In late 2020, models predicted that a strong La Niña would take place for the first time since 20... more In late 2020, models predicted that a strong La Niña would take place for the first time since 2013, and we assessed whether physical and biological indicators in 2021 were similar to past La Niñas in the California Current Ecosystem (CCE). The Pacific Decadal Oscillation and Oceanic Niño Index indeed remained negative throughout 2021; the North Pacific Gyre Oscillation Index, however, remained strongly negative. The seventh largest marine heatwave on record was unexpectedly present from April to the end of 2021; however, similar to past La Niñas, this mass of warm water mostly remained seaward of the continental shelf. As expected from past La Niñas, upwelling and chlorophyll were mostly high and sea surface temperature was low throughout the CCE; however, values were close to average south of Point Conception. Similar to past La Niñas, abundances of lipid-rich, northern copepods off Oregon increased. In northern California, unlike past La Niñas, the body size of North Pacific kril...
Blue sharks (Prionace glauca) are globally distributed, large-bodied pelagic sharks that make ext... more Blue sharks (Prionace glauca) are globally distributed, large-bodied pelagic sharks that make extensive migrations throughout their range. In the North Pacific, mark-recapture studies have showntrans-Pacific migrations, but knowledge gaps in migration frequency hinder understanding of regional connectivity and assessments of regional demography for stock assessments. Here, we use oceanographic gradients of stable isotope ratios (i.e., regional isoscapes) to determine exchange rates of blue sharks between the East and West North Pacific Ocean (EPO and WPO). We generated regional δ13C and δ15N distributions for blue sharks from published values in the North Pacific (n= 180; both sexes, juveniles and adults combined). Discriminant analysis suggested lowtrans-Pacific exchange, categorizing all western (100%) and most eastern (95.3%) blue sharks as resident to their sampling region, with isotopic niche overlap of WPO and EPO highly distinct (0.01–5.6% overlap). Limitedtrans-Pacific movem...
Reviews: Methods and Technologies in Fish Biology and Fisheries, 2001
... Mobile tracking systems have been used to study the behaviour of several pecies of sharks in ... more ... Mobile tracking systems have been used to study the behaviour of several pecies of sharks in lagoons, and on reefs, banks and seamounts in both tem-perate and tropical waters. Studies have encompassed space utilisation and diel patterns of activity (Standora and Nelson ...
The metabolic rates of three tropical tunas [yellowfin tuna (Thunnus albacares), kawakawa (Euthyn... more The metabolic rates of three tropical tunas [yellowfin tuna (Thunnus albacares), kawakawa (Euthynnus affinis) and skipjack (Katsuwonus pelamis)] were estimated using a large water-tunnel respirometer. Experiments lasting up to 31 h were used to determine the effects of velocity (U) on tuna over a range of U (17–150 cm s−1) and temperatures (18–30°C). Replicate tests were carried out on several fish. The swimming of yellowfin is temperature-dependent (Q10=1.67, determined over intervals of 3–5°C). For yellowfin and skipjack, it was also possible to partition metabolic costs between maintenance and locomotion. The standard metabolic rate was estimated by extrapolation of the function to U=0. Comparisons of for different size groups of yellowfin show that the mass-specific scaling exponent for is −0.40. The of tuna is comparable to values determined previously by stasis respirometry and is approximately three times higher than that of salmonids. Further comparisons with salmonids show ...
A project was initiated in the autumn of 2000 to document the mortality of striped marlin caught ... more A project was initiated in the autumn of 2000 to document the mortality of striped marlin caught on recreational fishing tackle, with a follow-up study conducted in autumn of 2001. Fish were caught using typical recreational fishing methods and 80 pop-up satellite archival tags were deployed with new software and mechanical release mechanisms that allowed tags to detach and transmit early if the fish died. The first year study was also designed to compare the effectiveness and associated mortality of circle hooks versus J-hooks, while the second year study compared offset and non-offset circle hooks. All fish were caught on live bait. Circle hooks were found to be equally effective in hooking and landing striped marlin and far less likely to cause serious bleeding or become lodged in areas other than the mouth. Non-offset and 5° offset circle hooks had very similar performance. Depth and temperature records allowed us to determine the fate of individual marlin following release. In ...
