Mackerel: easy to catch, good to eat - and beautifully designed

On the rare occasions when I visit the coast from land-locked Hertfordshire, I like to go out mackerel fishing, in company with other holidaymakers. Boat owners run these trips alongside those for sightseeing, and the necessary tackle is provided. Local knowledge of where shoals of fish are likely to be found is invaluable and, after chugging out to a suitable location, the boat’s engine is turned off and instruction given on how to lower the weighted line to the sea bed, raise it a little, let it drop, raise it again, etc. No bait is used, but hooks (at least three) are held out on traces that have brightly coloured feathers attached. In no time, the tug of fish is felt and the line is reeled in, sometimes with a mackerel on each hook, and everyone seems to have success. Occasionally, other fish are caught, but it is mackerel that make up almost all the catch and, on good days, they begin to pile up in trays, or buckets, on deck.

For many people on the trip, catching mackerel is pleasure enough but, for others, the freshly-caught fish make a splendid supper. Whereas meat, and especially game, improves with hanging, fish are best eaten as fresh as possible. There are a number of ways in which mackerel can be enjoyed and they are both delicious and good for one’s health. The simplest approach is to barbecue, or they might be eaten as a ceviche of raw fish, and they can also be smoked to allow preservation for several days, or even weeks. [1] My own favourite recipe comes from childhood when we were given freshly-caught mackerel by Mr Revell, who lived along our road and always seemed to have an excess when he went fishing from the end of Paignton Pier. We had them soused in vinegar, [2] with bay leaves placed into slashes in the flesh, and I can remember the taste well.

Everyone catching Atlantic mackerel (Scomber scombrus), whether to eat or not, is impressed by the appearance and muscularity of the fish. The muscles used for swimming are arranged in blocks and run along the body, from just behind the head to the tail, and they drive the caudal fins (tail). If we looked closely, we would see that three types of muscle are present. Running along the sides of the fish are red muscles, while ca. 90% of the bulk of the flesh consists of white muscles, or intermediate pink muscles. [3] Red muscles are very different in structure and function to the other types. They are well supplied with oxygen and do not tire easily and this contrasts with the white muscles, which show the opposite qualities, with the pink muscles (lying within the white muscle mass) having a slightly longer endurance. Red muscles are thus used in cruising, while the white and pink muscles are used for bursts of acceleration, such as are needed when avoiding prey or in predation.

In addition to powering the caudal fins, the muscles also provide the outline of the fish. Mackerel have an “idealised streamlined shape”; one where the widest part of the body is about one third from the front and where the length is about four times the width. This shape is shown in the diagram below and one needs to visualise it in 3-D. The mackerel makes a good fit and, to understand why this is advantageous, we need to imagine that water is arranged into sheets and that turbulence results when these sheets are disrupted. At some point along the body, the sheets of water passing over the mackerel peel away from close contact with the surface and this is referred to as the separation point (SP, see arrows in the diagram below). Beyond the SP, the sheets of water stop flowing smoothly and this results in drag, but the streamlined shape means that the water layers hold to the body for longer, resulting in a smaller turbulent wake behind the fish. Its shape thus results in less drag, so less power is then needed by the fish in both slow, and fast, swimming

Scales that are sunk into the skin cause micro-turbulence in the water flowing just over the surface of the fish and this provides a “lubricant” over which the fast-moving sheets just a little further away from the body can slide, further diminishing the risk of separation. Of course, this is only one function of the scales, as they also serve for protection. More obvious features of the surface are the fins and these are rigid and can be held out into the smooth flow of water passing over the fish when they are needed most during rapid swimming. They function like the flights of arrows, or darts, in counteracting pitch, roll and yaw and, like the body profile and the musculature, are elegant designs.

However, mackerel did not have a designer and all the structures that we see evolved over time. So, too, did other features of these fish, such as their good eyesight (that enabled them to spot the feathers on my fishing line); the swim bladder (an extension of the gut) that allows them to float without expending energy; their efficient means of acquiring oxygen through the gills; and many other modifications, including their extraordinary musculature (which is so good to eat). All evolved and we can only speculate how: were there dramatic mutations, or more gradual changes in anatomy, morphology and physiology? Sometimes, belief in a Creator seems like an easier way to get answers.

