The Canadian Field-Naturalist Volume 130, Number 1 January –March 2 016 Influence of Environmental Variables on the Diel Movements of the Greenland Shark ( Somniosus microcephalus ) in the St. Lawrence Estuary JEffrEy J. GaLLant 1, 5, M arco a. roDríGuEz 2,MIchaEL J. W. S tokESbury 3, and chrIS harVEy -c Lark 4 1Greenland Shark and Elasmobranch Education and research Group, 1990 Saint-Jacques Street, Drummondville, Quebec J2b 7V5 canada 2Département des sciences de l’environnement, université du Québec à trois-rivières, 3351 boulevard des forges, trois-rivières, Quebec G9a 5h7 canada 3Department of biology, acadia university, 33 university avenue, Wolfville, nova Scotia b4P 2r6 canada 4university Department of animal care, Dalhousie university, halifax, nova Scotia b3h 4r2 canada 5corresponding author: [email protected] Gallant, Jeffrey J., Marco a. rodríguez, Michael J. W. Stokesbury, and chris harvey-clark. 2016. Influence of environmental variables on the diel movements of the Greenland Shark ( Somniosus microcephalus ) in the St. Lawrence Estuary. canadian field-naturalist 130(1): 1–14. the geographic distribution of the Greenland Shark ( Somniosus microcephalus ) extends from the arctic ocean to the north atlantic ocean. however, little is known about the habitat of this species, as it is generally found at great depths or in the high arctic. In the St. Lawrence Estuary, Greenland Sharks undertake diel vertical movements into shallow water (≤ 30 m), but the reasons for these movements are unknown. to test the hypothesis that environmental variables drive the movements of this shark in the St. Lawrence Estuary, eight Greenland Sharks were tagged with acoustic telemetry transmitters during the summer of 2005. three environmental factors, temperature, light, and tides, were associated with their movements. Movement patterns indicate a preference for deep, cold water during daylight hours and shallow, warmer water during the night. ascending into shallow water mostly coincided with darkness and high tide. this improved understanding of the spatio-temporal distribution of the Greenland Shark will allow for assessment of the risk to these sharks from commercial fisheries, as occurs in the Greenland halibut ( Reinhardtius hippoglossoides ) longline fishery. In addition, temperature-driven behavioural patterns may change as the thermal structure of the water column shifts due to global warming. key Words: acoustic telemetry; depth; habitat; light; St. Lawrence river; temperature; tide; shark; Greenland Shark; Somniosus microcephalus Introduction ature preference within the narrow range observed in the Greenland Shark ( Somniosus microcephalus ) is the arctic ocean at Svalbard, norway ( fisk et al. 2012 ), the largest arctic fish, reaching lengths up to 730 cm and baffin Island, canada (Skomal and benz 2004), (compagno 1984). Despite its size and widespread dis - thermal preference may exist in the shallower waters of tribution, extending over the waters adjoining at least the St. Lawrence Estuary, where temperatures fluctuate six countries in the north atlantic and arctic oceans by as much as 23°c (Stokesbury et al. 2005; JG, unpub - (yano et al. 2007; chernova et al. 2015), the Greenland lished data). Shark remains largely unknown. Little is known about Sightings of Greenland Sharks at shallow depths are its life cycle, habitat use, and the environmental factors not limited to the St. Lawrence. the species has been that influence its movements. Most studies have focused harvested by harpoon at the surface on baffin Island on its geographic distribution, diet, and contaminant or (beck and Mansfield 1969), and the Inuit from cumber - parasite loads (Macneil et al. 2012). land Sound, nunavut, occasionally observe these sharks because of the paucity of visual observations in sur - from the surface as they swim along the sea floor (Idrobo face waters until recently, the Greenland Shark was long 2008). however, this behaviour is associated with hunt - considered a primarily cold water bathybenthic species, ing activities when marine mammals are being butchered found at depths of up to 2200 m (herdendorf and berra on the shore, which is not the case in the St. Lawrence 1995). In the St. Lawrence Estuary, Greenland Sharks since the beluga ( Delphinapterus leucas ) fishery in undertake diel vertical movements into shallow depths Quebec was terminated in 1960. natural encounters (≤ 30 m) (Stokesbury et al. 2005), but the reasons for with scuba divers have also taken place in the Sague - these movements are unknown. although more recent nay fjord, Quebec (harvey-clark et al. 2005), and at studies indicate that Greenland Sharks show no temper - Qaanaaq, Greenland (JG, unpublished data) . A contribution towards the cost of this publication has been provided by the Thomas Manning Memorial Fund of the Ottawa Field-Naturalist’s Club. 1 ©The Ottawa Field-Naturalists’ Club (2016) 2 thE canaDIan fIELD -n