First Trip
I got back from my first trip on Friday but went away for the weekend, hence the delay in posting. The boat was really nice and the catches were generally interesting. I didn’t get much new stuff and as my camera broke early on I don’t have any photos really to show. However, I did get one animal whose rareness of appearance in catches meant I borrowed a camera to document its presence, and that’s what I wanted to write about here.
Before I start I want to preface this by saying that it is incredibly rare for boats around the Falklands to catch this animal. My boat has been fishing here for about 6 years and it’s the first one it’s ever had. No one else I’ve spoken to has had one, so while it’s really sad, it’s a rare event and should be taken as a chance event rather than an inevitable consequence of fishing.
So by now I’m sure you’re wondering what on earth I’m on about. I’m on about a sea lion (Otaria byronia). We were fishing in international waters well away from land which makes it even stranger. I was working in the factory when there was commotion around the fish bin (where the fish are stored after being emptied from the net but prior to processing). I saw something really large and dark and got excited thinking maybe it was a greenland shark but when I got closer I realised it wasn’t shark-like. It was pulled out and was told it was a ‘lobo de mar’ which didn’t mean anything to me. It was winched out onto the deck and I saw that it was a sea lion.
(I should state now that the red in the mouth is damage inflicted post mortem by one of the crew after the teeth as a souvenir). It was big (195 cm) and was a male. The power was palpable and I initially felt quite nervous walking around it as although I was sure it was dead, if it wasn’t then I was in trouble!
When I came to examine it properly I had a close look as it’s not often you get the chance to get so close to this type of animal. The ears were tiny, the flippers were huge and there were toe-nails which really surprised me!
I decided to have a look inside. I had debated for about an hour whether or not to – on the one hand it felt disrespectful to such an amazing animal, on the other it was dead and when do you ever get the opportunity to autopsy a sea lion? Science (and curiosity) won and one of the guys opened it up for me.
It’s the first time I’ve ever dealt with a mammal this size (the last time I dissected a mammal it was a rat the first year at Auckland) and I was surprised at how different it was to fish. Firstly, I’m used to the anus being about midway along the animal and it acts as a very good starting point when trying to get inside so when I saw a depression about halfway down the torso I assumed it was the anus only to realise it was a belly-button!
When it was cut open the first thing that was apparent was how human-like it was. The ribs (again something I’m not used to encountering) were really prominent, the lungs were huge, as was the liver, and the intestines were really long. Having a proper look required getting my hands dirty and it was then I had yet another shock – it was warm! The animal was well and truly dead but due to the fantastic insulation provided by the fur and blubber the head hadn’t yet dissipated. It was the first time I’ve ever felt warmth during a dissection and it was quite freaky!
Looking closely at the structure of the skin I saw there were layers. The top layer had the fur, then there was a layer of creamy-white blubber about an inch thick. Below that was a dark-red layer which, I later realised, was a layer that was extremely important for keeping the sea lion warm. It was a layer of blood vessels called the rete mirabile. This is a counter-current exchange system which is a posh way of saying that heat is prevented from reaching the outside. It’s a system which is extremely simple in theory but enables mammals (and birds and even a few large fish) to venture into temperatures far colder than they would otherwise be able to endure.
It’s such a cool system I’m going to try and explain it with the help of my lovely picture below. The blood comes from the ‘normal tissue’ which is found all around the animal and is full of blood vessels supplying tissues and organs. Some of the blood enters capillaries in the rete mirabile which is the last main area of tissue. If I remember correctly there are a few capillaries in the blubber to supply the skin holding the fur with blood but these are relatively insignificant compared to the number of capillaries in the rete mirabile. The capillaries run in parallel very close to each other and form loops. The blood enters a capillary at 100% of the body temperature of the animal. Due to its close proximity to the part of the capillary carrying blood back to the body and the fact that this blood is warmer than the blood re-entering the core, the heat is transferred. Not all of the heat is transferred immediately but as the blood travels towards the outer part of the region it transfers more and more of its heat. It can do this because there is always a temperature difference between the blood coming out of the core and the heat going in. This is known as a counter-current exchange system and means that the vast majority of the heat of the animal is trapped in the core and doesn’t reach the extremities. Combined with the blubber it means that a sea lion can dive in water only a few degrees above freezing and can survive in sub-zero temperatures on land.
As I mentioned, this counter-current exchange system is found in other animals besides mammals. Large sharks such as the great white have a similar system which is why they can survive in cold water outside the normal range for sharks; large tuna such as the bluefin also have it enabling them to dive to depths and survive in temperate waters. It’s also found in birds such as penguins which is why they can stand on ice without freezing to death – most of their body heat doesn’t reach their feet.
