Habitat use and diel vertical migration of bigeye thresher shark: Overlap with pelagic longline fishing gear

Abstract

Pelagic longliners targeting swordfish and tunas in oceanic waters regularly capture sharks as bycatch, including currently protected species as the bigeye thresher, Alopias superciliosus. Fifteen bigeye threshers were tagged with pop-up satellite archival tags (PSATs) in 2012-2014 in the tropical northeast Atlantic, with successful transmissions received from 12 tags for a total of 907 tracking days. Marked diel vertical movements were recorded on all specimens, with most of the daytime spent in deeper colder water (mean depth = 353 m, SD = 73; mean temperature = 10.7 °C, SD = 1.8) and nighttime spent in warmer water closer to the surface (mean depth = 72 m, SD = 54; mean temperature = 21.9 °C, SD = 3.7). The operating depth of the pelagic longline gear was measured with Minilog Temperature and Depth Recorders (TDRs), and the overlap with habitat utilization was calculated. Overlap is taking place mainly during the night and is higher for juveniles. The results presented herein can be used as inputs for Ecological Risk Assessments for bigeye threshers captured in oceanic tuna fisheries, and serve as a basis for efficient management and conservation of this vulnerable shark species.

Migrations and habitat use of the smooth hammerhead shark (Sphyrna zygaena) in the Atlantic Ocean

“…The fishing sets were carried out following the general practices of the European shallow pelagic longline fleet that targets mainly swordfish, with gear setting typically starting in the late afternoon, and retrieval commencing at dawn of the next morning. Details of the fishing gear are described in Coelho et al [ 21 ], consisting of a standard US-style polyamide monofilament mainline, with five branch lines (~ 18 m long and with a J-style hook in the terminal tackle) between floats. Two different size options for the float line are typically used by this fleet: either 12 m or 16 m. Consequently, this variability of the fleet fishing strategy was considered in the study design, with the TDRs equally deployed on sections using both sizes of float lines.…”

Skating on thin ice: Identifying the need for species‐specific data and defined migration ecology of Rajidae spp.

“…Therefore, without a complete understanding of movement, the use of spatial and/or temporal closures may result in the inaccurate estimation of exploitation rates, considering that skates may cross management boundaries into areas of heightened fishing mortality (Hunter, Berry, Buckley, Stewart, & Metcalfe, ; Hunter et al., 2005a). In addition, although skates are considered benthic fishes, like other elasmobranchs, vertical ranging behaviours (as reviewed below) may make them vulnerable to fishing gears which operate at various depths within the water column and across continental shelves (Coelho, Fernandez‐Carvalho, & Santos, ).…”

Plasticity in the diel vertical movement of two pelagic predators (Prionace glauca and Alopias vulpinus) in the southeastern Indian Ocean

“…Normal DVM patterns were detected in the majority (83%) of behavioural sections in the present study. Diel vertical movement is common among large pelagic sharks and has been recorded in many species including Cetorhinus maximus (Shepard et al., ), Rhincodon typus (Brunnschweiler & Sims, ) , Lamna nasus (Francis, Holdsworth, & Block, ), A. superciliosus (Coelho et al., ), A. vulpinus (Cartamil, Wegner, Aalbers, et al., ), and P. glauca (Campana et al., ; Queiroz et al., ). Diel vertical movement of blue sharks has been hypothesised to be related to foraging, thermoregulation, predator avoidance, or orientation (Campana et al., ).…”

“…Normal DVM patterns were detected in the majority (83%) of behavioural sections in the present study. Diel vertical movement is common among large pelagic sharks and has been recorded in many species including Cetorhinus maximus (Shepard et al, 2006), Rhincodon typus (Brunnschweiler & Sims, 2011), Lamna nasus (Francis, Holdsworth, & Block, 2015), A. superciliosus (Coelho et al, 2015),…”

“…Movement patterns of sharks are important in understanding their ecology, refining assessments of fisheries encounterability, and developing bycatch mitigation measures (Cartamil, Wegner, Aalbers, et al, ; Coelho, Fernandez‐Carvalho, & Santos, ; Hobday et al, ; Musyl et al, ; Speed, Field, Meekan, & Bradshaw, ; Vaudo et al, ). For many marine species, vertical movement patterns have received less attention than those in the horizontal plane.…”