We report the isolation and characterization of CAn microsatellite loci from the Mola mola genome... more We report the isolation and characterization of CAn microsatellite loci from the Mola mola genome using a variation of the hybrid capture method. Five loci exhibit high levels of heterozygocity and two show significant sequence similarity to genes from the closely related Fugu rubripes. These microsatellite markers should be useful in multidisciplinary efforts to understand population characteristics of the giant ocean sunfish.
Journal of Experimental Marine Biology and Ecology, 2015
The common ocean sunfish, Mola mola, occupies a unique position in the eastern Pacific Ocean and ... more The common ocean sunfish, Mola mola, occupies a unique position in the eastern Pacific Ocean and the California Current Large Marine Ecosystem (CCLME) as the world's heaviest, most fecund bony fish, and one of the most abundant gelativores. M. mola frequently occur as bycatch in fisheries worldwide and comprise the greatest portion of the bycatch in California's large-mesh drift gillnet fishery. In this first long-term tagging study of any ocean sunfish species in the eastern Pacific, 15 M. mola (99 cm to 200 cm total length) were tagged in the southern California Bight (SCB) between 2003 and 2010 using 14 satellite pop-off archival tags (PATs) and one Fastloc Mk10 GPS tag. Ten tags provided positional data for a cumulative dataset of 349 tracking days during the months of July through March. Thirteen tags provided temperature and depth data. All M. mola remained within~300 km of the coast, and nearly all exhibited seasonal movement between the SCB and adjacent waters off northern and central Baja California, Mexico. No tagged individuals were tracked north of the SCB. Tag depth data showed diel vertical migration and occasional deep (N500 m) dives. Data from the Fastloc GPS tag allowed close examination of the relationship between the movements of the largest tagged ocean sunfish (2 m TL) and fine-scale oceanographic features. Near-instantaneous satellite sea surface temperature images showed this individual associated with upwelling fronts along its migration path, which exceeded 800 km and ranged from 6 to 128 km from the coast. Tag depth data showed active use of the water column within the frontal zones. Synthetic aperture radar (SAR) images demonstrated that surface slicks, which often indicate convergent circulation, coincided with this type of front. Zooplankton tows in the southern region of tracking off central Baja California, Mexico revealed dense populations of salps toward the warm side of these fronts. Satellite tag and ecosystem data suggest that bio-physical interactions in coastal upwelling fronts create favorable foraging habitat.
Journal of Experimental Zoology Part A: Comparative Experimental Biology, 2003
Tunas (family: Scombridae, Tribe: Thunnini) exhibit anatomical, physiological, and biochemical ad... more Tunas (family: Scombridae, Tribe: Thunnini) exhibit anatomical, physiological, and biochemical adaptations that dramatically increase the ability of their cardiorespiratory systems to transfer oxygen from the water to the tissues. In the present study the vascular anatomy of the skipjack tuna, Katsuwonus pelamis, gill was examined by light and scanning electron microscopic analysis of methyl methacrylate vascular corrosion replicas prepared under physiological pressure. The gill filament contains three distinct blood pathways, respiratory, interlamellar, and nutrient. The respiratory, or arterio‐arterial (AA) pathway, is the site of gas exchange and consists of the afferent and efferent filamental arteries (AFA and EFA) and arterioles (ALA and ELA) and the lamellae. Each ALA in the basal filament supplies ten or more lamellae and they anastomose with their neighbor to form a continuous vascular arcade. Four modifications in the lamellar circulation appear to enhance gas exchange eff...
