Thomas A. Jefferson

U.S. Department of Commerce, Washington, Washington, D.C., United States

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Publications (99)179.84 Total impact

  • Thomas A. Jefferson · Brian D. Smith
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    ABSTRACT: The IUCN Red List designation of the Indo-Pacific humpback dolphin (Sousa chinensis) is re-assessed in light of its newly recognized taxonomic status (it has recently been separated into three species) and findings that humpback dolphins along the coast of Bangladesh, and possibly eastern India, are phylogenetically distinct from other members of the Sousa genus. Sousa chinensis is found in Southeast/South Asia (in both the Indian and Pacific oceans), from at least the southeastern Bay of Bengal east to central China, and then south to the Indo-Malay Archipelago. There are no global population estimates, and the sum of available abundance estimates add up to about 5700 individuals, although only a portion of the range has been covered by surveys. This species occurs in shallow (<30m deep), coastal waters of the tropics and subtropics, and feeds mainly on small fishes. It has a similar reproductive biology to other large dolphins, occurs mostly in small groups, and generally has individual movements of about 50-200km2. Major threats throughout the range include entanglement in fishing nets (primarily gillnets) and habitat destruction/degradation, although in some more industrialized areas, vessel traffic, and environmental contamination from organochlorines are also serious issues. Conservation management is largely lacking in most parts of the species' range, although there has been significant (though still inadequate) attention in some parts of China (e.g. Hong Kong and adjacent areas, and Taiwan). Much greater efforts are needed toward conservation of Indo-Pacific humpback dolphins to stop apparent declines, and to lower the species' extinction risk. Sousa chinensis meets the IUCN Red List requirements for Vulnerable (under criteria A4cd), with fisheries bycatch and habitat loss/degradation being the main pervasive threats.
    No preview · Article · Sep 2015 · Advances in Marine Biology
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    Thomas A. Jefferson · Mari A. Smultea · Cathy Bacon

    Full-text · Dataset · Jun 2015
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    Mari A. Smultea · Thomas A. Jefferson · Sarah Courbis · David Steckler

    Full-text · Conference Paper · Apr 2015
  • Thomas A. Jefferson · Howard C. Rosenbaum

