Overfishing, shark finning and bycatch are major threats to sharks and I have decided to focus on overfishing. In my childhood, I ate a lot of shark. We never really thought all those years where the sharks were coming from. I decided to do some research to know more about the sharks we had a children. This is of interest to me, since one of the reasons I am taking this class is after my mom and I watched a program on overfishing, it went over some of the fish that had been over fished and we were surprised to find that a lot of the oceanic food we consumed as children are not able to recuperate their numbers as fast as we thought. This is partially because it takes a long time to sexually mature for some species. Additionally, some of the fish don’t reproduce in the numbers we had once expected to see. Others have specific range. This information also applies to sharks. Many of them take a long time to reproduce. Additionally, sharks may take many years to reach reproductive age. Some of them have complex lifestyles and life cycles. Some of them are hard to track due to migration.
Overfishing is a difficult thing to control. The US has tried to control its own fishing waters. The Magnuson Fisheries Management and Conservation Act, passed in 1976 proclaimed the area 3-200 miles off the coast of the shore as the US Fishery Conservation Zone which would later be renamed into the Exclusive Economic Zone. This was to help keep foreign fishing controlled, yet also provide conservation for the fish. It has been difficult to implement though due to US Fisheries expanding capacity after foreign fisheries left. This was meant to be an incentive, but had irrefutable repercussions, since the fishers profited so much they were overfishing on an even larger scale. The regional fishing management counsels were not effective since they did not take steps to end overfishing and restore fish numbers. It is very difficult to enforce the Act.
Now, overfishing and habitat loss are affecting many fish. Yields are down in production of many major fish species including the flounder, yellowtail flounder, swordfish and red snapper. This has effects on the animals which feed off of them as well. Some fish and sharks are incidentally killed as bycatch. There is a lot of waste in the fishing industry. US fisheries are only about to operate at 60% due to overfishing and loss of habitat. Sharks are fished by accident and on purpose. Since they are sometimes fished simply for finning, and this has not been banned world-wide, even though it is not permitted in the US, it still occurs in other world shark populations.
The loss of sharks makes the other marine ecosystems suffer. There are not adequate hunters to remove unhealthy prey. This leads to a less healthy marine environment. Reef Sharks, for example, are vital to the ecosystem. With their numbers depleted, this is making things difficult for other animals. Shark number are declining. Sharks are apex predators in coral reefs and they help maintain reef ecosystems and keeping them healthy. We need to document the reefs and how the effect of the shark loss is implemented in the ecosystem. This may mean there are unhealthy animals, overpopulation of some species and more effects we still have yet to see. Whitetip and grey reef sharks are reducing in number. We can examine the Australian Great Barrier Reef for more information on a health reef. Shark populations here give an idea of the efficiency of the predators.
As we continue to view shark behavior, we find that they have natural tendency to return to their home. They do roam ranges, but they are primarily believed to poses philopatry, or the desire to return home or stay in a home area, natal are or adopted local region. Sharks are large, hard to study and they do have migrations. They are difficult to tag and they are not easy to track using normal methods. They have low genetic variation and are therefore not easy to resolve through population genetics to get answers. Although they have long range migration for some sharks in some species, the find that there is strong sex-specific desires which means there is sex segregation. This is a good example, when studying the Scyliorhinus canicula. O her sharks such as blacknose sharks have also been seeing and studied for their movements which they also return to an original home. In this example in Florida. Tampa Bay sharks were also show through CSR tags put on by the National Marine Fisheries Service in Panama, City Florida, to also show philopatry.
Philopatry has effects on fishing through a variety of reasons. It is one reason why areas tend to get wiped out of certain shark populations. Since they are leaving, this reduces the local numbers. Other sharks are less likely to migrate to a region they were not raised in. By comparing genetic evidence, there is some support for philopatry, which also contributes to the reduction of fish populations. Since the fish numbers are low in some regions, they are not able to make up their numbers. The entire area is reduced! The confirmation of philopatry is still being determined in shark populations, but behavior, genetics and fishery data all show that there is a philopatric desire for sharks to remain near the nurseries, mating areas and feeding areas which may have evolved in their early years. This is partially because this is one of the best regions for young to survive. But as we overfish, sometimes in these areas, the numbers dwindle, and it in fact becomes a dangerous place for them to be. Local stock can be depleted.
SOURCE
Where Have All The Fishes Gone. Safina, Carl. Science and Technology. Spring 1994. http://blueocean.org/files/Safina1994SciandTech.pdf
Ongoing Collapse of Coral-Reef Shark Populations. William D. Robbins, Mizue Hisano, Sean R. Connolly, J. Howard Choat. Current Biology. Volume 16, Issue 23, 5 December 2006, Pages 2314–2319. http://www.sciencedirect.com/science/article/pii/S0960982206022767
Evidence of Philopatry in Sharks and Implications for the Management of Shark Fisheries. J. Northw. Atl. Fish. Sci., Vol. 35: 239–247. 17 November 2004. R. E. Hueter and M. R. Heupel and E. J. Heist and D. B. Keeney. http://journal.nafo.int/dnn/Portals/0/2005/7-hueter.pdf
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