A busy day with bull sharks in the Everglades with Phil Matich

We had another great day in the field on Saturday.  Dolphins, alligators, roseate spoonbills, and other birds added to the experience of catching six more sharks!  We caught one shark on each of the first three longlines - 1 two-year old which we implanted a transmitter into to track its movements, and 2 one-year-olds, one of which was a shark we caught in August.  The marks from collecting tissue samples were already incredibly well-healed! (see the picture below). 

On the fourth set we had a lot more activity - while deploying the longline I felt a tug on the line after putting out ~15 hooks and then an immediate splash at the surface.  When we investigated what had caused the splashed we found a small neonate that was born a within the last few months  and we processed it before continuing to set the line.  Immediately after we resumed setting the line, another little bull shark took the bait from the first hook in the water, so we processed her and then resumed setting the line.  The sharks allowed us to finish before any more bites, but when we pulled in the line another shark of the same size was on a hook.  Each of the three sharks had recently closed umbilical scars (see picture) telling us that they were born sometime during the summer and are probably still developing their foraging (hunting) skills - it can take sharks time to learn how to catch prey, and a free - or seemingly free - meal is  easier than catching a fish.  We put transmitters in each of the three newborns so we can track their movements to see what areas of the estuary newborn sharks are using compared to older individuals, and to investigate any individual variability in the movements of sharks as they grow . 

Hopefully our luck continues to be good when we go out again in 2 weeks - I’ll let you know.

A flat calm day!

 

Umbilical scar on a young shark.

 

Bull shark fieldwork in the coastal Everglades

Phil Matich - Aug 13, 2013

 

We just got back from an amazing trip last Tuesday!  As always, we left early in the morning and were fortunate enough to catch the tail end of the Perseid meteor shower as we drove to the boat ramp.  On our way to the field site we saw the sun rise over the water and the mangroves, and then got right to work catching sharks.  On the first live, we caught two sharks, 79 and 85 cm total length, and surgically implanted the smaller individual with an acoustic transmitter so that we could track its movements.  Surprisingly, the larger shark was an individual we had caught and tagged in July, and is one of the first sharks we’ve recaptured in the last three years!  After only a month, the shark has grown 2 cm and gained 1 kg in body mass; the scar from the surgery has completely healed, and one of the sutures had already dissolved, and the other marks from tissue collections were healing (see the picture of the fin clip).  On the second set, we caught three more sharks (74, 81, and 104 cm TL), and acoustically tagged the 81 cm TL shark to track its movements.  After only a few hours on the water he had caught five sharks and deployed two transmitters!  On the third set we caught another shark (104 cm TL). What  an awesome day!  And, we got to hang out with a dolphin for a little while on the ride back.  We won’t be out again until I get back from the Keys in September, but I’m looking forward to more days like this in the future.

 

 

Phil Matich: overview of "seasonal variability in the trophic interactions of juvenile bull sharks in a coastal estuary" paper

Hey everyone.  Our manuscript, “Multi-tissue stable isotope analysis and acoustic telemetry reveal seasonal variability in the trophic interactions of juvenile bull sharks in a coastal estuary” has just been published in Journal of Animal Ecology (http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12106/abstract).  The manuscript details our investigation of bull sharks’ use of freshwater prey from adjacent marsh habitats that migrate into the Shark River Estuary seeking refuge during the dry season when marsh water levels drop and the marsh dries up.  Tracking data show that during the late dry season, sharks significantly increase their use of areas where prey enter the estuary, and stable isotope data reveal that sharks increase the proportion of freshwater taxa in their diets at this time.  These findings are really exciting, because other predators, like snook, also show similar changes in their behavior in response to this event, and data suggest it’s an important component to their annual energy budget.  If this is also true for bull sharks, then annual variability in the magnitude and timing of this pulse of freshwater prey could affect survival and growth rates of bull sharks within the nursery.  Thus, if marsh water levels are affected by restoration efforts and/or climate change (precipitation), then the availability of food for bull sharks during the dry season may change, and in turn affect their behavior and ecological role within the ecosystem.

To see a video summary of our work, go to: http://vimeo.com/69532148

Intro to Phil Matich and bull sharks in the Everglades

Hi everyone.  My name is Phil Matich and I’m currently a PhD student in the Heithaus Lab.  I started working with the lab as a volunteer at our field site in Shark Bay, WA in 2008, and after arriving in Miami, I immediately started working on my research in the Shark River Estuary in the Florida Everglades.  My project has focused on understanding what factors shape juvenile bull shark behavior and how predicted changes in the environment will affect their ecological roles.  Over the last five years I have been catching, tagging and tracking sharks using passive acoustic telemetry to investigate individual differences in movement patterns and the degree of plasticity among shark movements within the nursery, and I have been collecting tissue samples from sharks to investigate dietary patterns using stable isotope analysis.  Thus far we’ve found that bull sharks, like other predators in the ecosystem, can exhibit a high degree of individual variation in their behavior.  For example, some sharks have more specialized diets and prefer marine or estuarine taxa, while others are more generalized in their trophic interactions.  Also, some sharks make repeated movements between refuge and foraging areas, while others tend to just roam around.  My current research aims to quantify the effects of an extreme cold weather event, that occurred in 2010, on the shark nursery, and we’re finding that changes in abundance and competition among age-classes may be leading to more rapid ontogenetic shifts in habitat use and diet.  Since this cold snap event, we’ve caught 60 juvenile bull sharks in the estuary, and have acoustically tagged 36 individuals to track their movements, of which 27 sharks are still in the estuary and providing us with an abundance of movement data that we download and evaluate every 2-4 months.  Over the next few years we should begin to understand the long-term effects of this event on the nursery.  Thanks for reading, stay tuned for future posts on fieldwork, manuscripts and other exciting news.

