Research by marine biologists from Wageningen University has shown that feeding on zooplankton by scleractinian corals has been greatly underestimated.
|Largest coral fish first to go|
|Written by Douglas Fenner, Ph.D.|
The largest fish on coral reefs were the first to go. “You don’t know what you’ve got ‘till it’s gone,” as we're only now finding out. Read more about the current ongoing decline of large coral fish populations.
Many reef scientists (including the author) have spent their entire careers diving on reefs that have few big fish, and have never questioned whether that was normal or natural. Seeing big fish like sharks, humphead wrasse, bumphead parrots, mantas, goliath grouper and giant grouper, is very exciting for divers, and a big attraction for dive operators. One dive operator in Australia estimated that a single shark that he could reliably bring divers to might be worth $25,000 to his operation. In part, they are so exciting because they are so rare today. They are rare on most reefs anywhere near people.
Figure 1: The giant manta ray (Manta birostris) is one of the most exciting animals divers may encounter whilst traversing the tropical seas (photograph: Hans Leijnse).
I dove for years in the Caribbean, and only once saw a goliath grouper, which was just a juvenile. I’ve been diving for years in many places in the Indo-Pacific, and have only twice seen schools of bumphead parrots, both times of only about a dozen individuals. I’ve only once seen a full size adult humphead wrasse. It is very easy to assume that reefs have always been the way that we first saw them, and judge their future condition based on that. As reefs degrade, each generation uses a lower condition as the baseline to judge further losses. This is called the “shifting baseline” (Sheppard, 1995).
In the last few years, there have been flurries of reports on the fish communities at very remote coral reefs in the Pacific, which are nearly pristine. First, a report on the Northwestern Hawaiian Islands was published by Friedlander and De Martini (2002). Tourists can only go to the “main Hawaiian Islands” at the southeast end of the chain. The islands and reefs in the Northwest beyond Kaui are too small (though Midway briefly had a dive tourism operation). As it turns out, they are virtually swarming with big fish compared to the main Hawaiian Islands. The most common big fish there is giant trevally (Caranx ignobilis), which reaches 1.7 meters in length (5 feet) and an impressive 68 kg (150 pounds) maximum. But there are also lots of sharks such as grey reef sharks and Galapagos sharks. These big predator fish are called “apex predators” because they are at the apex of the food chain. Amazingly, they compose around half of all the weight (“biomass”) of all the reef fish on these reefs (Birkeland and Friedlander, 2001). In contrast, when large areas of reefs around the main Hawaiian Islands are surveyed, there are very few sharks at all. I have snorkeled a lot in the main Hawaiian Islands (and wrote a book on Hawaiian corals, “Corals of Hawaii”), but can’t remember ever seeing a shark there. If you snorkel or dive in Hawaii, you will be surrounded by beautiful small fish (only), very different from a natural reef.
Figure 2. Reef fish community composition in Hawaii. There are very few humans in the NW Hawaiian Islands, and many in the main Hawaiian Islands. Redrawn from Birkeland and Friedlander (2001).
More recently, studies in the Line Islands south of Hawaii, have found that there, too, about half of the fish biomass is represented by big fish (Stevenson, 2006; Pala, 2007; Sandin et al. 2008). The fish expert, Dr. Gerry Allen, reports that in the Phoenix Islands (west of the Line Islands), in a one-hour dive, an average of about 15 sharks were seen. On many reefs near people, you may have to dive 100 or more dives to see one shark. In the Phoenix Is., you would see about 1500 sharks in those 100 dives... a stunning difference.
A recent report from Australia reports that while the Cocos-Keeling Islands in the Indian Ocean (owned by Australia) which have no fishing have abundant sharks, sharks are much less abundant on the Great Barrier Reef (GBR) in areas open to fishing (which until recently was most of the reef) (Robbins et al. 2006). In the few little areas of the GBR where people are not allowed to go, sharks are abundant like in Cocos-Keeling. Surprisingly, in areas where fishing is not allowed but people can go, sharks are in low abundance similar to in areas where fishing is allowed. Apparently, people are poaching sharks in no-take MPAs, and only no-go areas provide enough protection. The authors were able to measure the rate at which sharks are declining on the GBR, and it is rapid. Fishing in Queensland (where the GBR is) is controlled by the Queensland Department of Primary Industries, which so far has refused to tighten up shark fishing regulations, and claims it is well regulated. The facts show otherwise for reef sharks. The story is going around that fishermen who fish for coral cod (grouper) on the GBR and who make quite a bit of money off that, do not like to pull up just the head of a coral cod that a shark has eaten while it was on their line. So they deliberately catch sharks, kill them, and throw them back.
