Samuel H. 'doc' Gruber: Shark Science Pioneer
Doc Gruber began studying sharks in 1961,
perhaps before any other scientist had done full-time research on a
living shark. During his long career, he founded the Bimini
Biological Field Station (Shark Lab), the Shark Specialist Group of
the International Union for the Conservation of Nature, (IUCN), a
United Nations organization based in Switzerland, and the American
Elasmobranch Society. He has published over 200 scientific papers,
and his research is still ongoing today.
His decision to study sharks was as unplanned as it was final.
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| Doc in 1957 with black grouper |
As a young man growing up in Florida, he loved to dive, and often
went off for weekends of scuba diving and spear fishing on a 30 metre
schooner called the Blue Goose. The ship had belonged to Hermann
Göring, commander-in-chief of the German Luftwaffe (Air Force) under
the Nazis, and it had found its way to Miami when it was liberated at
the end of World War II. A weekend of diving fun on the Blue Goose
cost only seven dollars, and at that time, there were still big fish!
On one of these outings in 1958, Gruber had speared a grouper
hiding in a submarine cave, and was emerging with it into open water
when he saw a hammerhead shark approaching. It was the largest shark
he had ever seen, and as it glided towards him, it seemed to be the
size of a submarine! Sure that he was about to die, he plunged back
into the cave with his fish, and found himself in the same position
that the grouper had just been in, as he looked out. Watching in awe
as the momentous shark passed him, he was seized with the desire to
know what sort of an animal it was.
When he returned to the university, he asked his professor what
was known about sharks, and found that no one knew much at all. So he
decided then and there to become a marine biologist and study them.
His research begins
With the idea of becoming a medical doctor, Gruber was attending
Emory University at the time, and was majoring in pre-medical
studies. He had been especially intrigued by the study of comparative
anatomy in which he had dissected a shark, a giant salamander, and a
cat. That summer he was taking courses at the University of Miami,
and had asked if he could assist the comparative anatomy laboratory
dissecting the animals.
Now, inspired by his riveting meeting with the hammerhead shark,
he transferred to the University of Miami, earned his under-graduate
degree in zoology and chemistry, and applied to graduate school to
study sharks.
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| Gruber in 1963 studying sharks' eyes |
In 1960, the University of Miami’s Marine School had hired Dr.
Warren Wisby as professor and researcher in marine animal behaviour,
with an emphasis on sharks. As a student of the famous professor
Arthur Davis Hasler, Wisby was best known for having discovered the
actual mechanism of homing in salmon. By marking hatchling salmon,
and going back to their streams when they returned to spawn, Wisby
had found that they came back to the exact stream in which
they had hatched.
So Gruber’s timing was perfect. He was given a research
assistantship, and didn’t have to pay for tuition. In fact he was
paid the huge sum of 103 dollars a month as a graduate student there!
Wisby told him that the Navy had given them a grant to study shark
senses. When aircraft went down at sea, it happened at times that
sharks attacked the flyers in the water. In those days flyers wore
two types of suits—high visibility suits called International
Orange, and the standard khaki flying suits. According to a Navy
report, the flyers wearing International Orange suits were attacked
to a man, while the ones wearing khaki suits were left alone.
As a result, the Navy had started calling those orange suits yum
yum yellow.
Wisby directed Gruber to look at the literature and report back on
the possibility that sharks have colour vision. So he examined all
the old reports. They were mostly in German, and they concluded that
sharks could not see colours because they lacked the cone-shaped
photoreceptors in the eye’s retina that permit colour vision in
humans and other animals.
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| Gruber and Wisby collecting shark eyes to study at a fishing tournament |
The Duplexity Theory of vision was introduced in the 1860s
by a German scientist named Max Schultze, and states that rods and
cones in the retinas of an animal that possesses both, have two
functions. Rods are used in night vision when there is little light,
while the cones take over during the day, providing the ability to
see colours, fine details, and to discern rapidly flashing lights.
