New Study Reveals Movements of Basking Sharks (Cetorhinus maximus) in the Eastern North Pacific Using Satellite Telemetry

A team of researchers have released a study that aims to fill in the gaps in our knowledge about basking sharks (Cetorhinus maximus) in the Eastern Pacific Ocean. Four sharks were tagged off the coast of California using pop-off satellite archival tags from 2010 to 2011.

basking_shark
Oceana (photographer). (n.d.). Retrieved from https://oceana.org/marine-life/sharks-rays/basking-shark

 

During this time, each shark’s habitat use and geographic movement was monitored and recorded by the tag between 9 and 240 days until the tags popped off and transmitted their data back via satellite.  During the summer months, these sharks moved north along the Californian coast line from San Diego towards Monterey. The two sharks that recorded data into the fall months (180 and 240 days) each took different routes once offshore. One moved south towards the Baja Peninsula, while the other headed west towards Hawaii.

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Figure 1. Geographic movements of three basking sharks tagged off California. Movements of (A) shark A over 51 days, (B) sharks D over 180 days, and (C) shark C over 240 days including tagging (green triangle) and tag pop-up (red triangle) location, GPS locations and light-based geolocation estimates. Gray shows error estimates around the light-based geolocation estimates. Inset shows an expansion of the movements of shark D off Central CA. The dashed line indicated to path of the acoustic survey. (Dewar, et al, 2018)

 

These sharks also displayed a range in vertical habitat use both among and within individuals. Nearshore, the sharks spent most of their time in a mixed layer within the water column. However, they did spend some time below this mixed layer in cooler waters as well. As the sharks moved offshore, their vertical position in the water column depended on their location. The shark that moved west towards Hawaii had a distinct diel pattern, spending days between 450-470 m and rising at night to 250-300 m. This shark spent almost no time at the surface. In contrast, the shark that moved south to Baja did spend progressively more time in deeper waters than when this shark was nearshore. However, this individual still made daily trips to the surface even when offshore. Most likely these shifts in vertical habitat use are linked to prey availability during their migration.

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Figure 6. Time series data showing diel patterns in vertical movements. Time series data showing (A) the temperature and depth data for a representative day for shark C when offshore with the inset showing the temperature profile, and (B) all depth data for shark C over the final 2 months. The darker gray indicates local nighttime and the light gray the range of time for sunrise and sunset over the period the data were obtained (Dewar, et al, 2018).

 

The IUCN Red List currently has basking sharks listed as vulnerable (Fowler, 2015). While some populations in the Atlantic Ocean have seen been slowly recovery from over fishing, the fate of the Pacific Ocean populations is not so certain. Once they were abundant all throughout the Pacific, however the harpooning fishery industry off Japan decimated populations until in the 1980’s there were only a few sightings per year. Today, the finning industry still threatens these sharks. One fin can be valued at more that $50,000 USD, which is a lot of incentive for targeting these incredible animals.

BaskingSharkMarch2016
Lin, V. (Photographer). (2016). 6m, over 1 tonne basking shark was caught in a set net at Yokosuka, Kanagawa on 29th of March [Digital Image]. Retrieved from http://elasmollet.org/
The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

Remember you can make a difference for marine ecosystems by contacting your Congress man or woman and telling them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics.

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Featured Image Source

Alamy (Photographer). (n.d.). Basking Shark [Digital Image]. Retrieved from https://www.telegraph.co.uk/news/newstopics/howaboutthat/11712525/Sunbathers-flee-beach-after-shark-spotted-in-Kent.html

Literature Cited

Dewar, H., Wilson, S. G., Hyde, J. R., Snodgrass, O. E., Leising, A., Lam, C. H., … & Kohin, S. (2018). Basking Shark (Cetorhinus maximus) Movements in the Eastern North Pacific Determined using Satellite Telemetry. Frontiers in Marine Science5, 163.

Fowler, S.L. 2005. Cetorhinus maximus. The IUCN Red List of Threatened Species 2005: e.T4292A10763893. http://dx.doi.org/10.2305/IUCN.UK.2005.RLTS.T4292A10763893.en

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