Page 1. Environmental Biology of Fishes 40: 109-124,1994. 0 1994 Kluwer Academic Publishers. Prin... more Page 1. Environmental Biology of Fishes 40: 109-124,1994. 0 1994 Kluwer Academic Publishers. Printed in the Netherlands. Basic concepts relevant to heat transfer in fishes, and their use in measuring the physiological thermoregulatory abilities of tunas* ...
This study describes the feeding ecology of three pelagic shark species in the California Current... more This study describes the feeding ecology of three pelagic shark species in the California Current: shortfin mako (Isurus oxyrinchus); blue (Prionace glauca); and thresher (Alopias vulpinus) sharks. Stomach contents of sharks collected from 2002 to 2008 were identified to the lowest taxonomic level and analyzed using univariate and multivariate methods. Of 330 mako sharks sampled (53 to 248 cm fork length [FL]), 238 stomachs contained 42 prey taxa, with jumbo squid (Dosidicus gigas) and Pacific saury (Cololabis saira) representing the most important prey based on the geometric index of importance (GII). In addition, 158 blue sharks were sampled (76 to 248 cm FL) and 114 stomachs contained 38 prey taxa, with jumbo and Gonatus spp. squids representing the most important prey. Lastly, 225 thresher sharks were sampled (108 to 228 cm FL) and 157 stomachs contained 18 prey taxa with northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) identified as the most important prey. Overall, mako sharks had the most diverse diet based upon Simpson's diversity index (1/D) (8.43±1.16), feeding on many species of teleosts and cephalopods, followed by blue sharks (6.20±2.11) which consumed a wide range of prey (primarily cephalopods), while thresher sharks were most specialized (2.62±0.34), feeding primarily on coastal pelagic teleosts. Dietary overlap was lowest between blue and thresher sharks (Sørensen similarity index00.321 and Simplified Morisita Horn index0 0.006), and seasonal variability in diet was greatest for blue sharks (Simplified Morisita Horn index0 0.260, Analysis of Similarity (ANOSIM) p<0.001). In addition, size class, and subregion were significant factors that affected diet of each species differently (ANOSIM p<0.001). Despite similarities in life history characteristics and spatial and temporal overlap in habitat, diets of these three common shark species are distinct in the California Current.
Background: Although much is known about the behavior of white sharks in coastal regions, very li... more Background: Although much is known about the behavior of white sharks in coastal regions, very little is known about their vertical movements offshore in the eastern Pacific where they spend up to five months. We provide the first detailed description of the offshore habitat use of white sharks in the eastern North Pacific. Methodology/Principal Findings: This study uses 2-min data from four recovered pop-up satellite archival tags deployed at Guadalupe Island (2002 and 2005). Deployments ranged from 5.4 to 8.2 months. Two predominant vertical patterns were described. The first was a bimodal vertical pattern with time spent at the surface and at depth, which was observed while traveling. The second was a repetitive oscillatory diving mode displayed by sharks in the Shared Offshore Foraging Area (SOFA). For all four datasets the average maximum daily dive depths ranged from 442.5 to 492.8 m and were typically associated with dissolved oxygen concentrations of above 1.7 ml L 21. Although infrequent, occasional dives to near 1000 m with a minimum temperature of 3.9uC and a minimum O 2 level of 0.3 ml L 21 were observed. Conclusions/Significance: Recovered pop-up satellite tags from Guadalupe Island white sharks advance our understanding of the vertical habitat use of white sharks while offshore. The bimodal vertical pattern during traveling is most likely related to geolocation. The oscillatory dive pattern is likely associated with foraging. While feeding is not documented, foraging is likely occurring in association with the deep scattering layer. Diving depths were not limited by temperature but were constrained by O 2 levels below approximately 1.5 ml L 21. While oxygen may limit the extent of sharks' vertical movements, it will also impact prey distribution. Consequently, the shallow oxygen minimum zone in the SOFA may act to concentrate prey, thus enhancing foraging opportunities in these oligotrophic waters.
