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Christophe Guinet - One of the best experts on this subject based on the ideXlab platform.
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depredation of Patagonian Toothfish dissostichus eleginoides by two sympatrically occurring killer whale orcinus orca ecotypes insights on the behavior of the rarely observed type d killer whales
Marine Mammal Science, 2016Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Christophe GuinetAbstract:Sympatric forms of ecologically distinctive killer whales (Orcinus orca) have been documented worldwide. This study focused on a new case of such sympatric occurrence of the “Crozet” type and the recently described “type D” killer whales off the Crozet Islands. The two ecotypes are morphologically and genetically distinct, but they both depredate the same local longline fishery. We used observational, photo-identification, and fishing data, collected between 2003 and 2015, to examine differences in their patterns of depredation. Of the 828 sets where ecotype could be confirmed, type D killer whales interacted with 82 (11%) of the sets, including 9 (1%) sets that were simultaneously depredated by both ecotypes. Associations between the two types were never observed. Type D killer whales typically occurred in larger groups and both ecotypes preferentially depredated Patagonian Toothfish (Dissostichus eleginoides). GLMM modeling revealed that the probability of type D depredation significantly increased throughout the study period, especially in deep waters, and photo-identification data suggested that a subset of all individuals were habituating to depredation. This study documents the partitioning of resources between two distinct ecotypes of killer whales and provides preliminary insight into the feeding ecology of the rare type D killer whale.
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Long-term studies of Crozet Island killer whales are fundamental to understanding the economic and demographic consequences of their depredation behaviour on the Patagonian Toothfish fishery
ICES Journal of Marine Science, 2015Co-Authors: Christophe Guinet, Paul Tixier, Nicolas Gasco, Guy DuhamelAbstract:This paper provides a synthesis of results obtained as part of a long-term collaborative study involving biologists, fishers, and resource managers— centring on the occurrence of killer whales in the Crozet Archipelago before and after the implementation of a demersal longline fishery for Patagonian Toothfish. Depredation behaviour was reported as soon as the fishery was initiated, with dramatic effects on both the demographic trajectories of the killer whales and on the amount of fish lost by the fishers. Killer whales interacting with the fishery exhibited very high mortality rates when illegal fishing took place, while killer whales not interactingwere unaffected.However, after illegal fishing ended, killer whales interacting with the fishery exhibited both higher fecundity and survival rates compared with killer whales not interacting. Since whales typically removed fish entirely from the hooks, an adapted methodology that did not rely on determining the number of damaged fish was developed to estimate depredation rates. In the Crozet EEZ over a 10-year period, 33.9% of the total amount of Patagonian Toothfish caught, representing a total of 28 million E, was estimated to be lost due to the combined effects of killer whale and sperm whale depredation. In an effort to reduce depredation losses, modifications to fishing methods, such as changing the fishing season, changing fishing areas when exposed to depredation and changing longline length and hauling speed were successfully tested. Acoustic deterrent deviceswere ineffective in deterring killer whales from depredating longlines. Alternative fishing gears, such as fish pots,were also tested.However, while providing encouraging results regarding the suppression of depredation and seabird bycatch, fish potswere not efficient enough to sustain an economically viable fishery. In conclusion, we discuss how the findings of this comprehensive study can be used elsewhere in fisheries confronted with depredation.
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observations of a distinctive morphotype of killer whale orcinus orca type d from subantarctic waters
Polar Biology, 2011Co-Authors: Robert L. Pitman, John W Durban, Michael Greenfelder, Morton Jorgensen, Paula A Olson, Jordi Plana, Paul Tixier, Christophe Guinet, Jared R. TowersAbstract:Studies have shown that killer whale (Orcinus orca) communities in high latitudes regularly comprise assemblages of sympatric ‘ecotypes’—forms that differ in morphology, behavior, and prey preferences. Although they can appear superficially similar, recent genetic evidence suggests that breeding is assortative among ecotypes within individual communities, and species-level divergences are inferred in some cases. Here, we provide information on a recently recognized ‘type D’ killer whale based on photographs of a 1955 mass stranding in New Zealand and our own six at-sea sightings since 2004. It is the most distinctive-looking form of killer whale that we know of, immediately recognizable by its extremely small white eye patch. Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. School sizes are relatively large (mean 17.6; range 9–35; n = 7), and although nothing is known about the type D diet, it is suspected to include fish because groups have been photographed around longline vessels where they reportedly depredate Patagonian Toothfish (Dissostichus eleginoides).
