East Pepperell, MA, United States
East Pepperell, MA, United States

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Logan J.M.,University of New Hampshire | Golet W.J.,University of New Hampshire | Golet W.J.,University of Maine, United States | Golet W.J.,Gulf of Maine Research Institute | And 2 more authors.
Environmental Biology of Fishes | Year: 2015

Atlantic herring (Clupea harengus) are the primary forage for Atlantic bluefin tuna (Thunnus thynnus; ABFT) in the Gulf of Maine. Recent studies have documented significant declines in ABFT somatic condition and shifts in their size and spatial distribution in the Gulf of Maine, which may be linked to trophic changes. We collected stomachs (n = 122) as well as liver (n = 110) and white muscle (n = 382) samples for carbon and nitrogen stable isotope analysis and lipid analysis to determine if diet composition had changed relative to the late 1980’s to early 2000’s for large, commercially harvested ABFT (≥185 cm curved fork length (CFL)). Samples of smaller ABFT (<185 cm CFL) were also collected (stomachs: n = 21; liver: n = 17; white muscle: n = 19) to compare diet between size classes. Large ABFT diet was similar among current and historic studies, Atlantic herring being the main prey (39.5 to 52.8 % weight). Small ABFT fed at a lower trophic position (TP = 3.9) than larger individuals (TP = 4.9) due to higher consumption of sand lance (Ammodytes spp.) and euphausiids (65.6 vs. 4.5 % weight). Mean and maximum lipid stores of large ABFT increased from spring through fall, but lean fish were observed in all seasons. In the fall, lean ABFT were lighter with lower nitrogen and higher carbon isotope values than co-occurring ABFT with higher lipid stores. These patterns are consistent with shelf vs. offshore isotope baseline differences in the western North Atlantic and variable arrival and residency patterns for ABFT in the Gulf of Maine. © 2014, Springer Science+Business Media Dordrecht.


The findings, to be published March 7 in the Proceedings of the National Academy of Sciences, suggest that the current life-history model for western Atlantic bluefin, which assumes spawning occurs only in the Gulf of Mexico, overestimates age-at-maturity. For that reason, the authors conclude that western Atlantic bluefin may be less vulnerable to fishing and other stressors than previously thought. Prior to this research, the only known spawning grounds for Atlantic bluefin tuna were in the Gulf of Mexico and the Mediterranean Sea. The evidence for a new western Atlantic spawning ground came from a pair of Northeast Fisheries Science Center (NEFSC) research cruises in the Slope Sea during the summer of 2013. "We collected 67 larval bluefin tuna during these two cruises, and the catch rates were comparable to the number collected during the annual bluefin tuna larval survey in the Gulf of Mexico," said David Richardson of NOAA's Northeast Fisheries Science Center (NEFSC), lead author of this study. "Most of these larvae were small, less than 5 millimeters, and were estimated to be less than one week old. Drifting buoy data confirmed that these small larvae could not possibly have been transported into this area from the Gulf of Mexico spawning ground." Larvae collected during the cruises were identified as bluefin tuna through visual examination and genetic sequencing. To confirm the identification, larvae were sent to the Alaska Fisheries Science Center laboratory in Juneau, where DNA sequences verified that the larvae were Atlantic bluefin tuna. A single bluefin tuna can spawn millions of eggs, each of which is just over a millimeter in diameter, or the size of a poppy seed. Within a couple of days these eggs hatch into larvae that are poorly developed and bear little resemblance to the adults. Larval bluefin tuna can be collected in plankton nets and identified based on their shape, pigment patterns and body structures. Atlantic bluefin tuna (Thunnus thynnus) is a high value species with a unique physiology that allows it to range from the tropics to the sub-arctic, in coastal to international waters. As a highly migratory species, Atlantic bluefin tuna is assessed by the Standing Committee on Research and Statistics (SCRS) of the International Commission for the Conservation of Atlantic Tunas (ICCAT) as distinct eastern and western stocks separated by the 45 degree west meridian (or 45 w longitude). The U.S. fishery harvest from the western Atlantic stock is managed through NOAA Fisheries' Atlantic Highly Migratory Species Fishery Management Plan. For many years, global overfishing on this species was prevalent, resulting in substantial population declines. However, recent international cooperation in managing catches has contributed to increasing trends in the abundance of both the eastern and western management stocks. The western stock, targeted by U.S. fishermen, is harvested at levels within the range of the SCRS' scientific advice. This research may help to resolve a longstanding debate in Atlantic bluefin tuna science. It had long been assumed that bluefin tuna start spawning at age 4 in the Mediterranean Sea and age 9 in the Gulf of Mexico. Electronic tagging studies begun in the late 1990s revealed that many bluefin tuna, assumed to be of mature size, did not visit either spawning ground during the spawning season as expected. This led some to propose that these larger fish were not spawning, and instead the age-at-maturity for western Atlantic bluefin tuna was 12-16 years, rather than 9 years, as was assumed in the stock assessment. Molly Lutcavage at the Large Pelagics Research Center of the University of Massachusetts Boston, a co-author on the study, was a consistent supporter of an alternate hypothesis—fish that did not visit the Gulf of Mexico and Mediterranean Sea were spawning elsewhere. The research team used electronic tagging data from the Lutcavage lab to present an alternate model of western Atlantic bluefin tuna spawning migrations. Only the largest bluefin tuna, those over about 500 pounds, migrate to the Gulf of Mexico spawning area. After these fish exit the Gulf of Mexico, they swim through the Slope Sea rapidly, on their way to northern feeding grounds. On the other hand, smaller fish, ranging in size from 80 to 500 pounds, generally spend more than 20 days in the Slope Sea during the spawning season, a duration consistent with spawning. "Last year, we demonstrated using endocrine measurements that bluefin tuna in the western Atlantic mature at around 5 years of age. That study, and ones before it, predicted that these smaller fish would spawn in a more northerly area closer to the summertime foraging grounds in the Gulf of Maine and Canadian waters," Lutcavage said. "The evidence of spawning in the Slope Sea, and the analysis of the tagging data, suggests that western Atlantic bluefin tuna are partitioning spawning areas by size, and that a younger age at maturity should be used in the stock assessment." Researchers also found that individual tuna occupy both the Slope Sea and Mediterranean Sea in separate years, contrary to the prevailing view that individuals exhibit complete fidelity to a spawning site. Reproductive mixing between the eastern and western stocks may occur in the Slope Sea and the authors contend that population structure of bluefin tuna may be more complex than is currently thought. "Past analyses of Atlantic bluefin tuna population structure and mixing between the western and eastern Atlantic stocks may need to be revisited because they do not account for the full spatial extent of western Atlantic spawning," Richardson said. "So much of the science and sampling for Atlantic bluefin tuna has been built around the assumption that the Gulf of Mexico and Mediterranean Sea are the only spawning grounds. This new research underscores the complexity of stock structure for this species and identifies important areas for future research." The authors expect these findings could potentially lead to a lower estimated age-at-maturity, a critical component of the stock assessment, and could reopen consideration of the nature and level of mixing between the western and eastern Atlantic populations. This new information will be considered along with other pertinent research as part of the regular ICCAT SCRS stock assessment process. The scientific team for this study comprises researchers from NOAA's Northeast Fisheries Science Center (NEFSC) and Alaska Fisheries Science Center (AFSC), the Large Pelagics Research Center at the University of Massachusetts Boston, the School of Marine Science and Technology at the University of Massachusetts Dartmouth, and NOAA's Greater Atlantic Regional Fisheries Office (GARFO). The sampling for this study was supported by NOAA, the Bureau of Ocean Energy Management, and the US Navy through interagency agreements for the Atlantic Marine Assessment Program for Protected Species (AMAPPS). Explore further: New study maps spawning habitat of bluefin tuna in the Gulf of Mexico More information: Discovery of a spawning ground reveals diverse migration strategies in Atlantic bluefin tuna (Thunnus thynnus) , Proceedings of the National Academy of Sciences, , www.pnas.org/cgi/doi/10.1073/pnas.1525636113