In late 2020, models predicted that a strong La Niña would take place for the first time since 20... more In late 2020, models predicted that a strong La Niña would take place for the first time since 2013, and we assessed whether physical and biological indicators in 2021 were similar to past La Niñas in the California Current Ecosystem (CCE). The Pacific Decadal Oscillation and Oceanic Niño Index indeed remained negative throughout 2021; the North Pacific Gyre Oscillation Index, however, remained strongly negative. The seventh largest marine heatwave on record was unexpectedly present from April to the end of 2021; however, similar to past La Niñas, this mass of warm water mostly remained seaward of the continental shelf. As expected from past La Niñas, upwelling and chlorophyll were mostly high and sea surface temperature was low throughout the CCE; however, values were close to average south of Point Conception. Similar to past La Niñas, abundances of lipid-rich, northern copepods off Oregon increased. In northern California, unlike past La Niñas, the body size of North Pacific kril...
Blue sharks (Prionace glauca) are globally distributed, large-bodied pelagic sharks that make ext... more Blue sharks (Prionace glauca) are globally distributed, large-bodied pelagic sharks that make extensive migrations throughout their range. In the North Pacific, mark-recapture studies have showntrans-Pacific migrations, but knowledge gaps in migration frequency hinder understanding of regional connectivity and assessments of regional demography for stock assessments. Here, we use oceanographic gradients of stable isotope ratios (i.e., regional isoscapes) to determine exchange rates of blue sharks between the East and West North Pacific Ocean (EPO and WPO). We generated regional δ13C and δ15N distributions for blue sharks from published values in the North Pacific (n= 180; both sexes, juveniles and adults combined). Discriminant analysis suggested lowtrans-Pacific exchange, categorizing all western (100%) and most eastern (95.3%) blue sharks as resident to their sampling region, with isotopic niche overlap of WPO and EPO highly distinct (0.01–5.6% overlap). Limitedtrans-Pacific movem...
Reviews: Methods and Technologies in Fish Biology and Fisheries, 2001
... Mobile tracking systems have been used to study the behaviour of several pecies of sharks in ... more ... Mobile tracking systems have been used to study the behaviour of several pecies of sharks in lagoons, and on reefs, banks and seamounts in both tem-perate and tropical waters. Studies have encompassed space utilisation and diel patterns of activity (Standora and Nelson ...
The metabolic rates of three tropical tunas [yellowfin tuna (Thunnus albacares), kawakawa (Euthyn... more The metabolic rates of three tropical tunas [yellowfin tuna (Thunnus albacares), kawakawa (Euthynnus affinis) and skipjack (Katsuwonus pelamis)] were estimated using a large water-tunnel respirometer. Experiments lasting up to 31 h were used to determine the effects of velocity (U) on tuna over a range of U (17–150 cm s−1) and temperatures (18–30°C). Replicate tests were carried out on several fish. The swimming of yellowfin is temperature-dependent (Q10=1.67, determined over intervals of 3–5°C). For yellowfin and skipjack, it was also possible to partition metabolic costs between maintenance and locomotion. The standard metabolic rate was estimated by extrapolation of the function to U=0. Comparisons of for different size groups of yellowfin show that the mass-specific scaling exponent for is −0.40. The of tuna is comparable to values determined previously by stasis respirometry and is approximately three times higher than that of salmonids. Further comparisons with salmonids show ...
A project was initiated in the autumn of 2000 to document the mortality of striped marlin caught ... more A project was initiated in the autumn of 2000 to document the mortality of striped marlin caught on recreational fishing tackle, with a follow-up study conducted in autumn of 2001. Fish were caught using typical recreational fishing methods and 80 pop-up satellite archival tags were deployed with new software and mechanical release mechanisms that allowed tags to detach and transmit early if the fish died. The first year study was also designed to compare the effectiveness and associated mortality of circle hooks versus J-hooks, while the second year study compared offset and non-offset circle hooks. All fish were caught on live bait. Circle hooks were found to be equally effective in hooking and landing striped marlin and far less likely to cause serious bleeding or become lodged in areas other than the mouth. Non-offset and 5° offset circle hooks had very similar performance. Depth and temperature records allowed us to determine the fate of individual marlin following release. In ...
