South America, mediated by both dispersal pathways, to address these issues using data from a panel of polymorphic SNPs. First, genetic diversity and the number of effective breeders (Nb) were higher among artificial than natural populations. Contemporary gene flow was common between adjacent artificial and natural as well as adjacent natural populations but uncommon between geographically distant populations. Second, genetic structure revealed four distinct clusters throughout the Chinook salmon distributional range with varying levels of genetic connectivity. Isolation-by-distance resulted from weak differentiation between adjacent artificial and natural as well as natural populations and with strong differentiation between distant populations experiencing strong genetic drift. Third, genetic mixture analyses revealed the presence of at least six donor geographic regions from North America, some of which likely hybridized as a result of multiple introductions. Relative propagule pressure or the proportion of Chinook salmon propagules introduced from various geographic regions according to government records significantly influenced genetic mixtures for two of three artificial populations. Our findings support a model of colonization in which high-diversity artificial populations established first; some of these populations exhibited significant admixture resulting from propagule pressure. Low-diversity natural populations were likely subsequently founded from a reduced number of individuals
Canadian Journal of Fisheries and Aquatic Sciences, Feb 1, 2005
Snow crab (Chionoecetes opilio) migrations in the eastern Bering Sea have long been ignored. Base... more Snow crab (Chionoecetes opilio) migrations in the eastern Bering Sea have long been ignored. Based on preliminary information, we hypothesized that females undergo an extensive ontogenetic migration, tracking down environmental gradients. We analyzed a 25-year time series of survey data and defined ontogenetic stages in terms of a "shell condition index" calibrated with radiochemical methods. "Pseudo-cohorts" of mature females (groups of females that undergo puberty molt in a given year) "recruit" to the mature female pool in the Middle Domain (50-100 m) of the intermediate shelf. Females undergo puberty molt and primiparous mating in winter. Over the next year, they migrate an average net distance of 73.5 nautical miles towards the shelf edge following a predominantly northeastsouthwest direction. Maximum post-terminal molt life span is 6-7 years. Results support the hypothesis that the variable tracked is near-bottom temperature. Although near-bottom temperature fields vary from year to year, the corresponding vector field is a conservative template, which explains the consistency observed in the pattern of migration. Elucidation of the life history schedule of mature female snow crabs in the eastern Bering Sea revealed that it is very similar to that reported for eastern Canada, although patterns of migration may differ substantially between the two systems. Résumé : L'étude des migrations du crabe des neiges (Chionoecetes opilio) dans l'est de la mer de Béring a longtemps été négligée. Sur la base de données préliminaires, nous posons l'hypothèse selon laquelle les femelles complètent une importante migration ontogénique, en suivant des gradients environnementaux. Nous avons analysé une série temporelle de 25 années de données d'inventaire et nous avons défini les stades ontogéniques d'après un « indice de condition de la carapace » calibré au moyen de méthodes radiochimiques. Des « pseudo-cohortes » de femelles matures (des groupes de femelles qui subissent la mue de puberté dans une même année) s'incorporent comme « recrues » dans le pool de femelles adultes dans le domaine central (50-100 m) de la plate-forme intermédiaire. Les femelles complètent leur mue de puberté et leur accouplement de primipare au cours de l'hiver. Dans l'année qui suit, elles migrent sur une distance moyenne nette de 73,5 milles marins vers la marge de la plate-forme, en s'orientant dans une direction surtout nord-est et sud-est. La longévité maximale après la mue terminale est de 6-7 ans. Nos résultats appuient l'hypothèse qui veut que la variable qui est suivie soit la température près du fond (NBT). Bien que les champs de NBT varient d'une année à l'autre, le champ vectoriel qui en résulte a une structure relativement stable, ce qui explique la constance qui existe dans les patrons de migration. L'élucidation du calendrier du cycle biologique des crabes des neiges femelles matures dans l'est de la mer de Béring montre qu'il est très semblable à celui qui a été signalé dans l'est du Canada, bien que les patrons de migration puissent différer considérablement entre les deux systèmes. [Traduit par la Rédaction] Ernst et al. 268
The tsunami that hit the Juan Fernández islands of Chile has tested the resilience of the traditi... more The tsunami that hit the Juan Fernández islands of Chile has tested the resilience of the traditional tenure system of the fishing community of the area.Fil: Ernst, Billy. Departamento de Oceanografía, Universidad de Concepción; ChileFil: Chamorro, Julio. Sindicato de Trabajadores Independientes Pescadores Artesanales, Juan Fernández; ChileFil: Manríquez, Pablo. Sindicato de Trabajadores Independientes Pescadores Artesanales, Juan Fernández; ChileFil: Orensanz, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentin
... Billy Ernst, Pablo Manríquez, JM (Lobo) Orensanz, Rubén Roa, Julio Chamorro, and Carolina Par... more ... Billy Ernst, Pablo Manríquez, JM (Lobo) Orensanz, Rubén Roa, Julio Chamorro, and Carolina Parada ... The authority refers to SERNAPESCA, the Chilean Servicio Nacional de Pesca. Seasons Source of data Percentage of trips sampled Documented by 197071, 197172 ...
