1.1 Sharks: solitary or group animals?  (Page 10/10)

However, why don’t male S. canicula pursue the females into the shallows to copulate? Sims et al found (2006a) that male catsharks will actually refuse to approach warmer water. The persistence of this behavior indicates that cost of fitness lost is greater than the benefits gained through copulation with the female catsharks. Sims found that the costs incurred are greater than any benefit gained by approaching females when the temperature is too high: not only is energy usage greater in increasingly warm water (due to increased metabolic rates), but spermatogenesis is also compromised (Sims, 2003). By using diel vertical movement to remain in the optimal temperature range (11-16oC), the male S. canicula can save up to 4% of energy as well as also maximizes its growth rate (Sims et al, 2006a). Spermatogonia division and testosterone biosynthesis also peak in this temperature interval, maximizing fitness (Sims, 2003). Thus male S. canicula behaviors are best explained thermal niche-fecundity hypothesis: by strictly adhering to specific temperature ranges, male catsharks minimize fitness loss.

Concluding thoughts

After journeying through the causes and benefits of size and sexual segregation, one main conclusion is reached: sharks are more instinctive creatures rather than rational thinkers. With the exception of protective segregation and sexual segregation practiced by female Sychliorhinus canicula , all the social behaviors mentioned were merely the sharks’ response to shifts their own physiology as well as biotic and abiotic factors. Overall, size segregation occurs due to prey-based aggregation, and sexual segregation, the more social grouping behavior, revolved around minimizing reproductive loss in response to environmental factors.

Discussion questions

1. Looking at the evidence provided, especially on the catsharks, Sychliorhinus canicula, and bonnethead sharks, Sphyrna tiburo, do you believe that sharks are in the process of evolving more social behaviors? What selective pressures might be involved in this evolution?
2. What other abiotic factors might influence shark populations? Biotic factors?

Glossary

• Abiotic - nonliving factors in the environment that affect animals living in a particular habitat
• Aggregations - a group of organisms formed through common interest in a particular resource
• Biotic - living factors in the environment, including variables within the organism itself, that affect animals living in a particular habitat
• Elasmobranch - members of the class Chondrichtyes, the class in which sharks are taxonomically classified
• Focal foraging – a foraging pattern that consists of continuous patrolling in areas near the initial place of prey aggregation
• Foraging dispersal – a foraging patter that consists of continuous patrolling in areas about 500-600 km away from the initial site of prey aggregation; the organism actively moves through depths of 0-2 m to 60 m
• Habitat segregation - a subcategory of social segregation dealing with the separation of the sexes where each sex uses a different habitat; can overlap with spatial segregation if the habitats are in two different areas (Conradt, 1998)
• Habitat selection - the conscious actions of an organism's usage of space affected by a variety of co-factors in both the environment and physiology of the organism
• Monomorphism – no difference in body size between the females and males of a certain species
• Oviparous - a form of reproduction where produced eggs mature outside of the mother's body after expulsion
• Ovoviviparous - a form of reproduction where produced eggs, which development independent of the mother, aren't expulsed but rather matures and hatches inside the female's body
• Refuging system – a group of organisms that gather during a certain time period for social or environmental reasons and disperse to forage individually, in pairs, or in groups the during the other time periods (Klimley&Nelson, 1984)
• Segregation – a type of grouping behavior practiced by many organisms where they sort themselves into groups by phenotypic trait, i.e. size or sex.
• Sexual dimorphism - difference in body size between the females and males of a certain species
• Size segregation - separation of the species into size-specific groups according to physical body size
• Social groups - a group of organisms formed to mutually increase the fitness of all the members
• Social segregation - separation of the sexes into two different groups within a species
• Solitary animal - organisms that don't practice intersexual segregation since they don't socially interact between the sexes let alone the opposite sex; habitat and spatial segregation could still be applied to solitary animals if they gather in aggregated populations whose ranges overlap
• Spatial segregation - a subcategory of social segregation dealing with separation of the sexes where each sex lives in a different area; can overlap with habitat segregation if the habitats are found in different areas (Conradt, 1998)
• Viviparous - a form of reproduction where the young depends on the mother for development and is birthed alive

References

• Alexander, Richard D. (1974). The Evolution of Social Behavior. Annual Review of Ecology and Systematics. 5, 325-383. 20 Mar 2010.<http://www.jstor.org/stable/2096892>.