Sippel T.,Southwest Fisheries Science Center | Paige Eveson J.,CSIRO | Galuardi B.,Large Pelagics Research Center | Lam C.,Large Pelagics Research Center | And 8 more authors.
Fisheries Research | Year: 2015

Tag-recapture data have long been important data sources for fisheries management, with the capacity to inform abundance, mortality, growth and movement within stock assessments. Historically, this role has been fulfilled with low-tech conventional tags, but the relatively recent and rapid development of electronic tags has dramatically increased the potential to collect more high quality data. Stock assessment models have also been evolving in power and complexity recently, with the ability to integrate multiple data sources into unified spatially explicit frameworks. However, electronic tag technologies and stock assessment models have developed largely independently, and frameworks for incorporating these valuable data in contemporary stock assessments are nascent, at best. Movement dynamics of large pelagic species have been problematic to resolve in modern assessments, and electronic tags offer new opportunities to resolve some of these issues. Pragmatic ways of modeling movement are often not obvious, and basic research into discrete and continuous processes, for example, is ongoing. Experimental design of electronic tagging research has been driven mostly by ecological and biological questions, rather than optimized for stock assessment, and this is probably a complicating factor in integration of the data into assessment models. A holistic overview of the current state of assessment models, electronic tag technologies, and experimental design is provided here, with the aim to provide insight into how stock assessment and electronic tagging research can be conducted most effectively together. © 2014 Elsevier B.V.


