Seals use signals from acoustic tags to find fish

michelleMichelle Jewell is a Zoologist specialized in predator/prey behaivour and the Scientific Communicator for EDNA Interactive.  She has spent the past 4 years studying the behaviour of white sharks and Cape fur seals at Geyser Rock, ‘Shark Alley’, South Africa.  

Anyone who has worked with seals knows they are crafty critters that will always find the easiest way to eat fish.  Take the rise and fall of acoustic deterrent devices in aquaculture farms that were designed to scare away seals and other predators.  They had limited success and resident predators habituated to the sound when they realized there was no immediate danger.  These devices have been shown to actually attract more predators over time, especially passing pinnipeds.

Scientists have used acoustic tags to monitor fish movements since the 1950s, and hundreds of species have been implanted with these tags (a ‘few’ studies listed here) throughout rivers, lakes, estuaries, and the ocean.  Could marine mammals associate tag signals with food and do they do this in the wild?  A recent laboratory study from St. Andrews (free to download here) answers the first half of this question, showing that grey seals Halichoerus grypus  were able to use the signals transmitted from Vemco V9–2H tags to identify boxes that contained fish.

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Agents of seal: stealthy seals use subsurface structures to sneak by sharks

michelleMichelle Jewell is a Zoologist specialized in predator/prey behaivour and the Scientific Communicator for EDNA Interactive.  She has spent the past 4 years studying the behaviour of white sharks and Cape fur seals at Geyser Rock, ‘Shark Alley’, South Africa.  

Predators are highly influential in ecosystems because of the many top-down effects they can have.  The most obvious and direct way predators influence an ecosystem is by eating and reducing the number of prey animals in the system, but another equally important way is the indirect influence they have on the behaviour of prey animals.

If you have avoided parking on a risky-looking street, taken a different route between classes to avoid a bully, or abandoned a forest hike because of snapping twigs in the distance, you have been indirectly affected by perceived ‘predators’.  In the wild, prey animals will also change their behaviour when they perceive that predators are around, and these altered behaviours often influence other species, ultimately shaping the ecosystem.

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Great white shark movements at Geyser Rock

michelleMichelle Wcisel is a Zoologist specialized in predator/prey behaivour and the Scientific Communicator for EDNA Interactive.  She has spent the past 4 years studying the behaviour of white sharks and Cape fur seals at Geyser Rock, ‘Shark Alley’, South Africa.  

 

Animal movement is often shaped by natural barriers; a fish can’t leave the river it swims in, a tortoise is going to struggle to climb a cliff face, and a pangolin can’t swim across the sea.  These barriers come quite naturally to the animals, yet researchers have often struggled to account for these constraints in movement analysis, particularly when it comes to estimating home range (or ‘Utilization Distributions’, UDs).  Unfortunately, the few solutions that have attempted to account for barriers are often incredibly complicated without providing much improvement overall, so previous studies have been forced to simply ‘clip out’ the parts of the estimate that extend over these inconceivable areas (i.e. Heupel et al. 2004; Hammerschlag et al. 2012; Jewell et al. 2012).

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Shark of Darkness: Wrath of Submarine is a fake documentary

Shark Week has done it again with their Shark of Darkness nonsense.  This show goes after everyone, from the whale watching industry, to shark cage diving, to South Africa as a country, and literally broke my heart to watch.

As always, a brief and vague disclaimer appears after all the credits have rolled.

As always, a brief and vague disclaimer appears during the show.

The fake-u-mentary is supposedly based in Hout Bay, but continually shows a map of Dyer Island and Geyser Rock and refers to Shark Alley that are all in Gansbaai, ~100km to the east.  So why would they say Hout Bay?  If you google “boat capsized in Hout Bay”, you will find that there was a boat which capsized outside of Hout Bay in 2012, killing 2 passengers onboard.  This boat was capsized by heavy swell in the middle of the day and had nothing to do with a shark, let alone a mythical one.  So I can only assume that Discovery Channel chose to include this very real tragedy in order to somehow legitimize their fake-u-mentary.  This is horribly insensitive. Read More