Secrets of the deep - Test 1

C1 Advanced · Gapped Text · Cambridge English Advanced 1, Cambridge University Press

You are going to read a magazine article about whale sharks. Six paragraphs have been removed from the article. Choose from the paragraphs A-G the one which fits each gap (1–6). There is one extra paragraph which you do not need to use.

Secrets of the deep

Until recently, little was known about the movements of the whale shark. But a pioneering project is shedding new light on this ocean giant. Project scientist Jonathan Green reports.

There may be a number of explanations: the sharks might have rubbed up against rocks, or the tags may have been ripped off by associated species, such as silky sharks, that interact with them for prey. Having begun with a 1.8-metre tether, we shortened this to 1.5 metres, which seemed to be more effective.

After three months, all the sharks that had retained their tags proceeded to head south. They converged on three mountain chains that run westwards from the edge of Peru's continental shelf. There, one by one, they shed their tags and continued on to destinations unknown.

However, it wasn't until we overlaid them onto a map of the sea floor that we saw that these movements were apparently in response to geological features deep in the ocean that the sharks couldn't possibly see. It became clear that they must somehow be using faults, fissures and plate boundaries. But how?

After all, the marine environment, in comparison to that on land, has few apparent points of reference. The waters are often murky and the maximum penetration of light only extends into the upper levels. So how do marine creatures navigate over long distances?

We undertook one of the most ambitious whale shark programmes to date. The fieldwork was carried out in three 15-day sorties.

The frequency of transmissions from the tags depended on the behaviour of the individual sharks. Some spent a lot of time on or near the surface, and their tags reported on a regular basis. Others, such as the single male we tagged, spent a great deal of the time diving – for six weeks we didn't receive a single transmission.

If spotted at the same location at a later date, or a different location, the shark was 'recaptured' on a database, which stores photos of whale sharks from around the globe, thus providing details of their movements geographically and over time.

That, among other things, was what The Galapagos Whale Shark Project was attempting to find out. Established to study the population of sharks that visits the islands each year, the primary aim of the research was to find out more about whale shark movements on a local scale.

This involved two main processes. To begin with, we had to be able to identify individual sharks. We used a modified version of photo software initially developed for the mapping of stars and deep-space objects. This worked because the characteristic white spots of the whale shark resemble the human fingerprint in that each pattern is individually unique. By running photographs of the sharks' sides through the software, we could catalogue the patterns of spots, and figure out which shark was which.

We also attached tags to the sharks to track their movements. This was done by inserting a small dart through the thick skin into a fatty layer beneath using a pneumatic spear gun and then tethering the tags with a piece of steel cable. They were intended to be towed alongside or above the dorsal fin in order to break the surface and transmit data by satellite. But getting the tags to stay on was easier said than done. For reasons unknown, some came off in less than 24 hours.

The sharks used common departure routes soon after we had tagged them. They headed due north, following a series of sea features until they reached the Galapagos Rift Valley system. This zone is where the divergence of two oceanic plates has created a rift system similar to that which runs through eastern Africa. Many reached the margin between the two plates and most then turned west.

Conversely, one juvenile female's track was astounding, overlaying almost perfectly the rift system as it runs west. It's clear that she and the other whale sharks are using geological features as route indicators, just as motorists use, say, familiar buildings. But how the sharks perceive such features thousands of metres below on the ocean floor is as yet unrecognised.

The theory we are working on is that the Earth's magnetic field reverses its polarity intermittently over the course of time, thus supplying a source of directional information. Fault systems, rift valleys, ocean trenches and plate margins all emit a distinct magnetic signature that can be used by whale sharks and other species as a virtual map.

When an animal the size of a very large double-decker bus – the largest fish in the ocean – makes a sudden 90° turn, it has to be for a good reason. As the satellite tracks started to come in from whale sharks which we had tagged off the Galapagos Islands, they clearly showed that as the sharks were swimming away from the islands, they were all reaching a certain point and then making a very abrupt change in direction. ___ That, among other things, was what The Galapagos Whale Shark Project was attempting to find out. Established to study the population of sharks that visits the islands each year, the primary aim of the research was to find out more about whale shark movements on a local scale. ___ This involved two main processes. To begin with, we had to be able to identify individual sharks. We used a modified version of photo software initially developed for the mapping of stars and deep-space objects. This worked because the characteristic white spots of the whale shark resemble the human fingerprint in that each pattern is individually unique. By running photographs of the sharks' sides through the software, we could catalogue the patterns of spots, and figure out which shark was which. ___ We also attached tags to the sharks to track their movements. This was done by inserting a small dart through the thick skin into a fatty layer beneath using a pneumatic spear gun and then tethering the tags with a piece of steel cable. They were intended to be towed alongside or above the dorsal fin in order to break the surface and transmit data by satellite. But getting the tags to stay on was easier said than done. For reasons unknown, some came off in less than 24 hours. ___ The sharks used common departure routes soon after we had tagged them. They headed due north, following a series of sea features until they reached the Galapagos Rift Valley system. This zone is where the divergence of two oceanic plates has created a rift system similar to that which runs through eastern Africa. Many reached the margin between the two plates and most then turned west. ___ Conversely, one juvenile female's track was astounding, overlaying almost perfectly the rift system as it runs west. It's clear that she and the other whale sharks are using geological features as route indicators, just as motorists use, say, familiar buildings. But how the sharks perceive such features thousands of metres below on the ocean floor is as yet unrecognised. ___ The theory we are working on is that the Earth's magnetic field reverses its polarity intermittently over the course of time, thus supplying a source of directional information. Fault systems, rift valleys, ocean trenches and plate margins all emit a distinct magnetic signature that can be used by whale sharks and other species as a virtual map.

Available as a free printable PDF worksheet with an optional answer key.

More C1 Advanced Gapped Text practice · All C1 Advanced practice