We report the isolation and characterization of CAn microsatellite loci from the Mola mola genome... more We report the isolation and characterization of CAn microsatellite loci from the Mola mola genome using a variation of the hybrid capture method. Five loci exhibit high levels of heterozygocity and two show significant sequence similarity to genes from the closely related Fugu rubripes. These microsatellite markers should be useful in multidisciplinary efforts to understand population characteristics of the giant ocean sunfish.
Journal of Experimental Marine Biology and Ecology, 2015
The common ocean sunfish, Mola mola, occupies a unique position in the eastern Pacific Ocean and ... more The common ocean sunfish, Mola mola, occupies a unique position in the eastern Pacific Ocean and the California Current Large Marine Ecosystem (CCLME) as the world's heaviest, most fecund bony fish, and one of the most abundant gelativores. M. mola frequently occur as bycatch in fisheries worldwide and comprise the greatest portion of the bycatch in California's large-mesh drift gillnet fishery. In this first long-term tagging study of any ocean sunfish species in the eastern Pacific, 15 M. mola (99 cm to 200 cm total length) were tagged in the southern California Bight (SCB) between 2003 and 2010 using 14 satellite pop-off archival tags (PATs) and one Fastloc Mk10 GPS tag. Ten tags provided positional data for a cumulative dataset of 349 tracking days during the months of July through March. Thirteen tags provided temperature and depth data. All M. mola remained within~300 km of the coast, and nearly all exhibited seasonal movement between the SCB and adjacent waters off northern and central Baja California, Mexico. No tagged individuals were tracked north of the SCB. Tag depth data showed diel vertical migration and occasional deep (N500 m) dives. Data from the Fastloc GPS tag allowed close examination of the relationship between the movements of the largest tagged ocean sunfish (2 m TL) and fine-scale oceanographic features. Near-instantaneous satellite sea surface temperature images showed this individual associated with upwelling fronts along its migration path, which exceeded 800 km and ranged from 6 to 128 km from the coast. Tag depth data showed active use of the water column within the frontal zones. Synthetic aperture radar (SAR) images demonstrated that surface slicks, which often indicate convergent circulation, coincided with this type of front. Zooplankton tows in the southern region of tracking off central Baja California, Mexico revealed dense populations of salps toward the warm side of these fronts. Satellite tag and ecosystem data suggest that bio-physical interactions in coastal upwelling fronts create favorable foraging habitat.
Journal of Experimental Zoology Part A: Comparative Experimental Biology, 2003
Tunas (family: Scombridae, Tribe: Thunnini) exhibit anatomical, physiological, and biochemical ad... more Tunas (family: Scombridae, Tribe: Thunnini) exhibit anatomical, physiological, and biochemical adaptations that dramatically increase the ability of their cardiorespiratory systems to transfer oxygen from the water to the tissues. In the present study the vascular anatomy of the skipjack tuna, Katsuwonus pelamis, gill was examined by light and scanning electron microscopic analysis of methyl methacrylate vascular corrosion replicas prepared under physiological pressure. The gill filament contains three distinct blood pathways, respiratory, interlamellar, and nutrient. The respiratory, or arterio‐arterial (AA) pathway, is the site of gas exchange and consists of the afferent and efferent filamental arteries (AFA and EFA) and arterioles (ALA and ELA) and the lamellae. Each ALA in the basal filament supplies ten or more lamellae and they anastomose with their neighbor to form a continuous vascular arcade. Four modifications in the lamellar circulation appear to enhance gas exchange eff...
