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Fisheries Management and the Role of APEX Predators
- 6. An ecosystem: “the complex of a community of organisms and its environment functioning as an ecological unit”
Editor's Notes
- Today's talk is on fisheries management, and the role of APEX predators in coastal fisheries. We will be looking at the impact of overfishing by man, and what role do large predators (sharks, rays, etc.) play on overall fisheries and then we are going to look at how we study age and growth on these animals and the impacts of potential restoration, habitat enhancement and the restoration of these fisheries.
- This is an image of Earth from space. It is one of the most common ones seen that NASA has produced. It’s significant in the fact that what it demonstrates is the amount of oceanic surface area as compared to land mass. But, what is really critical is the interface between the oceans and the coastal zones; because the continental shelves of these areas are the ones that are the most productive in all of our fisheries, and where the impact to fisheries may occur.
- This is a satellite shot of the north-central Gulf of Mexico, and we are looking at the shorelines with it’sbarrier islands, and also the changing color of the water which is what you are seeing here and is the output of the riverene systems into the Gulf of Mexico. Obviously in this slide you can see the Mississippi River and the deltaic estuary formed by the outflow of the Mississippi River, and if you scan back to the east, you will see the Mobile Bay riverene system, and then just some smaller outputs over by Apalachicola Bay. What this tells you is that you have two major river systems that dump into the Gulf of Mexico (the Mississippi and the Mobile Bay system). Together, these two river systems drain the entire central part of the United States. I like to use a visual. If you look at all the land mass east of the Rocky Mountains and west of the Appalachians, any moisture that falls within those boundaries ends up into the Gulf of Mexico. So, these are very significant inputs into an oceanic system. Mobile Bay alone, has 43 billion gallons of water that pour into the Bay every day, and this water carries nutrients (food resources) that help to spawn plankton growth and then help to feed the entire food chain of the Gulf of Mexico.
- This is a great 3-D representation of the continental shelves within the Gulf of Mexico. You can see how the Gulf varies in size from the coast of Texas to Louisiana and Mississippi, and the wide shelf off of Florida. The shelf is very important in the fact that 90% of all fisheries, commercial and recreational, takes place along these continental shelves - a direct result of the inflow of riverene water into the oceans. In the early 80s, the United States was asked by Japan if they could come into the Gulf of Mexico for tuna long-line fisheries, and since there was not an established long-line fishery coming off any of the states along the Gulf of Mexico, the federal government allowed the tuna fisheries to come in. Unfortunately, these tuna boats came in and spent many, many months depleting the stock of yellow fin tuna, and part of the by catch issue of the yellow fin tuna were large predator sharks. This caused a demise in these large sharks, and to this day it is still seen by us as scientists, in that we don’t find some of these large predator sharks as a result of that fishery. By 1987, they closed off this, and the exclusive economic zone was established by the United States, so no foreign fleets were allowed within 200 miles of the continental shelves of the United States for fisheries purposes.
- What you see in this slide is a representation of a relatively new scientific approach to studying fisheries and that is the Ecosystem Based Fisheries Management, and in designated areas called Large Marine Ecosystems. The reason this is of significance in fisheries is that for many, many years we looked at fisheries from a single species point of view. We would look at Gulf menhaden or we might look at red fish as a single species and then we would go about trying to manage based on catch data, both commercial and recreational. But, what was missing in that whole plan of management was the fact that these fish interact ecologically with everything else in that habitat, and so to manage a species as an individual without looking at the entire ecosystem and trying to come up with a plan that manages the entire ecosystem would only result in a very poor assessment and a very poor management for that species. So, today we start looking that these things called “ecological units”. Basically, we want to know everything that is going on in these habitats to the best of our knowledge. So, it may involve plankton, benthic sampling, water column sampling, chemistry, as well as the organisms themselves, because all of that has an impact on the fisheries itself.
- This slide shows a common reef species found in the Gulf of Mexico and along the Atlantic coast as well, and that would be the red snapper. This is a highly managed fish that is very, very controversial today in that quotas for commercial and recreational fisherman have consistently gone down as mandated by a federal law that manages these species. So, in order to have a better understanding of the reproduction rates of these fish, scientists like Dr. Will Patterson (in the left hand photograph) actually do age and growth studies to determine how old are some of these large fish and what type of egg production goes on within these animals. One of the methods of doing that is to take out what is called the otolith, or ear bone, which lies behind the gill plate in these fish. That ear bone, or otolith, has rings, and those rings are attributable to yearly growth.
