The Blog Aquatic » whale shark News, opinions, photos and facts from Ocean Conservancy Thu, 28 Aug 2014 17:32:30 +0000 en-US hourly 1 Interview: Dr. Eric Hoffmayer on Tracking Whale Sharks in the Gulf of Mexico Thu, 30 Jan 2014 13:00:08 +0000 Alexis Baldera

Dr. Hoffmayer and a whale shark in the Gulf of Mexico. [Photo: Jim Franks]

(This blog is part of a series of interviews with scientists who are championing marine research in the Gulf of Mexico.)

A preeminent whale shark expert and ecophysiologist, Dr. Eric R. Hoffmayer is a research fishery biologist with the National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories. His interest in coastal shark species ranges from their reproduction and life history to their specific abundance, distribution and feeding ecology in nursery grounds. He has pursued a particular interest in the Gulf of Mexico’s whale sharks, the largest fish in the ocean, compiling information on their basic biology, habitat use and movement patterns.

Ocean Conservancy:  How much is known generally about the whale sharks found in the Gulf of Mexico? What is the size of the population?

Dr. Hoffmayer:  Ironically, even though whale sharks are the largest fish in the ocean, we still know so little about them, specifically here in the Gulf of Mexico. We know from our research efforts, as well as from research efforts of our colleagues in the southern Gulf, that whale sharks are relatively common in the Gulf. Unfortunately, due to their highly migratory nature and preference for offshore habitats, we still do not have a good population estimate for this region. However, colleagues working in the southern Gulf have estimated that between 500 and 900 individuals occur off the Yucatan Peninsula. In the northern Gulf, whale sharks occur along the continental shelf edge from Brownsville, Texas, to the Florida Keys and commonly occur off the mouth of the Mississippi River.

OC:  Tell us about the relationship between tuna and whale sharks.

Dr. H.:  Whale sharks associate with other tuna species (e.g., yellowfin, blackfin and skipjack) in the fall. Whale sharks work together with the tuna to feed on sardines. Tuna will concentrate the sardines at the surface and whale sharks will position themselves vertically in the water column to feed on the sardines. It is amazing to see a whale shark feeding vertically in the water column. We don’t know how often whale sharks associate with tunas during this time, but there have been days where every large school of tuna that we came across had at least one whale shark in the middle feeding.

OC:  What do we know about whale shark movements through the Gulf?

Dr. H.:  We know from various tagging efforts that whale sharks move throughout the waters of the Gulf of Mexico. During summer, they tend to aggregate off the mouth of the Mississippi River in the northern Gulf and off the Yucatan Peninsula in the southern Gulf. They radiate throughout the Gulf during the fall; however, the biggest mystery is where the sharks reside during winter and spring. Our satellite tag data is relatively limited during this time, due to the short retention times of the tags (less than six months). As technology improves, we are hoping to be able to track individuals for longer periods (one to two years), and we should be able to gain a better understanding of their seasonal movement patterns in this region.

OC:  How many Gulf sightings of whale sharks were logged in 2013?

Dr. H.:  There were 35 whale shark sightings reported to us from the northern Gulf during 2013, the majority of which occurred during May and June. We have been averaging about 80 sightings a year since 2008, but our numbers were down in 2012-13.

OC:  How many whale sharks did you and your colleagues tag in the Gulf during 2013?

Dr. H.:  In collaboration with our partners at the Louisiana Department of Wildlife and Fisheries (LDWF) we were able to deploy satellite tags on 10 whale sharks this year. Five sharks were tagged with pop-up satellite tags that provide daily position estimates along with detailed temperature and depth data, and five were tagged with towable satellite position tags (SPOT) that only provide detailed location data. The SPOTs only send data to the satellites when the sharks are at or near the surface. Our data has shown that whale sharks in the northern Gulf spend roughly 80 percent of their time in surface waters, usually coming to the surface 10 to 12 times a day.

While the pop-up satellite tags tend to remain attached to the sharks anywhere from one to six months, the satellite position tags will stay on the shark from about two weeks to three months. We are currently in the second year of a three-year project. Our goal is to tag and track the movements of 20 to 30 whale sharks to gain a better understanding of their movement and habitat-use patterns in the northern Gulf.

Left side view of a whale shark showing the distinctive markings by which researchers identify individuals. [Photo: Andy Murch]

OC:  Why is whale shark tagging important?

Dr. H.:  Our tagging work, which consists of the use of photo identification and satellite tags, will help us answer basic questions about movement and habitat-use patterns as well as help estimate population size for whale sharks in the northern Gulf. For example, we are trying to get a basic understanding of what the population is doing. Is it a migratory population? A resident population? A mixture of both?

Ultimately, if we tag enough sharks, we can start identifying their essential habitat requirements in the Gulf. Then we can compare habitat use based on satellite tag and sightings data to get a better understanding of their movements and distribution. Ultimately, we want to know their long-term migratory patterns.