"Inferred and projected declines such as ours appear sufficient to warrant “Critically Endangered” status under the IUCN Red List criteria for coral shark species" – Robbins et al, 2006
Robbins et al. (2006) wrote, “Our data suggest that for coral-reef sharks, immediate and substantial reductions in shark fishing will be required for their ongoing collapse to be reversed.” ”Together, these findings indicate that extirpation of these species from fished coral-reef ecosystems is an imminent likelihood in the absence of substantial changes to coral-reef management.” “Inferred and projected declines such as ours appear sufficient to warrant “Critically Endangered” status under the IUCN Red List (A3d) criteria for this study area for both species.” “Moreover, the magnitude of the population decline is severe: Median rates of population decline are 7% per annum for whitetip reef sharks and 17% for grey reef sharks. If current population trends continue unabated, the abundance of whitetip reef sharks and grey reef sharks present on legally fished reefs will be reduced to only 5% and 0.1% respectively, of their present-day no-entry abundance levels within 20 years.” “The minimum change in mortality necessary to produce a median estimated population growth rate of 1.0 (i.e., population stability) was calculated for each species. Analyses indicate that reductions in annual mortality by one-third (36%) for the whitetip shark and one half (49%) for the gray reef shark would be required to halt these ongoing declines. However, with commercial catches of sharks nearly quadrupling on the Great Barrier Reef between 1994 and 2003, and recreational fishing also removing large numbers of sharks in Australia, the trend is strongly in the opposite direction.” “For instance, on coral reefs, food-web models indicate that trophic cascades initiated by overfishing of sharks may have contributed to the collapse of Caribbean coral-reef ecosystems.”
Figure 3. Composition of reef fish communities on islands in the Line Islands. Fishing is heaviest at Christmas and lightest at Palmyra (Redrawn from Stevenson et al. 2006).
The renowned coral reef scientist, J.E.N. “Charlie” Veron writes, “When I first worked on the Great Barrier Reef, I always felt a moment of anxiety after rolling backwards off the side of a boat to go for a dive. We all felt that. We waited for the bubbles to clear just to make sure that there wasn't a big tiger among the sharks that always gathered around. Now, anywhere in the Asian region, I swim long distances over deep water without the slightest concern, for there are virtually no sharks left, big or small. I haven't even seen big fish in any numbers around an Asian reef in years. The plight of sharks is symptomatic of what is happening to reefs.”
The vulnerability of sharks is highlighted in this quote from Nichols (1993): “Sharks possess particular biological characteristics which render then especially susceptible to high fishing pressure, and as such, qualify them as a special case for management. As apex predators, they have few natural enemies. The biological characteristics of sharks – long lived, slow growth rates, low fecundity and reproductive rates (some species do not reproduce every year), long gestation period, relatively large size at first spawning, and strongly density dependent recruitment – result in shark fisheries being particularly sensitive to overfishing.”
Knowlton and Jackson (2008) wrote, "The areas of biggest concern for the immediate future are apex predators at the top, because they are globally so rare, and corals at the bottom, because of their continuing decline, apparent vulnerability to even modest local human impacts, and extreme sensitivity to all aspects of global change. Both risk extinction if nothing is done to halt their global downward trajectories." McKleod et al. (2005) wrote, “The key interactions among species within an ecosystem are essential to maintain if ecosystem services are to be delivered. Removing or damaging some species can dramatically affect others and disrupt the ability of the system to provide desired services. Small changes to these key interactions can produce large ecosystem responses. For example, the absence of large-bodied predators at the apex of marine food webs can result in large-scale changes in the relative abundances of other species.”
"The areas of biggest concern for the immediate future are apex predators at the top and corals at the bottom. Both risk extinction if nothing is done to halt their global downward trajectories” – Knowlton & Jackson, 2008
Humphead wrasse, also called Napoleon wrasse and Maori wrasse (Chelinus undulatus) are threatened by fishing similar to sharks. These fish grow to be giants, up to 2.3 meters long (7 feet) and 191 kg (420 pounds), so more massive than most reef sharks. They are found in the Indo-Pacific, and feed mainly on shelled invertebrates. They are taken in the live food fish trade from an expanding area that covers much of the western Pacific, and sold in Hong Kong and Taiwan, where they fetch amazingly high prices. Because huge numbers are taken in the life food fish trade (the trade is worth around US$1 billion per year), they have been put on the CITES list, which is to protect them from international trade that would deplete them. But they are also taken by local fishers wherever there are people. Their abundance is inversely correlated with the abundance of people- where the human population is greatest they are nearly absent, but where there are no people or fishing is not allowed, they are most abundant. The Phoenix Islands and Wake Island (a U.S. military base) have some of the most abundant populations known (Sadovy et al. 2003).