  Source provided information on group behavior: causes and effects, detriments and benefits. Also introduced the different types of groups as well as relationships within groups.

• Coelho, R., Hazin, F.H.V., Rego, M., Tambourgi, M., Oliveira, P., Travassos, P., Carvalho, F., Burgess, G. (2009). Notes on the reproduction of the oceanic whitetip shark, Carcharhinus longimanus, in the southwestern equatorial Atlantic Ocean. Collect. Vol. Sci. Pap. ICCAT. 64, 1734-1740. Web. 20 Feb 2010.<http://www.iccat.int/Documents/CVSP/CV064_2009/no_5/CV0640501734.pdf>.

  Carcharhinus longimanus is used as an example indicating the existence of spatial size-segregation within sharks by observing the shark population caught in the Gulf of Mexico. Indications of sexual segregation setting in after adulthood is seen due to the lack of sexual segregation observed in juvenile whitetip sharks.

• Conradt, Larissa. (1998). Measuring the degree of sexual segregation in group-living animals. Journal of Animal Ecology. 67, 217-26. Web. 15 Mar 2010.<http://www.jstor.org/stable/2647490>.

  Social segregation is defined and broken down into subcategories. A factor that measures segregation is called the degree of segregation that identifies groups to be not segregated, partially segregated, or completely segregated. The concept of solitary animals is also introduced.

• Dicken, M.L., Smale, M.J., Booth, A.J. (2006). Spatial and seasoning distribution patterns of the ragged-tooth shark Carcharias taurus along the coast of South Africa. African Journal of Marine Science. 28, 603-616. Web. 20 Feb 2010.<http://www.sasaa.co.za/sasaaftp/spatialseasonalraggies1.pdf>.

  Size segregation is observed in ragged-tooth shark, Carcharias taurus, according to population distributions along the European/African shores. Sharks of different ages aren't evenly distributed throughout the coastline but segregated to certain positions along the coasts. Temperature is found to be a large factor that governs the prey of C. taurus so relationship between the abundance of the sharks are found to be directly influenced by how abundant their prey is.

• Ebert, D.A. (2002). Ontogenetic changes in the diet of the sevengill shark (Notorynchus cepedianus). Mar. Freshwater Res.53, 517-523. Web. 20 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=DA&aulast=Ebert&atitle=Ontogenetic+changes+in+the+diet+of+the+sevengill+shark+(Notorynchus+cepedianus)&title=Marine+and+freshwater+research&volume=53&issue=2&date=2002&spage=517&issn=1323-1650>.

  In Notorynchus cepedianus, ontogenetic changes causes the sharks to go after larger prey and due to the experienced hunters moving away from the younger sharks' prey and geographic area, their survivorship greatly increases. This is another example of size segregation and why it occurs.

• Ebert, D.A., Ebert, T.B. (2005). Reproduction, diet and habitat use of leopard sharks, Triakis semifasciata (Girard), in Humboldt Bay, California, USA. Mar. Freshwater Res. 56, 1089-1098. Web. 19 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=DA&aulast=Ebert&atitle=Reproduction,+diet+and+habitat+use+of+leopard+sharks,+Triakis+semifasciata(Girard),+in+Humboldt+Bay,+California,+USA&title=Marine+and+freshwater+research&volume=56&issue=8&date=2005&spage=1089&issn=1323-1650>.

  Triakis semifasciata also exhibits sexual segregation sinc e the shallows around California is predominantly inhabited by females and their young. The source of sexual segregation doesn’t appear to be for protective purposes since T. semifasciata have been found to reproduce annually. Cooperation among individuals isn’t observed; they appear to forage as a loosely aggregated group with members "eavesdropping" on other’s kills. They have been observed to forage in conspecific groups as well as with other shark species such as M. henlei, N. cepedianus, and M. californica.

• Gruber, S.H., Nelson, D.R., Morrissey, J.F. (1988). Patterns of activity and space utilization of lemon sharks, Negaprion brevirostris, in a shallow Bahamian lagoon. Bulletin of Marine Science. 43, 61-76. Web. 20 Feb 2010.<http://www.ingentaconnect.com/content/umrsmas/bullmar/1988/00000043/00000001/art00003>.

