Tag and Release

After a short recess, the benthic catshark tag and release program is up and running again! This year we have added an additional two sites to the sampling protocol, namely: Santos and Darwin.

Since August 2012 we have tagged a total of 17 catsharks: Leopard = 1, Pyjama Jacket = 3 and Puffadder = 13. Unfortunately, with no recaptures yet, however, there are possible reasons for this. Negatives: (i) the tag may have fallen off – any scars would likely have healed as sharks have incredible regenerative capabilities, (ii) tagged sharks have died due to natural predation, or alternatively have been caught by fishermen and killed - as they are considered a pest species. Positives: (i) these sharks are abundant and there is a low probability of capturing the same individual more than once. Let’s hope it’s the latter!

Although most species of catshark occurring in Mossel Bay are endemic to South Africa, despite their relative abundance – information is still limited. This tag and release project therefore represents an effective, low cost tool to obtain vital information on these little studied species.

This research project aims to investigate the following key questions relating to the biology and ecology of these endemic sharks:

              i.        Diversity of benthic catsharks in Mossel Bay reef systems

            ii.        Degree of spatial variation in benthic catshark composition between Mossel Bay reef systems

           iii.        Population composition and abundance of benthic catsharks sampled in Mossel Bay

The insight gained from this study will contribute to a more comprehensive understanding about the role these catsharks play in community dynamics. These benthic sharks likely represent predators within their micro-scale habitats and are thus considered to have top-down predatory effects at the community level at which they occur.

Furthermore, most of these catsharks are listed as Near Threatened on the IUCN Red List of Threatened Species – prioritising them as species of conservation concern!!

Shark Chronicles 083 - Not only chumming

As with any research project, there are factors that cannot be controlled. Midway through this month we had trouble finding white sharks. Due to big swells and high winds we were unable to stay out for long, if we made it out at all. Instead of chumming we put in some extra hours at the office, entering tracking data from previous years and writing articles for Beyond Blue. Beyond Blue is an online magazine founded by Oceans Community. The magazine is for everyone and focuses on marine research, conservation, and exploration.

We also had a presentation by Enrico about the Great White shark research projects going on at Oceans, their findings, and the importance of those findings. He stressed the value of communicating the results to the general public and explaining how those results affect their life. Fellow conservationists and researchers make an effort to know the current issues. However, the majority of people in the world are either unaware of current issues or believe they don’t concern them. The research going on at Oceans has helped keep swimmers and surfers safe by alerting the public to where the white sharks are and when they are in the area. As disappointing as it can be not to see our beloved Great Whites, it was good to see how the work we do furthers the research that goes on to affect the community.

On the third week of our internship month we finally had a chance to do some shark tagging as well we started seeing white sharks again during our chumming trips! After a successful shark collection at Mitch’s Reef for our benthic shark aquarium in the Shark Lab, it was finally time for us to release the old sharks. The benthic sharks are kept for four months at the aquarium and then tagged and released when we collect new ones. This is part of an ongoing project to measure the population of the benthic shark species in Mossel Bay. Two of the species, the Pyjama Jacket and Leopard sharks are priority because we think their population may be threatened.

Each shark was weighed and measured and photos of their total length, mouth, and defining features were taken. Every tag that we fitted on the shark had an identification number and mailing address for ORI’s tag and release database. The tag was fitted by making a small incision anterior to the dorsal fin of the shark. For female species we always make the incision on the right side of the dorsal fin and left side of the dorsal fin for male species. It was difficult to penetrate the tough skin of the sharks, which are composed of small denticles, or teeth like scales. One through it is fairly easy to insert the tag into the thick wall of muscle that forms the sharks back.

Two Pyjama-jacket sharks and one Leopard shark were being tagged that day. One of the Pyjama-jacket was male and two other sharks were female. As the Pyjama-jacket sharks that we have were quite feisty, it took a couple of intern to hold the shark while the incision was being made. One intern took pictures of the shark during the whole process while another intern made the incision for the shark tag. We try our best to put the least amount of stress on the shark while we fitted the tag.

After all the sharks were tagged we loaded them on to the boat and took them back to the waters off Mitch reef. We are hopeful that the catch, tag and release study will provide us information on the population of benthic sharks on Mitch’s Reef, Mossel Bay.

Rachael Cashman and Karina Harum - Oceans Research interns

Shark Chronicles 073 - First Shark Lab's experiments

It’s been an active week at the aquarium. We wrapped the preliminary trials for the shark metabolic studies. The study was truly a group effort with all of the interns spending many a midnight hour camped out in the aquarium’s wet lab anxiously attempting to count gill movement on a swimming shark with a solitary red headlamp.

For the initial protocol, one male and one female shark were kept in isolation for several weeks, and after feeding to satiation, we monitored gill movement rates and time until feeding response to establish baseline metabolic rates for the sharks over a range of different temperatures. Preliminary results were as expected, with both sharks showing faster feeding response times in warmer temperatures. While there are still all the standard little glitches to be ironed out, the trials themselves were a great success as they should provide valuable insight into the set up and operation of future wet lab studies.

