Lamniformes (Mackerel Sharks)
p. 131-137
Bernhard Grzimek
Synopsis of the Article
According to the article, Mackerel sharks belong to class Chondrichthyes and order Lamniformes. As the surviving members of the larger lamniforme sharks that have long become extinct, mackerel sharks are characterized with over 15 surviving species which do not compare directly with the countless number of shark fossils that have been discovered. It is worth noting that most of the fossils obtained encompass isolate teeth with most of lamniforme teeth being widespread in a plethora of marine localities in almost all the continents of the world. However, there is a paucity of more complete lamniforme fossils. The few complete remains in existence include the over 90 million years old partial skeleton of the goblin shark from Lebanon with panoptically similar features to the existing goblin shark. As the author notes, lamniformes have been widely studied and are hence well known to human beings compared to other sharks. This assertion is supported by the fact a number of most common species of lamniformes were outlined in the eighteen century, about five in the nineteenth, and over six in the twentieth century with a good number of studies also centered on the relationship between lamniformes and genera.
The relative sizes of mackerel sharks range from about 3 feet to 46 feet in length making the species one of the largest families of sharks in existence today. The sharks also exhibit unique teeth and intestines that are overly recognizable.
Even with the existence of some variances in the body structures of most lamniforme species, mackerel sharks, fundamentally, have two dorsal fins of dissenting heights, ostentatiously lofty pectoral fins, as well as a small anal fin. According to the author of the article, the caudal fin of the mackerel shark is lunate or sometimes semilunate with the thresher sharks having caudal fins almost the same size of their bodies. On the same note, the author asserts that the goblin, sand tiger, megamouth, and crocodile sharks, unlike the thresher sharks have greatly reduced caudal fins. Besides having round black eyes that are not protected unlike most other sharks, mackerel sharks have five pairs of gills, small denticles and staggeringly reduced spiracles. The sharks are commonly blue or blue-gray and have their body temperatures maintained at slightly higher temperatures than the surrounding water. The shark manage to maintain their body temperatures in a similar manner as the tunas and bony fishes which achieve higher body temperatures than their surroundings through having counter-current vascular heat exchange systems. The essence of this slightly higher body temperature relative to the surrounding temperatures is to enable the mackerel sharks maintain a higher rate of metabolism thence warranting great bursts of energies.
Majorly, mackerel sharks inhabit tropical and temperate marine waters in the world over. The sharks prefer shallow waters while others like the goblin sharks opt for marine waters with sloping beds. Little is known about the behaviors of the few species mackerel sharks that inhabit deep oceans. However, it is known that the sharks, regardless of their preferred habitat, display varying behaviors in terms of feeding and metabolism. The active species of the mackerel sharks are slightly warm-blooded (laeterothermic) hence are emblematic for their ability to swim at surprisingly impressive speeds; the filter feeding species are relatively more sluggish for unknown reasons. Most of the mackerel sharks can leap out of water to evade predators, snatch prey or get rid of parasites, thanks to their lunate caudal fin. A big percentage of sharks are innately predatory with an inclination to feed on fishes and as mention above, some exhibit filter-feeding habits. Notwithstanding, there are some species of the mackerel sharks that feed principally on zooplanktons.
The article also insightfully states that lamniforme species are commonly preyed upon by other sharks including their own kinds. The sharks give birth to live young ones that develop in the utero while feeding on the content of the yolk sacs. Different species of mackerel sharks have differing gestation periods that are obscure. As the author of the article asseverates, some mackerel sharks have gestation periods between eight to one year while others stay in enceinte state for as long as eighteen months. The shark showcase similar courtship behavior to other sharks; the male sharks bite the female sharks to make them subservient prior to copulation and during copulation.
The flesh of mackerel sharks is edible by human beings and is mostly consumed in, smoked, frozen, fresh or dried-salted forms. Their fins are widely sought by some industries that use them in making shark fin soup; industries that the author describe as “destructive”. Sport fishing of the sharks is also commonly practiced worldwide. Some of the species of mackerel sharks, for instance the sand tiger shark, grace the list of exhibition sharks in most public aquaria besides attracting tourists.