Tanzania with Kirk and Jeremy

June 19^th

Today is our first day on the water with the hired boat and captain.  We planned to fish but everyone was eager to get on the water so there was not enough room to take the gear.  After a walk that I will never forget down the fisherman lined beach towards our boat, we got underway in the 5m boat with our skipper, deck hand, and eight scientific crew… now you might believe us that there was NO room for the fishing gear.  From the beach at Bagamoyo we had about a 10km run to the mouth of the Ruvu River.  This is one of the stretches of water where having a captain with local knowledge really paid off.  There are a lot of rocky reefs and sand banks not easily spotted in the plume water and with a tide range of up to 4m (13') we need to know where they are to safely navigate.  We were able to collect some preliminary environmental information including water salinity, dissolved oxygen, temperature, conductivity, and river depth profiles.  About 20km upriver we also came across a local family that had a small roadside market where a variety of fresh produce was available as well as some fresh boiled corn… our captain was especially happy about that!!! 

This system definitely looks like Shark River in the Everglades!  Tomorrow, we will start setting our lines across the major salinity gradients of the river from the mouth to freshwater areas, including brackish waters.  We have seen a diversity of plant and bird species today and took as many pictures as possible to document biodiversity across the river.  We also saw our first hippo footprints in the river… but no hippos. 

When we got off the water we visited some more fish landings and documented 3 other species of elasmobranchs caught today ( the rays Himantura fai, Himantura uarnak and the shark Carcharhinus sorrah).  We will definitely be getting our lines in the water tomorrow!!!  

Tanzania June 18

June 18^th

This morning we had to introduce ourselves to the local authorities (water services) and request permission to enter the waters and start any research activities in the Ruvu River.  After meeting with a few of the people working at the District Commissioners office and having our heads spun from all the Swahili conversations, we ended up being directed to the office of Ndugu Jakaya Mrisho Kikwete, Bagamoyo’s Representative of The President of The United Republic of Tanzania.  He was very welcoming and after a few more formalities were exchanged in Swahili, the conversation changed to English so that we could be included.  We gave a brief explanation of the ecological assessment we hope to be able to conduct and stressed the importance of this work.  After a few more formalities he welcomed us to undergo our mission and wished us much success.  On our way out of his office he left us each with a handshake and the words “asante sana”, Swahili for “thank you very much”.

Now that we have been granted permission to start our research we can hit the water… after we get a proper boat sorted that is.  It just so happens that on our way into the Commissioner’s office we spotted a 5m fiberglass boat with a 75hp Suzuki.  Keep in mind that this is the ONLY fiberglass boat in the town of Bagamoyo and it is strictly used as a patrol boat by the local fisheries officer.  We enquired about the boat and organized to hire it.  We also hired a skipper, a local fisherman who knew the waters, and laborers.  It appears that we are all sorted!!! 

After our productive morning filled with meetings and organizing logistics we went down to the beach to see what the local fishermen were landing with their beach seines.  Some of us even jumped in to help with the final haul!!!  Included in the catch were a variety of species including blue swimmer crabs, puffers, flatheads, grunts, tarpon, mackerel, sole, grouper, catfish, milk sharks, and a variety of sardines and herrings to name a few.  We noticed that all of the fish seemed small for their respective size potential and were probably using the near-shore seagrass habitat as a nursery.  We also collected a few seagrass samples (Thalassodendron ciliatum) that were snagged in the fishermen’s nets. We should definitely be able to get samples from seagrass (other species, other samples) and small fishes but also need to try and get as many predators and sharks as possible throughout the trip. We will also try to extend this sampling to freshwater and brackish communities.

In the last few hours of daylight we decided to give the inflatable a try, if nothing else to see the river and get an idea of the system we will be working in.  Our initial concerns about the small inflatable were quickly validated and after the deck started to fold in on itself during an attempt to get on plane. We turned around and walked the boat back ashore…

Ok, time to turn the blog over to Kirk Gastrich and Jeremy Kiszka who just returned from a trip to Tanzania where they conducted a rapid ecosystem assessment of the Ruvu estuary.  They are still going through their pictures so we will roll them out as fast as we can!

June 17^th

Day 1… off to Bagamoyo!  In the morning we were met at the Tamigamiga Hotel in Kawe Beach, Dar es Salaam, by our driver and Mukama, a fish biologist from Tanzania.  On our way to Bagamoyo we stopped at the University of Dar es Salaam’s aquatic center to pick up the buoys and anchors we will need to properly deploy our longline gear.  After a very interesting drive we arrived in the town of Bagamoyo.  Our guest house, the Downtown Bagamoyo Lodge, was in the center of the small town “where all the action is” as one of our Tanzanian colleagues so aptly put it.  We quickly came to realize the truth of her statement as there was, at all hours, a seemingly endless supply of swiftly traveling  motorbikes always quick to honk their horns… always!!!  After we settled into our rooms we stocked up on some bottled water since the water from the taps was not always good to drink.  Shortly after, we met with some local people from the Basin to introduce ourselves and present our ideas for the project.  A small inflatable boat with a 25hp Yamy has been brought by the Basin, but is not likely to be usable for transect and fishing surveys. We will try to use it for preliminary surveys and to map out transects in the Ruvu River until we can sort out another boat. We also visited a fish market that showed some great diversity of pelagic teleosts caught by the local fisherman in the coastal waters… can’t wait to get our own gear soaking and see what we catch!!!  Oh yeah I almost forgot, we need to learn some Swahili and fast (especially Kirk)!!!  Hakuna matata!!!