The cephalopod component of the diet of Patagonian toothfish, Dissostichus eleginoides, around So... more The cephalopod component of the diet of Patagonian toothfish, Dissostichus eleginoides, around South Georgia was analysed from stomach contents collected between March and May 2000. Cephalopods occurred in 7% of D. eleginoides stomachs. A total of 363 cephalopod beaks were found, comprising 16 cephalopod species, of which 15 had not been previously recorded in the diet. Octopodid A (probably Pareledone turqueti) was the most important cephalopod species by number of lower beaks (36 beaks; 20.2% of the lower beaks) and Kondakovia longimana was the most important in terms of estimated mass (76% of the cephalopod component). When the cephalopod component of D. eleginoides was compared with other predators between March and May 2000, D. eleginoides fed more on octopods (25% of the lower beaks) than black-browed and grey-headed albatrosses (<1% of the lower beaks). The low frequency of the squid Martialia hyadesi in the diet of D. eleginoides around South Georgia was also noticed in the diet of albatrosses, and suggests that M. hyadesi was not present in these waters in 2000 (probably due to migratory movements or reproduction failure), despite being a candidate for commercial exploitation. The presence of the squid Mesonychoteuthis hamiltoni in the diet of D. eleginoides and being caught by a longline hook whilst presumably feeding on D. eleginoides, may indicate that juveniles of Mesonychoteuthis hamiltoni are prey of D. eleginoides adults, and when Mesonychoteuthis hamiltoni reach a large size as adults, they become the predator.
Please find attached the final pdf file of your contribution, which can be viewed using the Acrob... more Please find attached the final pdf file of your contribution, which can be viewed using the Acrobat Reader, version 3.0 or higher. We would kindly like to draw your attention to the fact that copyright law is also valid for electronic products. This means especially that: • You may not alter the pdf file, as changes to the published contribution are prohibited by copyright law. • You may print the file and distribute it amongst your colleagues in the scientific community for scientific and/or personal use.
The short life span of cephalopods suggests a potential for high sensitivity to the arti®cial sel... more The short life span of cephalopods suggests a potential for high sensitivity to the arti®cial selective eects of human exploitation. To explore the eects of such selection life-history optimisation was applied using data for a semelparous squid, Illex argentinus with a life span of one year. Survival and fecundity functions were combined to generate a life time reproductive potential function. The maximum reproductive potential identi®ed the optimum age for the squid to mature. In a situation of a constant mortality rate the maximum reproductive potential was achieved at an earlier age of maturation as mortality rate increased. The exact age when the optimum maturation occurs is sensitive to the rate of mortality and the form of the assumed growth curve but covers the age range when maturation is known to occur in this species. A more realistic seasonal ®shing mortality function produced a more complex ®tness curve with a temporally more restricted optimal age of maturity. The selection eects will be stronger in a seasonal ®shery suggesting potentially very rapid evolutionary rates. Developing analyses speci®cally considering frequencydependence and environmental-feedbacks will be valuable to clarify the potential of squid to show rapid evolutionary responses to selection. Strong selection for early age of maturation could aect the yield from the ®shery but more importantly, could also make the migratory strategy, on which the ®shery is based, an unviable option, resulting in collapse of the ®shery that exploits the migratory component of the species.
Marine fisheries provide around 20% of animal protein consumed by man worldwide, but ineffective ... more Marine fisheries provide around 20% of animal protein consumed by man worldwide, but ineffective management can lead to commercial extinction of exploited stocks. Fisheries that overlap nationally controlled and high seas waters cause particular problems, as few management data are available for the high seas. The Argentinean short-finned squid, Illex argentinus, exemplifies such a &amp;quot;straddling stock&amp;quot;. Here we demonstrate that light emitted by fishing vessels to attract squid can be detected via remote-sensing. Unlike conventional fisheries data, which are restricted by political boundaries, satellite imagery can provide a synoptic view of fishing activity in both regulated and unregulated areas. By using known levels of fishing effort in Falkland Islands waters to calibrate the images, we are able to estimate effort levels on the high seas, providing a more comprehensive analysis of the overall impact of fishing on the stock. This innovative tool for quantifying fishing activity across management boundaries has wide-ranging applications to squid fisheries worldwide.