[1] http://www.theguardian.com/lifeandstyle/2014/jul/18/mary-ellen-mctague-recipes-food-and-drink

[2] http://www.rivercottage.net/recipes/soused-mackerel/

[3] J.J.Videler (1993) Fish Swimming. London, Chapman & Hall

Our fascination with dinosaurs

Unlike the majority of scientific finds, descriptions of new dinosaurs are often reported widely by the World’s media, as they grip the imagination of readers and viewers. A recent example is the discovery of Dreadnoughtus schrani in Argentina, where about 45% of the skeleton was found. [1, 2] Individual bones were cleaned carefully and these allowed the reconstruction shown in the illustration below, with the bones recovered shown in white. The skeleton was then completed using assumptions based on a scholarly prediction of the size, and shape, of the missing parts. Dr Lacovara of Drexel University and his colleagues were delighted to have both a femur and a humerus, as measurements taken from these two bones allow a reasonably accurate estimate of the mass of the living Dreadnoughtus to be made - at nearly 60,000 kg, [3] equivalent to more than 10 African elephants. [2]

Both a BBC article, [1] and the one by Drexel University, [2] use the same artist’s impression of a living Dreadnoughtus, although the BBC piece blanks out the background, something that gives context and scale, as does comparison with the size of contemporary humans (see the illustration above). But how accurate is the image of the reconstructed dinosaur to the living form? Fortunately, there are sufficient bones from this specimen to assess the insertion of muscles and thus the outline of some parts of the animal, based on very close examination of bone surfaces by experts. [3] However, while almost all the tail bones were recovered, there is little of the neck and even less of the head, so what is the basis for their appearance in the artist's impression? 

 

There is a problem in making reconstructions of whole animals from skeletal fragments and I’m sure that many dinosaurs are painted with far less evidence of structure than is available for Dreadnoughtus. However, it is the illustrations that grab the attention, although the size of mounted skeletons, or casts, in museums certainly give a sense of the huge size of some of these reptiles. Dinosaurs have been afforded another level of presentational skill in being used in animatronics and computer simulations [4,5] that often feature colour, sounds and even behaviour and may be based on a little too much imagination. Nevertheless, these images are widely held to be accurate by enthusiastic onlookers. 

Our fascination with dinosaurs goes back to the time of the popularisation of fossil hunting and of Natural History in the Nineteenth Century. Among the more famous exhibits of that time are the life-size models of dinosaurs commissioned for the move of the Great Exhibition to the newly-constructed Crystal Palace in 1854. These models remain in the grounds of the demolished Palace (see below) and are still visited by families, whose children delight in their scary nature, despite their obvious lack of life.

In the Nineteenth Century, we knew that dinosaurs existed millions of years before the present and this widely accepted interpretation provided a challenge to those who believed in the literal account of Creation in The Bible. Faced with this conflict, Philip Henry Gosse, wrote Omphalos, [6] in which he advanced a theory that suggested that fossils of such age did not compromise the belief that everything was created over six days, just a few thousand years ago. In the first section of his book, Gosse describes several fossil discoveries accurately and accepts that they were present during different geological time periods, as advanced by Lyell, amongst others. The text is illustrated by artist’s impressions of the living animals in their natural habitats, several in the form of signed woodcuts by Gosse himself and two of these are shown below.

As a brilliant Natural Historian, Gosse was fascinated by the biology of these creatures:

..the most characteristic animals [of the Lias] were great marine Reptiles, of strange and uncouth forms, to which the present world presents us no known analogy. One of these was the Icthyosaurus, which closely resembled a porpoise in form, but thirty or forty feet in length, with a vertical fish-like tail, and two pairs of paddles; a mouth set with stout crocodilian teeth, and enormous eyes. Another form was that of the Plesiosaurus, scarcely less in size than its fellow, which in the outline of its body it resembled: it was distinguished, however, by an extraordinary length of neck, slender and swan-like.. [6]

However, his theory concluded that they had only had the appearance of being alive as everything was created by God at that huge event a few thousand years ago and this included the Earth’s strata and the fossils that they contain. It is, of course, a rather silly theory produced by someone with complete faith in the words of The Bible, yet accepting the logic of geological time. There was no doubting his enthusiasm for dinosaurs, however, even if he believed that they had never existed. Interestingly, in the context of the quote given above, Gosse put forward his view that sightings of “sea serpents” may be explained by the continued existence of reptiles like ichthyosaurs and plesiosaurs. [7]

