Bottlenose dolphins in Doubtful Sound
December 2011. Doubtful Sound's resident pod of bottlenose dolphins have had the best two breeding seasons for some time.
Over the last two summers, the dolphins have had the most surviving calves for more than a decade. This gives the Department of Conservation (DOC), Otago University researchers, and the local tourism industry optimism about their future.
DOC's marine mammal ranger Kath Blakemore said alarm has been raised about the rapid rate of decline this well-researched population has been undergoing in recent years. Calf survival rates have been low since around 2002. This is more critical as research shows that this small group of dolphins lives separately from others, living almost exclusively within Doubtful Sound.
16 calves born - 11 survived
Sixteen calves have been born over the last two summers and 11 of these have survived so far. Otago University researcher, Shaun Henderson said that in 20 years of the University's research there has only been one other year with more calves born. If most of these calves survive it will be a significant boost to the population.
"While we don't know the reason for this increased rate of births, everyone involved is hoping this trend continues," Mr Henderson said.
Dolphin watching rules
Since 2009, DOC has been working with boat operators to implement a set of rules for vessel use in Doubtful Sound to minimise any potential impacts from the dolphins interacting with boats. In addition, a research programme has begun to explore some of the other potential causes of the decline, such as genetics, habitat modification, broad-scale climate changes and diet.
The commitment from the Doubtful Sound tourism industry to work alongside DOC and others to help these dolphins has been encouraging. All boat operators, private or commercial, must be familiar with the protection guidelines before heading into Doubtful Sound. These are readily available from the DOC website or your local DOC office. The guidelines aim to reduce the amount of time dolphins spend interacting with boats so they can spend more time doing what dolphins should naturally do.
http://www.wildlifeextra.com/go/news/doubtful-dolphins.html
Showing posts with label bottlenose dolphins. Show all posts
Showing posts with label bottlenose dolphins. Show all posts
Friday, December 16, 2011
Friday, November 25, 2011
Pregnancy is a drag for bottlenose dolphins
Lumbering around during the final weeks before delivery is tough for any pregnant mum. Most females adjust their movements to compensate for the extreme physical changes that accompany the later stages of pregnancy. However, no one had been able to find a distinct gait change – such as a change in stride length or frequency – associated with the latter stages of pregnancy.
Intrigued by the ways that newborn dolphins learn to swim after birth, Shawn Noren from the Institute of Marine Science, University of California Santa Cruz, realised that she had the perfect opportunity to find out how pregnancy affects female dolphins. Joining a pod of dolphins at Dolphin Quest, Hawaii, just before two of the females gave birth, Noren analysed the impact of pregnancy on the animals' streamlined shape and mobility. She publishes her discovery that pregnant dolphins are significantly disadvantaged by their burden and adopt a new swimming style (gait) in The Journal of Experimental Biology.
'The pregnant females had huge protrusions where the fetus was sitting towards the back end of the body', says Noren, who donned SCUBA gear and spent a large portion of the final fortnight of the dolphins' pregnancies filming under water as they swam parallel to her camera between their trainers. Noren also filmed the dolphin mothers immediately after their calves were born and at regular intervals until the calves were 2 years old. Comparing the footage before and after delivery, Noren realised that pregnant females were slower. Their top speed was restricted to 3.54 m/s, whereas they were able to swim at much higher speeds after giving birth. 'Two to three metres per second is a comfortable speed for most bottlenose dolphins,' says Noren, 'but these pregnant animals did not feel comfortable going beyond that.'
She also measured the animals' girth and calculated their frontal surface area, and realised that the pregnancy had a colossal impact, increasing their frontal surface area by an enormous 51%. And when Noren measured the drag experienced by the animals as they glided through the water, she discovered that it doubled when the mothers were close to delivery.
The pregnant dolphins also had another problem: their increased fat stores in preparation for lactation had also increased their buoyancy. 'The buoyancy issue is going to be problematic when you are going down on a dive to capture prey and they are going to need extra energy to overcome that buoyant force', says Noren. So, pregnancy had a dramatic effect on the dolphin's hydrodynamics, but had it changed their swimming style? Did the pregnant dolphins move with a different gait?
Manually digitising the position of the animals' flukes (tail fins) as they beat up and down, Noren discovered that the pregnant females were unable to sweep their flukes as far as they could after birth. They had reduced the amplitude of their tail beat by 13% and they compensated for the reduced propulsion by beating their flukes faster. The pregnant dolphins had changed gait.
