Posted by: Rob Viens | February 16, 2012

St. Paul’s Rocks II: Sharks, Boobies, and Bugs

February 16th was the day Darwin set foot on St. Paul’s Rocks for a few hours.  Yesterday I touched on the physical aspects of the island. Today I will hit on (quite literally) the biological.

QSL Card of St Paul’s rocks:St. Paul's Rocks

(A) Terrestrial ecology

First, Darwin (correctly) noted that the islets themselves are void of plant life (including lichens). Not much more to discuss here.

Second, in just a few hours he had the zoology of the islands virtually figured out. Compare the two statements regarding the inhabitants of the island below – the first is from and 1983 paper on the ecology of the islands, the second from Darwin:

“The terrestrial fauna is dominated by three species of sea-bird and a land crab. Also reported from on land are a few species of insects, ticks and spiders, an endemic pseudoscorpion, and a centipede; the majority of these species are associated with the seabirds.” (The ecology of Saint Paul’s Rocks (1983) Alasdair Edwards & Roger Lubbock – Journal of Zoology)

“We found on St. Paul’s only two kinds of birds—the booby and the noddy…a large and active crab (Graspus)… a fly (Olfersia) living on the booby, and a tick which must have come here as a parasite on the birds; a small brown moth, belonging to a genus that feeds on feathers; a beetle (Quedius) and a woodlouse from beneath the dung; and lastly, numerous spiders, which I suppose prey on these small attendants and scavengers of the waterfowl.” (Voyage of the Beagle)

You missed the centipede and pseudoscorpian, but otherwise, spot on Charles!

To be fair, the “three species of sea birds” referred to in the 1983 paper include a brown booby (Sula leucogaster) and two noddies – a brown noddy (Anous stolidus), and black noddy (Anous minutus).  So Darwin was also technically correct about the bird species present, as well.

Species of sea bird species found on St. Paul’s Rocks (from Wikipedia commons):

Boobies and Noddies

Boobies and noddies are both types of sea birds found throughout the world’s oceans. On islands, such as these, they tend to nest on the ground (because (a) there are no major predators to worry about and (b) well, there are no trees anyway). As Darwin points out, boobies are a type of gannet (family Sulidae) and noddies are a type of term (family Sternidae).  One of the interesting things about the Sulidae is that they are a type of fishing bird that “plunge-dive” for fish. Check out this link to see 1922 footage of brown boobies on St Paul’s Rocks (from a film about the Shackleton Antarctic Expedition).  (The second half of the footage shows the nesting boobies.) If you want to spy on another type of gannet, try this live web cam from Iceland that is aimed at a living gannet colony (just remember it is about 8 hours ahead of Pacific Standard Time). Kinda cool.

Yet again Darwin made an astute ecological observation that went against the common believes of his time.  And as so true with Darwin, he was correct:

“The often repeated description of the stately palm and other noble tropical plants, then birds, and lastly man, taking possession of the coral islets as soon as formed, in the Pacific, is probably not quite correct; I fear it destroys the poetry of this story, that feather and dirt-feeding and parasitic insects and spiders should be the first inhabitants of newly formed oceanic land.” (Voyage of the Beagle)

(As a brief aside, it is virtually impossible to read a Wikipedia page about a plant or animal that does not talk about its evolutionary links with other species.  Darwin is everywhere!)

(B) Marine ecology (well one part of it anyway)

As the crew fished for provisions in the rich waters around the islands, sharks tried to steal their harvest.  Fitzroy states:

“While our party were scrambling over the rock, a determined struggle was going on in the water, between the boats’ crews and sharks. Numbers of fine fish, like the groupars (or garoupas) of the Bermuda Islands, bit eagerly at baited hooks put overboard by the men; but as soon as a fish was caught, a rush of voracious sharks was made at him, and notwithstanding blows of oars and boat hooks, the ravenous monsters could not be deterred from seizing and taking away more than half the fish that were hooked.” (Fitzroy’s Narrative, Feb 16)

Surveys from the 1970’s report that the waters around the archipelago are home to one of the densest populations of sharks in the Atlantic – the most common variety being the Blacktip Sharks (Carcharhinus limbatus).  As these sharks like to feed on fish in shallow waters, the islands provide one of the few feeding grounds for 100’s of km. No wonder they hang out there.  Recent studies suggest the population in this region is decline and I’m sad to say that the Blacktail sharks are considered endangered today.