Dodge K.L.,University of New Hampshire | Galuardi B.,Large Pelagics Research Center | Lutcavage M.E.,Large Pelagics Research Center
Proceedings. Biological sciences / The Royal Society | Year: 2015

Leatherback sea turtles (Dermochelys coriacea) travel thousands of kilometres between temperate feeding and tropical breeding/over-wintering grounds, with adult turtles able to pinpoint specific nesting beaches after multi-year absences. Their extensive migrations often occur in oceanic habitat where limited known sensory information is available to aid in orientation. Here, we examined the migratory orientation of adult male, adult female and subadult leatherbacks during their open-ocean movements within the North Atlantic subtropical gyre by analysing satellite-derived tracks from fifteen individuals over a 2-year period. To determine the turtles' true headings, we corrected the reconstructed tracks for current drift and found negligible differences between current-corrected and observed tracks within the gyre. Individual leatherback headings were remarkably consistent throughout the subtropical gyre, with turtles significantly oriented to the south-southeast. Adult leatherbacks of both sexes maintained similar mean headings and showed greater orientation precision overall. The consistent headings maintained by adult and subadult leatherbacks within the gyre suggest use of a common compass sense. © 2015 The Author(s) Published by the Royal Society. All rights reserved.


Dodge K.L.,University of New Hampshire | Dodge K.L.,Large Pelagics Research Center | Galuardi B.,Large Pelagics Research Center | Lutcavage M.E.,Large Pelagics Research Center
Proceedings of the Royal Society B: Biological Sciences | Year: 2015

Leatherback sea turtles (Dermochelys coriacea) travel thousands of kilometres between temperate feeding and tropical breeding/over-wintering grounds, with adult turtles able to pinpoint specific nesting beaches after multi-year absences. Their extensive migrations often occur in oceanic habitat where limited known sensory information is available to aid in orientation. Here, we examined the migratory orientation of adult male, adult female and subadult leatherbacks during their open-ocean movements within the North Atlantic subtropical gyre by analysing satellite-derived tracks from fifteen individuals over a 2-year period. To determine the turtles' true headings, we corrected the reconstructed tracks for current drift and found negligible differences between current-corrected and observed tracks within the gyre. Individual leatherback headings were remarkably consistent throughout the subtropical gyre, with turtles significantly oriented to the south-southeast. Adult leatherbacks of both sexes maintained similar mean headings and showed greater orientation precision overall. The consistent headings maintained by adult and subadult leatherbacks within the gyre suggest use of a common compass sense. © 2015 The Author(s) Published by the Royal Society. All rights reserved.


PubMed | University of New Hampshire and Large Pelagics Research Center
Type: Journal Article | Journal: Proceedings. Biological sciences | Year: 2015

Leatherback sea turtles (Dermochelys coriacea) travel thousands of kilometres between temperate feeding and tropical breeding/over-wintering grounds, with adult turtles able to pinpoint specific nesting beaches after multi-year absences. Their extensive migrations often occur in oceanic habitat where limited known sensory information is available to aid in orientation. Here, we examined the migratory orientation of adult male, adult female and subadult leatherbacks during their open-ocean movements within the North Atlantic subtropical gyre by analysing satellite-derived tracks from fifteen individuals over a 2-year period. To determine the turtles true headings, we corrected the reconstructed tracks for current drift and found negligible differences between current-corrected and observed tracks within the gyre. Individual leatherback headings were remarkably consistent throughout the subtropical gyre, with turtles significantly oriented to the south-southeast. Adult leatherbacks of both sexes maintained similar mean headings and showed greater orientation precision overall. The consistent headings maintained by adult and subadult leatherbacks within the gyre suggest use of a common compass sense.


Musyl M.K.,University of Hawaii at Manoa | Brill R.W.,Virginia Institute of Marine Science | Curran D.S.,National Oceanic and Atmospheric Administration | Fragoso N.M.,Large Pelagics Research Center | And 4 more authors.
Fishery Bulletin | Year: 2011

From 2001 to 2006, 71 pop-up satellite archival tags (PSATs) were deployed on five species of pelagic shark (blue shark [Prionace glauca]; shortfin mako [Isurus oxyrinchus]; silky shark [Carcharhinus falciformis]; oceanic whitetip shark [C. longimanus]; and bigeye thresher [Alopias superciliosus]) in the central Pacific Ocean to determine species-specific movement patterns and survival rates after release from longline fishing gear. Only a single postrelease mortality could be unequivocally documented: a male blue shark which succumbed seven days after release. Meta-analysis of published reports and the current study (n=78 reporting PSATs) indicated that the summary effect of postrelease mortality for blue sharks was 15% (95% CI, 8.5-25.1%) and suggested that catch-and-release in longline fisheries can be a viable management tool to protect parental biomass in shark populations. Pelagic sharks displayed species-specific depth and temperature ranges, although with significant individual temporal and spatial variability in vertical movement patterns, which were also punctuated by stochastic events (e.g., El Niño-Southern Oscillation). Pelagic species can be separated into three broad groups based on daytime temperature preferences by using the unweighted pair-group method with arithmetic averaging clustering on a Kolmogorov-Smirnov D max distance matrix: 1) epipelagic species (silky and oceanic whitetip sharks), which spent >95% of their time at temperatures within 2°C of sea surface temperature; 2) mesopelagic-I species (blue sharks and shortfin makos, which spent 95% of their time at temperatures from 9.7° to 26.9°C and from 9.4° to 25.0°C, respectively; and 3) mesopelagic-II species (bigeye threshers), which spent 95% of their time at temperatures from 6.7° to 21.2°C. Distinct thermal niche partitioning based on body size and latitude was also evident within epipelagic species.

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