Having found how pregnancy affects soon-to-be dolphin mothers, Noren outlines the additional risks that the females face. Unable to outrun predators, heavily pregnant dolphins are more vulnerable to attack and they may not be able to keep up with the pod if pursued by fishing vessels. Explaining that tuna are still fished using massive nets in the eastern tropical Pacific, Noren says, 'Here is a fast speed event, so it is possible the near term pregnant females are being left behind in the chase. They are reliant on a large pod for protection and cooperative feeding and once the animal is separated it would be hard for it to find the pod again.'
More information: Noren, S. R., Redfern, J. V. and Edwards, E. F. (2011). Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus). J. Exp. Biol. 214, 4149-4157.
http://www.physorg.com/news/2011-11-pregnancy-bottlenose-dolphins.html
Intrigued by the ways that newborn dolphins learn to swim after birth, Shawn Noren from the Institute of Marine Science, University of California Santa Cruz, realised that she had the perfect opportunity to find out how pregnancy affects female dolphins. Joining a pod of dolphins at Dolphin Quest, Hawaii, just before two of the females gave birth, Noren analysed the impact of pregnancy on the animals' streamlined shape and mobility. She publishes her discovery that pregnant dolphins are significantly disadvantaged by their burden and adopt a new swimming style (gait) in The Journal of Experimental Biology.
'The pregnant females had huge protrusions where the fetus was sitting towards the back end of the body', says Noren, who donned SCUBA gear and spent a large portion of the final fortnight of the dolphins' pregnancies filming under water as they swam parallel to her camera between their trainers. Noren also filmed the dolphin mothers immediately after their calves were born and at regular intervals until the calves were 2 years old. Comparing the footage before and after delivery, Noren realised that pregnant females were slower. Their top speed was restricted to 3.54 m/s, whereas they were able to swim at much higher speeds after giving birth. 'Two to three metres per second is a comfortable speed for most bottlenose dolphins,' says Noren, 'but these pregnant animals did not feel comfortable going beyond that.'
She also measured the animals' girth and calculated their frontal surface area, and realised that the pregnancy had a colossal impact, increasing their frontal surface area by an enormous 51%. And when Noren measured the drag experienced by the animals as they glided through the water, she discovered that it doubled when the mothers were close to delivery.
The pregnant dolphins also had another problem: their increased fat stores in preparation for lactation had also increased their buoyancy. 'The buoyancy issue is going to be problematic when you are going down on a dive to capture prey and they are going to need extra energy to overcome that buoyant force', says Noren. So, pregnancy had a dramatic effect on the dolphin's hydrodynamics, but had it changed their swimming style? Did the pregnant dolphins move with a different gait?
Manually digitising the position of the animals' flukes (tail fins) as they beat up and down, Noren discovered that the pregnant females were unable to sweep their flukes as far as they could after birth. They had reduced the amplitude of their tail beat by 13% and they compensated for the reduced propulsion by beating their flukes faster. The pregnant dolphins had changed gait.
Having found how pregnancy affects soon-to-be dolphin mothers, Noren outlines the additional risks that the females face. Unable to outrun predators, heavily pregnant dolphins are more vulnerable to attack and they may not be able to keep up with the pod if pursued by fishing vessels. Explaining that tuna are still fished using massive nets in the eastern tropical Pacific, Noren says, 'Here is a fast speed event, so it is possible the near term pregnant females are being left behind in the chase. They are reliant on a large pod for protection and cooperative feeding and once the animal is separated it would be hard for it to find the pod again.'
More information: Noren, S. R., Redfern, J. V. and Edwards, E. F. (2011). Pregnancy is a drag: hydrodynamics, kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops truncatus). J. Exp. Biol. 214, 4149-4157.
http://www.physorg.com/news/2011-11-pregnancy-bottlenose-dolphins.html
Monday, August 22, 2011
Decline in bottlenose dolphins is linked to pollutants
Are PCB's responsible for decline in Bottlenose dolphins?
August 2011. Many people have been thrilled at the sight of playful, energetic bottlenose dolphins around our coasts. But they may be surprised to hear that numbers of the local population around Cornwall are gradually declining. Conservationists are concerned that eventually we may lose them altogether. The reason for the drop in numbers has been a mystery until now, as local scientists think they know why.
Strandings
Over a period of six years, volunteers of Cornwall Wildlife Trust's Marine Strandings Network have collected bodies of stranded bottlenose dolphins washed ashore. They then take them to the pathologists at the Animal Health and Veterinary Laboratories Agency (AHVLA) at Polwhele in Truro to be examined. Having researched the decline in the population over a number of years, the Marine Strandings Network was keen to know why they died and wanted to find out more. Could there be a reason why, despite sightings of calves and young dolphins, the pod didn't appear to be thriving?
