Porpoise Killing Seals…Dramatic New Behaviour!

Scientists have discovered through DNA analysis that harbour porpoises (Phocoena phocoena) that have washed up severely mutilated and dead along the Dutch as well as the Belgian and northern France coastline beaches with an unknown cause of death and mutilation were actually attacked by grey seals (Halichoerus grypus). This is a new behaviour for the normally fish eating mammals.

Grey Seal. Image via www.theanimalfiles.com

Grey Seal. Image via http://www.theanimalfiles.com

Two different papers came out this past month (Leopold et al and Jauniaux et al) confirming this behaviour in the North Sea though DNA analysis (as well as a Note in Marine Ecology Progress Series on the ability to extract usable DNA from bite wounds). By collecting swab samples from bite marks on washed up harbour porpoises scientist were able to confirm that the injuries and death had been inflicted by Grey Seals.  Along the Dutch coastline 721 of 1,081 stranded porpoises were examined by Leopold et al between 2003 and 2013 of these at least 17% were subject to attack by grey seals. If we take into account that individuals with larger wounds would have sunk without recovery and that some porpoises may have escaped attack and later died from wounds this number may be much higher and mean that seal attacks are a significant contributor to harbour porpoise death in the North Sea alongside fisheries bycatch (approx. 20%), infectious disease (approx. 18%) and emaciation (approx. 14%).

The Jauniaux et al study along the French and Belgian coastline the scientists instead looked at five stranded porpoises with bite-like skin lesions which they swabbed for genetic material. They used these to confirm that even after several days in seawater genetic material of grey seals can be recovered from wounds and that bite-like skin lesions found on the dead porpoises is definitely the result of grey seals attacks. It was also found that some wounds (puncture) from grey seal attacks more readily retain genetic material than others (lacerations).

Scroll down to the bottom to see some of the rather graphic images of mutilated porpoises.

So how, when, why, where did this all start?!?

These are all very good questions and it will be hard for scientists to come up with a definitive answer for all of them. Leopold et al speculate that grey seals could have progressed from opportunistically feeding on harbour porpoise that had become entangled in fishing gear to full on attacking them as prey. The first confirmed victim of a grey seal attack washed up in 2003 and between then and 2013 the number of mutilated carcasses increased the authors states that there would

have to have been the perfect set of prerequisite in place for this to have come to be:

“These include sympatry of predator and prey, and possibly a high incidence of fisheries bycatch of the prey in static fishing nets to induce this behaviour.”

The study by Jauniaux et al even used the head of a recently dead grey seal to mimic bite-like skin injuries on a porpoise carcass to confirm seal DNA transfer. They believe that the injuries are likely from predation although cases of aggressive behaviour can not be ruled out for all attacks.

So what does this mean for harbour porpoises?

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What’s In A Vessel?

I have had the opportunity to work on a few different platforms during my brief time as a marine biologist and all of them have their ups and downs; with some I favour over others. In this post I thought I would go into a little detail on the pros and cons of different vessel sizes.

SEACR Vessel 2

View from a small vessel with a gray whale off the bow.

Small Vessel

From small vessels which vary between little “tinnys” to high powered ribs you are close to the water level and therefore closer to your species of study.

Using small vessels you can more easily manoeuvre in your study area and conduct focal follows, take samples (such as blow or faecal samples) and switch off your engines. They enable you to travel into areas that would otherwise be impossible with something larger including shallow channels, small inlets and waterways between islands.

View Off Small Vessel 2

View from the stern of a small boat.

They are cheaper to run and you don’t need to have a full crew and Captain, it can just be you (with the correct license and permits) alongside whomever you are collecting data with. You will cover a smaller area over a days research and are a slave to how much fuel you can carry and the weather conditions. If your vessel is completely open then you will also be personally impacted by the elements, think soggy trousers and chilly toes!

KPII - At Sea

Example of a large research vessel.

Large Vessel

From large vessels you are on a much higher platform. You can see a greater distance and can usually travel a lot further off shore, over a longer time period and in more adverse weather conditions.
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The WA Shark Cull Has To End

It was all over the news for a while and Facebook and probably your Twitter feed too. The Western Australia (WA) shark cull.

It all started because of a high number of shark attacks in quick succession in WA, causing the government to act quickly and rashly, imposing a trial lethal drum-line programme. Now after the end of the trial period (January 25th – April 30th 2014) the WA government are proposing to extend it to a 3-year lethal drum line programme. This time however they need to pass a federal environmental assessment unlike the trial which was granted temporary exemption under national environmental law because it was apparently deemed in the “national interest” of protecting public safety.

The outcomes from a similar 16 year lethal long-line programme operated in Hawaii (1959-1976) were ignored. At the end of the Hawaiian cull scientist concluded that it made no difference to shark attacks. It didn’t matter though as the Australian government decided to go ahead with the 13 week trial despite all the facts stacked against them. Using baited drum lines there were horrific scenes as sharks were baited and hooked then dragged out to sea alive and killed.

Over the 13 week trail 172 sharks were killed 163 of these were tiger sharks (Galeocerdo cuvier) while zero were white sharks (Carcharodon carchariasthe species believed to be those involved in the recent attacks.

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Somethings Going Right!

We do hear a lot about the negatives in conservation. What’s going wrong, which species are not recovering and how we are contributing to that! This is all very important, we need to share and publicise the areas that require our attention and need to be focused on.

However, in the news recently has been a brilliant success sorry and sometimes we need positives and successes to keep us going, to know that what we are doing works and that we are making a difference.

So this latest and greatest success story is that the North Atlantic right whale (Eubalaena glacialis). This whale is the most endangered of all the large or “great” whales (Blue, Fin, Sei, Bryde’s, Bowhead, Humpback, Gray, Minke, Sperm and Right Whales). Having been greatly impacted by whaling both historic and modern its numbers dwindled with the numbers of individuals in the population being as low as 300 when monitoring began over three decades ago.

Following the moratorium (1986) on whaling this species has been at risk from two main threats affecting its recovery. These are (1) Ship Strikes and (2) Entanglement in Fishing Gear. The Bay of Fundy, Canada and Cape Cod Bay, USA which are critical habitat areas for North Atlantic right whales are also where there exists a large risk from these two threats for this species.

North Atlantic Right Whale Skim Feeding (Photo Credit: NOAA/NEFSC)

The good news however is that now more than 500 individuals have been recorded in the latest census. This is absolutely amazing and a massive bounce back from being close to the brink of extinction.

How has this happened?
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