What is it about dinosaurs that make them more fascinating to us than other fossil animals? In part, it relates to their size, although many small dinosaurs do not have the glamour, and almost mythological status, of larger forms. It is also because we really want to see living forms, rather than impressions of various kinds. Some hope that, like the sea serpents sighted in the Nineteenth Century, aquatic dinosaurs continue to exist, even though the chances are miniscule. In the United Kingdom, we are familiar with the “monster” that is believed to inhabit Loch Ness, but studies using sonar, and other techniques, have, predictably, drawn a blank. Wouldn’t it be fun if we did find a living dinosaur, though?

[1] http://www.bbc.co.uk/news/science-environment-29050114

[2] http://drexel.edu/now/archive/2014/September/Dreadnoughtus-Dinosaur/

[3] http://www.nature.com/srep/2014/140904/srep06196/full/srep06196.html

[4] http://www.nhm.ac.uk/about-us/news/2011/march/age-of-the-dinosaur-exhibition-animatronics-arrive95706.html

[5] https://www.youtube.com/watch?v=C0r5P-PzIPU

[6] Philip Henry Gosse (1857) Omphalos: an attempt to untie the geological knot. London, John Van Voorst.

[7] Philip Henry Gosse (1860) The Romance of Natural History. London, J. Nisbet & Co.

Solitary walks in Nature

Walking at a good pace is regarded as an excellent way of keeping fit, both physically and mentally. Some prefer to use treadmills in a gymnasium, others to be part of a social exercising group, and yet others prefer to take solitary walks in Nature. My enjoyment of walking started when I was growing up in Devonshire and went with my family into the countryside (I’m the little chap, aged 3, leading in the picture below). I preferred my own company on walks in my teenage years, but also hiked with friends on many occasions and enjoyed our conversations. I had no idea of the physical and mental benefits; I just enjoyed walking through lanes, over Dartmoor, or at the coast - including jumping from rock to rock around headlands, something that carried the risk of falling, or of being cut off from the tide. Other walks held little danger, although barking sheepdogs, and dogs other breeds, running from farms, or other properties, could be off-putting. Aside from that, it was all about the enjoyment of striding out, looking at Nature, feeling the warmth (or cold) and generally becoming lost in the experience. It’s still the way I feel when taking country walks, and I still prefer to go alone. 

Although I’ve rarely sought explanations for the enjoyment of solitary walks, others have. For example, Rousseau writes of his introspection:

The habit of searching into myself caused me, at length, to lose the feeling, and almost the remembrance, of my misfortunes. I thus learnt, by my own experience, that the source of true happiness is within us, and that it does not depend on man to render truly miserable him who knows how to determine to be happy. These four or five years I have constantly tasted those internal delights which kind and gentle souls find in contemplation. Such raptures, such exstasies, I sometimes experienced in thus walking alone, were enjoyments I owed my persecutors; without them I should never have felt or known the treasures I carried within me. [1]

My pleasure is not driven by persecutors and comes from a combination of the exercise and what I see, hear and smell. Even the same route has something different to offer through the seasons. I once asked a low handicap golfer if he ever became bored playing the same links course every day and he replied that it was never the same 18 holes. There were differences in the direction of the wind and its strength; together with differences in dampness, both of the air and of the ground, and all these factors needed to be taken into account when making decisions about the choice of club, or of shot. The golf course was always changing in subtle ways and country walks are never really repeats, for similar reasons to those put forward by the golfer.

What is the scientific evidence for the benefits of country walks? Recently, I read an interesting article in New Yorker by Ferris Jabr, entitled “Why Walking Helps Us Think”. [2] He writes:

What is it about walking, in particular, that makes it so amenable to thinking and writing? The answer begins with changes to our chemistry. When we go for a walk, the heart pumps faster, circulating more blood and oxygen not just to the muscles but to all the organs - including the brain. Many experiments have shown that after or during exercise, even very mild exertion, people perform better on tests of memory and attention.. ..Because we don’t have to devote much conscious effort to the act of walking, our attention is free to wander - to overlay the world before us with a parade of images from the mind’s theatre. This is precisely the kind of mental state that studies have linked with innovative ideas and strokes of insight.

