Some definitions
Sharks, rays and skates are classified as Elasmobranchs
- A skeleton made of cartilage.
- No swim bladders.
- Five to seven pairs of gills opening individually to the exterior.
- Rigid dorsal fins.
- Rough skin made up of small dermal denticles.
- The upper jaw is not fused to the skull and they have several rows of teeth, which are continually replaced.
Dimorphism
The term dimorphism means that there is a difference in traits or characteristics within a given species. In shark species this usually refers to the difference in size between male and female. Dimorphic traits may differ so radically between sexes that they can be reliably used to differentiate males from females.
Source 1
Whale Shark
Female whale sharks grow slower yet larger than males.
Source:
https://www.earth.com/news/female-whale-sharks-grow-slower-yet-larger-than-males/
By Chrissy Sexton
Earth.com staff writerA new study that tracked the development of whale sharks over ten years has produced the first evidence that males and females of this species develop differently. The investigation revealed that even though the male sharks grow at a faster rate, the females ultimately outgrow them.
The research, published by Frontiers, shows that male whale sharks grow at a faster rate, but their body development plateaus around the time they reach 8 or 9 meters. The female sharks develop more slowly, gradually reaching an average length of about 14 meters to overtake the males.
Study lead author Dr. Mark Meekan is a fish biologist at the Australian Institute of Marine Science (AIMS). He noted that whale sharks have been reported up to 18 meters long.
“That’s absolutely huge – about the size of a bendy bus on a city street. But even though they’re big, they’re growing very, very slowly. It’s only about 20cm or 30cm a year.”
The research was conducted along Western Australia’s Ningaloo Reef during 11 seasons from 2009 to 2019. The experts tracked the growth of 54 whale sharks based on the unique “fingerprint” of spots that can be used to identify individuals. According to AIMS marine scientist Dr. Brett Taylor, the team recorded more than 1, 000 whale shark measurements using stereo-video cameras.
“It’s basically two cameras set up on a frame that you push along when you’re underwater,” explained Dr. Taylor. “It works the same way our eyes do – so you can calibrate the two video recordings and get a very accurate measurement of the shark.”
For the females, there are huge advantages to being big, said Dr. Meekan. “Only one pregnant whale shark had ever been found, and she had 300 young inside her. That’s a remarkable number, most sharks would only have somewhere between two and a dozen.”
Dr. Meekan suggested the massive females are probably getting big because of the need to carry a whole lot of pups.
Ningaloo Reef in Western Australia is one of the only places in the world where whale sharks appear regularly near the shore. Swimming with the sharks at Ningaloo Reef boosts the local economy by $24 million a year. However, the iconic fish were listed as endangered in 2016.
Dr Meekan said the new findings have huge implications for conservation, with whale sharks threatened by targeted fishing and ships strikes. “If you’re a very slow-growing animal and it takes you 30 years or more to get to maturity, the chances of disaster striking before you get a chance to breed is probably quite high, and that’s a real worry for whale sharks.”
Dr Meekan said the findings also explains why groups of whale sharks that gather in tropical regions are made up almost entirely of young males. “They gather to exploit an abundance of food so they can maintain their fast growth rates.”
According to Dr. Taylor, the discovery that whale sharks plateau in their growth goes against everything scientists previously thought.”This paper has really re-written what we know about whale shark growth.”
The study is published in the journal Frontiers in Marine Science.
By Chrissy Sexton, Earth.com Staff Writer
Source:
https://www.earth.com/news/female-whale-sharks-grow-slower-yet-larger-than-males/
By Chrissy Sexton
Earth.com staff writerA new study that tracked the development of whale sharks over ten years has produced the first evidence that males and females of this species develop differently. The investigation revealed that even though the male sharks grow at a faster rate, the females ultimately outgrow them.
The research, published by Frontiers, shows that male whale sharks grow at a faster rate, but their body development plateaus around the time they reach 8 or 9 meters. The female sharks develop more slowly, gradually reaching an average length of about 14 meters to overtake the males.
Study lead author Dr. Mark Meekan is a fish biologist at the Australian Institute of Marine Science (AIMS). He noted that whale sharks have been reported up to 18 meters long.
“That’s absolutely huge – about the size of a bendy bus on a city street. But even though they’re big, they’re growing very, very slowly. It’s only about 20cm or 30cm a year.”
The research was conducted along Western Australia’s Ningaloo Reef during 11 seasons from 2009 to 2019. The experts tracked the growth of 54 whale sharks based on the unique “fingerprint” of spots that can be used to identify individuals. According to AIMS marine scientist Dr. Brett Taylor, the team recorded more than 1, 000 whale shark measurements using stereo-video cameras.
“It’s basically two cameras set up on a frame that you push along when you’re underwater,” explained Dr. Taylor. “It works the same way our eyes do – so you can calibrate the two video recordings and get a very accurate measurement of the shark.”
For the females, there are huge advantages to being big, said Dr. Meekan. “Only one pregnant whale shark had ever been found, and she had 300 young inside her. That’s a remarkable number, most sharks would only have somewhere between two and a dozen.”