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interactions of Patagonian Toothfish fisheries with killer and sperm whales in the crozet islands exclusive economic zone an assessment of depredation levels and insights on possible mitigation strategies
Ccamlr Science, 2010Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Morgane Viviant, Matthieu Authier, Christophe GuinetAbstract:Within the Crozet Islands Exclusive Economic Zone (EEZ), the Patagonian Toothfish (Dissostichus eleginoides) longline fishery is exposed to high levels of depredation by killer (Orcinus orca) and sperm whales (Physeter macrocephalus). From 2003 to 2008, sperm whales alone, killer whales alone, and the two species co-occurring were observed on 32.6%, 18.6% and 23.4% respectively of the 4 289 hauled lines. It was estimated that a total of 571 tonnes (€4.8 million) of Patagonian Toothfish were lost due to depredation by killer whales and both killer and sperm whales. Killer whales were found to be responsible for the largest part of this loss (>75%), while sperm whales had a lower impact (>25%). Photo-identification data revealed 35 killer whales belonging to four different pods were involved in 81.3% of the interactions. Significant variations of interaction rates with killer whales were detected between vessels suggesting the influence of operational factors on depredation. When killer whales were absent at the beginning of the line hauling process, short lines ( 40 n miles to prevent killer whales from finding them within a few hours. Although more data are still needed to better understand the way killer whales search and detect vessels, this study gives preliminary insights into possible mitigation solutions to the widespread depredation issue.
Mark Belchier - One of the best experts on this subject based on the ideXlab platform.
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Genetic structure of Patagonian Toothfish populations from otolith DNA
Antarctic Science, 2016Co-Authors: Lola Toomey, Mark Belchier, Dirk Welsford, Sharon Appleyard, Andrea Polanowski, Cassandra Faux, Bruce Deagle, James Marthick, Simon JarmanAbstract:The Patagonian Toothfish, Dissostichus eleginoides, is a valuable fishery species and has a discontinuous distribution across the Southern Ocean. Identification of the genetic stock structure of Toothfish would allow evaluation of the suitability of the spatial scale at which fisheries management operates. Genetic subdivision seems likely given the species distribution. Population genetics studies of this species have been performed; however, they have been limited by sample size, spatial coverage and/or the type of markers investigated. As a potential solution, we developed methods for extracting Toothfish DNA from otoliths that are available in large numbers from collections held at several research institutes. Genetic differentiation between the three oceanic sectors was investigated. Four mitochondrial and four nuclear markers with multiple single nucleotide polymorphisms were sequenced by high throughput sequencing for samples from six locations. Genetic differentiation was found between three sectors with nuclear markers. However, only the Pacific sector was differentiated from other sectors with mitochondrial markers. This study demonstrates the usefulness of otolith DNA as a means of increasing sample sizes for population genetics research of fish. Additionally, the combination of nuclear and mitochondrial markers may allow insight into how the observed differences in movements between male and female Toothfish impact population structure.
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the impact of predation by marine mammals on Patagonian Toothfish longline fisheries
PLOS ONE, 2015Co-Authors: Marta Soffker, Martin A Collins, Mark Belchier, Phil N Trathan, James H Clark, Robert ScottAbstract:Predatory interaction of marine mammals with longline fisheries is observed globally, leading to partial or complete loss of the catch and in some parts of the world to considerable financial loss. Depredation can also create additional unrecorded fishing mortality of a stock and has the potential to introduce bias to stock assessments. Here we aim to characterise depredation in the Patagonian Toothfish (Dissostichus eleginoides) fishery around South Georgia focusing on the spatio-temporal component of these interactions. Antarctic fur seals (Arctocephalus gazella), sperm whales (Physeter macrocephalus), and orcas (Orcinus orca) frequently feed on fish hooked on longlines around South Georgia. A third of longlines encounter sperm whales, but loss of catch due to sperm whales is insignificant when compared to that due to orcas, which interact with only 5% of longlines but can take more than half of the catch in some cases. Orca depredation around South Georgia is spatially limited and focused in areas of putative migration routes, and the impact is compounded as a result of the fishery also concentrating in those areas at those times. Understanding the seasonal behaviour of orcas and the spatial and temporal distribution of “depredation hot spots” can reduce marine mammal interactions, will improve assessment and management of the stock and contribute to increased operational efficiency of the fishery. Such information is valuable in the effort to resolve the human-mammal conflict for resources.