Ferris then goes on to mention the research of Marily Oppezzo and Daniel Schwartz of Stanford University on the link between walking and creativity and also a study by Marc Berman and colleagues at the University of Michigan on the importance of walking in Nature. That stimulated me to read their original research papers.

Oppezzo and Schwartz [3] used separate experiments to allow them to compare sitting, walking on a treadmill, and walking outside, with subjects being assessed using psychological tests. In a thorough discussion of all the possible explanations for their results, they found that:

Walking substantially enhanced creativity.. ..[and] is an easy-to-implement strategy to increase appropriate novel idea generation. When there is a premium on generating new ideas in the workday, it should be beneficial to incorporate walks..

..Walking outdoors on a busy campus did not significantly increase appropriate novelty compared with walking indoors, although the more varied stimulation did appear to increase novelty. This suggests that walking may be effective in many locations that do not have acute distractions. The social context also needs investigation. Participants were encouraged to talk aloud to a friendly researcher. Will the effects generalize to solitary walks?

A good question. It was the effect of walking outdoors that was investigated by Berman et al.. [4] They used two experiments, in the first of which subjects were compared after walking in the city of Ann Arbor and after walking in the relative tranquillity of Ann Arbor Arboretum. There was an improvement in directed-attention ability in the subjects that had walked in the arboretum. Interestingly, a second experiment that showed subjects pictures of nature compared to urban areas in a quiet room produced similar results on cognitive functioning.

Walking in a natural environment is thus shown to be positive, supporting a commonly-held view, and certainly one which I now realise conditioned my love of country walks. It is interesting that Oppezzo and Schwartz allude to solitary walking as this is certainly my preference as it is/was for others. Ferris Jabr comments that Wordsworth:

..walked as many as a hundred and eighty thousand miles in his lifetime, which comes to an average of six and a half miles a day starting from age five. [2]

Such prodigious amounts of walking through the countryside (perhaps there is a little exaggeration here?), led to creativity, but also to deeper thoughts. As Wordsworth wrote [5]:

..this prayer I make,

Knowing that Nature never did betray

The heart that loved her; ‘tis her privilege,

Through all the years of this our life, to lead

From joy to joy: for she can so inform

The mind that is within us, so impress

With quietness and beauty, and so feed

With lofty thoughts, that neither evil tongues,

Rash judgements, nor the sneers of selfish men,

Nor greetings where no kindness is, nor all

The dreary intercourse of daily life,

Shall e’er prevail against us, or disturb

Our cheerful faith that all which we behold

Is full of blessings..

I suppose that is what solitary walks in the countryside are really all about - an immediate pleasure from exercise in such surroundings, the enhancement of creativity, and adding to a store of deep thoughts. They also bring respect for plants, animals and landscape that reminds us that we, too, are part of the natural World. So much of our time is spent in such an unnatural one and walking in the countryside takes us back to the environment in which we evolved, and which we are trying to destroy in many ways. Is that too fanciful an idea? Perhaps I should attempt to answer that question after taking a few long walks and then report back in a future blog post?

In conclusion, I’ll give another quote from Berman et al. [4]:

Imagine a therapy that had no known side effects, was readily available, and could improve your cognitive functioning at zero cost. Such a therapy has been known to philosophers, writers and laypeople alike: interacting with nature.

[1] Jean-Jacques Rousseau (1783) The Reveries of the Solitary Walker (translated from the French). London, J.Bew.

[2] Ferris Jabr (2014) Why Walking Helps Us Think. http://www.newyorker.com/tech/elements/walking-helps-us-think

[3] Marily Oppezzo and Daniel L. Schwartz (2014) Give Your Ideas Some Legs: The Positive Effect of Walking on Creative Thinking. Journal of Experimental Psychology 40: 1142-1152.

[4] Marc G. Berman, John Jonides, and Stephen Kaplan (2008) The Cognitive Benefits of Interacting With Nature. Psychological Science 19: 1207-1212.

[5] William Wordsworth (1798) Lines written a few miles above Tintern Abbey. Lyrical Ballads. London, J. & A. Arch.

I would like to thank Jo Atherton, the well-known potter and flotsam weaver (http://flotsamweaving.com/), for alerting me to Ferris Jabr’s article in a reference on her Facebook page.