Thursday, February 13, 2014
Shark Week (or why you should support community radio) Part 1
Note: This program first aired on February 8, 2014.
I want to try something a little different this week, because it seems to work so well for the Discovery Channel. Millions of people tune in to Discovery Channel’s week long bonanza of programming related to our cartilaginous friends of the ocean. And because it is fundraising week here on WERU, we could use that kind of excitement and exposure. So, today on the World Around Us, I bring you Shark Week.
To be fair, and a bit more accurate, Shark Week shouldn’t just be about sharks. Sharks are in the phylum Chordata, like us, meaning they have something called a notochord as part of they embryonic development. The notochord is the primary axis of the developing embryo, and is found where, in most of us, our spinal columns end up. The notochord actually develops into the discs that end up between each of our vertebrae. If we go a bit further out on the branch of this phylogenetic tree, we see that Sharks are members of the class Chondrichthyes, the cartilaginous fish. Chondrichthyes are a group of animals that are best known for their cartilaginous skeletons. Its actually calcified cartilage, so it is structurally quite strong and can support an animal of a very large size, its just very different from the bone that makes up our skeletons. This group includes not only sharks but skates and rays, chimaeras (also known as rat fish) and the super bizarre saw fish. They are mostly marine and mostly predatory. That being said there are a few that live partially or entirely in fresh water, and still others that are scavengers or even filter feeders. There’s always an exception to the rule, in biology.
Chondrichthyans date back to the Devonian period of Earth history, about 400 million years ago. Those cartilaginous skeletons don’t fossilize very well though there have been shark fossils found with the bones of fossilized prey still in their stomachs. Sharks’ teeth are very fossilizable, and they are undisputedly in the Devonian fossil record. They are thought to have evolved quite quickly and became rather “advanced” for the time. Many of today’s sharks strongly resemble fossil specimens. This group struck on a body plan and life history that was, and still is, highly effective.
That makes what I have to talk about next, all the more disturbing. A recent study showed that fully one quarter of chondrichthyan fish are threatened, using “Red List” criteria developed by the International Union for Conservation of Nature. The primary reason for this threatened status is over fishing, both targeted and incidental or bycatch, meaning fish that are caught by mistake, or aren’t the primary target species. About a third of threatened sharks are part of a targeted fishery, much has been made in the media in the past few years about the practice of hunting sharks for their fins, a culinary status symbol in parts of Asia. A related threat is the direct persecution of this group, particularly the sharks, simply because we are afraid of them. We kill them because they are sharks. However most of the threatened Chondrichthyans are simply bycatch, and five of the seven most threatened groups are actually rays.
The life history of Chondrichthyans makes them more vulnerable to overexploitation than your average species. They tend to be slow growing and slow to mature. They have long gestation periods, and reproduce slowly. These factors all add up to a slow population growth rate, in the literature they use the phrase “intrinsically more sensitive” and I think that sums it up. The study futher identified the particular risk factors that make certain species especially vulnerable. If you are large, live near shore in shallow water and have a narrow range of depths at which you function, you are much more likely to be a threatened species. You are just that much easier to catch, as most fishing is still quite near shore and in relatively shallow water.
These are not good odds. There are just over 1000 species of Chondrichthyans, and fully a quarter are threatened, some critically. The study found that for many species, there is insufficient data to accurately assess the threat level and estimated that that as many as half of the Chondrichthyans could actually be threatened. I’m just going to come out and say it. This is not OK. That we still have fishing practices that result in substantial bycatch is ridiculous. Is this not the 21rst century? We can do better, and those of us with the technology and resources to do better need to help those who lack such access. I don’t want to point the finger at any particular nationality or ethnicity, but seriously, soup made of sharkfins? Just to show off your wealth, and throw one more endangered species at your erectile dysfunction? Lastly, killing them just to kill them because they are scary and have big teeth and sometimes mistake us for their normal prey. I think that history has shown, over and over again, that this kind of problem solving never works.
So that is a little different perhaps, than what you would find on the Discovery Channel’s Shark Week, but it is an important part of the conversation. And that is what WERU does best, it gives voice to any one of us who wants to stand up and say our piece. If you support this kind of programming, that kind of conversation, please call 1 800 643 6273 or pledge your support on line at www.weru.org Thanks for listening, and as always join us next week for another look at the world around us.
Discovery Channel Shark Week website: http://www.discovery.com/tv-shows/shark-week
The original study and article: http://elife.elifesciences.org/content/3/e00590
Nicholas Dulvy from Simon Fraser College, and others. Here’s the abstract: “The rapid expansion of human activities threatens ocean-wide biodiversity. Numerous marine animal populations have declined, yet it remains unclear whether these trends are symptomatic of a chronic accumulation of global marine extinction risk. We present the first systematic analysis of threat for a globally distributed lineage of 1,041 chondrichthyan fishes—sharks, rays, and chimaeras. We estimate that one-quarter are threatened according to IUCN Red List criteria due to overfishing (targeted and incidental). Large-bodied, shallow-water species are at greatest risk and five out of the seven most threatened families are rays. Overall chondrichthyan extinction risk is substantially higher than for most other vertebrates, and only one-third of species are considered safe. Population depletion has occurred throughout the world’s ice-free waters, but is particularly prevalent in the Indo-Pacific Biodiversity Triangle and Mediterranean Sea. Improved management of fisheries and trade is urgently needed to avoid extinctions and promote population recovery.”
The Science Daily digest version: http://www.sciencedaily.com/releases/2014/01/140122202304.htm
The sponsoring organization, the International Union for Conservation of Nature: http://www.iucn.org/
On Shark Week ratings: http://www.businessweek.com/articles/2013-08-07/shark-week-is-discoverys-great-white-ratings-machine
Lots of pretty pictures and videos of various chondricthyans: http://www.bbc.co.uk/nature/life/Chondrichthyes
Tree of Life: http://eol.org/info/442
Not a bad overview of the group: http://en.wikipedia.org/wiki/Chondrichthyes
Lots of interesting stuff particularly about the fossil evidence and other strange details: http://petrifiedwoodmuseum.org/SOChondrichthyans.htm