This week also saw the official beginning of the Shark Labs’ participation in the national Oceanographic Research Institutes’ tag and release program. After taking measurements and collecting a photographic record of the sharks we were prepping for release: each shark was fitted with a plastic tag with an individual identification number and mailing address for ORI’s tag and release database. Then the two pyjama sharks, two puffadder shysharks, and two smooth hound sharks were loaded on to the boat and taken back to the waters off Mitch reef, where they were returned to their natural environment. While we were sad to see them go, we are excited and looking forward to the possibility of collecting important information about their population size, habitat use, and growth rate in the future.

Since an empty aquarium is never good, Saturday was spent on a collection run. A team of two snorkelers and two divers worked to collect new sharks using chum bags to draw them in, while hoping the scent didn’t attract anything too big to the location. Seal Island was only a few hundred meters away after all! Luckily the trip was a success, with three leopard catsharks, two puffadder shysharks, and one new pyjama shark added to the Shark Lab’s guests. After spending the evening acclimating to their new residence our guests were catalogued, measured and ready to begin work! Their first assignment – a new study comparing the ease of induction and total duration of tonic among the different species found locally, and the potential for using tonic induction as a tool for handling and working with the sharks in the Lab.

Shark Chronicles 067 – Tracking Pinocchio

Having arrived in Mossel Bay just a couple of days previously, Monday morning found our group of new interns chumming for white sharks just off Seal Island. Having been prepared to spend an hour or two waiting for our first glimpse of dorsal fin, we were almost unprepared when, within 10 minutes, the first shark appeared at our bait.

This arrival was greeted with a flurry of activity; recording data on the shark (particularly noting physical characteristics) and taking photo’s of the dorsal fin to record the pattern of notches that appear on the fins trailing edge – all to be used for identification should we encounter the same shark at a later date.

This shark was soon followed by a second female. It was decided that this second shark provided a good opportunity for tagging, as she was in the target range for the size of sharks wanted for data collection (at approximately 2.5 metres), and seemed interested in the bait enough to keep her around the boat long enough to get all three tags in her before she moved away. The shark was named Pinocchio as preparations for tagging were made.

The first tag was designed to measure the internal body temperature of the shark, from inside the stomach. The tag was prepared inside the body of a tuna that was then offered to Pinocchio. After a couple of cursory passes of the bait she took the tuna, effortlessly tearing it from the bait float.

The remaining two tags were applied simultaneously, via a modified spear gun, to the shark just below the dorsal fin. The first was also designed to give body temperature data, but this time from the white muscle tissue, and the third gave external (water) temperature as well as information on depth.

Data from the tags was collected from each tag, via a unidirectional hydrophone, to a box known as the VR100. This registered each data receipt with an audible ‘ping’ that would come to govern our lives over the next few days. The stronger the signal (dependant on the direction and distance of the tags, and hence the shark, relative to the hydrophone), the louder the ping – this was the information that allowed us to judge the sharks position and track her movements.

The first sets of data from the shark were confusing – the shark appeared to be in two places at once. It was apparent that rather than swallow the tuna, she had spat it out. We anxiously followed her movements with the remaining two tags and hoped that she would return to finish her meal, while a replacement stomach tag was prepared. Eventually, she returned to the boat and was offered a second tag laden tuna, which she duly took and consumed – resulting in a mass of high fiving and a very excited crew on the boat!

Having successfully tagged the shark, the personnel on the boat was swapped out. We returned to shore, and the first tracking shift kicked into gear. I went home to get some rest and prepare for my tracking shift, which was due to start at 2 o’clock the following morning.

2 am found us back at the tracking boat. Our shark had moved away from Seal Island, and was cruising slowly near the moth of Kleinbraak river. The high oxygen content of the water near the river mouth makes an ideal environment for a resting shark. The shark spent most our 7 hour shift cruising near the coast in shallow water.

Spending the hours of darkness on a small boat with the constant ping of the VR100 and the lights from shore was quite a surreal experience, interrupted occasionally by Enrico and his riddles! There were four of us on the boat, rotating between spending an hour tracking, piloting the boat, collecting positional data, and resting. The South African sunrise signalled that our shift was close to an end way before we felt ready to return to shore, but before long the next shift had been ferried out to our position and we were heading home.

2 am again, and our second shift saw us following Pinocchio back towards the island with some urgency – it must be time for breakfast! Our conclusions that he shark was hungry was backed up by the swimming pattern of the shark, as it took a yo-yo pattern moving from the surface to deeper water in it’s search for fish.

The shark circled Seal Island before we ‘witnessed’ it’s first meal since it took our tuna. I use the word ‘witnessed’ loosely as, although we did not visually observe any predation we were able to track it’s effects on the stomach temperature of the shark, which we saw take a dramatic drop as the shark ingested a mouthful of cold water with its meal. It may be rare to witness a shark predation, but how may people can say they’ve tracked the stomach temperature of a feeding white shark?