In this study, we consider the in¯uence of mesoscale oceanographic processes around the Falkland ... more In this study, we consider the in¯uence of mesoscale oceanographic processes around the Falkland Islands (Islas Malvinas) in the Southwest Atlantic, during the period in which the commercial squid ®shery for Illex argentinus operates. Spatially referenced ®shery data and satellite-derived advanced very high resolution radiometry (AVHRR) sea surface temperature (SST) data were examined using geographic information system (GIS) techniques. The distribution and relative abundance of I. argentinus in the Falkland Islands ®shery was examined for the period 1989±96. Three consistent areas of high abundance were observed to the northeast (shelf-break region) and northwest (shelf region) of the islands, and close to the northern coast of East Falkland. Areas of high sea surface temperature gradients (thermal gradients) extracted from remotely sensed satellite images were used as an indicator of mesoscale oceanographic activity and compared with the location of the ®shery. I. argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used in this analysis allow the overlay and analysis of physical oceanographic and ®shery data with potential applications in ®sheries management and operational ®sheries oceanography.
ABSTRACT Dosidicus gigas (Humboldt or jumbo squid) (Orbigny, 1835) is the largest ommastrephid sq... more ABSTRACT Dosidicus gigas (Humboldt or jumbo squid) (Orbigny, 1835) is the largest ommastrephid squid, reaching up to 1.2m mantle length and 65kg in weight. This pelagic squid is endemic to the eastern Pacific Ocean and is particularly abundant in the highly productive waters of the California and Humboldt Current systems, and the Costa Rica Dome upwelling region. The intra-specific population structure of D. gigas is complex, since this species quickly responds to environmental variability driven by El Niño and LaNiña events in both current systems by rapidly changing its biological characteristics, such as somatic and reproductive investment. Oocyte development is asynchronous and the potential fecundity averages around 18–21 million oocytes; the maximum value estimated (32 million oocytes) is the largest ever recorded for any cephalopod so far. Hatching occurs between 6 to 9 days after fertilization at 18°C, but temperatures below 15°C and above 25°C do not allow complete embryonic development. D. gigas passes through a post-hatching paralarval stage called the rhynchoteuthion and during this stage the two tentacles are fused into a well-developed proboscis. During the paralarval and subsequent juvenile stages Humboldt squid have a monthly growth rate of up to 80 mm in mantle length, and grow up 60 mm per month in the later stages. This is the highest growth rate reported for any cephalopod species, and enables this species to reach the reported maximum mantle lengths in a short lifespan (12 to 24 months). Although the lack of population structure across its large range suggests a high level of gene flow and substantial horizontal migration, specific migratory pathways in the Pacific Ocean have not yet been demonstrated. Long-distance migration is an important element in the life-history of Humboldt squid and may be associated with differential growth rates and size and at full maturity. The recent poleward range expansion of D. gigas is likely associated with warmer periods following El Niño/La Niña events, an ongoing expansion of the oxygen minimum zone (OMZ) in the Eastern Pacific, and changing ecosystem interactions including food availability, competition and predation. Humboldt squid feed primarily on small mesopelagic (midwater) fishes, crustaceans, and cephalopods as well as commercially important coastal fishes and squid in the recently expanded range. Typical daily behavior involves vertical migrations from near-surface waters at nighttime to mesopelagic depths above or within the OMZ during the daytime. Whereas the OMZ restricts the depth distribution of many competing vertebrate predators to the upper surface layers due to limited hypoxia tolerance, D. gigas circumvents similar restrictions via metabolic suppression. In addition to its critical role both as prey and predator in the eastern Pacific, D. gigas is an economically important species and the target of what has recently become the world’s largest invertebrate fishery.
Exploited populations of ommastrephid squid are found under a wide range of oceanographic regimes... more Exploited populations of ommastrephid squid are found under a wide range of oceanographic regimes. However, to date most scientific attention has focussed on those found in northern hemisphere western boundary current systems, and these systems have become the paradigm for ...
... by new data, presented at the First International Symposium on Pacific Squids at the VIII Con... more ... by new data, presented at the First International Symposium on Pacific Squids at the VIII Congreso Latinamericano de Ciencias del Mar, on distribution ( Taipe et ... There is also a growing body of literature on the species from the Southwest Atlantic ( Hatfield and des Clers, 1998). ...