  Lemon sharks (Negaprion brevirostris) have been seen to interact with other species such as schools of jacks (Caranx) and barracudas (Sphyraena barracuda), nurse sharks (Ginglymostoma cirratum), southern stingrays (Dasyatis americana), and under special conditions, Echeneis naucrates. In situations of interaction, the lemon shark would mimic the other by matching its swim gait and follow it to keep it visible - no alarmed reactions between species. Also, lemon sharks appear to communicate among themselves since intraspecific interactions were observed where two or more individuals have been seen traveling together. These sharks are not solitary individuals: mostly seen in aggregations.

• Guttridge, T.L., Gruber, S.H., Gledhill, K.S., Croft, D.P. Sims, D.W., Krause, J. (2009). Social preferences of juvenile lemon sharks, Negaprion brevirostris. Animal behavior. 78, 543-548. Web. 4 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=TL&aulast=Guttridge&atitle=Social+preferences+of+juvenile+lemon+sharks,+Negaprion+brevirostris&id=doi:10.1016/j.anbehav.2009.06.009&title=Animal+behaviour&volume=78&issue=2&date=2009&spage=543&issn=0003-3472>.

  Found that juvenile sharks tend to congregate in groups with individuals of approximately the same size and age. Sexual and size segregation were hypothesized to be a product of either communication, courtship, predatory, or protective behavior. An experiment in a controlled environment was commited on the Negaprion brevirostris.

• Heupel, M.R., Hueter, R.E. (2002). Importance of prey density in relation to the movement patterns of juvenile blacktip sharks (Carcharhinus limbatus) within a coastal nursery area. Mar. Freshwater Res. 53, 543-550. Web. 19 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=MR&aulast=Heupel&atitle=Importance+of+prey+density+in+relation+to+the+movement+patterns+of+juvenile+blacktip+sharks+(Carcharhinus+limbatus)+within+a+coastal+nursery+area&title=Marine+and+freshwater+research&volume=53&issue=2&date=2002&spage=543&issn=1323-1650>.

  Juvenile Carcharhinus limbatus was observed to aggregate in the nurseries a certain point that doesn’t correlate with the highest prey abundance. Thus such behavior was attributed to a factor other than prey location and it was hypothesized that this aggregation was an act towards group protection.

• Heupel, M.R., Simpfendorfer, C.A. (2005). Quantitave analysis of aggregation behavior in juvenile blacktip sharks. Marine Biology. 147, 1239-1249. Web. 4 Feb 2010.<http://www.springerlink.com.ezproxy.rice.edu/content/v7148857lg2135m2/>.

  Juvenile Carcharhinus limbatus were observed to aggregate at certain times of the days in what are observed as diel rhythms. The conclusion that such behavior is for group protection and feeding efficiency was drawn.

• Heupel, M.R., Simpfendorfer, C.A., Hueter, R.E. (2004). Estimation of shark home ranges using passive monitoring techniques. Environmental Biology of Fishes. 71, 135-142. Web. 20 Feb 2010.<http://www.science.fau.edu/sharklab/courses/elasmobiology/readings/heupel.pdf>.

  It is noted that Carcharhinus limbatus spent a significant portion of their first year (6 months) within the nursery area and spent 95% of their time in the kernel, making occasional forays away from it for food. Changes in atmospheric pressure was noticed to change the home range of the juvenile sharks so it was concluded that behavior isn’t only due to the influence of prey and protection but also environment factors.

• Hight, B.V., Lowe, C.G. (2007). Elevated body temperatures of adult female leopard sharks, Triakis semifasciata, while aggregating in shallow nearshore embayments: Evidence for behavioral thermoregulation? Journal of Experimental Marine Biology and Ecology. 352, 114-128. Web. 20 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=BV&aulast=Hight&atitle=Elevated+body+temperatures+of+adult+female+leopard+sharks,+Triakis+semifasciata,+while+aggregating+in+shallow+nearshore+embayments:+Evidence+for+behavioral+thermoregulation%3F&id=doi:10.1016/j.jembe.2007.07.021&title=Journal+of+experimental+marine+biology+and+ecology&volume=352&issue=1&date=2007&spage=114&issn=0022-0981>.

  Female Triakis semifasciata are found to bask in the warmest patches of water during the day despite an obvious lack of prey. They are found to become more active during the night so sexual segregation was concluded to support the thermal niche-fecundity hypothesis in conserving the energy of the sharks during the day to improve reproduction and to expand energy in colder waters to forage.