Dr. Meekan suggested the massive females are probably getting big because of the need to carry a whole lot of pups.
Ningaloo Reef in Western Australia is one of the only places in the world where whale sharks appear regularly near the shore. Swimming with the sharks at Ningaloo Reef boosts the local economy by $24 million a year. However, the iconic fish were listed as endangered in 2016.
Dr Meekan said the new findings have huge implications for conservation, with whale sharks threatened by targeted fishing and ships strikes. “If you’re a very slow-growing animal and it takes you 30 years or more to get to maturity, the chances of disaster striking before you get a chance to breed is probably quite high, and that’s a real worry for whale sharks.”
Dr Meekan said the findings also explains why groups of whale sharks that gather in tropical regions are made up almost entirely of young males. “They gather to exploit an abundance of food so they can maintain their fast growth rates.”
According to Dr. Taylor, the discovery that whale sharks plateau in their growth goes against everything scientists previously thought.”This paper has really re-written what we know about whale shark growth.”
The study is published in the journal Frontiers in Marine Science.
By Chrissy Sexton, Earth.com Staff Writer
source 2
Hammer Head Variety
https://link.springer.com/article/10.1007/BF00002325
A. Pete Klimley Environmental Biology of Fishes volume 18, pages27–40 (1987)
Sexual segregation in the scalloped hammerhead shark, Sphyrna lewini
Female scalloped hammerhead sharks move offshore at a smaller size than do males to form schools composed primarily of intermediate size female sharks. This movement results in smaller females feeding more on pelagic prey than do males and with greater predatory success. It is contended that this change in habitat causes females to grow more rapidly to reproductive size. Intermediate size females grow at a more rapid rate than males. Female scalloped hammerhead sharks mature at a size larger than males. For many elasmobranch species, females: (1) occupy a different habitat, (2) grow more rapidly prior to maturity and continue growth following maturation, (3) feed on different prey with increased feeding success, and (4) reproduce at a size larger than males.
It is suggested that female segregation increases fitness, resulting in more rapid growth for the former sex. The females reach maturity at the larger size necessary to support embryonic young, yet similar age to males, matching the female reproductive lifetime to that of males.
A. Pete Klimley Environmental Biology of Fishes volume 18, pages27–40 (1987)
Sexual segregation in the scalloped hammerhead shark, Sphyrna lewini
Female scalloped hammerhead sharks move offshore at a smaller size than do males to form schools composed primarily of intermediate size female sharks. This movement results in smaller females feeding more on pelagic prey than do males and with greater predatory success. It is contended that this change in habitat causes females to grow more rapidly to reproductive size. Intermediate size females grow at a more rapid rate than males. Female scalloped hammerhead sharks mature at a size larger than males. For many elasmobranch species, females: (1) occupy a different habitat, (2) grow more rapidly prior to maturity and continue growth following maturation, (3) feed on different prey with increased feeding success, and (4) reproduce at a size larger than males.
It is suggested that female segregation increases fitness, resulting in more rapid growth for the former sex. The females reach maturity at the larger size necessary to support embryonic young, yet similar age to males, matching the female reproductive lifetime to that of males.
Source 3
https://www.republicworld.com/entertainment-news/whats-viral/female-sharks-grow-at-slower-rate-than-males-may-live-up-to-150-years.html
Male and female whale sharks grow at different rates, with females doing so more slowly but getting much larger than the males, recent research published on September 17 stated. Whale sharks are large filter-feeding carpet sharks and can be identified through their brownish-greyish colour on the back and sides with white spots, with a white underside.
For the purpose of the study, which was published in Frontiers in Marine Science, researchers tracked down the growth of 54 whale sharks over a period of 10 years. The research was conducted in the Ningaloo Reef off Australia’s west coast, where hundreds of these slow-swimming endangered fish migrate annually. Currently, the longest known whale shark is recorded to reach a height of 60 feet that is 18 meters.
As a result, they discovered that regardless of the gender, whale sharks grew maximum as a juvenile, that is about 8-12 inches annually. In addition, they also concluded that males were found to grow slightly more quickly than females, plateauing at around 26 feet (8 meters) long after reaching sexual maturity at about 30 years old. Females plateaued at around 14 meters (46 feet) when they reached sexual maturity at about age 50. Scientists also speculated that whale shark may live up to 100 to 150 years.
"Whale sharks are remarkable in that females to have massive litters of pups, up to 300 at one time. Being very large is almost certainly a prerequisite for carrying this many young inside a female’s body,” said Australian Institute of Marine Science marine biologist Mark Meekan who led the study.
Meanwhile, another study has revealed that sharks lead a more complex social life that was previously thought. According to reports, a new study published earlier this week in the Proceedings of the Royal Society journal observed grey reef sharks and discovered the sea creatures capable of cultivating deep meaningful bonds with one another that can even last for years in some cases.
Male and female whale sharks grow at different rates, with females doing so more slowly but getting much larger than the males, recent research published on September 17 stated. Whale sharks are large filter-feeding carpet sharks and can be identified through their brownish-greyish colour on the back and sides with white spots, with a white underside.