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the south georgia and the south sandwich islands mpa protecting a biodiverse oceanic island chain situated in the flow of the antarctic circumpolar current
Advances in Marine Biology, 2014Co-Authors: Philip N Trathan, Martin A Collins, Judith Brown, Mark Belchier, Susie M Grant, David K A Barnes, Iain J StanilandAbstract:South Georgia and the South Sandwich Islands (SGSSI) are surrounded by oceans that are species-rich, have high levels of biodiversity, important endemism and which also support large aggregations of charismatic upper trophic level species. Spatial management around these islands is complex, particularly in the context of commercial fisheries that exploit some of these living resources. Furthermore, management is especially complicated as local productivity relies fundamentally upon biological production transported from outside the area. The MPA uses practical management boundaries, allowing access for the current legal fisheries for Patagonian Toothfish, mackerel icefish and Antarctic krill. Management measures developed as part of the planning process designated the whole SGSSI Maritime Zone as an IUCN Category VI reserve, within which a number of IUCN Category I reserves were identified. Multiple-use zones and temporal closures were also designated. A key multiple-use principle was to identify whether the ecological impacts of a particular fishery threatened either the pelagic or benthic domain.
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lead radium dating provides a framework for coordinating age estimation of Patagonian Toothfish dissostichus eleginoides between fishing areas
Marine and Freshwater Research, 2011Co-Authors: Allen H Andrews, Mark Belchier, Julian R Ashford, G Duhamel, Cassandra M Brooks, K Krusicgolub, Craig C Lundstrom, Gregor M CaillietAbstract:Patagonian Toothfish (Dissostichus eleginoides) or ‘Chilean sea bass’ support a valuable and controversial fishery, yet their life history is not well understood and longevity estimates range from ~20 to >50 years. In this study, lead–radium dating provided valid ages for juvenile to older adult groups, which were consistent with the counting of otolith growth zones in transverse otolith sections, and longevity estimates exceeding 30 years. Lead–radium dating revealed minor biases between the radiometric age and interpretation of growth zone counting for regional fishing areas monitored by two facilities, Center for Quantitative Fisheries Ecology (CQFE) and the Central Ageing Facility (CAF), using different age estimation techniques. For CQFE, under-ageing of ~3.3 years was observed for individuals with estimated ages under 20 years. For the CAF, ages were overestimated for young fish and underestimated for the oldest fish. Lead–radium dating detected underlying problems in coordinating age estimation between geographically separated fish stocks, and provided a framework to objectively assess otolith interpretation and growth modelling between laboratories based on age-validated data.
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the Patagonian Toothfish biology ecology and fishery
Advances in Marine Biology, 2010Co-Authors: Martin A Collins, Paul Brickle, Judith Brown, Mark BelchierAbstract:Patagonian Toothfish (Dissostichus eleginoides) is a large notothenioid fish that supports valuable fisheries throughout the Southern Ocean. D. eleginoides are found on the southern shelves and slopes of South America and around the sub-Antarctic islands of the Southern Ocean. Patagonian Toothfish are a long-lived species (>50 years), which initially grow rapidly on the shallow shelf areas, before undertaking an ontogenetic migration into deeper water. Although they are active predators and scavengers, there is no evidence of large-scale geographic migrations, and studies using genetics, biochemistry, parasite fauna and tagging indicate a high degree of isolation between populations in the Indian Ocean, South Georgia and the Patagonian Shelf. Patagonian Toothfish spawn in deep water (ca. 1000 m) during the austral winter, producing pelagic eggs and larvae. Larvae switch to a demersal habitat at around 100 mm (1-year-old) and inhabit relatively shallow water (<300 m) until 6-7 years of age, when they begin a gradual migration into deeper water. As juveniles in shallow water, Toothfish are primarily piscivorous, consuming the most abundant suitably sized local prey. With increasing size and habitat depth, the diet diversifies and includes more scavenging. Toothfish have weakly mineralised skeletons and a high fat content in muscle, which helps neutral buoyancy, but limits swimming capacity. Toothfish generally swim with labriform motion, but are capable of more rapid sub-carangiform swimming when startled. Toothfish were first caught as a by-catch (as juveniles) in shallow trawl fisheries, but following the development of deep water longlining, fisheries rapidly developed throughout the Southern Ocean. The initial rapid expansion of the fishery, which led to a peak of over 40,000 tonnes in reported landings in 1995, was accompanied by problems of bird by-catch and overexploitation as a consequence of illegal, unreported and unregulated fishing (IUU). These problems have now largely been addressed, but continued vigilance is required to ensure that the species is sustainably exploited and the ecosystem effects of the fisheries are minimised.
