Tuesday, September 17, 2013

Tanzania - the rest of the story

June 20th
Today is our first fishing day!  After an early breakfast followed by picking up some fruit for our day on the water, we made our way towards the beach to find bait.  The tide was flooding in so all the fishing boats could reach their near shore moorings and allow the fisherman to come ashore.  They were all displaying their catches on the beach in hopes of attracting a buyer and small ‘fish auctions’ were going on all over the beach.  Mukama, being from Tanzania, acted as our liaison for a lot of our dealings with the locals and helped us organize some fresh kingfish (mackerel) and queenfish (trevally) at the market.    We also spotted a young bull shark (less than 1 meter) caught earlier by fishermen… we loaded our boat and got underway with our hopes high!!!

We did two 50 hook sets in the downstream portion of the river… but no sharks.  We caught three catfish (Arius africanus) and a large mud crab.  As in the Everglades, our baits were most likely eaten by scavengers.  

The other half of our team was land-based today and conducted an assessment of vegetation along the downstream portion of the river. We continued to record birds and also saw our first monkeys along the shore, confirming that we are NOT in the Everglades!!!

June 21st – 28th
During the last week of our trip we fished in as many locations as we could, making sure to hit all the areas in and around the Ruvu River estuary.  We fished in freshwater upstream areas all the way out to the offshore coral reefs.  Although we had some great encounters with hippos, Nile crocodiles, blue monkeys, and yellow baboons, we still only caught a few more catfish.  Even when we fished in the coral reef habitat… nothing.  We didn’t even see fish swimming around.  It is also interesting to note that during our entire time on the waters in and around the Ruvu, we didn’t observe any dolphins, sea turtles, sharks, or schooling fish.   Artisanal fishing may be a big player here, however, more standardized fishing will be needed to say for sure.

In the last few days, the tides were really against us for getting on the water.  We were experiencing spring tides with ranges up to 4m and in Bagamoyo that means very little water at and around low tide.  During these times it wasn’t possible to get our boat off the trailer or get into the Ruvu River even if we could have launched the boat.  We took advantage of this time and visited the local fisherman on the beach to try and get another look at their hauls to get a better understanding of the local fish communities… and some samples!!!  After a bit of wheeling and dealing by Tanzanian fish biologist, Mukama, we had more fish than we had room for. 

Our time was running out quickly, but we knew the importance of getting as many of these fish sampled as possible.  We took them back to the Downtown Bagamoyo guest house where we were staying and got to work.  Each fish was identified to species, weighed, measured, and sampled for fin and epaxial white muscle.  It was a big team effort but after two straight days of processing fish, we had samples from over 250 individuals and 35 different species.  We also managed to attract every fly within the area and reinforced the utility of the electric tennis racket bug zapper!! 

On the last day of our official business in Tanzania, we travelled west to Morogoro on a formal invitation from Vivienne Abbot, the director of the Republic of Tanzania’s Integrated Water Sanitation and Hygiene program (iWash) and part of a larger Global Water for Sustainability (GLOWS) program.  We briefed her on the field excursion and plans for moving forward were discussed, including the possibility of more collaborations with FIU biologists and personnel!  It seems the Tanzania adventure may not be over yet!!!  Asante sana Tanzania… it has been an esteemed pleasure!!!

Thursday, September 12, 2013

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.


Wednesday, September 4, 2013

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.