The fishery for IUex argentinus in the Southwest Atlantic is subject to large inter-annual variab... more The fishery for IUex argentinus in the Southwest Atlantic is subject to large inter-annual variability in recruitment strength. In this paper we attempt to build a predictive model using sea surface temperature (SST) to examine links between recruitment to the Falkland Islands fishery and environmental variability during the juvenile and adult life history stages. SST data from the National Center for Atmospheric Research (NCAR) were found to be comparable with near-surface data derived from in situ expendable bathy-thermograph (XBT) profiles in the southern Patagonian shelf. Variation in SST during the early Me stages appears to be important in determining recruitment of I. argentinus. SST in the hatching grounds of the northern Patagonian shelf during the period of hatching (particularly June and July) was negatively correlated with catches in the fishery in the following season. SST anomaly data from positions in the Pacific and Southwest Atlantic were used to examine teleconnections between these areas. Links were seen at a lag of 2 yr between the Pacific and southern Patagonian shelf, and at about 5 yr between the Pacific and northern Patagonian shelf. This is consistent with SST anomalies associated with El Nifio in the Pacific propagating around the globe via the Antarctic Circumpolar Wave (ACW). Predicting cold events via teleconnections between SST anomalies in the Pacific and Atlantic would appear to have the potential to predict the recruitment strength of I. argentinus in the Southwest Atlantic.
Interannual variability in the mesoscale oceanography of the inferred hatching area of winter-spa... more Interannual variability in the mesoscale oceanography of the inferred hatching area of winter-spawned Illex argentinus (i.e. those belonging to the Southern Patagonic Stock) was examined during the hatching months of June and July. The hatching area was de®ned as the region 32°±39°S, 49°±61°W, and indicators of the surface oceanography in this area were derived from remotely sensed advanced very high resolution radiometer (AVHRR) sea-surface temperature (SST) data. Interannual variability in the mesoscale oceanic circulation in the inferred hatching area was examined in terms of (1) the area occupied by``frontal'' waters (de®ned as areas with SST gradients of ³3°C over an area of 15 km by 15 km), and (2) the area occupied by waters of``favourable'' SST (de®ned as those with temperatures in the range 16±18°C). Oceanographic indicators were compared with an index of I. argentinus recruitment to the Falkland Islands (Malvinas) ®shery (catch per licensed vessel) for the period 1987 to 1999. The two oceanographic indicators were seen to co-vary, with a decrease in the proportion of the inferred hatching area occupied by frontal waters corresponding to an increase in the proportion of water of favourable SST. High squid abundance was found to be associated with a lower proportion of frontal waters or a higher proportion of favourable-SST waters within the inferred hatching area in the year preceding the ®shery. Interannual variability in the interaction of the Brazil and Falkland Currents in the inferred hatching area during the early life stages is shown to be important in in¯uencing the population size of I. argentinus, and mechanisms inuencing squid recruitment in this highly dynamic region are discussed.
The cephalopod component of the diet of Patagonian toothfish, Dissostichus eleginoides, around So... more The cephalopod component of the diet of Patagonian toothfish, Dissostichus eleginoides, around South Georgia was analysed from stomach contents collected between March and May 2000. Cephalopods occurred in 7% of D. eleginoides stomachs. A total of 363 cephalopod beaks were found, comprising 16 cephalopod species, of which 15 had not been previously recorded in the diet. Octopodid A (probably Pareledone turqueti) was the most important cephalopod species by number of lower beaks (36 beaks; 20.2% of the lower beaks) and Kondakovia longimana was the most important in terms of estimated mass (76% of the cephalopod component). When the cephalopod component of D. eleginoides was compared with other predators between March and May 2000, D. eleginoides fed more on octopods (25% of the lower beaks) than black-browed and grey-headed albatrosses (<1% of the lower beaks). The low frequency of the squid Martialia hyadesi in the diet of D. eleginoides around South Georgia was also noticed in the diet of albatrosses, and suggests that M. hyadesi was not present in these waters in 2000 (probably due to migratory movements or reproduction failure), despite being a candidate for commercial exploitation. The presence of the squid Mesonychoteuthis hamiltoni in the diet of D. eleginoides and being caught by a longline hook whilst presumably feeding on D. eleginoides, may indicate that juveniles of Mesonychoteuthis hamiltoni are prey of D. eleginoides adults, and when Mesonychoteuthis hamiltoni reach a large size as adults, they become the predator.
Please find attached the final pdf file of your contribution, which can be viewed using the Acrob... more Please find attached the final pdf file of your contribution, which can be viewed using the Acrobat Reader, version 3.0 or higher. We would kindly like to draw your attention to the fact that copyright law is also valid for electronic products. This means especially that: • You may not alter the pdf file, as changes to the published contribution are prohibited by copyright law. • You may print the file and distribute it amongst your colleagues in the scientific community for scientific and/or personal use.