- These are three different images. The one on the left is that of an otolith being removed from the back of the gill head area of the fish. There are two otoliths, one on each side. The upper right hand photograph is that of a sea trout otolith, and then using a microscope after the otolith has been polished down with a diamond stone, you can actually start to look at and see the rings that are associated with age and growth. That is what allows us to age these animals, and if they are females we can actually look at the age of the female and the number of eggs that she is carrying, and that will help give us a better understanding of the reproductive capacity of that fish. As you might imagine, there is a huge economic impact when fisheries regulations take place that limit the number of any species of fish that is being regulated by state waters and/or by the federal government. For example, red fish in the 1980s and 90s were highly, highly regulated. No large red fish could be caught mainly because that population was heavily fished off the Louisiana coast, and the reproductive large females were caught and this resulted in fewer numbers of juvenile fish over the next five to ten years.Conservation efforts from groups like the Coastal Conservation Association (CCA) were able to help regulate, and help inform fisherman about the need to conserve these species and limit fishing. The end result for red fish during this time frame was that the red fish populations slowly grew and today we have a very strong component of redfish from juveniles to reproductive adults; but, that’s through these conservation efforts. So, they do play a very important role in fueling the economy, both commercially and in sport fishing. When you look at a fishery from a sports perspective, you have to take into account the sales of boats, gasoline, oil, fishing gear, tackle, and all the other resources that go along with the fisheries (hotel rooms, restaurants, etc.). So, any limitation impacts that fisheries, and if the limitation is one that is very restrictive, then the economic impact can be very large for that fisheries.
- In this slide you see the red drum. Red drum is a coastal species from inshore to offshore, from Louisiana and Texas all the way over to Florida. For many years this species was never actually fished for very much other than some sports fishing, but in the 1980s, Chef Paul Prudhomme, from New Orleans, started the fad of blackened red fish. This led to a major depletion in the fisheries of brood stock red snapper that were being caught from offshore. The net result of that overfishing harvest was that the National Marine Fisheries Service had to close all red snapper fishing for many years. An organization starting in Texas and then grown Gulf-wide, the Coastal Conservation Association (CCA), got its start because of this fish, the red drum, and the organization worked very diligently to restore the stocks of red drum.Today, the red drum can be found in all of our coastal waters. There are still limits on size and numbers that you can catch, but they are plentiful for recreational fisherman. Here you see Matt Kenworthy, a graduate student at the Dauphin Island Sea Lab, and he studies these red drum. He is actually raising some in an aquaculture facility in Gulf Shores, part of the State Conservation Program.
- At this time, I’d like to take you all through the basis and analysis of a research project that involves studying APEX predators and their role in the food web of our coastal oceans. Obviously, sharks form the APEX predator in the Northern Gulf of Mexico, and so we will take a look at how we go about setting up a study and the analysis of our data, and then what our findings are when we start looking at the repercussions of eliminating one level of the food chain.
- In this very simplistic example of a coastal ocean food pyramid, it has a very important role in the understanding production in the coastal seas: the highly productive diatoms (dinoflagellates); the consumption of the primary producers by copepods, anchovies and sardines; and as we move into the upper levels of the food chain, the faster swimming and highly mobile species, the tunas and the mackerels. Finally, in the top level of the food web of our coastal oceans is the shark, and when you affect any one level of the food pyramid, it alters the entire regime in the coastal ecological oceans though that alteration. We are going to talk about how those alterations come about and some of the aspects of studying that.
- Scientists here at the Dauphin Island Sea Lab work closely with the National Marine Fisheries Service collecting data along the north-central Gulf of Mexico. In this slide, you can see long=line data that the National Marine Fisheries Service has collected since 1995 and the wide range of sample sites. Each one of those little stars is a site in which a bottom long-line was set and data collected. Also note the US Exclusive Economic Zone (EEZ). That zone, as I described earlier, was established out to 200 miles along the continental shelf of US waters. That establishment of the EEZ prohibited foreign fleets to come within the 200 mile EEZ for fishing, and left those rights to US fisherman.
