Chondrichthyes & Human Hunters

Human Hunters a. The natural enemies of sharks include other sharks, killer whales and the most dangerous to sharks, by far, are humans a. The natural enemies of sharks include other sharks, killer whales and the most dangerous to sharks, by far, are humans b. Gill nets kill sharks and mammals when the intended catch is actually fish. Sharks can drown if they do not have water running over their gills.

Gill Net

 Thresher Shark caught in gill net

Gill Net

Lemon Shark Caught in Gill Net

Gill Net

Life history strategy of sharks  Because sharks are slow breeders their populations are very vulnerable to an increase in adult mortality and/or a reduction in survival of offspring.  In recent years fishing has drastically increased adult mortality and caused many shark populations to decline sharply.

Fishing and sharks   Historical records by early explorers, merchants and others often mention the number and large size of the sharks that trailed their ships.   Sharks were competitors for the schools of herring, mackerel, capelin and other commercial that humans hunted, but sharks themselves were not fished for.   In the early 20 th century the seas of the world still teemed with sharks, but that has changed dramatically.

Fishing and sharks  In the 1950’s long-line fisheries for tuna, swordfish, marlin and other prized species treated sharks as a nuisance by-catch and many were cut free.  Today the growing wealth of Asian countries, where shark fins are a delicacy, has made them a valuable catch.  Imports have tripled since 1980  Hong Kong & China are the world’s largest importers

Fishing and sharks  Shark Fin Soup: Upwards of $100/bowl  Traditionally served at celebrations

Fishing and sharks  “Boosts sexual potency,” “enhances skin quality,” “increases one’s qi”

Fishing and sharks  Connected to many Chinese medicines

Shark Fins

Market in Singapore

Fishing and sharks  Dried sharkfin can cost more than $500 a kilo and sharkfin soup up to $100 a bowl.  Longliners can set lines as much as 80 miles long that contain 30,000 baited hooks.  In 1997 Hawaiian longliners caught more than 100,000 sharks and tossed almost 99% of the body mass back. Why? They just kept the fins.

projects/projects/ Shark_Finning_ -_dead_shark_in_ocean.jpg

Fishing and sharks  As worldwide fish stocks have declined, and often collapsed, less desirable species including sharks have been targeted by commercial fishing fleets.  As cod stocks collapsed, species such as spiny dogfish (marketed as “rock cod”) began to be served as a replacement in fish and chips.

Fishing and sharks  Some species populations have been devastated.  Once the oceanic whitetip was probably the commonest large animal in the world. Today it’s numbers have declined 150-fold in the Gulf of Mexico and probably by the same amount elsewhere.

Oceanic whitetip (Red Sea)

Fishing and sharks  Along with declines in numbers another pattern common to other fisheries has emerged, the sizes of the animals caught has fallen.  Between the 1950’s and 1990’s the size of individuals caught fell in a variety of species.

Fishing and sharks  Percentage decline in size of individuals caught Oceanic whitetips (-33%) Oceanic whitetips (-33%) Mako (-50%) Mako (-50%) Blue (-50%) Blue (-50%) Dusky (-60%) Dusky (-60%) Silky (-83%) Silky (-83%)

Fishing and sharks

 This decline is because fishing often preferentially removes older animals, and even if it doesn’t, fishing pressure is so intense that animals don’t live long enough to grow large.

Fishing and sharks  The simple truth is that shark populations cannot be intensively harvested sustainably.  They are long-lived, slow maturing and slow reproducing.  Summary Summary

Current Failures: 3rd: 72.76% Average5 th : 84.13% Average (38, F, P) (46, F) (41, F, P) (59, F) (43, F, P) (45, F, P)6 th : 83.85% Average (46, F, P) (48, P) (59, F) Exam on Tuesday (52, P) Summative Aquarium Data due Friday (54, P) (55, F) 4 th : 83.24% Average (19, F, P), (48, P) (63, P) F = Failed Exam P = Missing Project

Today: 02/19/2014 1) 1) Water changes/tank maintenance. If you have a canister filter you need to clean that out today. If your tank has a blue star drawn on it you MUST turn in a copy of your tank chemistry 2) 2) Once you have finished, continue to work on your lab. The chondrichthyes specimens will not be out today, so I recommend that you work on “Station #5” 3) 3) Once everyone has finished with their tanks we will take a quiz 4) 4) If you need a few bonus points, come talk to me. I have a couple of tanks that need some extra care. 5) 5) 3 rd Period – We will have an observer tomorrow

Lab Groups: 1) 1) No more than 3 per group 2) 2) You must move through the stations as a group. 3) 3) I will be monitoring who is helping & who is not. 4) 4) DO NOT touch any of the specimen unless you are wearing gloves. m.Socrative.com  Completion quiz grade Room:

Lab Charts:

1. Ganges shark (Freshwater species) 2. Borneo shark 3. Basking shark - North Pacific & Northeast Atlantic sub-populations 4. Speartooth shark 5. Whitefin Topeshark 6. Angular Angel shark - Brazilian sub- population 7. Smoothback Angel shark 8. Spinner shark - Northwest Atlantic sub- population 9. Pondicherry shark 10. Smoothtooth Blacktip Top 20 Most Endangered Species of Sharks

11. Blacktip shark - Northwest Atlantic sub- population 12. Dusky shark - Northwest Atlantic & Gulf of Mexico sub-populations 13. Grey Nurse shark (aka Sand Tiger) 14. Great White shark 15. Gulper shark 16. Basking shark 17. School shark (aka Tope shark) 18. Bluegray Carpetshark 19. Porbeagle shark 20. Whale Shark