Whale shark aggregation in the Gulf in June 2010. [Photo: Jennifer McKinney]

OC:  Tell us a bit more about the questions that still need to be answered about whale sharks.

Dr. H.:  There are always more questions to be answered. We still need to answer some very basic questions. For example, do whale sharks tend to stay together in aggregations or are they solitary most of the time and only sporadically form these large aggregations? In the southern Gulf, large aggregations of whale sharks occur consistently in relatively localized areas off the Yucatan Peninsula. We are just starting to understand the aggregation behavior in the northern Gulf.

We are also eager to learn more about where whale sharks go in the winter and spring. There is some indication whale sharks from both the northern and southern Gulf regions move to an area in the southwestern Gulf to overwinter. This could represent another seasonal aggregation site for whale sharks in the Gulf. Additional tagging data collected during winter and spring will help answer this question.

Then there are questions about age-based movements. Are the smaller sharks staying local and the larger animals moving? Or vice versa? It appears from our work that the large aggregations we encounter predominantly consist of smaller sharks. Are the larger sharks more nomadic?

We’re also lacking information on multiple-year movement patterns that will help us answer some of these questions. I hope that as technology advances, we will be able to address some of the longer-term movement questions.

OC:  What do we know about whale shark aggregation in the northern Gulf?

Dr. H.:  Whale sharks tend to aggregate in large numbers in the northern Gulf during summer at some of the topographic features along the continental shelf edge. One of those features that we have been monitoring the last few years is Ewing Bank. We would not have known about these aggregation sites without the help of the various “citizen scientists” who contributed to our Northern Gulf of Mexico Whale Shark Sightings Survey. The numerous reports of aggregations from the public allowed us to direct our fieldwork to places such as Ewing Bank to maximize our research effort.

OC:  Why do aggregations occur in certain areas, such as Ewing Bank, west of the mouth of the Mississippi River?

Dr. H.:  Most of the aggregations reported to us occurred around Ewing Bank near the continental shelf edge. Other banks may also be utilized by whale sharks, but we need more sightings and tag data to direct us to them. When we investigated the Ewing Bank area we found that sharks were feeding on fish eggs.

Thus far, we have had four aggregation encounters where whale sharks were feeding on little tunny (Euthynnus alletteratus) eggs. All four aggregations documented in the northern Gulf occurred in June, all around the time of a full moon. The little tunny spawn during full moons, so we are conducting surveys around full moons to see if sharks are aggregating and eating these fish eggs. As a side note, four of the five SPOT-tagged sharks from 2013 spent eight consecutive days near Ewing Bank after we tagged them, presumably feeding on little tunny spawn. We need to gain a better understanding of the dynamics of these aggregation events.

OC:  The Northern Gulf of Mexico Whale Shark Research Program originated at the University of Southern Mississippi Gulf Coast Research Laboratory, but the program has been expanded in recent years?

Dr. H.:  Yes, our Whale Shark Research Program has several partners, including the University of Southern Mississippi’s Gulf Coast Research Laboratory, NOAA’s National Marine Fisheries Service, LDWF and On Wings of Care. In fact, LDWF has been funding our most recent tagging efforts.

OC:  The Northern Gulf of Mexico Whale Shark Research Program encourages public involvement in this ongoing research effort, and there’s a website for reporting sightings, correct?

Dr. H.:  Yes, we are interested in sightings and photographs. As the website will also tell you, we are very interested in photographs of whale sharks, especially underwater photographs from the left side. We can identify individual animals using the unique spot patterns on their left sides. People can report sightings here:

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Can’t Get Enough of Sharks? Check Out Our Best Shark Posts Fri, 02 Aug 2013 17:05:20 +0000 Leigh Franke Lemon Shark

Credit: Jillian Morris

“SHARK!” Does the word conjure up images of a fin slicing toward you in the open ocean or on the edge of your seat completely absorbed in one of the year’s best television specials?

In preparation for Shark Week, which starts this Sunday, we’ve put together a roundup of some of our best shark blog posts from the past year:

What’s Your Shark IQ? How much do you think you know about sharks? Before taking a deep dive into the world of these complex creatures, test your basic knowledge with our short quiz. Do you know which shark swims the fastest?

Dreaming of Swimming with Sharks? Start with “the Domino” Now that you’re schooled on these big fish, take a look at the biggest of all, the whale shark. They are nicknamed “dominoes” because of their unique spots that can be used to track individual animals throughout their lifetimes. Watch what it’s like to swim in the water with the fish that can grow as big as a school bus.