The short life span of cephalopods suggests a potential for high sensitivity to the arti®cial sel... more The short life span of cephalopods suggests a potential for high sensitivity to the arti®cial selective eects of human exploitation. To explore the eects of such selection life-history optimisation was applied using data for a semelparous squid, Illex argentinus with a life span of one year. Survival and fecundity functions were combined to generate a life time reproductive potential function. The maximum reproductive potential identi®ed the optimum age for the squid to mature. In a situation of a constant mortality rate the maximum reproductive potential was achieved at an earlier age of maturation as mortality rate increased. The exact age when the optimum maturation occurs is sensitive to the rate of mortality and the form of the assumed growth curve but covers the age range when maturation is known to occur in this species. A more realistic seasonal ®shing mortality function produced a more complex ®tness curve with a temporally more restricted optimal age of maturity. The selection eects will be stronger in a seasonal ®shery suggesting potentially very rapid evolutionary rates. Developing analyses speci®cally considering frequencydependence and environmental-feedbacks will be valuable to clarify the potential of squid to show rapid evolutionary responses to selection. Strong selection for early age of maturation could aect the yield from the ®shery but more importantly, could also make the migratory strategy, on which the ®shery is based, an unviable option, resulting in collapse of the ®shery that exploits the migratory component of the species.
Marine fisheries provide around 20% of animal protein consumed by man worldwide, but ineffective ... more Marine fisheries provide around 20% of animal protein consumed by man worldwide, but ineffective management can lead to commercial extinction of exploited stocks. Fisheries that overlap nationally controlled and high seas waters cause particular problems, as few management data are available for the high seas. The Argentinean short-finned squid, Illex argentinus, exemplifies such a &amp;quot;straddling stock&amp;quot;. Here we demonstrate that light emitted by fishing vessels to attract squid can be detected via remote-sensing. Unlike conventional fisheries data, which are restricted by political boundaries, satellite imagery can provide a synoptic view of fishing activity in both regulated and unregulated areas. By using known levels of fishing effort in Falkland Islands waters to calibrate the images, we are able to estimate effort levels on the high seas, providing a more comprehensive analysis of the overall impact of fishing on the stock. This innovative tool for quantifying fishing activity across management boundaries has wide-ranging applications to squid fisheries worldwide.
In this study, we consider the in¯uence of mesoscale oceanographic processes around the Falkland ... more In this study, we consider the in¯uence of mesoscale oceanographic processes around the Falkland Islands (Islas Malvinas) in the Southwest Atlantic, during the period in which the commercial squid ®shery for Illex argentinus operates. Spatially referenced ®shery data and satellite-derived advanced very high resolution radiometry (AVHRR) sea surface temperature (SST) data were examined using geographic information system (GIS) techniques. The distribution and relative abundance of I. argentinus in the Falkland Islands ®shery was examined for the period 1989±96. Three consistent areas of high abundance were observed to the northeast (shelf-break region) and northwest (shelf region) of the islands, and close to the northern coast of East Falkland. Areas of high sea surface temperature gradients (thermal gradients) extracted from remotely sensed satellite images were used as an indicator of mesoscale oceanographic activity and compared with the location of the ®shery. I. argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used in this analysis allow the overlay and analysis of physical oceanographic and ®shery data with potential applications in ®sheries management and operational ®sheries oceanography.
ABSTRACT Dosidicus gigas (Humboldt or jumbo squid) (Orbigny, 1835) is the largest ommastrephid sq... more ABSTRACT Dosidicus gigas (Humboldt or jumbo squid) (Orbigny, 1835) is the largest ommastrephid squid, reaching up to 1.2m mantle length and 65kg in weight. This pelagic squid is endemic to the eastern Pacific Ocean and is particularly abundant in the highly productive waters of the California and Humboldt Current systems, and the Costa Rica Dome upwelling region. The intra-specific population structure of D. gigas is complex, since this species quickly responds to environmental variability driven by El Niño and LaNiña events in both current systems by rapidly changing its biological characteristics, such as somatic and reproductive investment. Oocyte development is asynchronous and the potential fecundity averages around 18–21 million oocytes; the maximum value estimated (32 million oocytes) is the largest ever recorded for any cephalopod so far. Hatching occurs between 6 to 9 days after fertilization at 18°C, but temperatures below 15°C and above 25°C do not allow complete embryonic development. D. gigas passes through a post-hatching paralarval stage called the rhynchoteuthion and during this stage the two tentacles are fused into a well-developed proboscis. During the paralarval and subsequent juvenile stages Humboldt squid have a monthly growth rate of up to 80 mm in mantle length, and grow up 60 mm per month in the later stages. This is the highest growth rate reported for any cephalopod species, and enables this species to reach the reported maximum mantle lengths in a short lifespan (12 to 24 months). Although the lack of population structure across its large range suggests a high level of gene flow and substantial horizontal migration, specific migratory pathways in the Pacific Ocean have not yet been demonstrated. Long-distance migration is an important element in the life-history of Humboldt squid and may be associated with differential growth rates and size and at full maturity. The recent poleward range expansion of D. gigas is likely associated with warmer periods following El Niño/La Niña events, an ongoing expansion of the oxygen minimum zone (OMZ) in the Eastern Pacific, and changing ecosystem interactions including food availability, competition and predation. Humboldt squid feed primarily on small mesopelagic (midwater) fishes, crustaceans, and cephalopods as well as commercially important coastal fishes and squid in the recently expanded range. Typical daily behavior involves vertical migrations from near-surface waters at nighttime to mesopelagic depths above or within the OMZ during the daytime. Whereas the OMZ restricts the depth distribution of many competing vertebrate predators to the upper surface layers due to limited hypoxia tolerance, D. gigas circumvents similar restrictions via metabolic suppression. In addition to its critical role both as prey and predator in the eastern Pacific, D. gigas is an economically important species and the target of what has recently become the world’s largest invertebrate fishery.
