Shark aggregation in coastal waters of British Columbia

Abstract

A concentration of pelagic sharks was observed in an area of western Queen Charlotte Sound, British Columbia, during systematic shipboard line-transect surveys conducted (2004 to 2006) for marine mammals throughout coastal waters of British Columbia. Surveys allowed only brief observations of sharks at the surface, providing limited opportunity to confirm species identity. Observers agreed, however, that salmon sharks Lamna ditropis (Lamnidae) were most common, followed by blue sharks Prionace glauca (Carcharhinidae). Both conventional and model-based distance sampling statistical methods produced large abundance estimates (~20 000 sharks of all species combined) concentrated within a hotspot encompassing ~10% of the survey region. Neither statistical method accounted for submerged animals, thereby underestimating abundance. Sightings were made in summer, corresponding with southern movement of pregnant salmon sharks from Alaska. The previously undocumented high density of these pelagic sharks in this location has implications for understanding at-sea mortality of returning Pacific salmon Oncorhynchus spp. (Salmonidae) and for assessing conservation status of sharks in Canada and beyond. We recommend that a dedicated Canada-US sightings and biological sampling programme be considered, perhaps under the UN Transboundary Species Fishery programme.

Spatial ecology of blue shark and shortfin mako in southern Peru: local abundance, habitat preferences and implications for conservation

“…Hypotheses for the importance of shark aggregation include reproductive and feeding opportunities. Comparable with other species (Williams et al 2010), the tendency of many pelagic sharks to aggregate makes them especially vulnerable to overexploitation (Litvinov 2006, Dulvy et al 2008. In the present study, the greatest abundance of P. glauca and I. oxyrinchus was found far offshore (>150 km from the shore) in the southwest corner of the study area where there was a statistically significant clustering of elevated CPUE (hot spots), corroborating high catch rates in the study area identified by onboard observers (Doherty et al 2014).…”

“…Many shark species, however, aggregate for foraging or reproduction purposes, and hot spots in abundance and aggregations of pelagic sharks have been found in the Northeast Pacific (Williams et al 2010) and the North Atlantic (Vandeperre et al 2014, Queiroz et al 2016). The present study adds to these findings by describing hot spots in the Southeast Pacific.…”

Shark Predation on Migrating Adult American Eels (Anguilla rostrata) in the Gulf of St. Lawrence

“…The congeneric salmon shark ( Lamna nasus ) that inhabits the subarctic and temperate waters of the North Pacific is also known to regularly feed on migrating anadromous salmonids. Indeed, salmon sharks appear to aggregate during the summer months at specific locations along migration routes and in bays near the spawning grounds of returning adult Pacific salmon [38] , [39] . During this time, the stomach contents of sampled sharks at these locations revealed that adult salmon were indeed the main prey [38] .…”

Pliocene stratigraphic paleobiology in Tuscany and the fossil record of marine megafauna

“…Time-series analyses carried out on modern whale-fall communities at slope depths (range 382-2893 m: Lundsen et al, 2010) suggests that carcasses up to 17 m are rapidly degraded, with the deepest whale carcasses disappearing after only seven years of exposure on the seafloor. Larger skeletons may persist on deeper settings for decades, but if Cockcroft et al, 1989;Compagno, 2002;Boldrocchi et al, 2017 Carcharocles megalodon Cockcroft et al, 1989, Cortés, 1999 Carcharhinus limbatus Cockcroft et al, 1989;Cortés, 1999 (continued on next page) Cockcroft et al, 1989;Cortés, 1999;Boldrocchi et al, 2017 Prionace Cortés, 1999;Greenpeace International, 2009;Williams et al, 2010;Queiroz et al, 2012;Barría et al, 2015 Sphyrna not buried, they also ultimately undergo complete destruction. Although environmental forcing triggered by higher temperatures, active currents and sediment transport, clearly plays a role, a specialised whale-fall fauna rapidly consumes both soft and mineralised tissues.…”