Page 1. Environmental Biology of Fishes 40: 109-124,1994. 0 1994 Kluwer Academic Publishers. Prin... more Page 1. Environmental Biology of Fishes 40: 109-124,1994. 0 1994 Kluwer Academic Publishers. Printed in the Netherlands. Basic concepts relevant to heat transfer in fishes, and their use in measuring the physiological thermoregulatory abilities of tunas* ...
This study describes the feeding ecology of three pelagic shark species in the California Current... more This study describes the feeding ecology of three pelagic shark species in the California Current: shortfin mako (Isurus oxyrinchus); blue (Prionace glauca); and thresher (Alopias vulpinus) sharks. Stomach contents of sharks collected from 2002 to 2008 were identified to the lowest taxonomic level and analyzed using univariate and multivariate methods. Of 330 mako sharks sampled (53 to 248 cm fork length [FL]), 238 stomachs contained 42 prey taxa, with jumbo squid (Dosidicus gigas) and Pacific saury (Cololabis saira) representing the most important prey based on the geometric index of importance (GII). In addition, 158 blue sharks were sampled (76 to 248 cm FL) and 114 stomachs contained 38 prey taxa, with jumbo and Gonatus spp. squids representing the most important prey. Lastly, 225 thresher sharks were sampled (108 to 228 cm FL) and 157 stomachs contained 18 prey taxa with northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) identified as the most important prey. Overall, mako sharks had the most diverse diet based upon Simpson's diversity index (1/D) (8.43±1.16), feeding on many species of teleosts and cephalopods, followed by blue sharks (6.20±2.11) which consumed a wide range of prey (primarily cephalopods), while thresher sharks were most specialized (2.62±0.34), feeding primarily on coastal pelagic teleosts. Dietary overlap was lowest between blue and thresher sharks (Sørensen similarity index00.321 and Simplified Morisita Horn index0 0.006), and seasonal variability in diet was greatest for blue sharks (Simplified Morisita Horn index0 0.260, Analysis of Similarity (ANOSIM) p<0.001). In addition, size class, and subregion were significant factors that affected diet of each species differently (ANOSIM p<0.001). Despite similarities in life history characteristics and spatial and temporal overlap in habitat, diets of these three common shark species are distinct in the California Current.
Background: Although much is known about the behavior of white sharks in coastal regions, very li... more Background: Although much is known about the behavior of white sharks in coastal regions, very little is known about their vertical movements offshore in the eastern Pacific where they spend up to five months. We provide the first detailed description of the offshore habitat use of white sharks in the eastern North Pacific. Methodology/Principal Findings: This study uses 2-min data from four recovered pop-up satellite archival tags deployed at Guadalupe Island (2002 and 2005). Deployments ranged from 5.4 to 8.2 months. Two predominant vertical patterns were described. The first was a bimodal vertical pattern with time spent at the surface and at depth, which was observed while traveling. The second was a repetitive oscillatory diving mode displayed by sharks in the Shared Offshore Foraging Area (SOFA). For all four datasets the average maximum daily dive depths ranged from 442.5 to 492.8 m and were typically associated with dissolved oxygen concentrations of above 1.7 ml L 21. Although infrequent, occasional dives to near 1000 m with a minimum temperature of 3.9uC and a minimum O 2 level of 0.3 ml L 21 were observed. Conclusions/Significance: Recovered pop-up satellite tags from Guadalupe Island white sharks advance our understanding of the vertical habitat use of white sharks while offshore. The bimodal vertical pattern during traveling is most likely related to geolocation. The oscillatory dive pattern is likely associated with foraging. While feeding is not documented, foraging is likely occurring in association with the deep scattering layer. Diving depths were not limited by temperature but were constrained by O 2 levels below approximately 1.5 ml L 21. While oxygen may limit the extent of sharks' vertical movements, it will also impact prey distribution. Consequently, the shallow oxygen minimum zone in the SOFA may act to concentrate prey, thus enhancing foraging opportunities in these oligotrophic waters.
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