Analysis of the article
This article is an indispensable addition to the available literature on sharks. This is in light of the fact that there is a dearth number of literature particularly touching on the ancestry of sharks, their feeding habits as well as their distribution in marine waters worldwide. Typic of any journal article, the article is infested with authors opinionated stand points that, as expected, influence the manner in which the author delivers his or her message that, in turn, might affect the readership of the article. Throughout the article, the author of the article is seen posting his opinions. Statements like “Living lamniformes are among the most intensely studied and best-known sharks”, “the great white and shortfin mako, are among the most popularly known and easily recognizable of all sharks” and “The behavior of sharks that inhabit oceanic realms is generally not well known”, are merely the authors opinions; it is, however, impossible to verify whether the statements are indeed the authors opinions owing to the fact that the article is not properly cited as well as the fact that there exists tremendously limited number of academically accepted literary works on the biology of sharks. It is openly acknowledged that an author’s personal perception of the world ultimately seeps to the author’s literary works. In some instances, authors might take biased stand points in a bid to promote their belief. This is very common in articles discussing contentious issues, particularly political and religious articles. I, however, find no biased contentions in this article perhaps because of the nature of topic that the article discusses- the article addresses no contentious issue.
On the same note, I must admit that most of the author’s opinions as presented in the article promote the admissibility of the article as an apposite addition into the available literature on sharks, specifically mackerel sharks. Statements like “the great white and shortfin mako are among the most popularly known and easily recognizable of all sharks” are just obstinate opinions of the author which serve to help anyone in readership of the article appreciate the fact that shortfin mako sharks are relatively more prevalent than any other species of sharks. With regards to the statement quoted above, “phrases like the great white and shortfin mako” and “popularly known” prompted me to carry out a web search to ascertain the “greatness” and the popularity of the shortfin mako sharks as attested by the author. By using keywords like “great” “shortfin mako sharks” and “popular”, I realized that there are a number of articles on the internet that regarded the shortfin mako sharks as the most popular of all the sharks though with no empirical data being given to support such an assertion. However, I came across no article that actually dubbed the shortfin mako sharks as “the great shortfin mako sharks”.
The author intensifies the objectivity of the article by using pictures and scientific names whenever he/she finds it appropriate. On the same note, I can suggest that the admissibility of this article would be greatly enhanced had the author included statistics of the various species of the lamniformes- this would have made the article even more objective.
Intellectual benefit of the article
I have heard several times that sharks have strong jaws and have the ability to move at very high speeds. However, I have heard very little about the existence of several species of sharks, their distribution worldwide, habitats, behavior, feeding ecology and diet, and most importantly reproductive biology. Through reading the article, I have come to the recognition that there exists several species of sharks, of which some are seldom discussed. In fact, before reading the article I never knew the names of some species of sharks like Megamouth shark (Megachasma pelagios), Thresher shark (Alopias vulpinus), Goblin shark (Mitsukurina owstonin Basking shark (Cetorhinus maximus), as well as their biological names. Similarly, little did I know that sharks are characterized by variant gestation periods with some having gestation periods of up to 18 months.
The article has also enlightened me on the feeding habits of sharks. From the outward look, anyone can perceive sharks, especially due to the visual aspect of their teeth, to be primarily carnivorous. However, the article succinctly states, although there are carnivores sharks, a good number of sharks are exhibit filter feeding habits. Moreover, it is stated in the article that humans do not appear anywhere in the sharks food chain.
As mentioned earlier, sharks are perhaps the greatest marine hunters. However, little is cognized about the source of their ability to attack with very spectacular agility. The article upholds that sharks have slightly higher body temperatures than their surrounding and other marine animals, as well. This enables them to have high metabolic rates hence are capable of unleashing an enormous amount of energy at once for movement and for subduing their prey. Furthermore, this mechanism enables the mackerel sharks leap out of water to evade predators snatch prey or get rid of parasites. All in all, the article is very much informative.
Reference
Grzimek, B. “Lamniformes (Mackerel Sharks),” Grzimek’s Animal Life Encyclopedia. 4(1): 131-137, n.d.
