30 porbeagle sharks tagged in DFO/OTN population survey

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The porbeagle is a fast-moving, torpedo-shaped species of mackerel shark found in cold and temperate marine waters both in the North Atlantic and Southern Hemisphere. Despite its popularity among commercial and recreational fishers, little is known about the species.

Heather Bowlby, research lead for the Canadian Atlantic Shark Research Laboratory at Fisheries and Oceans Canada (DFO) is working on the first comprehensive evaluation of this species since 2012.

OTN has collaborated with Bowlby’s team on a number of projects over the past ten years. Since this partnership began, OTN and DFO have tagged many species of shark including dogfish, Greenland sharks as well as blue and porbeagle sharks.

A newly tagged porbeagle shark is prepped for release.

This year, Bowlby’s primary research focus is to conduct a dedicated pelagic shark (species residing neither close to the bottom nor near the shore of the ocean) survey along the eastern Scotian Shelf and Grand Bank. The mission is a collaborative effort between the commercial swordfishing industry, several DFO departments and regions as well as several research groups, including OTN.

In support of this undertaking, OTN has provided 30 Vemco V13 acoustic tags to Bowlby’s team, which were externally anchored on porbeagle sharks at survey stations distributed throughout the Scotian Shelf. This brings the total number of porbeagles tagged through OTN/DFO to 45. The region was chosen because it has a comparatively high abundance of acoustic monitoring infrastructure deployed and maintained by OTN, making it an ideal location to tag and track sharks.

“Currently, there is a strong need to understand abundance, trends and distribution patterns of porbeagle sharks,” said Bowlby. “Since the closure of the commercial fishery in 2013, gathering this information has been difficult.”

The main objective of the collaborative tagging is to gather data on the distribution of porbeagle sharks. When tag detections are added to other sources of data, it may be possible to describe habitat use and generate maps on areas of porbeagle concentration. This type of information will be used to inform the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) and Species at Risk Public Registry processes. Additionally, this data is of high value to the International Commission for the Conservation of Atlantic Tunas because it assists in international fisheries assessment and management.

“This tagging is a continuation of the collaborative project between OTN and DFO from 2013 that focused on porbeagle and blue sharks,” said Brendal Townsend, OTN’s Senior Project Manager. “It’s important for us to understand the population and whereabouts of threatened species like the porbeagle shark in the Northwest Atlantic because it’s the first step in protecting them.”

       

Data are very limited for porbeagle sharks yet it is critical to be able to evaluate population trajectory and any changes in distribution, particularly because COSEWIC lists the population as Endangered. This is concerning given the fact that sharks are ecosystem regulators. There’s evidence that removing sharks and other top predators from the oceans creates a trickle-down effect that negatively affects entire ocean ecosystems — which, in turn, affects humans.

“Many Nova Scotians don’t realize that there are quite a few shark species off of our coast,” Bowlby explained. “They play an important role in our local ecosystems and they have cultural importance to our fishing communities. Conservation of the endangered porbeagle shark population in the Northwest Atlantic will partially depend on the public’s engagement and interest in these amazing creatures.”

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