The Juan Fernández Ridge (JFR) is a chain of topographical elevations in the eastern South Pacifi... more The Juan Fernández Ridge (JFR) is a chain of topographical elevations in the eastern South Pacific (~33-35°S, 76-81.5°W). Rich in endemic marine species, this ridge is frequently affected by the arrival of mesoscale eddies originating in the coastal upwelling zone off central-southern Chile. The impacts of these interactions on the structure and dynamics of the JFR pelagic system have, however, not been addressed yet. The present model-based study is focused on the coupled influence of mesoscale-submesoscale processes and biological behavior (i.e., diel vertical migration) on the horizontal distribution of planktonic larvae of the spiny lobster (Jasus frontalis) around the JFR waters. Two case studies were selected from a hydrodynamic Regional Ocean Modeling System to characterize mesoscale and submesoscales structures and an Individual-based model (IBM) to simulate diel vertical migration (DVM) and its impact on the horizontal distribution and the patchiness level. DVM behavior of these larvae has not been clearly characterized, therefore, three types of vertical mechanisms were assessed on the IBM: (1) no migration (LG), (2) a short migration (0-50 m depth, DVM1), and (3) a long migration (10-200 m depth, DVM2). The influence of physical properties (eddy kinetic energy, stretching deformation and divergence) on larval aggregation within meso and submesoscale features was quantified. The patchiness index assessed for mesoscale and submesoscale structures showed higher values in the mesoscale than in the submesoscale. However, submesoscale structures revealed a higher accumulation of particles by unit of area. Both migrational vertical mechanisms produced larger patchiness indices compared to the no migration experiment. DVM2 was the one that showed by far the largest aggregation of almost all the aggregations zones. Larval concentrations were highest in the submesoscale structures; these zones were characterized by low eddy kinetic energy, negative stretching deformation, and slight convergence.-Stretching deformation flow appeared to be triggered by the eddies-eddies interactions and the Robinson Island barrier effect, which likely promotes the aggregation of the spiny lobster larvae in the Juan Fernández system. These results highlighted the importance of the coupled effect of physical (meso and submesoscales oceanographic features) and biological processes (DVM) in the generation of larval patchiness and concentration of spiny lobster larvae around the JFR, which could be key for their survival and retention in those waters.
Protecting the ecological health of rivers relies on maintaining intact flows from source areas t... more Protecting the ecological health of rivers relies on maintaining intact flows from source areas to downstream navigable waters (1). Yet the U.S. Environmental Protection Agency (EPA) intends to rescind legal protection of tributary rivers, streams, and wetlands that do not have year-round flows (temporary waterways) and whose surface waters contribute flow to permanent navigable waters (2). This decision would severely damage the condition and uses of many U.S. waters, both temporary and navigable. Temporary waterways provide many ecosystem services, including water provision and purification, that contribute substantially to securing water quantity and quality (3–5). Fifty-eight percent of all waterways that provide drinking water to the continental United States are temporary or headwater streams, which support more than one-third of the United States’s population (6). Furthermore, temporary waterways harbor important biodiversity (5) and imperiled species (7) and underpin global carbon and nutrient cycles (8). Even when dry, they provide ecosystem services such as providing groundwater, attenuating toxicants, buffering floods, and providing habitat for unique biodiversity (5, 9). A comprehensive scientific review (10) of all the services provided by temporary waterways led to the decision in 2015 Edited by Jennifer Sills to recodify the definition of “waters of the United States” to include temporary waters hydrologically connected to navigable waters. This provided protection to many temporary waterways under the U.S. Clean Water Act and was hailed as a wise, well-informed decision (4). However, the recodification has not yet been implemented because the legal process is incomplete, and now reversal of the decision is expected (2). We urge the EPA to uphold its 2015 decision and to ratify the legal status and protection of temporary waterways. This would provide U.S. temporary waterways with a level of protection similar to that in other countries, such as Australia (5). Failure to do so sets a poor global precedent and, more importantly, risks costly (11) and potentially irreversible harm to the ecosystem services supported by temporary waterways in the United States, including the provision of secure potable water.