Guy Duhamel - One of the best experts on this subject based on the ideXlab platform.
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depredation of Patagonian Toothfish dissostichus eleginoides by two sympatrically occurring killer whale orcinus orca ecotypes insights on the behavior of the rarely observed type d killer whales
Marine Mammal Science, 2016Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Christophe GuinetAbstract:Sympatric forms of ecologically distinctive killer whales (Orcinus orca) have been documented worldwide. This study focused on a new case of such sympatric occurrence of the “Crozet” type and the recently described “type D” killer whales off the Crozet Islands. The two ecotypes are morphologically and genetically distinct, but they both depredate the same local longline fishery. We used observational, photo-identification, and fishing data, collected between 2003 and 2015, to examine differences in their patterns of depredation. Of the 828 sets where ecotype could be confirmed, type D killer whales interacted with 82 (11%) of the sets, including 9 (1%) sets that were simultaneously depredated by both ecotypes. Associations between the two types were never observed. Type D killer whales typically occurred in larger groups and both ecotypes preferentially depredated Patagonian Toothfish (Dissostichus eleginoides). GLMM modeling revealed that the probability of type D depredation significantly increased throughout the study period, especially in deep waters, and photo-identification data suggested that a subset of all individuals were habituating to depredation. This study documents the partitioning of resources between two distinct ecotypes of killer whales and provides preliminary insight into the feeding ecology of the rare type D killer whale.
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Long-term studies of Crozet Island killer whales are fundamental to understanding the economic and demographic consequences of their depredation behaviour on the Patagonian Toothfish fishery
ICES Journal of Marine Science, 2015Co-Authors: Christophe Guinet, Paul Tixier, Nicolas Gasco, Guy DuhamelAbstract:This paper provides a synthesis of results obtained as part of a long-term collaborative study involving biologists, fishers, and resource managers— centring on the occurrence of killer whales in the Crozet Archipelago before and after the implementation of a demersal longline fishery for Patagonian Toothfish. Depredation behaviour was reported as soon as the fishery was initiated, with dramatic effects on both the demographic trajectories of the killer whales and on the amount of fish lost by the fishers. Killer whales interacting with the fishery exhibited very high mortality rates when illegal fishing took place, while killer whales not interactingwere unaffected.However, after illegal fishing ended, killer whales interacting with the fishery exhibited both higher fecundity and survival rates compared with killer whales not interacting. Since whales typically removed fish entirely from the hooks, an adapted methodology that did not rely on determining the number of damaged fish was developed to estimate depredation rates. In the Crozet EEZ over a 10-year period, 33.9% of the total amount of Patagonian Toothfish caught, representing a total of 28 million E, was estimated to be lost due to the combined effects of killer whale and sperm whale depredation. In an effort to reduce depredation losses, modifications to fishing methods, such as changing the fishing season, changing fishing areas when exposed to depredation and changing longline length and hauling speed were successfully tested. Acoustic deterrent deviceswere ineffective in deterring killer whales from depredating longlines. Alternative fishing gears, such as fish pots,were also tested.However, while providing encouraging results regarding the suppression of depredation and seabird bycatch, fish potswere not efficient enough to sustain an economically viable fishery. In conclusion, we discuss how the findings of this comprehensive study can be used elsewhere in fisheries confronted with depredation.
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interactions of Patagonian Toothfish fisheries with killer and sperm whales in the crozet islands exclusive economic zone an assessment of depredation levels and insights on possible mitigation strategies
Ccamlr Science, 2010Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Morgane Viviant, Matthieu Authier, Christophe GuinetAbstract:Within the Crozet Islands Exclusive Economic Zone (EEZ), the Patagonian Toothfish (Dissostichus eleginoides) longline fishery is exposed to high levels of depredation by killer (Orcinus orca) and sperm whales (Physeter macrocephalus). From 2003 to 2008, sperm whales alone, killer whales alone, and the two species co-occurring were observed on 32.6%, 18.6% and 23.4% respectively of the 4 289 hauled lines. It was estimated that a total of 571 tonnes (€4.8 million) of Patagonian Toothfish were lost due to depredation by killer whales and both killer and sperm whales. Killer whales were found to be responsible for the largest part of this loss (>75%), while sperm whales had a lower impact (>25%). Photo-identification data revealed 35 killer whales belonging to four different pods were involved in 81.3% of the interactions. Significant variations of interaction rates with killer whales were detected between vessels suggesting the influence of operational factors on depredation. When killer whales were absent at the beginning of the line hauling process, short lines ( 40 n miles to prevent killer whales from finding them within a few hours. Although more data are still needed to better understand the way killer whales search and detect vessels, this study gives preliminary insights into possible mitigation solutions to the widespread depredation issue.