- In this slide, we are showing you some data collected from the National Marine Fisheries Service and some of our data collected from the Dauphin Island Sea Lab in looking at a single species, the blacktip shark. The blacktip shark is a small coastal species that gets three to five foot in length and is often caught by local fisherman in shallow waters. The red dots indicate long-line sites in which these blacktips were caught over these timeframes, and what is significant about this slide is that, if you take a look at the center of the slide where Mobile Bay is, and you will note that there are a plethora of red dots that are to the west of Mobile Bay. We believe that this was a significant finding that the blacktip sharks were caught more to the west of Mobile Bay then to the east and led us to establish our long-line survey particularly to answer some questions about the role of the input of freshwater from Mobile Bay into the Gulf of Mexico. Mobile Bay is the fourth largest drainage basin in North America. 43 billion gallons of water pour out of Mobile Bay and into the Gulf and we felt that this might have a significant role in feeding strategies by this shark and the abundance of pray items that may be found west of Mobile Bay because the long-shore current is east to west.
- The previous slide showed us data on captures of blacktip sharks and how they seem to be more abundant to the west of Mobile Bay than to the east. That led us to establishing these four quadrats west to east to set up our survey and then the blue line shows you a north to south transect that we set up as well. So, each month we would randomly select sites within these blocks and the north–south transect to go out and set a bottom long-line. This study took place over a three year period.
- This slide shows you our north-south component in our 2009 survey, and you will note that we have two distinct stations within the Mobile Bay estuary, and then we have stations set out from 20 meters of depth all the way out to 200 meters of depth. So, this gave us our north-south component.
- This is a slide of a blacktip shark caught on our long-line. You can see in the upper left-hand corner some information about sharks in general. The blacktip shark was not the targeted species. Although we had the information that there tended to be an abundance of them to the west of Mobile Bay, the bottom long-line, as you will see very shortly, is a non-selective method of fishing, and as such, we caught many coastal sharks of different species, and part of our study was to analyze the species that could be found in each of these blocks and our north-south transect, and the numbers, the quantities of those over time. So, we would have a seasonality component to our study as well as a physical east-west and north-south parameter built in to the study.
- We use what is called a bottom long-line. This bottom long-line starts from the back of the boat with buoys that are deployed out the back of the boat, a heavy weight as you can see in the lower part of the image here, and a monofilament line that is going out through that guide. That monofilament line is one-thousand pound test fishing line, and when we clip on that weight, it takes the line to the bottom. The method that we use, the bottom long-line, is an approved method that the National Marine Fisheries Service has been using for many years.So, we duplicate exactly the methodology that the National Marine Fisheries Service uses so that our data will be compatible with their data and we can analyze our data so that we are all comparing the same information.
- Obviously, when we set a bottom long-line we have to bait the long-line itself. The long-line is similar to a trout line that anyone has ever set in freshwater to try to catch catfish. Basically, we have two drums. Each drum contains 50 hooks. We used cut mackerel for bait, and we used circle hooks versus J-hooks. Circle hooks are the preferred method for a number of reasons, mainly because they catch at a higher catch ratio, and in addition they are much easier to turn the animal loose without damage than the J-hooks. So, we set 100 baited hooks over a one-mile distance, and the long-line lays on the bottom for one hour. So, that is the method, 100 hooks, one mile in length and one hour on the bottom. That is the soak time before we start retrieving the long-line.
- Here are two scientists, Mark Grace, holding the baited hook, and Marcus Dryman, our graduate student who is working on this project. They are getting ready to attach the ganget to the vertical long-line that is going out the back of the boat, which will then sink to the bottom.
- After one hour of soak time on the bottom, the long-line is slowly reeled back in, and here are two images of different species of sharks that have been caught on the long-line. Note in the lower image that the shark is hooked through the mouth, but that the circle hook has gone all the way through and the barb is sticking out the backside. This is not damaging to the shark, and it can be easily pushed back out so that the animal remains alive, which is the role of our whole technique, to keep these guys alive and tag and release them once we have the data.
- This is CharleneDindo. She is the director of the Pelican’s Nest Science Lab, a center in Fairhope, AL (a Kindergarten to First Grade school). She teaches marine science and about sharks to these young kids, so she accompanies some of our scientists out on our boats when we are capturing, and takes lots of photographs and helps in the data analysis. In that way she has a first-hand account to relate to the students in her classroom, and the students get a broader experience by seeing their own teacher involved in the research aspect of this APEX predator study.
- The is a scalloped hammerhead shark commonly found in our coastal waters. This guy was too large to bring on board to do our measurements as you will see in the next slide.
- Here, Marcus is untangling that scalloped hammerhead from the long-line and removing the hook from his mouth. We also took a length measurement while he was in the water because this animal was too large to bring on board and do our measurements on board. But, we do have good data that shows what a length to weight ratio will be on average for this animal, so we are able to record its length and then estimate its weight by its length.