Some animals, such as squirrels and iguanas, that are active in
daytime, have no rods in their eyes, and nocturnal animals or those
adapted to the darkness of caves or the deep sea, have no cones.
Therefore, the lack of cones found by early researchers in the
retinas of sharks, suggested that they were unable to distinguish
colours.
But Wisby questioned the old conclusions. He asked Gruber to go
out and actually collect sharks’ eyes, and see what he could find.
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| Collecting eyes at a shark tournament |
So Gruber went to shark tournaments and collected the eyes of
every species of large shark caught off the of the eastern seaboard
of the US. He put a catheter into their hearts while they were still
beating—the animals were brain-dead—and perfused gluteraldehyde,
a preservative chemical, through their arteries, to fix their eyes
for future study under the electron microscope.
On one occasion, he was notified that a young great white shark
was caught and was being held for him. This was the chance of a
lifetime for the young graduate student, as white sharks were very
rare. He ran out in a boat to where the fisherman was waiting with a
barely living 54 lb. specimen, successfully perfused the shark, and
collected the eyes.
Can sharks see colour?
Year after year, Gruber worked in a histology lab comparing the
retinas of the many species of sharks to see whether they had both
rods and cones. And, amazingly, every species he studied had them.
Some species seemed to have better retinas than others, but they all
had rods and cones. The great white shark had five rods to one cone,
which was an especially high ratio.
It seemed that the earlier scientists had studied the cold-water,
bottom-loving sharks of the northern seas off Europe, and those
species had very few cone cells because they were adapted to dark
conditions. Those inaccurate early findings had resulted in many
false ideas about sharks taking root. The idea that they had an
excellent sense of smell had spread because they came quickly to a
scent, and so the concept of a shark as a swimming nose, with poor
eyesight, was born a century ago.
The forebrain of a shark, called the telencephalon, is
considered one of the most important parts of the brain, like our
cerebral hemispheres. And in the shark, the telencephalon was thought
to be the centre that analysed scents, because that was how it looked
to the early researchers. They did not know how the forebrain worked,
and they had never looked at how sharks really behaved, or tried to
do neural examinations, yet their primitive ideas about sharks had
persisted.
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| diagram of the brain of a shark, showing the telencephalon |
Wisby was pleased with Gruber’s discovery, but pointed out that
just because the sharks had cone cells, didn’t mean that they could
see colours. “What do the rods and cones mean for sharks?” Wisby
asked, and directed Gruber to experiment to learn whether sharks see
colours, and investigate their other visual capabilities.
As the eyes of a human or animal adapt to darkness, rods take over
the function of vision, providing high sensitivity to light, but no
colour. The switching over between the cones and rods is something
that can be measured, and it was this line of research that Gruber
began to pursue in 1962 for his master, and later his doctorate
degrees.
He used the lemon shark as a model, and chose three methods to
test the Duplexity Theory of vision in sharks.
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| Image of the rods and cones in a shark's retina |
To assess the rod and cone activity in the retina, he put contact
lens electrodes on anaesthetized lemon sharks, and recorded the
electrical responses of the retina when illuminated. He used
electrophysiology to record electroretinograms, which are
similar to the electrocardiogram of doctors, in order to examine the
electrical activity of the associated neurons.
His second method involved a behavioural study, following the
Pavlovian method of testing called classical or respondent
conditioning, and the third was the Skinnerian method, which is
called operant conditioning.
Gruber’s results were unambiguous. The three methods gave the
same results—there was no doubt that sharks could see colour. The
rods functioned as expected in the dark, and the cones were most
active in the light-adapted state. He found that as sharks adjusted
to darkness, the sensitivity of their eyes became greater and
greater, and reached the maximum dark-adaptation after about an hour,
achieving a million-fold increase in sensitivity!
They adapted better than humans because unlike us, they possess
the tapetum lucidum. This is the mirror-like membrane at the
back of the eye which produces eye-shine in some animals. Light
entering the eye passes through the retina, and is reflected, as if
by a mirror, back from this membrane, potentially doubling the eye’s
sensitivity.