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Interactions between Cetacean and Fisheries in the Southern Ocean
Polar Biology, 2006Co-Authors: Karl-hermann Kock, Martin G Purves, Guy DuhamelAbstract:Soon after longlining on Patagonian Toothfish ( Dissostichus eleginoides ) started in the Southern Ocean in the second half of the 1980s, interactions of cetaceans with these fisheries became apparent. The two species primarily involved were orcas (killer whales) ( Orcinus orca ) and male sperm whales ( Physeter macrocephalus ). Both species took substantial number of fish from the line primarily during day light hours. Catch rates of longliners declined to less than 50% when orcas occurred close to longline vessels while the loss to sperm whales was much less obvious. They were seen diving close to the line down to 400 m where they apparently took fish. Their impact on catch rates was much less notable. Sperm whales became frequently entangled in the line and part of the line was lost in a number of cases. Other cetaceans were rarely seen in the vicinity of longline vessels. They became entangled in the line only occasionally and one whale (presumably a minke whale) died.
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can otolith elemental signatures record the capture site of Patagonian Toothfish dissostichus eleginoides a fully marine fish in the southern ocean
Canadian Journal of Fisheries and Aquatic Sciences, 2005Co-Authors: Julian R Ashford, Guy Duhamel, Cynthia M Jones, I Everson, Eileen E Hofmann, Carlos A Moreno, Richard WilliamsAbstract:Otolith chemistry has been successfully used to reconstruct the environmental history experienced by estuarine-dependent teleost fish, including movement between estuaries and coastal areas. However, application has been more limited in species exposed exclusively to oceanic waters, where gradients in physical and chemical properties are less extreme. To test whether otolith elemental signatures record spatial information in an oceanic species, we sampled otoliths from Patagonian Toothfish (Dissostichus eleginoides) and used an inductively coupled plasma mass spectrometer (ICP-MS) coupled to a laser ablation system to target the outer otolith edges corresponding to the period immediately before capture. Using multivariate analysis of variance and multivariate discriminant analysis, we found that edge signatures discriminated Toothfish by geographic region with near complete success: only 5% of fish caught off South America and in the Antarctic were misclassified to sampling areas in the other region. Moreover, edge signatures showed strong differences between sampling areas within each region: fish captured off South America classified to sampling areas therein with 79%–84% success, and Antarctic fish classified to sampling areas therein with 50%–67% success. These results compare favourably with rates of classification for estuarine-dependent fish, demonstrating that otolith elemental signatures can discriminate the geographic provenance of oceanic and estuarine-dependent fish.
Paul Tixier - One of the best experts on this subject based on the ideXlab platform.
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depredation of Patagonian Toothfish dissostichus eleginoides by two sympatrically occurring killer whale orcinus orca ecotypes insights on the behavior of the rarely observed type d killer whales
Marine Mammal Science, 2016Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Christophe GuinetAbstract:Sympatric forms of ecologically distinctive killer whales (Orcinus orca) have been documented worldwide. This study focused on a new case of such sympatric occurrence of the “Crozet” type and the recently described “type D” killer whales off the Crozet Islands. The two ecotypes are morphologically and genetically distinct, but they both depredate the same local longline fishery. We used observational, photo-identification, and fishing data, collected between 2003 and 2015, to examine differences in their patterns of depredation. Of the 828 sets where ecotype could be confirmed, type D killer whales interacted with 82 (11%) of the sets, including 9 (1%) sets that were simultaneously depredated by both ecotypes. Associations between the two types were never observed. Type D killer whales typically occurred in larger groups and both ecotypes preferentially depredated Patagonian Toothfish (Dissostichus eleginoides). GLMM modeling revealed that the probability of type D depredation significantly increased throughout the study period, especially in deep waters, and photo-identification data suggested that a subset of all individuals were habituating to depredation. This study documents the partitioning of resources between two distinct ecotypes of killer whales and provides preliminary insight into the feeding ecology of the rare type D killer whale.
