Are Tiger Sharks Reef Sharks or Pelagic Sharks? Movements of Tiger Sharks in the Western North Atlantic

The tiger shark (Galeocerdo cuvier) is a large, far-ranging species that exhibits a variety of movement patterns depending on location and season. These sharks are managed by NMFS as part of the “large coastal” species complex under the Atlantic Highly Migratory Species Fishery Management Plan, but are occasionally observed far at sea and caught in pelagic fisheries. To investigate movements of tiger sharks, we tagged 26 individuals in Bermuda in late summer of 2009 and 2010 with fin-mounted “spot” satellite transmitters. Although a number of sharks made fairly rapid (~2 weeks) and straight-line moves from Bermuda to the Bahamas, other sharks followed meandering paths eventually reaching the Bahamas after several months. Several smaller individuals remained in Bermuda over the winter. Some sharks spent the winter months moving within relatively small, near shore areas within the Bahamas, and subsequently moved north into pelagic waters where they remained during summer months. Other sharks left the Bahamas a short time after arrival, moving into pelagic waters during winter months. Several individuals tracked over consecutive winters (\u3e19 months) occupied similar wintering areas within the Bahamas. North-south seasonal movements for many sharks appeared to be related to water temperature, with the majority of time spent at 24-28oC. Most sharks demonstrated the ability to seamlessly shift between pelagic and insular habitats spending approximately equal time in both environments. Although movements vary substantially among individuals, tiger sharks demonstrate high mobility trophically connecting widespread and disparate marine ecosystems in the Western North Atlantic

Migratory patterns and habitat use of the sand tiger shark (Carcharias taurus) in the western North Atlantic

Globally, population declines for the sand tiger shark (Carcharias taurus) have resulted in calls for informed management of populations, including in the western North Atlantic, where they have been listed as a Species of Concern by NOAA Fisheries. However, information on movements and habitat use, critical for informed management of this sand tiger population, is limited. We investigated horizontal and vertical movements of sand tigers along the US east coast using pop-up archival satellite transmitters, supplemented by acoustic telemetry. Thirteen sand tiger sharks were tagged with satellite and acoustic transmitters in Delaware Bay in late August and early September 2008. Ten of these provided satellite data for horizontal tracks using a Kalman filter. Males left Delaware Bay in autumn and moved south along the continental shelf until reaching waters off North Carolina. Females moved east to waters near the edge of the continental slope. Average depth of males was positively correlated with shark size. All individuals spent at least 95% of their time in waters of 17-23;C. Sand tiger sharks appear most susceptible to fisheries in November and December. Slight expansion of the boundaries and timing of an existing shark-directed bottom longline area closure would likely reduce by-catch of sand tiger sharks and enhance recovery of the stock

Migratory Patterns and Habitat Use of Sand Tiger Sharks (Carcharias taurus) in the Northwest Atlantic

Though there is concern over declines in sand tigers (Carcharias taurus) in the Northwest Atlantic Ocean, details of their habitat use and movement patterns in the open ocean are limited. We report on the vertical and horizontal movements of sand tigers off the US east coast using archival pop-up satellite transmitters. Transmitters were deployed on 13 sand tigers (168 - 232 cm TL) in Delaware Bay in late summer 2008. Duration of tracks ranged from 12-154 days (x ̄=105), allowing reconstruction of 12 horizontal tracks using light-level data and a Kalman filter state-space model. Seven of the males exhibited directed movements south along the US east coast to waters off North Carolina, whereas all three females initially moved eastward into deeper offshore waters and remained largely in waters off New Jersey to Virginia. While in Delaware Bay, sand tigers spent the majority of their time at depths of less than 10 m and at 19-22oC. During their migration south, males occupied deeper water, primarily 20-80 m (max depth 188 m), and upon arrival in North Carolina waters in late 2008 or early 2009, some males moved into shallower water. Female sharks generally inhabited shallower water during their migrations, remaining predominantly at depths \u3c 50 m (maximum depth 92 m). Water temperatures occupied by sharks ranged from 13-26oC, with females averaging 21-23oC and males 19-24.5oC. These initial results suggest possible differences in the movement behavior of male and female sand tigers, but need confirmation by tracking more animals of each gender