For the purpose of the study, which was published in Frontiers in Marine Science, researchers tracked down the growth of 54 whale sharks over a period of 10 years. The research was conducted in the Ningaloo Reef off Australia’s west coast, where hundreds of these slow-swimming endangered fish migrate annually. Currently, the longest known whale shark is recorded to reach a height of 60 feet that is 18 meters.
As a result, they discovered that regardless of the gender, whale sharks grew maximum as a juvenile, that is about 8-12 inches annually. In addition, they also concluded that males were found to grow slightly more quickly than females, plateauing at around 26 feet (8 meters) long after reaching sexual maturity at about 30 years old. Females plateaued at around 14 meters (46 feet) when they reached sexual maturity at about age 50. Scientists also speculated that whale shark may live up to 100 to 150 years.
"Whale sharks are remarkable in that females to have massive litters of pups, up to 300 at one time. Being very large is almost certainly a prerequisite for carrying this many young inside a female’s body,” said Australian Institute of Marine Science marine biologist Mark Meekan who led the study.
Meanwhile, another study has revealed that sharks lead a more complex social life that was previously thought. According to reports, a new study published earlier this week in the Proceedings of the Royal Society journal observed grey reef sharks and discovered the sea creatures capable of cultivating deep meaningful bonds with one another that can even last for years in some cases.
Source 4
https://www.enchantedlearning.com/subjects/sharks/anatomy/Male.shtml
SEXUAL DIMORPHISM
Female sharks are larger than males.
Males have claspers, which are elongated pelvic fin edges. Claspers are used in reproduction. Females have a cloaca, one opening that serves digestive and reproductive functions.
Some scientists believe that when a male great white shark reaches a certain large size, it turns into a female.
SEXUAL DIMORPHISM
Female sharks are larger than males.
Males have claspers, which are elongated pelvic fin edges. Claspers are used in reproduction. Females have a cloaca, one opening that serves digestive and reproductive functions.
Some scientists believe that when a male great white shark reaches a certain large size, it turns into a female.
Differences in habitat selection and reproductive strategies of male and female sharks
https://www.cambridge.org/core/books/abs/sexual-segregation-in-vertebrates/differences-in-habitat-selection-and-reproductive-strategies-of-male-and-female-sharks/
OVERVIEW
Segregation of the sexes within a species is a widespread behavioural phenomenon in both terrestrial and aquatic animals. In the marine realm, sexual segregation is exhibited by many taxa including whales, seals, seabirds and fish. Of the latter group, sharks may be particularly appropriate model animals to test theories on the mechanisms underlying sexual segregation, because sexual segregation is a general characteristic of shark populations, with both sexually dimorphic and monomorphic species being well represented among the approximately 400 extant species (Springer, 1967; Compagno, 1999).
The reproductive modes of sharks are diverse ranging from egg-laying (oviparity) to placental live-bearing (viviparity) (Wourms & Demski, 1993). Among sexually dimorphic viviparity sharks (live bearing) species, it is generally the female that is larger than the male, whilst in some oviparous (egg laying) species males are larger than females. Sexually monomorphic (no gender is larger) species also occur. Therefore, sharks possess a number of characteristics that make them an interesting alternative to terrestrial animal models for investigating the causes of sexual segregation.
In this chapter the prevalence and nature of sexual segregation in sharks is described and the relationship with reproductive modes is explored. Hypotheses suggested to account for sexual segregation in sharks are examined with respect to new field and laboratory behaviour studies of males and females of a monomorphic species, the lesser spotted dogfish (Scyliorhinus canicula). The chapter concludes by drawing together the main points from all shark studies to date, and suggests future directions for research in this area.
https://www.cambridge.org/core/books/abs/sexual-segregation-in-vertebrates/differences-in-habitat-selection-and-reproductive-strategies-of-male-and-female-sharks/
OVERVIEW
Segregation of the sexes within a species is a widespread behavioural phenomenon in both terrestrial and aquatic animals. In the marine realm, sexual segregation is exhibited by many taxa including whales, seals, seabirds and fish. Of the latter group, sharks may be particularly appropriate model animals to test theories on the mechanisms underlying sexual segregation, because sexual segregation is a general characteristic of shark populations, with both sexually dimorphic and monomorphic species being well represented among the approximately 400 extant species (Springer, 1967; Compagno, 1999).
The reproductive modes of sharks are diverse ranging from egg-laying (oviparity) to placental live-bearing (viviparity) (Wourms & Demski, 1993). Among sexually dimorphic viviparity sharks (live bearing) species, it is generally the female that is larger than the male, whilst in some oviparous (egg laying) species males are larger than females. Sexually monomorphic (no gender is larger) species also occur. Therefore, sharks possess a number of characteristics that make them an interesting alternative to terrestrial animal models for investigating the causes of sexual segregation.
In this chapter the prevalence and nature of sexual segregation in sharks is described and the relationship with reproductive modes is explored. Hypotheses suggested to account for sexual segregation in sharks are examined with respect to new field and laboratory behaviour studies of males and females of a monomorphic species, the lesser spotted dogfish (Scyliorhinus canicula). The chapter concludes by drawing together the main points from all shark studies to date, and suggests future directions for research in this area.