Shark Reproduction...

Today students learned an introduction to sharks. We talked about the history of sharks, common characteristics of cartilaginous fish and then the reproductive strategies of sharks.

Not a lot is known about shark reproduction because in many cases it has never been observed. Sharks have internal fertilization and the male shark has two claspers for sperm delivery. These can be seen on male sharks protruding from the pelvic fin.

Shark reproduction is violent with males biting the female. As a result female shark skin is much thicker than the males so that this practice does not ham or kill her. She fights a little to ensure that only strong males with good genes are able to fertilize her eggs.

Some sharks are oviparous and lay eggs (pictured). These egg cases are known as mermaid's purses. You can see the baby shark and its nutrient-rich yolk through the leathery egg case.

Some sharks are viviparous and have live birth a lot like mammals.

And some sharks are ovoviviparous and keep their eggs inside the uterus before releasing them... so its making eggs and then kind of having live birth.

Shark Senses

Today we learned about shark senses. Sharks have a large brain to help process the sensory overload they must get from the SEVEN senses they have. They have the five we have plus a lateral line (pressure and vibrations) and the ampullae of lorenzini (electro-reception).

Follow this link for a cool interactive about how shark jaws stick out when they attack their prey! The interactive is down at the bottom.

If you are doing a final project on a shark... check out this new link! www.shark.ch

And once again... one try only... how much do you know about sharks? MsJ scored a 1467. Try Shark Weeks Ultimate Shark Challenge to see how much you know. Please limit yourself to 15 minutes.

Why sharks are Amazing Predators

Shark Attacks - Who Should Be Afraid?

These are some of my favorite shark graphics.

Appreciate and LEARN. 

Click on the images to make them larger.

Starting sharks!

Next up is SHARKS! Great whites in the waters off the coast of South Africa leap out of the water to chase the fur seals they want to eat that also leap out of the water.

Try Shark Weeks Ultimate Shark Challenge to see how much you know. (Play only once) MsJ scored 1370.

Fishing - Harvesting FIsh

Netting is the most popular method of commercial fishing because a lot of fish can be caught in short amount of time without a lot of effort.

One the major problems with most commercial fisheries is the amount of bycatch. Bycatch is anything caught in the net that you do not want. This could include edible fish that your company is just not equipped to process.

Most organisms brought up in nets as bycatch do not survive because they are crushed or drowned. Sea turtles and dolphins sometimes get swept into nets and drown because they cannot make it to the surface to breathe.

Most scientists and fisherman agree that the oceans have been and are being overharvested. People may not like regulations, but without regulations, many fish species that we used to commonly consume would be extinct.

Intelligent Seafood Choices

We started discussing marine harvesting and fishing today by talking about who harvests the most seafood (China), who eats the most seafood (China), and which people eat the most seafood pounds per person (the Maldives). Americans are about sixth on the list as far as consumption, but we are the number one consumer and importer of shrimp. Importing shrimp is damaging to the environment for two reasons.

1. Shrimp that are farmed in other countries are not as regulated as here in the states, so shrimp farm pollution is not as regulated and it damages coral reefs. Also many mangroves are cleared to build these farms.

2. US boats are required to have turtle excluder devices (TED) on trawl nets so that turtles do not get caught in shrimp nets and drown. Other countries do not regulate this and as a result catch and drown sea turtles.

To make a environmentally responsible seafood choices, choose shrimp that are farmed or caught in the US. For more sustainable seafood choices, check out Seafood Watch.

I went prawn fishing while in NZ!

Fish Spawning

Fish reproduce in a variety of ways. Most are broadcast spawners, meaning that when the time is right, the females release their eggs, the males release their sperm and they both meet and mix producing fertilized eggs that develop into fish fry (meroplankton) and eventually into adult fish. These snapper are spawning and you can tell by the large cloud of gametes in the water.

By producing a lot of eggs, the snapper hope to overwhelm any predators trying to make a meal so that there is no way all the fry are eaten and some will have a chance of surviving. Course there are predators that time their arrival with this spawning to eat all those nutritious eggs and gametes.... Yum!