Population density and abundance of basking sharks Cetorhinus maximus in the lower Bay of Fundy, Canada

Westgate, Andrew J.; Koopman, Heather N.; Siders, Zachary A.; Wong, Sarah N. P.; Ronconi, Robert A.

doi:10.3354/esr00567

Cited by 24 publications

(15 citation statements)

References 26 publications

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“…Aerial surveys based on the Bay of Fundy, Canada, estimated the total population size of eastern Canada as 6512 (CI: 4040-11886) 63 . In accordance with Hoelzel et al 21 (N e of 8200 animals worldwide, calculated from mitochondrial markers), and based on our microsatellite-derived N e estimates, the number of basking sharks in NEA waters are unlikely to exceed 10,000 individuals.…”

Section: Discussionmentioning

confidence: 99%

Spatio-temporal genetic tagging of a cosmopolitan planktivorous shark provides insight to gene flow, temporal variation and site-specific re-encounters

Lieber

Hall

Berrow

et al. 2020

Sci Rep

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Migratory movements in response to seasonal resources often influence population structure and dynamics. Yet in mobile marine predators, population genetic consequences of such repetitious behaviour remain inaccessible without comprehensive sampling strategies. Temporal genetic sampling of seasonally recurring aggregations of planktivorous basking sharks, Cetorhinus maximus, in the Northeast Atlantic (NEA) affords an opportunity to resolve individual re-encounters at key sites with population connectivity and patterns of relatedness. Genetic tagging (19 microsatellites) revealed 18% of re-sampled individuals in the NEA demonstrated inter/multi-annual site-specific re-encounters. High genetic connectivity and migration between aggregation sites indicate the Irish Sea as an important movement corridor, with a contemporary effective population estimate (N e) of 382 (CI = 241-830). We contrast the prevailing view of high gene flow across oceanic regions with evidence of population structure within the NEA, with early-season sharks off southwest Ireland possibly representing genetically distinct migrants. Finally, we found basking sharks surfacing together in the NEA are on

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Section: Discussionmentioning

confidence: 99%

Spatio-temporal genetic tagging of a cosmopolitan planktivorous shark provides insight to gene flow, temporal variation and site-specific re-encounters

Lieber

Hall

Berrow

et al. 2020

Sci Rep

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“…With Secchi depth as the primary means of comparing water clarity between the bay and ocean strata, we used data on percent correct detection as a guideline in assigning criteria for shallow, moderate, and deep detection depth ranges within which observers could detect turtles. Other surveys have used similar methods with animalshaped Secchi disks (Westgate et al 2014, Fuentes et al 2015.…”

Section: Detection Trialsmentioning

confidence: 99%

Loggerhead turtle Caretta caretta density and abundance in Chesapeake Bay and the temperate ocean waters of the southern portion of the Mid-Atlantic Bight

Barco¹,

Burt²,

DiGiovanni³

et al. 2018

Endang. Species. Res.

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We conducted aerial surveys of sea turtles in 2011 and 2012, incorporating corrections for perception and availability bias in Chesapeake Bay and near-shore continental shelf waters of the Mid-Atlantic Bight off the US states of Virginia and Maryland. Results of these surveys and ancillary research to determine surface times for loggerhead turtles provide us with a new baseline population estimate for turtles in the region. Prior surveys were conducted in Chesapeake Bay in the mid-1980s and early 2000s, and in ocean waters in the late 1970s and early 1980s. Although comparison of density estimates not corrected for availability between prior surveys and this effort suggests that the population of sea turtles, especially loggerhead turtles, is higher than previous estimates, differences between surveys may be the result of survey methodologies and cannot be assumed to be true changes in density. Surface time for availability corrections was calculated using dive summaries from satellite telemetry on 27 loggerhead turtles tracked between 2011 and 2015. We calculated stratified seasonal availability corrections for bay and ocean waters based on assumed differences in turtle behavior and water clarity between the 2 habitats. For each habitat, we provided seasonal corrections for 3 detection depth bins (shallow, moderate, and deep) to account for differences in sub-surface detection ranges. Differences and trends toward differences among availability corrections underscore the need to better understand the many variables that affect surface time for sea turtles in temperate waters, and the effect that availability has on abundance and density estimates.

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“…Furthermore, population size within New Zealand is likely to be <10,000 mature individuals, with a projected continuing decline over three generations (Criterion C) based upon estimates of global population size and trend (e.g. Westgate, Koopman, Siders, Wong, & Ronconi, ).…”

Section: Resultsmentioning

confidence: 99%

The extinction risk of New Zealand chondrichthyans

Finucci

Duffy²,

Francis

et al. 2019

Aquatic Conservation

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1. The national extinction risk of 103 New Zealand chondrichthyans (sharks, rays, and chimaeras),~10% of the global chondrichthyan fauna, was evaluated for the first time using the International Union for Conservation of Nature Red List of Threatened Species Categories and Criteria. Across 32 families, 103 species were assessed.2. New Zealand holds a high degree of species endemism (20%) with deepwater species dominating the fauna (77%). Sharks were the most speciose group with 68 species (66%), followed by 24 rays (23%), and 11 chimaeras (10%).3. Most species were assessed as Least Concern (60%, 62 species) or Data Deficient (32%, 33 species), with four (3.8%) species listed as Near Threatened and four (3.8%) in a threatened category (Vulnerable, Endangered, Critically Endangered).Threatened species are all oceanic pelagic, of which two are only visitors to New Zealand waters, and their status the result of broader regional declines.4. These results are in stark contrast to other recent regional assessments in Europe and the Arabian Sea and adjacent areas, where up to half of species were listed in a threatened category. However, given New Zealand's extensive deepwater fishing effort and rapid collapses of deepwater chondrichthyan fisheries elsewhere, it is possible that New Zealand populations of many deepwater species are the remnants of previously reduced populations that are now at a low, yet stable level.Ongoing species-level catch monitoring will be required to ensure these species do not become threatened. Recommendations for future research and conservation efforts include resolvingtaxonomic uncertainties, understanding habitat use, and increasing regional collaborations to better understand the effects of fishing on wider-ranging species.

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Population density and abundance of basking sharks Cetorhinus maximus in the lower Bay of Fundy, Canada

Cited by 24 publications

References 26 publications

Spatio-temporal genetic tagging of a cosmopolitan planktivorous shark provides insight to gene flow, temporal variation and site-specific re-encounters

Spatio-temporal genetic tagging of a cosmopolitan planktivorous shark provides insight to gene flow, temporal variation and site-specific re-encounters

Loggerhead turtle Caretta caretta density and abundance in Chesapeake Bay and the temperate ocean waters of the southern portion of the Mid-Atlantic Bight

The extinction risk of New Zealand chondrichthyans

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