Exploited populations of ommastrephid squid are found under a wide range of oceanographic regimes... more Exploited populations of ommastrephid squid are found under a wide range of oceanographic regimes. However, to date most scientific attention has focussed on those found in northern hemisphere western boundary current systems, and these systems have become the paradigm for ...
... by new data, presented at the First International Symposium on Pacific Squids at the VIII Con... more ... by new data, presented at the First International Symposium on Pacific Squids at the VIII Congreso Latinamericano de Ciencias del Mar, on distribution ( Taipe et ... There is also a growing body of literature on the species from the Southwest Atlantic ( Hatfield and des Clers, 1998). ...
The fishery for IUex argentinus in the Southwest Atlantic is subject to large inter-annual variab... more The fishery for IUex argentinus in the Southwest Atlantic is subject to large inter-annual variability in recruitment strength. In this paper we attempt to build a predictive model using sea surface temperature (SST) to examine links between recruitment to the Falkland Islands fishery and environmental variability during the juvenile and adult life history stages. SST data from the National Center for Atmospheric Research (NCAR) were found to be comparable with near-surface data derived from in situ expendable bathy-thermograph (XBT) profiles in the southern Patagonian shelf. Variation in SST during the early Me stages appears to be important in determining recruitment of I. argentinus. SST in the hatching grounds of the northern Patagonian shelf during the period of hatching (particularly June and July) was negatively correlated with catches in the fishery in the following season. SST anomaly data from positions in the Pacific and Southwest Atlantic were used to examine teleconnections between these areas. Links were seen at a lag of 2 yr between the Pacific and southern Patagonian shelf, and at about 5 yr between the Pacific and northern Patagonian shelf. This is consistent with SST anomalies associated with El Nifio in the Pacific propagating around the globe via the Antarctic Circumpolar Wave (ACW). Predicting cold events via teleconnections between SST anomalies in the Pacific and Atlantic would appear to have the potential to predict the recruitment strength of I. argentinus in the Southwest Atlantic.
Interannual variability in the mesoscale oceanography of the inferred hatching area of winter-spa... more Interannual variability in the mesoscale oceanography of the inferred hatching area of winter-spawned Illex argentinus (i.e. those belonging to the Southern Patagonic Stock) was examined during the hatching months of June and July. The hatching area was de®ned as the region 32°±39°S, 49°±61°W, and indicators of the surface oceanography in this area were derived from remotely sensed advanced very high resolution radiometer (AVHRR) sea-surface temperature (SST) data. Interannual variability in the mesoscale oceanic circulation in the inferred hatching area was examined in terms of (1) the area occupied by``frontal'' waters (de®ned as areas with SST gradients of ³3°C over an area of 15 km by 15 km), and (2) the area occupied by waters of``favourable'' SST (de®ned as those with temperatures in the range 16±18°C). Oceanographic indicators were compared with an index of I. argentinus recruitment to the Falkland Islands (Malvinas) ®shery (catch per licensed vessel) for the period 1987 to 1999. The two oceanographic indicators were seen to co-vary, with a decrease in the proportion of the inferred hatching area occupied by frontal waters corresponding to an increase in the proportion of water of favourable SST. High squid abundance was found to be associated with a lower proportion of frontal waters or a higher proportion of favourable-SST waters within the inferred hatching area in the year preceding the ®shery. Interannual variability in the interaction of the Brazil and Falkland Currents in the inferred hatching area during the early life stages is shown to be important in in¯uencing the population size of I. argentinus, and mechanisms inuencing squid recruitment in this highly dynamic region are discussed.
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