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Long-term studies of Crozet Island killer whales are fundamental to understanding the economic and demographic consequences of their depredation behaviour on the Patagonian Toothfish fishery
ICES Journal of Marine Science, 2015Co-Authors: Christophe Guinet, Paul Tixier, Nicolas Gasco, Guy DuhamelAbstract:This paper provides a synthesis of results obtained as part of a long-term collaborative study involving biologists, fishers, and resource managers— centring on the occurrence of killer whales in the Crozet Archipelago before and after the implementation of a demersal longline fishery for Patagonian Toothfish. Depredation behaviour was reported as soon as the fishery was initiated, with dramatic effects on both the demographic trajectories of the killer whales and on the amount of fish lost by the fishers. Killer whales interacting with the fishery exhibited very high mortality rates when illegal fishing took place, while killer whales not interactingwere unaffected.However, after illegal fishing ended, killer whales interacting with the fishery exhibited both higher fecundity and survival rates compared with killer whales not interacting. Since whales typically removed fish entirely from the hooks, an adapted methodology that did not rely on determining the number of damaged fish was developed to estimate depredation rates. In the Crozet EEZ over a 10-year period, 33.9% of the total amount of Patagonian Toothfish caught, representing a total of 28 million E, was estimated to be lost due to the combined effects of killer whale and sperm whale depredation. In an effort to reduce depredation losses, modifications to fishing methods, such as changing the fishing season, changing fishing areas when exposed to depredation and changing longline length and hauling speed were successfully tested. Acoustic deterrent deviceswere ineffective in deterring killer whales from depredating longlines. Alternative fishing gears, such as fish pots,were also tested.However, while providing encouraging results regarding the suppression of depredation and seabird bycatch, fish potswere not efficient enough to sustain an economically viable fishery. In conclusion, we discuss how the findings of this comprehensive study can be used elsewhere in fisheries confronted with depredation.
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observations of a distinctive morphotype of killer whale orcinus orca type d from subantarctic waters
Polar Biology, 2011Co-Authors: Robert L. Pitman, John W Durban, Michael Greenfelder, Morton Jorgensen, Paula A Olson, Jordi Plana, Paul Tixier, Christophe Guinet, Jared R. TowersAbstract:Studies have shown that killer whale (Orcinus orca) communities in high latitudes regularly comprise assemblages of sympatric ‘ecotypes’—forms that differ in morphology, behavior, and prey preferences. Although they can appear superficially similar, recent genetic evidence suggests that breeding is assortative among ecotypes within individual communities, and species-level divergences are inferred in some cases. Here, we provide information on a recently recognized ‘type D’ killer whale based on photographs of a 1955 mass stranding in New Zealand and our own six at-sea sightings since 2004. It is the most distinctive-looking form of killer whale that we know of, immediately recognizable by its extremely small white eye patch. Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. School sizes are relatively large (mean 17.6; range 9–35; n = 7), and although nothing is known about the type D diet, it is suspected to include fish because groups have been photographed around longline vessels where they reportedly depredate Patagonian Toothfish (Dissostichus eleginoides).
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interactions of Patagonian Toothfish fisheries with killer and sperm whales in the crozet islands exclusive economic zone an assessment of depredation levels and insights on possible mitigation strategies
Ccamlr Science, 2010Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Morgane Viviant, Matthieu Authier, Christophe GuinetAbstract:Within the Crozet Islands Exclusive Economic Zone (EEZ), the Patagonian Toothfish (Dissostichus eleginoides) longline fishery is exposed to high levels of depredation by killer (Orcinus orca) and sperm whales (Physeter macrocephalus). From 2003 to 2008, sperm whales alone, killer whales alone, and the two species co-occurring were observed on 32.6%, 18.6% and 23.4% respectively of the 4 289 hauled lines. It was estimated that a total of 571 tonnes (€4.8 million) of Patagonian Toothfish were lost due to depredation by killer whales and both killer and sperm whales. Killer whales were found to be responsible for the largest part of this loss (>75%), while sperm whales had a lower impact (>25%). Photo-identification data revealed 35 killer whales belonging to four different pods were involved in 81.3% of the interactions. Significant variations of interaction rates with killer whales were detected between vessels suggesting the influence of operational factors on depredation. When killer whales were absent at the beginning of the line hauling process, short lines ( 40 n miles to prevent killer whales from finding them within a few hours. Although more data are still needed to better understand the way killer whales search and detect vessels, this study gives preliminary insights into possible mitigation solutions to the widespread depredation issue.