Blacktail Shark from the SharkInfo web site:

Blacktail shark

(C) Bird “Hunting”

Even though he had heard of birds that had no fear of humans before, even Darwin was amazed at how unconcerned the birds where when the crew arrived, stating:

“We were surrounded on every side by birds, so unaccustomed to men that they would not move.” (Feb 15/16)

I know that 19th century sailors can be a rough bunch and that times are different now, but the descriptions of the glee with which the crew lays waste to the island’s birds is a little hard to swallow. The crew quickly took advantage of the situation, wasting no time to start a bloodbath:

“The first impulse of our invaders of this bird-covered rock, was to lay about them like schoolboys; even the geological hammer at last became a missile. “Lend me the hammer?” asked one. “No, no,” replied the owner, “you’ll break the handle;” but hardly had he said so, when, overcome by the novelty of the scene, and the example of those around him, away went the hammer, with all the force of his own right-arm.” (Fitzroy’s Narrative, Feb 16)

In the end, between the hunting and fishing, the 74-member crew had happily caught enough food to provide some variety to everyone’s diet:

“When the boats returned they were deeply laden with birds and fish, both welcome to those who had been living on salt provisions.” (Fitzroy’s Narrative, Feb 16)

OK – I can understand that these were hungry sailors, sick of eating stale biscuits and salted meat.  But we now know that this sort of decimation of a small ecosystem can have dramatic impacts.  For example, overkills such as these led to the extinction of several island bird species, including the famed dodo and great auk. It is hard to imagine the man who taught us to understand where species came from, could play a role in their loss.  Alas.

The islets today are an “environmentally protected area” under the jurisdiction of Brazil and visitors are very limited.

Stay tuned –  on the 17th Darwin finally crosses the line! (RJV)

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Responses

  1. What would you say, with our present rate of global warming? Will St. Peter and Paul be baptized by the rising ocean? The sharks that eat fish will still be happy, but those that gather for the glut of newly flying (crashing) young birds
    will just have to go somewhere else to feast! Will you be commenting on the possible big tidal wave when the west side of La Palma (the Canary Islands) slides into the ocean? I’m looking forward to that blog. What is it about our species and a few others that I know of, in that we will kill wantonly when given the chance. Example, the buffalo that were shot by the thousands for so called “sport”. The weasel is another species that will kill much more than it needs, seemingly just for the “sport” of it! Pat

    • I agree that sea level rise related to global climate change will have an impact on the islands. At 18 meters, they are high enough that the water level rise won’t completely inundate the land (even at the higher end of realistic predictions). But even a small rise in sea level will significantly increase the erosion of the islets, so they could be “eaten away” more quickly by the waves. One abstract I read even suggested that erosion may already be increasing. The one variable I don’t know is if (and how much) they continue to be uplifted.

      I mentioned the tsunami potential briefly when the Beagle is in the Canaries, but since Darwin didn’t stay there, I never really delved into it. We’ll see – I may get a chance again – I know at some point he discusses earthquakes in South America.

  2. […] (3) Strangely Darwin crossed out “Sulas”, which are the boobies, yet modern sources suggest they do nest on the islands.  Boobies were also common on St. Paul’s Rocks – were, alas, more gleeful bird-bashing occurred (for more on those birds see St. Paul’ s Rocks I). […]

  3. […] the “unexplored” shores of St. Paul’s Rocks (see St. Paul’s Rocks I and St. Paul’s Rocks II). Darwin got to be in the first boat to go ashore and explore.  McCormick got stuck on the second […]


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