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| eye-shine |
The learning rate of a shark
Another interesting finding that emerged from Gruber’s research
during his doctoral studies was the speed at which sharks learn.
He was working on Pavlovian training conditioning, doing an
experiment in which a shark would see a flash of light, and then
receive a mild electric shock. After a certain number of trials, when
the shark saw the light, it would have learned to anticipate the
shock, and have a reaction. This is called a conditioned response.
The reaction that Gruber planned to use for the experiment was the
pause in the shark’s heart-rate resulting from the fear of the
coming shock. Fear causes the heart to skip a beat, then accelerate,
so at the moment that the shark realized that it was about to receive
another shock, its heart paused, and this reaction could be measured.
The number of trials it took for the animal to learn the association
between the light and the shock, gave a measure of its ability to
learn.
While Gruber was flashing the light, and giving the shock, he was
looking at the readout on the oscilloscope, rather than at the shark,
which was trussed up underwater, with an electrode in its cardiac
chamber, looking out into the room through a big Plexiglas bubble.
Then one day, he happened to look at the shark at the moment in
which it anticipated the shock, and saw that it winked—the
nictitating membrane of the shark’s eye closed. This provided
another conditioned response to the light, which meant that there was
no need for the heart monitoring—all Gruber had to do was observe.
Due to the need for the heart monitoring, the sharks had been unable
to survive long enough for him to get them trained, so his discovery
was crucial to the success of this important experiment.
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| The nictitating membrane can be seen here as the lemon shark in the experiment winks. |
Now Gruber used a World War II infra-red sniper scope to observe
the shark in total darkness, and found that after about ten trials,
or repetitions, the shark would wink in expectation of the shock. It
was a conditioned response that he got from a shark in only about
three minutes!
One session consisted of 10 sets of 10 trials, and after about 80
trials, the shark was responding 100 percent of the time. The next
day it took only 3 or 4 trials to get the shark to respond, and it
responded 100% of the time after 40 trials. On the third day, it had
a 100% response from the start. So it took only about 10 trials for
the first response, 80 trials to get the 100% response, and only
three days to the state in which the shark was conditioned long term.
By chance, psychologists had been studying Pavlovian conditioning
in cats and rabbits using the same paradigm. They used the flash of
light as the initial stimulus, and followed it with a puff of air
onto the cornea, instead of an electric shock. As in Gruber's
experiment, the conditioned response was the movement of the
nictitating membrane, so the experiment was a terrestrial version of
precisely what Gruber had been doing with sharks.
What was surprising was that the sharks had learned the
relationship between the light and the shock ten times faster than
the cats and rabbits! These had taken about 800 trials to achieve
100% conditioning, while the sharks had taken only 80 trials!
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| Gruber working on the experiment in 1966 |
Gruber discovered many more interesting things in the course of
his research. He found that sharks have different “IQs” and
different personalities, and that some are left-handed and some are
right-handed. He also found that they have an occlusable tapetum,
a further refinement of their vision, as well as a mobile pupil in a
variety of shapes, which only sharks and rays, and no other fish,
have.
Published
Arthur A. Myrberg, the youngest full professor at the University,
took Wisby’s place in 1964, and mentored Gruber during the last
years of his master and doctorate degrees. While Gruber and his
student, Joel Cohen, were studying shark vision, Myrberg and his
students worked on their hearing, and others (not at the University
of Miami), were working on olfaction, taste, and electoreception.
In 1976, the Navy asked for a summary of all of the work it had
funded about the sensory systems of sharks, and they put their
findings together in a major book, which was published in the
government printing offices. Gruber’s discoveries about shark
vision filled a large chapter.
Ethology
With his findings published, Gruber no longer wanted to work in a
dark and damp laboratory, and longed to understand the role sharks
play in the marine environment. He dreamed of studying their
behaviour in a similar, systematic way, in the wild, and decided that
he would find a way to do it, using the lemon shark he had come to
know so well, and wanted to understand more deeply.