• Hulbert, L.B., Aires-da-Silva, A.M., Gallucci, V.F., Rice, J.S. (2005). Seasoning foraging movements and migratory patterns of female Lamna ditropis tagged in William Sound, Alaska. Journal of Fish Biology. 67, 490-509. Web. 6 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=LB&aulast=Hulbert&atitle=Seasonal+foraging+movements+and+migratory+patterns+of+female+Lamna+ditropis+tagged+in+Prince+William+Sound,+Alaska&id=doi:10.1111/j.0022-1112.2005.00757.x&title=Journal+of+fish+biology&volume=67&issue=2&date=2005&spage=490&issn=0022-1112>.

  In the Lamna ditropis caught and tagged, 95% were female so sexual segregation in this species was noted. Also, the hunting behavior was observed to not be cooperative but rather of three types: focal foraging, foraging dispersal, and direct migrations. The different types of behaviors in the feeding of the sharks is attributed to the conservation of energy best of the shark by finding the optimal balance between optimal temperature and optimal prey quantity/quality.

• Klimley, A.P., Nelson, D.R. (1984). Diel movement patterns of the Scalloped hammerhead Shark (Sphyrna lewini) in relation to El Bajo Espiritu Santo: a refuging central-position social system. Behav Ecol Sociobio. 15, 45-54. Web. 20 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=AP&aulast=Klimley&atitle=Diel+movement+patterns+of+the+scalloped+hammerhead+shark+(Sphyrna+lewini)+in+relation+to+El+Bajo+Espiritu+Santo:+a+refuging+central-position+social+system&id=doi:10.1007/BF00310214&title=Behavioral+ecology+and+sociobiology&volume=15&issue=1&date=1984&spage=45&issn=0340-5443>.

  Refuging system as cited as a type of social system found within sharks where the sharks participate in everyday activities in cooperative manners. This source will be used to show the growth of theory from the 1980s to the present day model of group aggregation rather than coordinated hunting.

• Klimley, A.P., Le Boeuf, B.J., Cantara, K.M., Richert, J.E., Davis, S.F., Van Sommeran, S., Kelly, J.T. (2001). The hunting strategy of white sharks (Carcharodon carcharis) near a seal colony. Marine Biology. 138, 617-636. Web. 12 Feb 2010.<http://www.seaturtle.org/PDF/author/Klimley_2001_MarBiol.pdf>.

  The hunting strategies of Carcharodon carcharis is seen to be completely uncoordinated and that sharks often approached each others’ kills in the hope of getting a bite. They were seen to aggregate only due to the common food source rather than a group assault on the prey.

• Klimley, A. P. (1987). The determinants of sexual segregation in the scalloped hammerhead, Sphyrna lewini. Environmental Biology of Fishes. 18, 27–40. 29 Mar 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=AP&aulast=Klimley&atitle=The+determinants+of+sexual+segregation+in+the+scalloped+hammerhead+shark,+Sphyrna+lewini&id=doi:10.1007/BF00002325&title=Environmental+biology+of+fishes&volume=18&issue=1&date=1987&spage=27&issn=0378-1909>.

  Introduced the concept that sexual dimorphism exist as a means for females to match male reproductive output. Also, introduced the idea that sexual dimorphism causes the sexes to practice habitat and spatial segregation due to dietary differences.

• Le Beouf, B.J. (2004). Hunting and migratory movements of white sharks in the eastern North Pacific. Mem. Natl Inst. Polar Res. 58, 89-100. Web. 13 Feb 2010.<http://polaris.nipr.ac.jp/~penguin/oogataHP/pdfarticles/09p89-100.pdf>.

  Showed that Carcharodon carcharis is a solitary hunter and they tend to eavesdrop on each other’s kills and aggregate at a common prey habitat.

• Lowry, D., Motta, P.J. (2008). Relative importance of growth and behaviour in elasmobranch suction-feeding performance over early ontogeny. J.R. Soc. Interface. 5, 641-652. Web. 10 Feb 2010.<http://rsif.royalsocietypublishing.org.ezproxy.rice.edu/content/5/23/641.full.pdf+html>.

  The skill at which sharks are able to capture their prey is seen to be directly proportional to the age of the shark. Also, relationship in the prey consumed and the shark’s age is made.

• Myrberg, A.A., Gruber, S.H. (1974). The behavior of the bonnethead shark, Sphyrna tiburo. Copeia. 2, 358-374. Web. 20 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=AA&aulast=Myrberg+Jr&atitle=The+behavior+of+the+bonnethead+shark,+Sphyrna+tiburo&id=doi:10.2307/1442530&title=Copeia&volume=1974&issue=2&date=1974&spage=358&issn=0045-8511>.