    No preview · Article · Apr 2015 · Marine Mammal Science
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    Meggie Moore · Thomas Jefferson · Mari Smultea · Cathy Bacon · Vanessa James
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    ABSTRACT: We conducted 18 aerial surveys for marine mammals in the Southern California Bight around San Clemente Island from October 2008 to July 2013. Data were collected to obtain density and abundance estimates, as well as focal behavioral observations of marine mammals. The primary platform used was a Partenavia P68-C or P68-OBS (glass-nosed) high-wing, twin-engine airplane. A total of 76,989 km were flown with 2,510 marine mammal groups sighted. Nineteen marine mammal species were identified. Density and abundance estimates were made using line-transect methods and DISTANCE 6.0 software. Due to limited sample sizes for some species, sightings were pooled to provide four detection function estimates for baleen whales, large delphinids, small delphinids, and California sea lions. Estimates were limited to species observed at least 20 times during line-transect effort. For the May-October warm-water season, the estimated average numbers of individuals present were as follows: short-beaked common dolphins (8,520), long-beaked common dolphins (3,314), Risso’s dolphins (1,450), California sea lions (818), bottlenose dolphins (496), fin whales (137), and gray whales (6). During the November-April cold-water season, estimates were: short-beaked common dolphins (15,955), longbeaked common dolphins (6,440), California sea lions (1,454), Risso’s dolphins (993), bottlenose dolphins (290), gray whales (221), and fin whales (140). Several other species were observed for which sightings were too few to estimate numbers present and/or were seen only off effort: blue, Bryde’s, minke, humpback, sperm, Cuvier’s beaked, and killer whales; Pacific white-sided and northern right whale dolphins; Dall’s porpoise; and northern elephant and harbor seals.
    Full-text · Conference Paper · Jan 2015
  • Ranil P. Nanayakkara · Tharaka Kusuminda · Thomas A. Jefferson
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    ABSTRACT: Until the last few years, the only records of Indian Ocean humpback dolphins (Sousa plumbea) in Sri Lanka were a small number of older stranding records and one unconfirmed sighting, but repeated verified sightings have been made since the early 2000s in the Puttalam Lagoon area of northwestern Sri Lanka. To determine dolphin status and distribution patterns, we conducted monthly surveys of the lagoon from July 2010 to June 2011 and sighted humpback dolphins in the lagoon in every month of the year. Repeated sightings of the same six individuals were made; and in March 2011, one of these humpback dolphins was killed by dynamite fishing. It appears that the population is very small, possibly now consisting only of these five individuals, and is resident in the lagoon. Although it is likely the species was more widespread and abundant in the past, it appears that Puttalam Lagoon may be the only location where this species persists in Sri Lanka at present. Additional research is needed to investigate possible mixing with populations in India, and urgent conservation measures are recommended to ensure the long-term survival of this enigmatic species in Sri Lanka.
    No preview · Article · Nov 2014 · Aquatic Mammals
  • Thomas A. Jefferson · Howard C. Rosenbaum
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    ABSTRACT: The taxonomy of the humpback dolphin genus Sousa has been controversial and unsettled for centuries, but recent work indicates that there are several valid species. A review of multiple lines of evidence from skeletal morphology, external morphology, coloration, molecular genetics, and biogeography, in combination provides strong support for the recognition of four species of Sousa. These include S. teuszii (Kükenthal, 1892), a species with uniform gray coloration and a prominent dorsal hump, which is found in the Atlantic Ocean off West Africa. The species S. plumbea (G. Cuvier, 1829) has similar external appearance to S. teuszii, but has a more pointed dorsal fin. It occurs in the Indian Ocean from South Africa to Myanmar (Burma). The original taxon, S. chinensis (Osbeck, 1765), is reserved for the species that has a larger dorsal fin with no prominent hump, and largely white adult coloration. It ranges from eastern India to central China and throughout Southeast Asia. Finally, we describe a new species of Sousa, the Australian humpback dolphin, which occurs in the waters of the Sahul Shelf from northern Australia to southern New Guinea. It has a lower dorsal fin, more extensive dark color on the body, and a dorsal “cape.” It is separated from the Indo-Pacific humpback dolphin by a wide distributional gap that coincides with Wallace's Line.
    No preview · Article · Jul 2014 · Marine Mammal Science
  • Thomas A. Jefferson

    No preview · Article · Apr 2014 · Marine Mammal Science

  • No preview · Technical Report · Jan 2014
  • Mari Smultea · Cathy Bacon · Thomas Jefferson