By then he had become an assistant professor at the University of
Miami Rosenstiel School of Marine and Atmospheric Sciences, teaching
advanced courses in animal behaviour, tropical marine biology, and
the physiology and behaviour of marine organisms.
He had done a post-doctoral study in 1971-72, at the Max-Planck
Institute in Germany, under Nobel laureate Konrad Lorenz, the famous
Austrian ethologist, just as Myrberg had done a decade before. Both
men were interested in pursuing their interest in ethology, and as a
side project, they had put together an observational study on a
captive colony of bonnethead sharks, which was published in the
journal Copeia in 1974. It remains the only ethogram, which is an
inventory of the repertoire of behaviour patterns displayed by a
species, that was ever published for sharks.
Then in 1976, they gathered together all of their information on
shark behaviour for a symposium in New Orleans, and it was published
in the journal American Zoologist.
Gruber and Myrberg developed a close personal friendship that was
to last all their lives. They travelled together as they pursued
their research in Europe and the Middle East. They dove with Cousteau
in Monaco, travelled through Europe visiting friends and colleagues,
and studied sharks in the Florida Keys and the Caribbean. And when
Gruber got engaged, it was at Myrberg’s home.
Gruber left Navy research in 1976, and in 1977 he proposed a study
to the National Science Foundation, on the role lemon sharks in the
tropical marine environment. His goal was to do an autecological
study designed to examine many aspect of this species’ biology,
with an emphasis on behavior and ecology. It was funded in 1978 and
is still continuing today in 2014.
At last he was fulfilling his dream, of discovering what a shark
is, and what it does in its life in the wild.
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| A watercolour portrait of a tiger shark (by the writer) |
Bio-energetics
Gruber chose bio-energetics as way of understanding the
biology of the lemon shark. Bio-energetics gives the researcher a
mathematical method to describe the workings of a living system. Like
all things in nature, a shark conforms to the laws of thermodynamics,
that decree that in a system, the energy that comes out, no matter
how it is channeled or converted, has to equal the energy that has
gone in.
In other words, the energy that goes into a shark as food, will
come out through growth, metabolism, waste, other biological
products. The processes of metabolism—the nerves, digestion,
muscles, respiration, and other biological processes—will likely
burn half of the calories, and such materials as mucus, urine, and
faeces can be burned up in a calorimeter to find how many calories
were lost that way. The calories consumed must be partitioned within
the body into only four unknowns, and the process can be analysed.
As an example, the common practice of dieting and exercising to
reduce one’s weight, utilizes the principle of bioenergetics to
achieve a goal. By decreasing the energy going into the body in the
form of food, we can force it to use stored fat to make up the
deficit, and thus lose weight.
Gruber described it this way, “It is possible to make an
equation that balances in four unknowns. It is a simple thing to do
mathematically and it reveals a great deal about the animal. It shows
how they make their living, what they require for food, their
metabolic needs, what they need to digest food, how much of what they
eat is assimilated, how much is lost in waste products, how quickly
they grow, and how much food it takes them to grow.
“That’s what you can tell about a shark’s life and what it
takes to grow a shark in the environment and that’s what we did. It
took us over ten years.”
Through a combination of laboratory research and studies in the
field, Gruber and his colleagues and students focused so much
research on the lemon shark that they discovered much about its life
history characteristics, its population dynamics, its growth,
reproduction, and genetics. He was determined to make sure that their
experiments were realistic by always comparing laboratory results to
what could be learned from sharks in the marine environment.
Fieldwork
Initially Gruber studied lemon sharks in Coupon Bight in the
Florida Keys. Using nets, he and his colleagues would reliably catch
100 to 120 juvenile lemon sharks there, each summer season, which
they would work up and release. But in the early eighties, their
numbers began to fall, and in three years he could not catch one
shark there. All of the work he had done during all of those years
was wasted.