  Sphyrna tiburo are observed to be a sexually segregated species where pairing and group travel have been observed in behaviors such as aggression, flight, food deprivation, and maintenance/courtship.

• Papastamatiou, Y.P., Wetherbee, B.M., Lowe, C.G., Crow, G.L. (2006). Distribution and diet of four species of carcharhinid shark in the Hawaiian Islands: evidence for resource partitioning and competitive exclusion. Marine Ecology Progress Series. 320, 239-251. Web. 20 Feb 2010.<http://www.hawaii.edu/HIMB/sharklab/Papastamatiou_MEPS06.pdf>.

  The overlapping diets of certain sharks bring them into interspecific competitions that determine their geographical habitats. Actual social interactions are not observed between species but rather competition of food determines their niches.

• Parker, G.A. (2006). Sexual conflict over Mating and Fertilization: An Overview. Philosophical Transactions: Biological Sciences. 361, 235-259. Web. 17 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=GA&aulast=Parker&atitle=Sexual+conflict+over+mating+and+fertilization:+an+overview&id=doi:10.1098/rstb.2005.1785&title=Philosophical+transactions.+Biological+sciences&volume=361&issue=1466&date=2006&spage=235>.

  Sexual conflict is conflict that arises between individuals of different sexes due to opposing evolutionary interests. The diel rhythms observed in the different species of sharks can be attributed to sexual segregation where the different sexes performs different behaviors at different times to optimize their lifetime reproductive fitness.

• Parsons, G.R., Hoffmayer, E.R. (2005). Seasonal changes in the distribution and relative abundance of the Atlantic Sharpnose Shark Rhizoprionodon terraenovae in the North Central Gulf of Mexico. Copeia. 4, 914-920. Web.<http://www.jstor.org/stable/4098665?&Search=yes&term=segregation&term=sharks&term=size&list=hide&searchUri=/action/doBasicSearch%3FQuery%3Dsize%2Bsegregation%2Bin%2Bsharks%26x%3D0%26y%3D0%26wc%3Don&item=15&ttl=314&returnArticleService=showArticle>.

  Environmental stress, along with the need to procreate, acts upon the Rhizoprionodon terraenovae to migrate away from the male’s normal geographic region. An environmental factor is shown to have great influence on the behavior of the shark, not only its biological needs.

• Simpfendorfer, C.A., Freitas, G.G., Wiley, T.R., Heupel, M.R. (2005). Distribution and habitat partitioning of immature bull sharks (Carcharhinus leucas) in a Southwest Florida estuary. Estuaries and Coasts. 28, 78-85. Web. 20 Feb 2010.<http://www.springerlink.com/content/g366332878168232/>.

  Carcharhinus leucas have been found to shift geographical sites of habitation as well as shift their diets with age and as a direct result of their size segregation, the younger sharks are able to have more food and have a higher fitness.

• Sims, D.W. (2003). Tractable models for testing theories about natural strategies: foraging behaviour and habitat selection of free-ranging sharks. Journal of Fish Biology. 63, 53-73.

  Different forms of reproduction and the general history of sharks were provided. Also, it discusses behaviors catsharks exhibit that indicate their segregation tendencies and what it says about why sexual segregation may occur.

• Sims, D.W., Nash, J.P., Morritt, D. (2001). Movements and activity of male and female dogfish in a tidal sea lough: alternative behavioural strategies and apparent sexual segregation. Marine Biology. 139, 1164-1175.

  Sexual segregation is observed in Scyliorhinus canicula since the female and male daily activities and habitats do not match – it’s hypothesized that it’s due to hurtful mating for the females that they avoid the males.

• Sims, D.W., Southall, E.J., Quayle, V.A., Fox, A.M. (2000). Annual social behaviour of basking sharks associated with coastal front areas. Proceedings: Biological Sciences. 267, 1897-1904. Web. 6 Feb 2010.<http://www.jstor.org/stable/2665771?cookieSet=1>.

  Sexual segregation is observed to end with courtship rituals in Cetorhinus maximus. During certain seasons of the year, sharks migrate along the thermal front and food-rich patches to copulate; in normal situations, basking shark is observed to be solitary and sexually segregated.