Hopefully this wasn’t too boring and the unfortunate and untimely demise of a magnificent specimen of a sea lion has provided some enlightenment of a little-known but valuable system.
Before I start I want to preface this by saying that it is incredibly rare for boats around the Falklands to catch this animal. My boat has been fishing here for about 6 years and it’s the first one it’s ever had. No one else I’ve spoken to has had one, so while it’s really sad, it’s a rare event and should be taken as a chance event rather than an inevitable consequence of fishing.
So by now I’m sure you’re wondering what on earth I’m on about. I’m on about a sea lion (Otaria byronia). We were fishing in international waters well away from land which makes it even stranger. I was working in the factory when there was commotion around the fish bin (where the fish are stored after being emptied from the net but prior to processing). I saw something really large and dark and got excited thinking maybe it was a greenland shark but when I got closer I realised it wasn’t shark-like. It was pulled out and was told it was a ‘lobo de mar’ which didn’t mean anything to me. It was winched out onto the deck and I saw that it was a sea lion.
(I should state now that the red in the mouth is damage inflicted post mortem by one of the crew after the teeth as a souvenir). It was big (195 cm) and was a male. The power was palpable and I initially felt quite nervous walking around it as although I was sure it was dead, if it wasn’t then I was in trouble!When I came to examine it properly I had a close look as it’s not often you get the chance to get so close to this type of animal. The ears were tiny, the flippers were huge and there were toe-nails which really surprised me!
I decided to have a look inside. I had debated for about an hour whether or not to – on the one hand it felt disrespectful to such an amazing animal, on the other it was dead and when do you ever get the opportunity to autopsy a sea lion? Science (and curiosity) won and one of the guys opened it up for me.It’s the first time I’ve ever dealt with a mammal this size (the last time I dissected a mammal it was a rat the first year at Auckland) and I was surprised at how different it was to fish. Firstly, I’m used to the anus being about midway along the animal and it acts as a very good starting point when trying to get inside so when I saw a depression about halfway down the torso I assumed it was the anus only to realise it was a belly-button!
When it was cut open the first thing that was apparent was how human-like it was. The ribs (again something I’m not used to encountering) were really prominent, the lungs were huge, as was the liver, and the intestines were really long. Having a proper look required getting my hands dirty and it was then I had yet another shock – it was warm! The animal was well and truly dead but due to the fantastic insulation provided by the fur and blubber the head hadn’t yet dissipated. It was the first time I’ve ever felt warmth during a dissection and it was quite freaky!
Looking closely at the structure of the skin I saw there were layers. The top layer had the fur, then there was a layer of creamy-white blubber about an inch thick. Below that was a dark-red layer which, I later realised, was a layer that was extremely important for keeping the sea lion warm. It was a layer of blood vessels called the rete mirabile. This is a counter-current exchange system which is a posh way of saying that heat is prevented from reaching the outside. It’s a system which is extremely simple in theory but enables mammals (and birds and even a few large fish) to venture into temperatures far colder than they would otherwise be able to endure.
It’s such a cool system I’m going to try and explain it with the help of my lovely picture below. The blood comes from the ‘normal tissue’ which is found all around the animal and is full of blood vessels supplying tissues and organs. Some of the blood enters capillaries in the rete mirabile which is the last main area of tissue. If I remember correctly there are a few capillaries in the blubber to supply the skin holding the fur with blood but these are relatively insignificant compared to the number of capillaries in the rete mirabile. The capillaries run in parallel very close to each other and form loops. The blood enters a capillary at 100% of the body temperature of the animal. Due to its close proximity to the part of the capillary carrying blood back to the body and the fact that this blood is warmer than the blood re-entering the core, the heat is transferred. Not all of the heat is transferred immediately but as the blood travels towards the outer part of the region it transfers more and more of its heat. It can do this because there is always a temperature difference between the blood coming out of the core and the heat going in. This is known as a counter-current exchange system and means that the vast majority of the heat of the animal is trapped in the core and doesn’t reach the extremities. Combined with the blubber it means that a sea lion can dive in water only a few degrees above freezing and can survive in sub-zero temperatures on land.
As I mentioned, this counter-current exchange system is found in other animals besides mammals. Large sharks such as the great white have a similar system which is why they can survive in cold water outside the normal range for sharks; large tuna such as the bluefin also have it enabling them to dive to depths and survive in temperate waters. It’s also found in birds such as penguins which is why they can stand on ice without freezing to death – most of their body heat doesn’t reach their feet.Hopefully this wasn’t too boring and the unfortunate and untimely demise of a magnificent specimen of a sea lion has provided some enlightenment of a little-known but valuable system.
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