He found out that it was due to overfishing. Fishermen had been
catching the little baby sharks in the nursery for crab traps and had
fished them all out. The mothers that were supposed to be coming back
to the place they were born to give birth had been fished too, so the
entire local population of sharks had disappeared.
Gruber knew that the sharks were in trouble again, because this
had already happened to him in Florida. So he began doing his
research at a small island in the Bahamas at the place where he would
later establish the Bimini Biological Field Station. Four times a
year, he went there for his field research using National Science
Foundation research vessels which were at his disposal from the
University of Miami.
Later, when he had the Bimini field station set up, they could do
permanent work there without the need to go back and forth to
Florida, which allowed them to expand their research.
The research
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| The Bimini Shark Lab that Gruber founded in the Bahamas |
The main thrust of Gruber’s research was trophic ecology or
autecology, the ecology of one species.
Bimini’s lagoon was like a marine lake, where the juvenile lemon
sharks were obliged to remain, and each shark could be looked at year
after year for six or seven years before it left the area. The
location was ideal. There were two to three hundred sharks divided
between three to four nursery areas, and he tagged nearly all of
them, and focused hard on learning all about their lives as he tried
to unravel the ecology of the lemon shark. How many sharks were
there? How many lived? How many died? How many grew up to maturity?
How fast did they grow? What would it take to grow a lemon shark up
from a pup to an adult of 80 kg?
Each spring, when the lemon shark pups were born, Gruber and the
students did a comprehensive tagging study. They built a large pen,
which could hold up to 150 sharks. Then they caught the sharks in
nets, tagged them with an electronic micro-tag, took a genetic
sample, weighed them, measured them, sexed them, and put them in the
giant pen. Every year they would catch, tag, and work up between 180
and 230 sharks. The sharks were released, and then the next year the
same sharks that survived, could be caught and measured again. The
year 2014 was their 20th year.
After more than a decade of research, they balanced the
bio-energetic equation for a young, fast-growing, 2 kg lemon shark at
25 degrees centigrade, and discovered that the little shark was an
energy conserver, and ate only about seven times its body weight in a
year. By comparison, many fish, such as tuna, blow a lot of energy
and have to eat a lot of food. And humans, in comparison with lemon
sharks, eat an enormous amount.
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| The shark pens are visible in the foreground |
With the sharks living free in a place where they could be watched
from year to year, many experiments were possible. For example, they
were able to study their movements, their relationship to
temperatures, their food, their place in the ecological system, and
their social networks. The nursery was a region of mangroves, and
certain little snails called Batillaria were low on the food
chain and were the keystone species. The next level was crabs, then
fish, then sharks—sharks were on the fifth level.
The countless studies took years and years, doctoral
dissertations, and masters theses, and thousands of students all
coming to Bimini to study sharks. Gruber taught a University of Miami
course there for 22 years, sometimes twice a year; now he teaches
five university courses at the station. He had graduate students,
built big holding pens at his research facility, and kept dozens of
lemon sharks.
And as time passed and he learned of its abilities and capacities,
the lemon shark became an animal of complete fascination. To Gruber,
the lemon shark had gone from a predatory fish with fins and teeth to
being more like a family member.
He said,
“As I went through my early career and I got married and we had
children, then we got a house and we got cars, I realized that the
lemon shark had provided a living for me in the human world, whereby
I could become a functional and useful citizen and have a family. It
was all because of the lemon shark. That’s why I get so nervous
when I think that they are having problems underwater, not only with
being overfished, but also with us handling them.
So I have not been able to remain objective in my feelings for
them, although I have tried to remain objective in my research of
them.”
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| Doc Gruber loves lemon sharks |
(c) Ila France Porcher
Illustrations courtesy of Dr. Gruber, except where indicated.
This first of three parts, was originally published in Shark Tales in X-ray Dive Magazine, issue 64. See Part two next!Illustrations courtesy of Dr. Gruber, except where indicated.
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