• Sims, D.W., Wearmouth, V.J., Southall, E.J., Hill, J.M., Moore, P., Rawlinson, K., Hutchinson, N., Budd, G.C., Righton, D., Metcalfe, J.D., Nash, J.P., Morritt, D. (2006a). Hunt warm, rest cool: bioenergetic strategy underlying diel vertical migration of benthic shark. Journal of Animal Ecology. 75, 176-190. Web. 14 Feb 2010.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=DW&aulast=Sims&atitle=Hunt+warm,+rest+cool:+bioenergetic+strategy+underlying+diel+vertical+migration+of+a+benthic+shark&id=doi:10.1111/j.1365-2656.2005.01033.x&title=Ecology+(Durham)&volume=75&date=2006&spage=176&issn=0012-9658>.

  Scyliorhinus canicula is used as a case study in order to determine why there’s diel DMV within sharks and this organism is being compared to the pelagic and mesopelagic organisms’ diel DMV. It’s seen that the DMV behavior of the catshark occurs as explained by the thermal niche-fecundity hypothesis in which they try to match energy conservation.

• Sims, D.W., Witt, M.J., Richardson, A.J., Southall, E.J., Metcalfe, J.D. (2006b). Encounter success of free-ranging marine predator movements across a dynamic prey landscape. Proc. R. Soc. B. 273, 1195-1201. Web.<http://ps4ps6lm2r.scholar.serialssolutions.com/?sid=google&auinit=DW&aulast=Sims&atitle=Encounter+success+of+free-ranging+marine+predator+movements+across+a+dynamic+prey+landscape&id=doi:10.1098/rspb.2005.3444&title=Proceedings+of+the+Royal+Society.+B,+Biological+sciences&volume=273&issue=1591&date=2006&spage=1195&issn=0962-8452>.

  Using a “random walk” model, sub-adult and adult shark predation behavior is concluded to not be random but rather something that is learned through experience. Thus size segregation is a byproduct of the sharks acting upon their instincts in hunting in an area with abundant prey.

• Wearmouth, V.J., Sims, D.W. (2008). Sexual Segregation in Marine Fish, Reptiles, Birds, and Mammals: Behavior Patterns Mechanisms and Conservation Implications. Advances in Marine Biology. 54, 107-170.

  Sexual segregation is hypothesized to be due to forage selection, predation-risk, active budget, thermal niches-fecundity, and social factors. Each is dependent on the individual organism and their lifestyle and the best way to optimize their lifetime reproductive fitness.

• Wetherbee, B. M.&Cortes, E. (2004). Food consumption and feeding habits. Biology of Sharks and their Relatives. 223–244. Web. 19 Feb 2010.<http://www.uri.edu/cels/bio/wetherbee/pubs_files/FeedingChap.pdf>.

  Overlap in habitat and prey is considered the factors that cause size segregation to occur in sharks since sharks’ diets change with their ontogeny and size. Thus size segregation wasn’t a conscious effort of the sharks. Dietary breadth is observed to generally increase with age and size.

• Wilga, C.D., Motta, P.J., Sanford, C.P. (2007). Evolution and Ecology of feeding in Elasmobranchs. Integrative and Comparative Biology. 47, 55-69. Web. 20 Feb 2010.<http://ps4ps6lm2r.search.serialssolutions.com/?sid=jstor:jstor&genre=article&issn=15407063&volume=47&pages=+55-69&spage=55&epage=69&atitle=Evolution+and+Ecology+of+Feeding+in+Elasmobranchs&date=2007&issue=1>.

  In elasmobranchs who hunt using suction, there is a positive relationship between body size and force of suction - indirectly, this infers that prey that are further away can be captured. Size segregation is again seen in that the prey hunted change with the size and age of the organism, so this affect the relative geographic locations of the sharks.

About the author

Born in and raised in Shanghai, China in 1991, I immigrated to America at the age of 6, meeting my parents for the first time since I was born. Since then, I've lived in San Antonio, Texas, a culturally diverse community seeped in history.

This topic on sharks was inspired after watching the Animal Planet Special, "Maneaters," which covered the increased aggressiveness of sharks off the coasts of Australia and the United States. I was fascinated by what made these animals tick. Sharks, being one of the living artifacts of the prehistoric age, are an awesome model for the study of the evolution of social behavior.

Thus in writing this paper, I attempted to explore fact and fiction: are sharks are primitive and instinctual as Hollywood stereotype them to be or are they a developing intellectual? After writing this paper, it made me understand sharks better as an organism.