After breakfast, the shark returned to it’s river mouth, and to resting.

Morning three, and our ongoing tracking activities are threatened by an incoming storm. Pinocchio spends much of her time resting around the river mouth. At the end of the shift we are beginning to feel the effects of the storm and decide to continue tracking, rather than ferry out the next shift for potentially just an hours tracking before the boat is forced back to port. The shark seems to sense the changing water conditions also, and begins to move along the coast. Our additional hour tracking eventually turns into 6, but our extra efforts are rewarded as we catch up with the shark at the surface, and watch her swim by the side of the boat – the two external tags clearly visible against the dark back of the shark. We were now tracking visually as well as acoustically. Unfortunately, hampered by the rapidly worsening sea conditions we lost contact with the shark. A brief search proves fruitless, and the conditions mean that we could not track the shark again if we were to find her. We turned the boat round and headed back, through the growing swells, to a very well earned beer (or 2)!

Chris Pulham – Mossel Bay Oceans Research intern

Shark Chronicles 010 - Zulu tagged

Today, SAMPLA launched its second major tracking effort of 2008. With a full compliment of interns in Mossel Bay, we now have the capacity for multiple-day shark-tracking (our longest effort to date being 103 hours following one shark in 2005). With the launch of our new vessel (Cheetah), we can keep one vessel at sea whilst the other plays ferry, shuttling new crews in and out every 12 hours.

At this time of year (autumn), large seal hunting sharks usually appear in the bay. During the winter they specialise on hunting seals moving to and from Seal Island. However, nature is capricious and the last couple of weeks have brought us only sub adult sharks. Yesterday, we made a strategic decision to target a smaller shark for tracking in the Hartenbos region, the daytime resting area for the seal hunters. We hoped to plant an acoustic tag on a sub adult shark ambitious enough to attempt hunting seals.

At 8.30am, after having chummed for 20minutes, a 3 metre female turned up at the vessel – our prospective seal hunter. Prior to tagging, Courtney recorded the necessary data for the shark, including taking photographs of her dorsal fin for identification, whilst Ben lured the shark into tagging range. At 8.35 we secured the transmitter on the right side of the Zulu's (her new name) dorsal fin, and switched from chumming mode to tracking mode. The anchor was pulled up, while chum and bait were swapped for the directional hydrophone and environmental sensing instruments. Follow this blog to get updates on Zulu’s movements and behaviour every 12 hours (following change over).

Shark Chronicles 007 – Following the paths of the Great White Shark

As anticipated in the last blog episode, SAMPLA has tagged its first white shark, a female of 2.7-2.8 meters (around 9 feet) long, which we named “Sampla”. The acoustic tag was deployed from our research vessel Lamnidae by SAMPLA’s technical director Stephen Swanson at 11 am on 17^th March 2008. It was a memorable moment for SAMPLA as it represents the beginning of SAMPLA’s data collection via acoustic tracking. We hope it will give us greater insight into the ecology of the white shark including providing information on the white shark’s habitat use, swimming depth preferences, and movements along the Mossel Bay coastline. The multitude of beach goers over the weekend appeared blissfully unaware of any white shark presence, as, or so it appeared, was the sharks to the presence of the beach goers. Despite the current peaceful coexistence of sharks and water users at Mossel Bay, it remains important for science and for the public to know where the sharks are!

The excitement and anticipation surrounding the tagging of SAMPLA’s first shark put the pressure on the SAMPLA field team, but Stephen’s arm was steady and our ‘first lady’ (nothing to do with Washington!) shark swam away, tag perfectly set. The acoustic tag emits a sound signal at approximately one second intervals over several months, and will allows us to follow the shark “Sampla”, by using a hydrophone (an underwater receiver with headphones). Subsequent to tagging Sampla, we set up the hydrophone and after allowing her ten minutes to settle, we started to track Sampla. She showed no signs of adverse affects from the tagging, and even came to investigate the boat (white sharks are curious) before resuming her sub surface course (we try and maintain a distance of not less than 20 m to reduce the effect of the vessel on a shark’s behaviour).

A great deal of excitement was generated by the tagging of Sampla. Where will she go, will she stay in the bay and allow us to track her? In 2005, current members of SAMPLA successfully tracked white sharks which stayed within the bay for 5-6 months, but Sampla is a new shark in a new year and tracking her could supply us with new information and/or new problems! The dilemma now is how long Sampla will stay in Mossel Bay? Our research vessel is not massive (6.5 meters – 21 feet long) and, like its crew, it is not equipped for long journeys in the open ocean. Within these restrictions (i.e. as long as Sampla remains in the bay) we will do our best, with the use of shifts and different tracking teams, to follow Sampla for as long as possible. Ultimately, the vagaries of nature do not allow us to dictate the terms by which we can track a shark!

Our next post will reveal the story behind our first 24 hour tracking of SAMPLA…

ENRICO & TOBY