Nicolas Gasco - One of the best experts on this subject based on the ideXlab platform.
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depredation of Patagonian Toothfish dissostichus eleginoides by two sympatrically occurring killer whale orcinus orca ecotypes insights on the behavior of the rarely observed type d killer whales
Marine Mammal Science, 2016Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Christophe GuinetAbstract:Sympatric forms of ecologically distinctive killer whales (Orcinus orca) have been documented worldwide. This study focused on a new case of such sympatric occurrence of the “Crozet” type and the recently described “type D” killer whales off the Crozet Islands. The two ecotypes are morphologically and genetically distinct, but they both depredate the same local longline fishery. We used observational, photo-identification, and fishing data, collected between 2003 and 2015, to examine differences in their patterns of depredation. Of the 828 sets where ecotype could be confirmed, type D killer whales interacted with 82 (11%) of the sets, including 9 (1%) sets that were simultaneously depredated by both ecotypes. Associations between the two types were never observed. Type D killer whales typically occurred in larger groups and both ecotypes preferentially depredated Patagonian Toothfish (Dissostichus eleginoides). GLMM modeling revealed that the probability of type D depredation significantly increased throughout the study period, especially in deep waters, and photo-identification data suggested that a subset of all individuals were habituating to depredation. This study documents the partitioning of resources between two distinct ecotypes of killer whales and provides preliminary insight into the feeding ecology of the rare type D killer whale.
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modelling spatial distribution of Patagonian Toothfish through life stages and sex and its implications for the fishery on the kerguelen plateau
Progress in Oceanography, 2016Co-Authors: Clara Peron, D Welsford, P E Ziegler, T D Lamb, Nicolas Gasco, Charlotte Chazeau, Romain Sinegre, G DuhamelAbstract:Abstract Size and sex specific habitat preferences are common in animal populations and can have important implications for sound spatial management of harvested species. Patagonian Toothfish (Dissostichus eleginoides) is a commercially exploited fish species characterised by its longevity (>50 yo) and its extremely broad distribution in depths ranging from 10 m to 2500 m on most of the Plateaux, banks and seamounts of the Southern Ocean. As many bentho-pelagic fish species, Patagonian Toothfish exhibits sexual dimorphism and ontogenetic habitat shift towards deeper waters as they grow. In this study, we modelled the spatial structure of Patagonian Toothfish population (median total length and sex composition) in a data-rich area, the Kerguelen Plateau (Southern Indian Ocean), to better understand the ecological drivers of their distributional patterns and inform current and future fishery management strategies. We applied spatially-explicit statistical models to quantify and predict the effects of the complex topography of the Kerguelen Plateau in structuring the spatial distribution of Patagonian Toothfish total length and sex ratio, while controlling for gear selectivity and season. Model predictions showed that juvenile Toothfish live in shallow regions (shelf and banks) and move downward progressively up to 600 m while they grow. Between 600 m and 1200 m, the downward movement stops and fish settle at their preferred depths. While in this depth range, fish are ∼75 cm long and most vulnerable to fisheries. As they approach maturity large fish move downward to deep-sea habitats (from 1200 m to >2300 m) and head towards the spawning grounds on the western side of the plateau and around Skiff Bank. Importantly, the sex ratio was not evenly distributed across the Plateau; prediction maps revealed a higher proportion of females in the South whereas a strong male-bias sex ratio (70%) occurred in the North-West. Large-scale prediction maps derived from our models assisted in developing hypotheses regarding ecological drivers of Patagonian Toothfish habitat-use and movement across different life stages and sex. Such hypotheses are crucial to inform management strategies of this multijurisdictional fishery (France and Australia) at the spatial and temporal scales over which natural processes and fishery extend.