    No preview · Technical Report · Jan 2014
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    Thomas A. Jefferson · Mari Smultea · Cathy Bacon
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    ABSTRACT: We conducted 18 aerial surveys for marine mammals in the Southern California Bight in the vicinity of San Clemente Island from October 2008 to July 2013. Data were collected to obtain density and abundance estimates, as well as focal behavioral observations of marine mammals. The primary platform used was a Partenavia P68-C or P68-OBS (glass-nosed) high-wing, twin-engine airplane. A total of 76,989 km were flown with 2,510 marine mammal groups sighted. Nineteen marine mammal species were identified. Density and abundance estimates were made using line-transect methods and DISTANCE 6.0 software. Due to limited sample sizes for some species, sightings were pooled to provide 4 detection function estimates for baleen whales, large delphinids, small delphinids, and California sea lions. Estimates were limited to species observed at least 20 times during line-transect effort. For the May-October warm-water season, the estimated average numbers of individuals present (and coefficient of variation) were as follows: short-beaked common dolphins (8,520, CV=54%), long-beaked common dolphins (3,314, CV=54%), Risso’s dolphins (1,450, CV=66%), California sea lions (818, CV=40%), bottlenose dolphins (496, CV=87%), fin whales (137, CV=49%), and gray whales (6, CV=13%). During the November-April cold-water season, estimates were: short-beaked common dolphins (15,955, CV=51%), long-beaked common dolphins (6,440, CV=51%), California sea lions (1,454, CV=53%), Risso’s dolphins (993, CV=51%), bottlenose dolphins (290, CV=61%), gray whales (221, CV=53%), and fin whales (140, CV=33%). Several other species were observed for which sightings were too few to estimate numbers present and/or were seen only off effort: blue, Bryde’s, minke, humpback, sperm, Cuvier’s beaked, and killer whales; Pacific white-sided and northern right whale dolphins; Dall’s porpoise; and northern elephant and harbor seals
    Full-text · Article · Jan 2014
  • Thomas A. Jefferson · Mari A. Smultea · Cathy Bacon
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    ABSTRACT: We conducted 18 aerial surveys for marine mammals in the Southern California Bight in the vicinity of San Clemente Island from October 2008 to July 2013. Data were collected to obtain density and abundance estimates, as well as focal behavioral observations of marine mammals. The primary platform used was a Partenavia P68-C or P68-OBS (glass-nosed) high-wing, twin-engine airplane. A total of 76,989 km were flown with 2,510 marine mammal groups sighted. Nineteen marine mammal species were identified. Density and abundance estimates were made using line-transect methods and DISTANCE 6.0 software. Due to limited sample sizes for some species, sightings were pooled to provide 4 detection function estimates for baleen whales, large delphinids, small delphinids, and California sea lions. Estimates were limited to species observed at least 20 times during line-transect effort. For the May-October warm-water season, the estimated average numbers of individuals present (and coefficient of variation) were as follows: short-beaked common dolphins (8,520, CV=54%), long-beaked common dolphins (3,314, CV=54%), Risso’s dolphins (1,450, CV=66%), California sea lions (818, CV=40%), bottlenose dolphins (496, CV=87%), fin whales (137, CV=49%), and gray whales (6, CV=13%). During the November-April cold-water season, estimates were: short-beaked common dolphins (15,955, CV=51%), long-beaked common dolphins (6,440, CV=51%), California sea lions (1,454, CV=53%), Risso’s dolphins (993, CV=51%), bottlenose dolphins (290, CV=61%), gray whales (221, CV=53%), and fin whales (140, CV=33%). Several other species were observed for which sightings were too few to estimate numbers present and/or were seen only off effort: blue, Bryde’s, minke, humpback, sperm, Cuvier’s beaked, and killer whales; Pacific white-sided and northern right whale dolphins; Dall’s porpoise; and northern elephant and harbor seals.
    No preview · Article · Jan 2014
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    ABSTRACT: 1. The global range of Risso's dolphin Grampus griseus is not well known, and there has been confusion in the literature as to whether the species has a broad, circumglobal range or only occurs along continental margins. 2. To clarify the species' distribution and habitat preferences, we compiled and reviewed all available (published and unpublished) records of sightings and cap-tures of this species for the past 62 years (1950–2012, n = 8068 records). Stranding records were not included. 3. The results showed that the species has a range that extends across ocean basins and spans between at least 64°N and 46°S, and is apparently absent from high-latitude polar waters. Although Risso's dolphins occur in all habitats from coastal to oceanic, they show a strong range-wide preference for mid-temperate waters of the continental shelf and slope between 30° and 45° latitude. 4. Although a number of misconceptions about the distributional ecology of Risso's dolphin have existed, this analysis showed that it is a widespread species. It strongly favours temperate waters and prefers continental shelf and slope waters to oceanic depths. These habitat preferences appear to hold throughout much or all of the species' range.
