Browsing by Author "Hammerschlag N"

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    Residency and movement patterns of an apex predatory shark (Galeocerdo cuvier) at the Galapagos Marine Reserve.
    (2017) Acuña-Marrero D; Smith ANH; Hammerschlag N; Hearn A; Anderson MJ; Calich H; Pawley MDM; Fischer C; Salinas-de-León P
    The potential effectiveness of marine protected areas (MPAs) as a conservation tool for large sharks has been questioned due to the limited spatial extent of most MPAs in contrast to the complex life history and high mobility of many sharks. Here we evaluated the movement dynamics of a highly migratory apex predatory shark (tiger shark Galeocerdo cuvier) at the Galapagos Marine Reserve (GMR). Using data from satellite tracking passive acoustic telemetry, and stereo baited remote underwater video, we estimated residency, activity spaces, site fidelity, distributional abundances and migration patterns from the GMR and in relation to nesting beaches of green sea turtles (Chelonia mydas), a seasonally abundant and predictable prey source for large tiger sharks. Tiger sharks exhibited a high degree of philopatry, with 93% of the total satellite-tracked time across all individuals occurring within the GMR. Large sharks (> 200 cm TL) concentrated their movements in front of the two most important green sea turtle-nesting beaches in the GMR, visiting them on a daily basis during nocturnal hours. In contrast, small sharks (< 200 cm TL) rarely visited turtle-nesting areas and displayed diurnal presence at a third location where only immature sharks were found. Small and some large individuals remained in the three study areas even outside of the turtle-nesting season. Only two sharks were satellite-tracked outside of the GMR, and following long-distance migrations, both individuals returned to turtle-nesting beaches at the subsequent turtle-nesting season. The spatial patterns of residency and site fidelity of tiger sharks suggest that the presence of a predictable source of prey and suitable habitats might reduce the spatial extent of this large shark that is highly migratory in other parts of its range. This highly philopatric behaviour enhances the potential effectiveness of the GMR for their protection.
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    Vulnerability of marine megafauna to global at-sea anthropogenic threats
    (Wiley Periodicals LLC on behalf of Society for Conservation Biology, 2025-11-14) VanCompernolle M; Morris J; Calich HJ; Rodríguez JP; Marley SA; Pearce JR; Abrahms B; Abrantes K; Afonso AS; Aguilar A; Agyekumhene A; Akamatsu T; Åkesson S; Alawa NG; Alfaro-Shigueto J; Anderson RC; Anker-Nilssen T; Arata JA; Araujo G; Arostegui MC; Arrizabalaga H; Arrowsmith LM; Auger-Méthé M; Avila IC; Bailleul F; Barker J; Barlow DR; Barnett A; Barrios-Garrido H; Baylis AMM; Bearzi G; Bejder L; Belda EJ; Benson SR; Berumen ML; Bestley S; Bezerra NPA; Blaison AV; Boehme L; Bograd SJ; Abimbola BD; Bond ME; Borrell A; Bouchet PJ; Boveng P; Braulik G; Braun CD; Brodie S; Bugoni L; Bustamante C; Campana SE; Cárdenas-Alayza S; Carmichael RH; Carroll G; Carter MID; Ceia FR; Cerchio S; Ferreira LC; Chambault P; Chapple TK; Charvet P; Chavez EJ; Chevallier D; Chiaradia A; Chilvers BL; Cimino MA; Clark BL; Clarke CR; Clay TA; Cloyed CS; Cochran JEM; Collins T; Cortes E; Cuevas E; Curnick DJ; Dann P; de Bruyn PJN; de Vos A; Derville S; Dias MP; Diaz-Lopez B; Dodge KL; Dove ADM; Doyle TK; Drymon JM; Dudgeon CL; Dutton PH; Ellenberg U; Elwen SH; Emmerson L; Eniang EA; Espinoza M; Esteban N; Mul E; Fadely BS; Fayet AL; Feare C; Ferguson SH; Feyrer LJ; Finucci B; Florko KRN; Fontes J; Fortuna CM; Fossette S; Fouda L; Frere E; Fuentes MMPB; Gallagher AJ; Borboroglu PG; Garrigue C; Gauffier P; Gennari E; Genov T; Germanov ES; Giménez J; Godfrey MH; Godley BJ; Goldsworthy SD; Gollock M; González Carman V; Gownaris NJ; Grecian WJ; Guzman HM; Hamann M; Hammerschlag N; Hansen ES; Harris MP; Hastie G; Haulsee DE; Hazen EL; Heide-Jørgensen MP; Hieb EE; Higdon JW; Hindell MA; Hinke JT; Hoenner X; Hofmeyr GJG; Holmes BJ; Hoyt E; Huckstadt LA; Hussey NE; Huveneers C; Irvine LG; Jabado RW; Jacoby DMP; Jaeger A; Jagielski PM; Jessopp M; Jewell OJD; Jiménez Alvarado D; Jordan LKB; Jorgensen SJ; Kahn B; Karamanlidis AA; Kato A; Keith-Diagne LW; Kiani MS; Kiszka JJ; Kock AA; Kopf RK; Kuhn C; Kyne PM; Laidre KL; Lana FO; Lander ME; Le Corre M; Lee OA; Leeney RH; Levengood AL; Levenson JJ; Libertelli M; Liu K-M; Lopez Mendilaharsu M; Loveridge A; Lowe CG; Lynch HJ; Macena BCL; Mackay AI
    Marine megafauna species are affected by a wide range of anthropogenic threats. To evaluate the risk of such threats, species’ vulnerability to each threat must first be determined. We build on the existing threats classification scheme and ranking system of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species by assessing the vulnerability of 256 marine megafauna species to 23 at-sea threats. The threats we considered included individual fishing gear types, climate-change-related subthreats not previously assessed, and threats associated with coastal impacts and maritime disturbances. Our ratings resulted in 70 species having high vulnerability (v > 0.778 out of 1) to at least 1 threat, primarily drifting longlines, temperature extremes, or fixed gear. These 3 threats were also considered to have the most severe effects (i.e., steepest population declines). Overall, temperature extremes and plastics and other solid waste were rated as affecting the largest proportion of populations. Penguins, pinnipeds, and polar bears had the highest vulnerability to temperature extremes. Bony fishes had the highest vulnerability to drifting longlines and plastics and other solid waste; pelagic cetaceans to 4 maritime disturbance threats; elasmobranchs to 5 fishing threats; and flying birds to drifting longlines and 2 maritime disturbance threats. Sirenians and turtles had the highest vulnerability to at least one threat from all 4 categories. Despite not necessarily having severe effects for most taxonomic groups, temperature extremes were rated among the top threats for all taxa except bony fishes. The vulnerability scores we provide are an important first step in estimating the risk of threats to marine megafauna. Importantly, they help differentiate scope from severity, which is key to identifying threats that should be prioritized for mitigation.