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Long-term studies of Crozet Island killer whales are fundamental to understanding the economic and demographic consequences of their depredation behaviour on the Patagonian Toothfish fishery
ICES Journal of Marine Science, 2015Co-Authors: Christophe Guinet, Paul Tixier, Nicolas Gasco, Guy DuhamelAbstract:This paper provides a synthesis of results obtained as part of a long-term collaborative study involving biologists, fishers, and resource managers— centring on the occurrence of killer whales in the Crozet Archipelago before and after the implementation of a demersal longline fishery for Patagonian Toothfish. Depredation behaviour was reported as soon as the fishery was initiated, with dramatic effects on both the demographic trajectories of the killer whales and on the amount of fish lost by the fishers. Killer whales interacting with the fishery exhibited very high mortality rates when illegal fishing took place, while killer whales not interactingwere unaffected.However, after illegal fishing ended, killer whales interacting with the fishery exhibited both higher fecundity and survival rates compared with killer whales not interacting. Since whales typically removed fish entirely from the hooks, an adapted methodology that did not rely on determining the number of damaged fish was developed to estimate depredation rates. In the Crozet EEZ over a 10-year period, 33.9% of the total amount of Patagonian Toothfish caught, representing a total of 28 million E, was estimated to be lost due to the combined effects of killer whale and sperm whale depredation. In an effort to reduce depredation losses, modifications to fishing methods, such as changing the fishing season, changing fishing areas when exposed to depredation and changing longline length and hauling speed were successfully tested. Acoustic deterrent deviceswere ineffective in deterring killer whales from depredating longlines. Alternative fishing gears, such as fish pots,were also tested.However, while providing encouraging results regarding the suppression of depredation and seabird bycatch, fish potswere not efficient enough to sustain an economically viable fishery. In conclusion, we discuss how the findings of this comprehensive study can be used elsewhere in fisheries confronted with depredation.
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multivariate effects on seabird bycatch in the legal Patagonian Toothfish longline fishery around crozet and kerguelen islands
Polar Biology, 2010Co-Authors: Karine Delord, Nicolas Gasco, Christophe Barbraud, Henri WeimerskirchAbstract:The effects of temporal, spatial, environmental and operational effects on seabird incidental mortality in the legal Patagonian Toothfish longline fishery operating, between 2003 and 2006, in French exclusive economic zones of Crozet and Kerguelen Islands were analysed. During the study period, the mean bycatch rate varied from 0.05 to 0.12 birds per 1,000 hooks. Two species were concerned by incidental mortality: white-chinned petrels (88%) and grey petrels (11.5%). Males of white-chinned petrel seemed more at a risk than females. Logbooks data tended to underreport mortality when compared with dedicated fishery observers. The results indicate that temporal (season or phenology) and spatial (area) factors reflecting mortality risk for seabirds played the most significant role in the incidental mortality of the two species. Operational (integrated weight mainline, number of scaring lines and number of hooks hauled) and environmental factors (wind/vessel angle, moon brightness) were also influential, although less significantly, in increasing this mortality risk. Our two steps analyses by separately modelling the probability of presence and the abundance given presence suggest that the decrease in seabird bycatch over the period was mainly due to an important decrease in probability (occurrence) of mortality.
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interactions of Patagonian Toothfish fisheries with killer and sperm whales in the crozet islands exclusive economic zone an assessment of depredation levels and insights on possible mitigation strategies
Ccamlr Science, 2010Co-Authors: Paul Tixier, Guy Duhamel, Nicolas Gasco, Morgane Viviant, Matthieu Authier, Christophe GuinetAbstract:Within the Crozet Islands Exclusive Economic Zone (EEZ), the Patagonian Toothfish (Dissostichus eleginoides) longline fishery is exposed to high levels of depredation by killer (Orcinus orca) and sperm whales (Physeter macrocephalus). From 2003 to 2008, sperm whales alone, killer whales alone, and the two species co-occurring were observed on 32.6%, 18.6% and 23.4% respectively of the 4 289 hauled lines. It was estimated that a total of 571 tonnes (€4.8 million) of Patagonian Toothfish were lost due to depredation by killer whales and both killer and sperm whales. Killer whales were found to be responsible for the largest part of this loss (>75%), while sperm whales had a lower impact (>25%). Photo-identification data revealed 35 killer whales belonging to four different pods were involved in 81.3% of the interactions. Significant variations of interaction rates with killer whales were detected between vessels suggesting the influence of operational factors on depredation. When killer whales were absent at the beginning of the line hauling process, short lines ( 40 n miles to prevent killer whales from finding them within a few hours. Although more data are still needed to better understand the way killer whales search and detect vessels, this study gives preliminary insights into possible mitigation solutions to the widespread depredation issue.