Shark Bites: How Dangerous Are They? Whale sharks are filter feeders, passively scooping up small fish and plankton that are nearby, but some sharks can pack a powerful bite. Yet, despite these sharks’ sensationalized reputation as cold-blooded killers, you’re actually more likely to have a fatal encounter with a vending machine. What other day-to-day objects and activities are more likely to kill us than the bite of a shark? You’d be surprised.

Shark Attack Survivors Fight to Save Sharks There are still, however, headlines of shark attacks every year that strike a fear in beachgoers. But you don’t often hear about what happens to the survivors after recovery. One attack survivor, Debbie Salamone, realized her unique platform for speaking up about sharks. She gathered a crew of fellow survivors, including a World Cup soccer player from South Africa, a Wall Street businessman and a surfer from Hawaii, and formed Shark Attack Survivors for Shark Conservation. If they can see the value in saving sharks, then surely everyone else can.

After all, with over 100 million killed by humans each year, sharks are a lot more vulnerable than they look. From finning to bycatch to habitat destruction, sharks face real threats to their survival.

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Test Your Ocean Knowledge: Bull Sharks, Polar Bears and Venom Thu, 11 Jul 2013 15:24:07 +0000 Carmen Yeung polar bear

Credit: Canadian Coast Guard

How much do you know about the waters that cover 70 percent of Earth’s surface and the creatures that call it home? Test your ocean knowledge with our short quiz.

Study these five questions and see how much you know:

  • What is the largest living structure on Earth?
  • How did bull sharks receive their name?
  • What is the biggest fish in the ocean?
  • What is the most venomous marine animal?
  • How are polar bears able to walk on ice?

Stumped? Click the link below to see the answers.

What’s the largest living structure on Earth?

The Great Barrier Reef. This stunning Australian wonder, visible from space, is composed of nearly 3,000 individual reefs and stretches for 1,600 miles.

How did bull sharks receive their name?

Bull sharks have a reputation for being fighters. This characteristic, accompanied by their short and blunt snouts, helped them gain the name “bull shark.”

What is the biggest fish in the ocean?

The whale shark. They can grow to be up to 50 feet long and weigh as much as 40 tons. These gentle giants eat mostly floating organisms that they strain from the water through their 3-feet-wide mouths as they swim.

What is the most venomous marine animal?

The Australian box jellyfish. The venom of these highly advanced predators, often called sea wasps, contains toxins that attack the heart, nervous system and skin cells. Their tentacles can reach 10 feet in length with body sizes reaching up to 1 foot in diameter.

How are polar bears able to walk on ice?

The rough pads and fur of a polar bear’s large paws help it grip the ice more easily and avoid slipping when walking on it.

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Filter Feeding Explained: Whale Sharks vs. Baleen Whales Thu, 31 May 2012 18:02:15 +0000 Carmen Yeung

Suddenly out of the deep blue water appears a whale shark directly beneath me. The gentle giant moved gracefully to the surface of the water and began feeding next to me. I had been snorkeling off the coast of Tofo in Mozambique and felt that this was a dream come true. Experiences like this make me appreciate the variety of nature’s feeding techniques. You see whale sharks and baleen whales are both filter feeders, animals that eat by straining tiny food, like plankton, from the water. But how they go about filter feeding is completely different.

In whale sharks, teeth don’t play a major role in feeding. In one of their filter-feeding methods, they suction water into their mouths at high velocities while remaining stationary. Food moves through filtering pads that cover the entrance of their throats. The filtering pads are broad mess pads full of millimeter-wide pores that act like a sieve, allowing water to pass through while capturing food particles.

Baleen whales feed in an entirely different way. There are 12 baleen whale species divided into 4 families, each of which has a slightly different feeding method. Baleen whales were named for the long plates of baleen that hang in a row (similar to the teeth of a comb) from their upper gumline. Baleen plates are flexible, strong, and made of a protein similar to our fingernails. These plates are broad at the whale’s gumline and taper into a fringe that forms a curtain inside the whale’s mouth. Generally, baleen whales strain large volumes of ocean water through their baleen plates, trapping the food on their baleen. Their food (tons of krill, other zooplankton, crustaceans, and small fish) are licked off their baleen using their tongue and swallowed.

Gray whales, a family of baleen whales, are bottom feeders. They suck sediment and small benthic crustaceans called amphipods from the sea floor. To do this, they slowly swim on their sides and filter their food through their baleen plates. By feeding this way, they often leave long trails of mud behind them, and “feeding pits” in the sea floor.

Like other baleen whales, right whales filter their food through their baleen plates, but they do it in a different way. They’re skimmers. Along the surface of the water, right whales swim with their mouth open, so food is caught in the baleen fringes inside their mouth. Check out the video below where a right whale narrowly misses eating a piece of plastic.

Whale sharks and baleen whales are both filter feeders, but when you look at the details of how they feed, you realize how different they are. Understanding animal behavior such as feeding means we can better protect them from our human activities and live together in harmony.

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