- Once the sharks are brought on board, they are handled very quickly, the hook is removed, they are measured for their length, their species is identified, their sex is identified, and you will see shortly how they are tagged and released. All of this data goes into a very large database for this APEX predator study.
- Here, again, you can get a better look at the circle hook as it is being removed from the shark’s mouth. You will note that the barb is already free of the jaw line and there has been very little damage to the animal. The other interesting aspect on this image is, if you look at the little brown objects attached to the shark in the left part of the image and again on the right part, these are parasites. One of the side aspects of doing this research is we are able to extract off these sharks these parasites and send them off to another scientist who is looking at the role of parasites in sharks.
- Part of our research is to have a better understanding of the movements of sharks along our coastal areas from inshore to offshore and east to west, and one method that we use to better understand that is the use of tags. This happens to be a tag that we insert in the muscle tissue just beneath the dorsal fin, and that tag has a number on it so we know the date that we captured this animal and all the parameters that we measured on this animal. It also has our phone number with a tag hotline. The objective of this is, once we release a shark back into the waters, in the future, perhaps, some fisherman will capture this animal, see that tag, call our number, and we can get data from him as to where he caught it, the date he caught it, and the length and weight of the animal when he caught it. This helps to fill some of the gaps in understanding the age and growth and distance travelled that these APEX predators do throughout the north central Gulf of Mexico.
- This is a different tag. It serves the same purpose, but this tag we use in smaller species in which that heavier tag might injure the animals. In this one here, we punch a hole through the dorsal fin and insert this tag through this pair of crimpers, and you will notice that this tag is a bright yellow tag in the dorsal fin easily recognized by a fisherman that may catch this animal.
- Once the animal has been measured for its length, its species has been identified, the sex of the animal has been identified, and its been tagged, we get the weight on the animal using various methods of scales. We even have for larger animals a mesh net that we can lower over the side that has a scale attached so that we can lift that net up to get the approximate weight of the shark that has been in the water.
- Once all of our measurements have been accomplished, we inject a small solution of tetracycline into the shark. This tetracycline is incorporated into the cartilage that makes up its vertebral column. As such, it is identified because it fluoresces under a florescent microscope. If this animal is caught and returned to us, we can extract the cartilaginous vertebral column, slice it very thin, polish it on a polishing wheel, and look at it under a microscope, and take a look at the tetracycline. Because the tetracycline does lay down the year that we injected it, we can get a pretty decent age on this animal based upon the date that we caught it. So, we again gather more data on the age and growth, which is very important in understanding the role of APEX predators in the ecosystem.
- Once all of our data parameters have been recorded, the animal is then lifted back over the side and tossed back into the ocean. The interesting this is, all of these measurements, the tagging techniques, removal of the hook from his mouth, all of this takes place in two to three minutes on the back of the deck of the vessel. We have to respond very quickly because our total objective in this is to return the animal healthy to the water so we can hopefully in the future gather even more information.
- Obviously, not all the sharks that we catch on the long-line survive, especially in the middle of the summer when the temperatures are very high (air temperatures in the 90s and water temperatures in the high 80s) and the oxygen levels are very low. So, sharks caught on the mile of long-line, as we slowly retrieve it, expire because of the low oxygen in the water. But, that’s not a waste, because these animals are brought back on board, brought back to the laboratory where many samples are pulled, from stomach to liver tissue to muscle tissue to look at all different aspects of this animal and its role in predation, from heavy metals to preyitems that it was feeding on. This gives us a broader understanding of the overall ecology of this animal.
- This is a very interesting slide. One of the female Atlantic sharpnose sharks that died, when we opened her up, had four baby sharks in each of her two uteri. You can see their eye formation. This was in the June, and they were getting ready to pup. Also in this slide you can see an egg developing on the left-hand side of the image that will become one of the baby sharks in the next year’s production.
- As I indicated earlier, sharks are not the only species that we get on the long-line, and data is recorded for all species caught on the long-line. This happens to be a large southern stingray. In which Dr. Driggers is removing the circle hook from the animal before we take it on board for measurements.
- We often catch red drum, this is a very large one in the 20-pound class, and we record the information for other graduate students. So, we are able to gather a lot of information from a single long-line survey.
- This loggerhead sea turtle did not bite our bait or get caught by a hook, but is swimming close to the surface as we were retrieving our long-line and got tangled into the long-line itself. We were easily able to roll the animal around and remove him from the long-line, and off he swam. You also have to have permits for what is called incidental catch, and we maintain those permits, but in almost all of our cases, these animals are released with no damage what so ever.