Figure 4. Abundance of humphead wrasse as a function of human population density. Redrawn from Sadovy et al. (2003).
Bumphead parrotfish (Bolbometopon muricatum) is another large reef fish species that lives in the Indo-Pacific. They grow to 1.3 m (4 feet) long and 46 kg (101 pounds). They eat coral and algae, and commonly travel in schools of 30-50. On the Great Barrier Reef, they are most common near the reef crest at the northern end of the reef, though they also extend to the southern end. At night they sleep in the same schools, either in the open or in holes that are not large enough for them to completely fit into. They tend to sleep in the same area each night. As a result, they are particularly easy to spear at night with a flashlight and SCUBA. A fisher that finds where a school sleeps can return night after night to the same spot and spear them until the entire school has been extirpated. Populations once again are inversely related to human populations, with low populations where there are lots of people and many more where there are no people (Bellwood et al. 2003). C. Birkeland and G. Davis report that big schools of bumphead parrots were common in Guam in the 1960’s, but they were spearfished out in the 1970’s, and now they are rare. In Fiji, interviews with people revealed that when night time SCUBA spear fishing came to an island, the markets were filled with bumphead parrots, they were half or more of all fish in the markets. Now, in those same areas, they are rare and not seen in the markets. On some islands they have actually gone locally extinct (Dulvy and Polunin, 2004). In the Solomon Islands, in some areas they currently dominate markets, and areas near people have few left and fishers go farther to find more abundant populations farther from people (Aswani and Hamilton, 2004). Professor Howard Choat reports that a small group of spear fishers can fill a large skiff with them in a single night. It appears that bumphead parrots are particularly vulnerable to being extirpated by fishing.
Figure 5. Abundance of bumphead parrotfish as a function of human population density. Based on Bellwood (2003).
Giant groupers (Epinephelus lanceolatus) in the Pacific (also called Queensland groupers in Australia) can get to well over 2.7 meters (8 feet) long and 300 kg (660 pounds). They appear to be rare everywhere, including reefs without people. However, the equivalent species in the Caribbean, the goliath grouper (Epinephelus itajara), which can get to at least 2.4 m (7 feet) and 310 kg (682 pounds, and possibly 455 kg or 1001 pounds!), is a different story. Although they are rare in the Caribbean, in Florida there are pictures of the trophy catches from tourist fishing boats called “headboats” that paint a different picture. The old photos show lots of huge goliath grouper, sometimes a whole row of them, from a single day’s fishing by one tour boat. Today, the photo of the trophy board is likely to have mostly smaller fish than that. But they have been protected in the Florida Keys since 1990. Now if you dive there, you have a good chance of seeing a juvenile, maybe 3 feet and 100 pounds. Under protection, their numbers are increasing rapidly, though it will be some time until giant sizes are reached. Meantime, some fishing companies have discovered that there are fishers who find it extremely exciting to hook a huge fish, even if the hook is barbless and the fish is released. So there are tour companies that specialize in catch and release fishing for goliath grouper.
In the meantime, problems are appearing. There are catch and release fisheries for other fish as well. When these smaller fish are released, goliaths and sharks quickly learn that the fish that is released is dazed and up in the water where there is no hiding place. So goliaths and sharks hang around some fishing boats and zoom in and eat the newly released fish. This does not please the fishers, as they want to be able to catch them again. There are rumors of fishers catching sharks and/or goliaths and taking them off somewhere and killing them.
Fishing has long been known to usually remove the big fish first (e.g., Jennings et al. 1999; Dulvy et al. 2004). The incentive is for a fisher to go for the big ones, more to feed your family, or more to sell. It is usually more profitable to take the big fish (though there are specific fisheries for small fish, such as anchovies, if large numbers can be found). You can even get a measure of fishing pressure by recording the sizes of fish present; the more fishing the fewer big ones (Graham et al, 2005). Over decades, fishing can begin with the largest fish, then once they are depleted move to the next size fish, and so on down to the smallest that are still profitable. This is called “Fishing down the food web.” (Pauly et al. 1998; Pauly and Palomares, 2005) Think of the size range for reef fish- if reefs in an area have 600 species of fish, how many are large enough that people fish them, and how many are so small no one would fish them? The most diverse families of fish on reefs are gobies and damselfish, and they are too small to be fished by any but the most desperately poor fishers. So at the small end of the range on reefs, there are huge numbers of species that are too small to be fished. At the large end of the size range, there are just a few species, which are highly prized catches. Trophy catches are the largest fish, not the smallest.
Figure 6: A terminal male humphead hanging next to a proud spearfisherman, American Samoa. A specimen such as this one is of great financial importance to native islanders (Photograph: © Leslie Whaylen).