    Full-text · Article · Jan 2014 · Mammal Review
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    ABSTRACT: Biological and fisheries data were analysed to assess the impact of fisheries mortality on a Critically Endangered subpopulation of <100 humpback dolphins Sousa chinensis in the eastern Taiwan Strait (ETS). Substantial interactions between ETS S. chinensis (hereafter Sousa) and fishing gear are known to cause dolphin mortality. In 2009, a total of 6318 motorised fishing vessels were operating from ports within Sousa habitats. An average of 32 fishing craft per kilo- metre was observed along a 200 km stretch of Sousa habitat. Based on a photo-identification cat- alogue, >30% of the ETS Sousa subpopulation exhibited injuries caused by fishing gear. Three individuals were photographed with fishing gear attached to their bodies, and 1 dolphin was found dead with fresh injuries caused by fishing gear. To ensure recovery of ETS Sousa, mortality due to human causes should be reduced to <1 individual every 7 yr. Fisheries bycatch is the most serious threat to these dolphins and needs to be eliminated as soon as possible to avoid extinction. Preventing the use of trammel nets, other gillnets and trawling throughout their habitat would be the single most effective conservation measure for ETS Sousa in the short term. Other fishing methods are available, and using the most selective, sustainable fishing methods available will benefit not only dolphins but also fish stocks, seabirds and other species, as well as the fishing industry, which depends on these species for its long-term viability. However, in the short term, there are costs associated with switching to more selective fishing gear.
    Full-text · Article · Dec 2013 · Endangered Species Research
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    ABSTRACT: The conservation of humpback dolphins, distributed in coastal waters of the Indo-West Pacific and eastern Atlantic Oceans, has been hindered by a lack of understanding about the number of species in the genus (Sousa) and their population structure. To address this issue, we present a combined analysis of genetic and morphologic data collected from beach-cast, remote-biopsied and museum specimens from throughout the known Sousa range. We extracted genetic sequence data from 235 samples from extant populations and explored the mitochondrial control region and four nuclear introns through phylogenetic, population-level and population aggregation frameworks. In addition, 180 cranial specimens from the same geographical regions allowed comparisons of 24 morphological characters through multivariate analyses. The genetic and morphological data showed significant and concordant patterns of geographical segregation, which are typical for the kind of demographic isolation displayed by species units, across the Sousa genus distribution range. Based on our combined genetic and morphological analyses, there is convincing evidence for at least four species within the genus (S. teuszii in the Atlantic off West Africa, S. plumbea in the central and western Indian Ocean, S. chinensis in the eastern Indian and West Pacific Oceans, and a new as-yet-unnamed species off northern Australia).
    Full-text · Article · Dec 2013 · Molecular Ecology
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    Thomas Jefferson · Mari Smultea · Cathy Bacon
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    ABSTRACT: We conducted 18 aerial surveys in the marine waters around San Clemente Island, California, from October 2008 to July 2013, to obtain both observations of marine mammal behavior and data suitable for developing marine mammal density estimates. The primary platform used was a Partenavia P68-C or P68-OBS (glass-nosed) high-wing, twin-engine airplane. Density and abundance estimates were made using line-transect methods and the software DISTANCE 6.0. During these surveys, 19 species of marine mammals were sighted. Due to limited sample sizes for some species, sightings were pooled to provide four estimates of the detection function for baleen whales, large delphinids, small delphinids, and California sea lions. Estimates of density and abundance were made for species observed a minimum of eight times during line-transect effort. For the warm-water season (May through October) in 2008–2013, the estimated average numbers of individuals present (in descending order) were 8,520 short-beaked common dolphins (Delphinus delphis), 3,314 long-beaked common dolphins (D. capensis), 1,450 Risso’s dolphins (Grampus griseus), 1,150 northern right whale dolphins (Lissodelphis borealis), 818 California sea lions (Zalophus californianus), 496 bottlenose dolphins (Tursiops truncatus), 207 Pacific white-sided dolphins (Lagenorhynchus obliquidens), 137 fin whales (Balaenoptera physalus), 30 blue whales (B. musculus), 7 humpback whales (Megaptera novaeangliae), and 6 gray whales (Eschrichtius robustus). During the cold-water season (November through April), the estimates were 15,955 short-beaked common dolphins, 6,440 long-beaked common dolphins, 2,956 northern right whale dolphins, 1,454 California sea lions, 993 Risso’s dolphins, 290 bottlenose dolphins, 221 gray whales, 140 fin whales, 53 Pacific white-sided dolphins, and 22 humpback whales. Blue whales were not observed during the cold-water season, and gray whales were only seen once during the warm-water season. Several other species were observed for which sightings were too few to estimate numbers present and/or were seen only off effort: minke whale (B. acutorostrata, n = 9 on-effort groups), northern elephant seal (Mirounga angustirostris, n = 5), Dall’s porpoise (Phocoenoides dalli, n = 3), Cuvier’s beaked whale (Ziphiius cavirostris, n = 2), killer whale (Orcinus orca, n = 2), harbor seal (Phoca vitulina, n = 1), Bryde’s whale (B. edeni, n = 1), and sperm whale (Physeter macrocephalus, n = 1).
    Full-text · Technical Report · Oct 2013
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    ABSTRACT: Although some progress has been made towards increasing what is known about this species since the previous 1996 listing as Data Deficient, the information is still insufficient for evaluation against the criteria, particularly with regard to population size, trends, and threats. There is reason to suspect that the species overall, and at least the South American subspecies, is continuing to decline in portions of its range. Further research is needed, especially to address the question of population structure within Argentina. In the future, separate assessments of the two recognized subspecies should be a priority. Similarly, population structure within South America may justify separate assessments of geographical populations. Further research is also needed to provide current abundance estimates for a larger proportion of the species’ total range, and quantitative information on recent and current human-caused mortality. http://www.iucnredlist.org/details/full/4159/0
    Full-text · Chapter · Jan 2013
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    ABSTRACT: There is inadequate information to assess this species against the criteria and therefore it must remain listed as Data Deficient pending a credible estimate of population size and/or better information on population trend. Heaviside’s Dolphins have a limited range and are not particularly common anywhere. Several threats have been identified, including entanglement in a variety of inshore fishing gear (e.g., beach seines, purse seines, trawls, and gillnets). http://www.iucnredlist.org/details/full/4161/0
    No preview · Chapter · Jan 2013
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    ABSTRACT: This species is considered to be Endangered A4d due to an ongoing and projected decline of greater than 50% over 3 generations (approx. 39 years, Slooten et al. 2000) considering both the past and the future. It is also important to consider that although its extent of occurrence and area of occupancy likely exceed the thresholds for criteria B1, B2 and D2, Hector’s Dolphin has the most limited range of any marine cetacean other than the Vaquita (Phocoena sinus). In a population viability analysis, the estimated rate of decline was 74% over 3 generations where the time period under consideration was from 1970-2009 (Slooten 2007). The main cause of population decline is ongoing bycatch in fisheries. http://www.iucnredlist.org/details/full/4162/0
    Full-text · Chapter · Jan 2013
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    ABSTRACT: The species was previously listed as Vulnerable but is now considered Data Deficient due to the limited amount of current information available on threats, ecology, and population numbers and trends. In areas where botos have been studied, they appear widespread and relatively abundant. However, these areas represent only a small proportion of the species’ total range and often are places where the dolphins have some protection. Therefore, the impressions from those areas may not be representative. Also, much of the information summarized in this assessment is dated and may no longer be valid. http://www.iucnredlist.org/details/full/10831/0
    No preview · Chapter · Jan 2013

Publication Stats

2k Citations
179.84 Total Impact Points

Institutions

  • 2011
    • U.S. Department of Commerce
      Washington, Washington, D.C., United States
  • 2004-2009
    • Southwest Fisheries Science Center
      لا هویا, California, United States
    • National Marine Fisheries Service
      Silver Spring, Maryland, United States
    • National Oceanic and Atmospheric Administration
      • Southwest Fisheries Science Center
      Boulder, Colorado, United States
  • 2000-2007
    • NOAA Fisheries
      Silver Spring, Maryland, United States
  • 2006
    • Moss Landing Marine Labs
      • Moss Landing Marine Laboratories
      California City, California, United States
    • Texas A&M University
      • Department of Wildlife and Fisheries Sciences
      College Station, Texas, United States