Fluctuations in abundance of commercially valuable crustacean stocks in sub-Arctic ecosystems hav... more Fluctuations in abundance of commercially valuable crustacean stocks in sub-Arctic ecosystems have been variously attributed to the effects of climatic forcing, fishing pressure, and predation, mostly by gadoid fishes. Landings of snow crab, Chionoecetes opilio (J. C. Fabricius, 1788), from the eastern Bering Sea declined after the early 1990s, reaching historical lows a decade later. At the same time, two phenomena became apparent in the dynamics of the primiparae (first-time female breeders): their geographic range contracted to the northwest along the middle shelf (50-100 m depth), and the contraction was punctuated by periodic recruitment to the mature female pool, with a period of approximately 7 yrs and declining amplitude. The first phenomenon has been addressed by the environmental ratchet hypothesis, which attributes the contraction to a combination of an ontogenetic female migration, circulation patterns, the spatial dynamics of benthic stages in relation to near-bottom temperature, and predation by Pacific cod, Gadus macrocephalus Tilesius, 1810. Mortality due to cod predation in the Middle Domain, apparently related to near-bottom temperature, increased after 1995, contributing to the ratchet effect and the disappearance of periodic pulses of primipara abundance. Cod predation does not, however, appear to have controlled the frequency of periodic recruitment fluctuations. On the other hand, amplitude of fluctuations of primipara abundance in the Middle Domain, purportedly the "engine" of renewal of this stock, do appear to be affected by both predation and climate, whose interaction is complex but perhaps interpretable. Top-down control of commercially valuable crustacean stocks from subarctic ecosystems, mostly with regard to predation by cod (Gadus spp.), has been the subject of much attention in recent years (Frank et al. 2005, Link et al. 2009). Those interactions are significant because of their role in the functioning of shelf ecosystems, their large spatial scale, and the economic significance of the species involved, both predators and prey (Worm and Myers 2003). Snow crab, Chionoecetes opilio (J. C. Fabricius, 1788), for example, is preyed upon by Atlantic cod, Gadus morhua Linnaeus, 1758, in eastern Canada (Chabot et al. 2008) and by Pacific cod, Gadus macrocephalus Tilesius, 1810, in the Bering Sea (Livingston 1989, Orensanz et al. 2004). Over the last two decades landings of snow crab have declined dramatically in the eastern Bering Sea (EBS; Fig. 1A), from a maximum of nearly 150,000 t in 1991 to historical lows on the order of 12,000 t during the early 2000s (NPFMC 2010). The stock, declared "overfished" in 1999, has recently been considered to be rebuilt. These fluctuations of abundance, variously attributed to climate, fishing, and predation, have MOTE SYMPOSIUM INVITED PAPER
Age structure, annual growth, and variance of size-at-age of the shrimp Heterocarpus reedi Ruben ... more Age structure, annual growth, and variance of size-at-age of the shrimp Heterocarpus reedi Ruben ~o a '~~~' , Billy ~r n s t~ '~nstituto de Fomento Pesquero. Sede Zonal V-IX Regiones. Casilla 347,
Alaska Sea Grant, University of Alaska Fairbanks eBooks, 2005
Male-only crab fi sheries often are assumed to be relatively well protected from recruitment over... more Male-only crab fi sheries often are assumed to be relatively well protected from recruitment overfi shing by virtue of male polygyny and female sperm retention. These fi sheries also off er the opportunity to directly assess the per capita female reproductive contribution. If the latter does not dwindle when a stock declines, then the decline cannot be attributed to overfi shing. We explored expedient ways to assess per capita female reproductive contribution of snow crab (Chionoecetes opilio) and Tanner crab (C. bairdi) of the Eastern Bering Sea (EBS) by measuring clutch volume and estimating an objective “clutch fullness index” (CFI) based on modeling the “maximum boundary line” (MBL) of scatterplots of clutch volume vs. body size. We investigated three estimation methods, selected quantile regression for further analysis, and examined the distribution of the CFI in extensive samples collected during trawl surveys conducted in 1992 and 1993. An objective protocol for the visual assessment of clutch size (based on an estimated MBL) was introduced in 1994, with a dramatic eff ect on estimated CFI. CFI distributions proved very useful for
Nursery ground, age structure and abundance of juvenile squat lobster Pleuroncodes monodon on the... more Nursery ground, age structure and abundance of juvenile squat lobster Pleuroncodes monodon on the continental shelf off central Chile Ruben ~o a \ Victor A. ~a l l a r d o~~~, Billy ~r n s t~
Knowledge about the spatial patterns and movements of crustaceans has gained importance since the... more Knowledge about the spatial patterns and movements of crustaceans has gained importance since the creation of marine protected areas and the development of spatial management for benthic ecosystems. The Juan Ferná ndez spiny lobster (Jasus frontalis) is an endemic marine species and most valuable resource that exhibits migratory dynamics in a highly spatially regulated fishery. To study movement patterns around Alexander Selkirk Island, a mark-recapture program was implemented in 2008, when approximately 7000 non-commercial (undersized) lobsters were tagged and followed for nearly 14 months. Using quantitative georeferenced data, this study revealed spatial structuring of Juan Ferná ndez spiny lobster and tested hypotheses about alongshore and inshore-offshore movements. Eight clusters were identified around Alexander Selkirk Island, with moderate timevarying connectivity between them. Seasonal inshore-offshore movements were detected all around the island, but more conspicuously to the north. Average travelling distance was 1.2 km (1.7 sd). Our results confirmed that towards the end of austral spring males and females embark in a seasonal offshore migration to deeper waters, returning to shallower waters only during winter. These findings quantitatively consolidate the conceptual migratory model that local fishermen had already inferred for this resource from about a century of sustainable fishing.