- In this slide here, you will see a nurse shark. We estimated its weight up to about 350 pounds in size, so we could not do a whole lot with it, and in this case, rather than trying to maneuver that hook out of the mouth of this animal because of his weight was so great, we just cut the hook off, and that hook deteriorates and falls out of the mouth of the shark.
- This is a juvenile tiger shark that was caught in the shallow waters along the Alabama-Florida line. It’s a very interesting species in that we know very little about its ecology and it’s early life, where it feeds and what it feeds on. We do know that as this animal grows to full adult, it’s a major predator in the open ocean on sea turtles. They get very large, in the eight to nine foot size and close to four to five hundred pounds.
- In an effort to help fill in some of these data gaps with these juvenile tiger sharks, the data is collected (you will note that they have a tag hanging just below the dorsal fin on this animal) and this should help us provide some information to fill that gap where the animal exists in shallow coastal waters.
- In addition to these tags that are attached to the animal, we have been using lately satellite tags. Satellite tags are very interesting, but they are very expensive. They run in the neighborhood of $1,500 to $2,000 a piece plus satellite time. But, what these do for us, is when we tag the shark with this, there is a little float that is attached to it, and as the shark nears the surface waters, that float brings an antenna to the surface, and a signal is broadcast to the satellite, which is then relayed back down to us at the Dauphin Island Sea Lab.We gather data as to the position of the shark at the time the antenna broke the surface, and the data logger has information as to where the shark has been, the depth that the shark was last feeding at, temperature and some salinity recordings as well as other parameters that can be taken from these satellite tags.So, we are able to track and monitor the movements of these sharks that are tagged with satellites, and have a much better understanding of where these guys go. In addition, what we are doing in the next couple of years is we are going to apply satellite tags, and we are going to allow schools to adopt the shark with the satellite tag and give them access to a computer at our laboratory which they can call into and better study that shark themselves, and follow its track and learn more about it. It will be a wonderful ecological learning lesson for these students that are involved in that.
- Another method used to look at sharks and rays and their movements to better identify their ecological parameters is called acoustic tags. We put a tag in the ray or the shark and have these monitors out, and every time the ray or shark passes these monitors we get a signal that is recorded so that we know how many times they have moved through that area, and this tells us if they are feeding in this area or not.
- Obviously, all young students realize that sharks are predators and top predators.
- One of the interesting aspects of our study and the reasons why we are intensely studying this that the larger oceanic pelagic sharks in the Gulf of Mexico have been pretty well caught out. They were caught out during the tuna fishing days back in the early 80s with the Japanese long-line fisheries. As a result, the large predator sharks, like silkys and duskys, their populations are extremely low. What we have been seeing is an increase in the population of rays and skates in our shoreline waters. Including cownose rays. The implications of the increase in the populations of cownose rays, as well as other rays, is their feeding habits, and that is that they eat shellfish. Some eat juvenile oysters and others eat clams and muscles, and so we see a decline in some of our shellfish habitat areas due to rays, which in result was a factor of their large predators being taken out of the ecosystem. This is just one example of an alteration of a part f the food pyramid and how it cascades up and down that food pyramid.
- I cannot end this talk on fisheries management without what has happened to the explosion of the Deep Horizon oil well off of Louisiana. The potential for this oil coming into shore and going into grass beds, slat marshes and oyster reefs will have a long term impact that will affect all of our fisheries for years to come. Precautions are being taken by all the Gulf coast governors, efforts are being made by the federal government to try to prohibit this oil from reaching shore. The worse case scenario would be for a storm, like a tropical storm or a hurricane, to take place while the storm is still out there and that would be devastating because it would push it further and further into the marshes. I cannot under estimate to you the cost that this will be to those fisheries. Systems do recover, but they don’t recover overnight. It takes years, and years, and years, and some are altered forever. So, this is a major man-induced catastrophe that should never have taken place. Time will tell whether the effects of Deep Horizon will ever be rectified trough nature itself. For more information, NOAA’s website has lots of critical information on the movement and the fate of that oil.
- Thank you for being a participant in the COSEE Central Gulf of Mexico summer institute. I hope that you learned a lot from this fisheries talk, and all the other presentations that you will participate in. I have posted two websites for you for more information, and as a teacher, I think it is going to be critical for you to go ahead and follow the results of the oil spill and what scientists will be reporting what is happening to the life in the northern Gulf of Mexico.