aturaLISt Vol. 130 the observed diel movements of the Greenland Stokesbury et al. 2005; campana et al. 2013) point to Shark are not unique for a shark of its size and north - conflicting diel movement patterns, and Stokesbury et ern distribution. a close relative, the Pacific Sleeper al. (2005) observed Greenland Sharks swimming most - Shark ( Somniosus pacificus ), travels mainly below the ly close to the bottom rather than ascending vertically. photic zone during daylight hours and approaches the In the present study, we tested the hypothesis that surface at night (hulbert et al. 2006). the Sixgill Shark environmental variables drive the movements of Green - (Hexanchus griseus ), another benthic species of com - land Shark in the St. Lawrence Estuary. to this end, we parable size found in cold water, has also been associat - tagged eight Greenland Sharks with acoustic transmit - ed with nocturnal tides but at greater depths (andrews ters equipped with depth and temperature sensors and et al. 2009). It remains to be determined whether Green - tracked their movements by telemetry during the sum - land Sharks respond to the same environmental stimuli mer of 2005. as these two boreal deepwater species. Several shark species follow circadian rhythms, re - Study Area maining in deep water during the day and then ascend - Greenland Sharks frequent four bays on the north ing through the water column to shallower depths at shore of the St. Lawrence Estuary in the region of baie- night: blue Shark ( Prionace glauca ; carey and Scha - comeau, Quebec, canada (figure 1). these boreal bays rold 1990), bigeye thresher ( Alopias superciliosus ; are characterized by a seasonally dynamic littoral envi - nakano et al. 2003; Weng and block 2004), caribbean ronment offering a wide variety of known prey species reef Shark ( Carcharhinus perezii ; chapman et al. of the Greenland Shark including fish, crusta ceans, mol - 2007), Mako Shark ( Isurus oxyrinchus ; klimley et al. luscs, and marine mammals. baie des anglais (sta - 2002), Megamouth Shark ( Megachasma pelagios ; nel - tion 1; 49.268°n, 68.127°W), the largest of the four son et al. 1997), Sixgill Shark (andrews et al. 2009), bays, is 4.4 km long and 4.0 km wide with a maxi - and the Small-Spotted catshark ( Scyliorhinus canicula ; mum depth of 90 m. baie du Garde-feu (station 2; Sims et al. 2006). however, studies on other shark spe - 49.281°n, 68.051°W) is 1.0 km long by 0.5 km wide cies, including the Sixgill Shark (hulbert et al. 2006) with a maximum depth of 70 m. baie-Saint-Pancrace and the Greenland Shark (Skomal and benz 2004; (station 3; 49.287°n, 68.046°W) has the second largest fIGurE 1. Location of acoustic sampling stations in the St. Lawrence Estuary near baie-comeau, Quebec. circles indicate maximum range (600 m) of each receiver. 2016 GaLLant ET AL .: G rEEnLanD Shark DIEL MoVEMEntS 3 surface area and is also the narrowest bay (approxi - Environmental Data mately 1.5 km long by 0.25 km wide); its maximum online tidal data, obtained from fisheries and depth is also 70 m. baie du Loup Marin (station 4; oceans canada (station 2840, baie-comeau), com - 49.280°n, 68.009°W) is only 0.03 km long by 0.2 km prised two variables: high tide included data from 3 h wide. baie du Loup Marin is different from the other before and 3 h after high water, and low tide included bays because of its steep incline (≥ 40°) and depth data from 3 h before and 3 h after low water. this dis - (> 150 m). the three other bays are characterized by a tinction was made to create a time-buffer period and, more gradual incline (≤ 25°). all four bays open on the thus, make allowance for sharks adjusting to the water St. Lawrence Estuary, which is approximately 56 km movement of flow and ebb tides. wide at the city of baie-comeau. the maximum depth of Surface water temperatures were obtained from an the Laurentian channel, which lies at the centre of the Institut Maurice Lamontagne (IML, fisheries and estuary, is 350 m. oceans canada) thermograph network buoy off baie- comeau (49.202°n, 68.057°W). these data were used Methods to monitor temperature at 1 m depth throughout the Acoustic Telemetry study period. to record the movements of Greenland Sharks, we Light levels for the baie-comeau area were classi - deployed acoustic transmitter tags on eight sharks (un - fied as “night” or “day” based on hourly data from known sex, mean length 3 m) at station 3 on 18 and 19 Mobile Geographics LLc (tides.mobilegeographics. June 2005. to reduce the risk of injury to the sharks and com/locations/332.html). Lunar phases obtained from divers, no shark was captured or restrained. acoustic the national aeronautics and Space administration coded tags (V16 transmitters; Vemco, halifax, nova (http://eclipse.gsfc.nasa.gov/SkycaL/SkycaL.html) Scotia, canada) were attached to the sharks by a scuba were classified as “full moon” (7 days before to 7 days diver equipped with a hawaiian sling type spear.