Landings of the snow crab Chionoecetes opilio (J. C. Fabricius, 1788), which supports a lucrative... more Landings of the snow crab Chionoecetes opilio (J. C. Fabricius, 1788), which supports a lucrative fishery in the eastern Bering Sea (EBS), dropped to historical lows by 2000, and the geographic range of reproductive females contracted to the northwest. Resilience of the mature female range through larval advection may be hampered because hatching now occurs downstream. These changes have been punctuated by four pulses of recruitment, with a remarkably regular period of 6-7 yrs. Major pulses of the fishery, during the 1990s, were sustained by recruitment pulses that originated in regions of the northwest section of the EBS shelf beyond the reach of the fishery. Here we present, for the first time, a conceptual model of snow-crab spatial dynamics that integrates empirical information with new results from modeling of circulation and larval transport. The geographic region of interest, defined by means of biophysical modeling and tracking ontogenetic migrations, consists of the middle and outer domains of the EBS shelf, bounded by the 50-and 200m isobaths. Connectivity analysis highlights the significance of subsystems in the southeast and northwest sections of the EBS's middle domain. Predicted settlement regions match historical regions of abundance of immature crabs and are consistent with observed fields of suitable near-bottom temperature. Our study, together with others, highlights the significance of climate change for the fate of important highlatitude fisheries. Scenarios of climate change have prompted concerns about the future of high-latitude fisheries (
<p>(A) Marked lobsters by sex for all tagging periods and (B) Size structure (sex combined)... more <p>(A) Marked lobsters by sex for all tagging periods and (B) Size structure (sex combined) from biological sampling during 2008/09 fishing season [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200146#pone.0200146.ref035" target="_blank">35</a>]. Vertical dashed lines correspond to size of 50% of maturity and minimum legal size.</p
Genetics data have provided unprecedented insights into evolutionary aspects of colonization by n... more Genetics data have provided unprecedented insights into evolutionary aspects of colonization by non-native populations. Yet, our understanding of how artificial (human-mediated) and natural dispersal pathways of non-native individuals influence genetic metrics, evolution of genetic structure, and admixture remains elusive. We capitalize on the widespread colonization of Chinook salmon Oncorhynchus tshawytscha in South America, mediated by both dispersal pathways, to address these issues using data from a panel of polymorphic SNPs. First, genetic diversity and the number of effective breeders (Nb) were higher among artificial than natural populations. Contemporary gene flow was common between adjacent artificial and natural as well as adjacent natural populations but uncommon between geographically distant populations. Second, genetic structure revealed four distinct clusters throughout the Chinook salmon distributional range with varying levels of genetic connectivity. Isolation-by-distance resulted from weak differentiation between adjacent artificial and natural as well as natural populations and with strong differentiation between distant populations experiencing strong genetic drift. Third, genetic mixture analyses revealed the presence of at least six donor geographic regions from North America, some of which likely hybridized as a result of multiple introductions. Relative propagule pressure or the proportion of Chinook salmon propagules introduced from various geographic regions according to government records significantly influenced genetic mixtures for two of three artificial populations. Our findings support a model of colonization in which high-diversity artificial populations established first; some of these populations exhibited significant admixture resulting from propagule pressure. Low-diversity natural populations were likely subsequently founded from a reduced number of individuals
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