Fishing pressure increases with the size of the fish. There is now a quantitative measure of vulnerability of fishing, which incorporates a variety of things about fish that make them vulnerable to fishing (Cheung et al. 2007). There is a website with a wealth of information about all the different kinds of fish around the world, called “Fish Base”. This website gives information on each species of fish. For each species, it now gives the “vulnerability index.” The index has a range from 0 for no vulnerability to 100 for maximum. Each of the different kinds of the largest reef fish, like sharks, humphead wrasse, bumphead parrots, and goliath grouper, all have vulnerabilities on the order of 75 (out of 100). Small fish have much lower vulnerabilities, often on the order of 25-35. The striped bristletooth (surgeon), Ctenochaetus striatus, is one of the most abundant reef fish most places where it is found in the Indo-Pacific (Lieske and Myers, 2001). It has a vulnerability of 14. The largest species of reef fish are highly sensitive to fishing, but the small fish are much more resistant to fishing, with the most abundant species being highly resistant. Sharks reproduce in a way that makes it particularly hard for them to recover quickly from fishing. Unlike bony fish, they produce a few large pups, instead of masses of tiny eggs. Reef sharks typically have about 1-5 pups, once a year or every other year. Thus, their ability to increase in population rapidly is extremely limited. By contrast large female reef fish can release millions of eggs a year. The probability of survival of a single tiny fish egg (likely about 1 mm or 1/16 inch diameter) is minute compared to the probability of survival of a single shark pup. The larger the individual the better the chance of survival. But if conditions are just right, a large bony fish can have so many offspring survive they can replenish their population in one year, but that is quite impossible for a shark (or ray).
Fishing always removes fish, and almost always results in a decrease in fish abundance and biomass. The biomass of fish on reefs is higher on more lightly fished reefs, and lower on more intensely fished reefs (Knowlton and Jackson, 2008). Much of those differences comes from the removal of the big fish (Birkeland and Friedlander, 2001). If only large predators are removed, then their prey can actually increase in abundance (Graham et al. 2003). However, in most cases smaller fish are taken as well as the large predators, and smaller fish decrease as well as the large fish. This is because although they are released from predation by predatory fish, they are taken in even larger numbers by predatory humans.
The degradation of coral reefs around the world has only been recently recognized, but it has been going on for a long time. Only recently have studies of near-pristine reefs and historical records shown how degraded most reefs are, and how long this has been going on. The historical studies confirm that the big fish were depleted before the small fish (Pandofi et al. 2003; 2005). There is even archeological data showing the decline of reef fish stocks before westerners arrived (Wing and Wing, 2001). On land, humans have been implicated in the extirpation of large mammals and birds, which often disappeared about the time humans arrived on a continent such as North America. While the megafauna disappeared, the smaller species survived.
How much is a big fish worth on the fish market? A couple hundred dollars? That’s a lot to a poor fisherman in a developing country. But how much can a dive operator charge to take a diver to see that fish alive on the reef? $50 or more? Divers go nuts over really big fish, they are so exciting. How about a boatload of divers? How about a boatload of divers every day? How much total money do those divers spend on hotel room, dining, car rental, and airfare? How many people are employed by all those businesses? A single, huge, famous fish can have divers spend over a million dollars a year to see it. Alive, that fish is made of gold. Dead, it’s not worth much in comparison. Mind you, you have to be in an area where you can attract divers, but diving is much more sustainable than fishing, and the goose can go on laying the golden egg year after year. If the hotel and the dive operation are owned by people from developed countries, then the local people may get little benefit from the big fish in their own country. So I prefer to stay in locally owned hotels and go with local dive operators.
“How much is a big fish worth on the fish market? A couple hundred dollars? That’s a lot to a poor fisherman in a developing country. But how much can dive operators charge to take a diver to see that fish alive on the reef? Alive, that fish is made of gold”. – Dr. Douglas Fenner
“Save the Big Reef Fish!!” Australia protects humphead wrasse, as does Niue. Palau has now protected all it sharks, plus its humphead wrasse and bumphead parrots. American Samoa has promised to protect all of its large reef fish species, including all sharks, humphead wrasse, bumphead parrots, giant grouper, and giant trevally. They will be illegal to take by any means, throughout the territory, at all times, for all sizes of those species, by anyone. They are being protected on the basis that they are uncommon or rare, and they are exploited, and thus there is a possibility that the exploitation could drive them into local extinction. It is much easier to demonstrate that a species is rare and exploited than to prove it is overfished, so this may be a rationale for protection that has wider applicability.
Figure 7, above: Large fish such as this grouper (Epinephelus sp.) may attract lots of divers, making these animals invaluable to local economies (photograph: Hans Leijnse).
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