Post mortem
The dolphins were post mortemed by local veterinary pathologists at AHVLA Polwhele, as part of the UK Cetacean Strandings Investigation Programme, which is funded by Defra. Samples were tested for various diseases by Nick Davison, a scientist at the AHVLA.
Nick explains "Dolphins carry lots of diseases and can live for years with some of them without being adversely affected. However, there are certain bacteria that some of them carry that can severely compromise their health and may lead ultimately to their death. One of these is a bacterium called Brucella ceti, which affects many different species of cetaceans all over the world. Even healthy looking animals can carry the disease."
Brucella ceti
"We ran a wide range of routine tests on the samples we had stored from all eight of the bottlenose dolphins, including the test for Brucella ceti. What really surprised us was that half of the bottlenose dolphins we tested carried Brucella, which is a rare thing to find in this species and in this region. In fact, no other isolations of Brucella species were found in 15 bottlenose dolphins from the rest of England and Wales between 1989 and 2008, and only one out of 36 dolphins examined in
Scotland during the same period. We also discovered that the levels of Brucella in the Cornwall dolphins were much higher than in the other species we'd examined."
PCBs
The second shock for the researchers was the very high levels of polychlorinated biphenyls (known as PCBs) in the blubber of two of the dolphins. One of them had the highest level of PCBs recorded in this species in the UK in the last 20 years.
PCBs are toxic chemicals that used to be added to paints and cements, fire retardants, adhesives and hydraulic fluids. Because of their toxicity, they were banned about 20 years ago, but they still persist in the marine environment, particularly in coastal waters. They get into the fish the dolphins eat and are readily absorbed into fat, so the dolphins' blubber is an ideal reservoir.
High exposure to PCBs may increase susceptibility of the bottlenose dolphins to infections, including Brucella ceti. PCBs have also been linked to fertility and reproductive issues in dolphins and can affect the immune system, exposing the dolphins to a number of serious diseases and conditions such as meningitis swelling of the brain.
Scientists now think that chemical pollutants such as PCBs may be one of the possible causes of the decline of the local bottlenose dolphins.
Jan Loveridge, Coordinator of the Strandings Network says,"Strandings and sightings data suggest that UK bottlenose dolphin populations, including ours in Cornwall, have declined markedly from historic levels and the loss of any individuals from such a small population will have a strong impact on its ability to survive. We're so fortunate to have this local laboratory to help us find out what's killing our dolphins."
"The bottlenoses are such a local icon; they're part of Cornwall's heritage and one of the reasons that people visit the county. It would be a tragedy if we lost those precious moments when we see them leap and flip in the air and I'd hate to think that our children and grandchildren might be denied that pleasure. We need to keep monitoring how they're doing, and do whatever we can to protect them. Research like this by Nick Davison is crucial if we're to understand what's going on in our marine environment."
Although Brucella can be passed to humans, the risk from dolphins is very small indeed. Nevertheless, the AHVLA recommends that people don't swim with dolphins or touch any bodies they find on the beach, just in case. Instead, they urge the public to call the Trust's Marine Strandings Network on 0845 201 2626 if they find a stranded dolphin.
The publication describing the findings of this research can be read on the Marine Strandings Network's website www.cwtstrandings.org/publications.htm.
http://www.wildlifeextra.com/go/news/dolphins-pcb.html
August 2011. Many people have been thrilled at the sight of playful, energetic bottlenose dolphins around our coasts. But they may be surprised to hear that numbers of the local population around Cornwall are gradually declining. Conservationists are concerned that eventually we may lose them altogether. The reason for the drop in numbers has been a mystery until now, as local scientists think they know why.
Strandings
Over a period of six years, volunteers of Cornwall Wildlife Trust's Marine Strandings Network have collected bodies of stranded bottlenose dolphins washed ashore. They then take them to the pathologists at the Animal Health and Veterinary Laboratories Agency (AHVLA) at Polwhele in Truro to be examined. Having researched the decline in the population over a number of years, the Marine Strandings Network was keen to know why they died and wanted to find out more. Could there be a reason why, despite sightings of calves and young dolphins, the pod didn't appear to be thriving?
Post mortem
The dolphins were post mortemed by local veterinary pathologists at AHVLA Polwhele, as part of the UK Cetacean Strandings Investigation Programme, which is funded by Defra. Samples were tested for various diseases by Nick Davison, a scientist at the AHVLA.
Nick explains "Dolphins carry lots of diseases and can live for years with some of them without being adversely affected. However, there are certain bacteria that some of them carry that can severely compromise their health and may lead ultimately to their death. One of these is a bacterium called Brucella ceti, which affects many different species of cetaceans all over the world. Even healthy looking animals can carry the disease."
Brucella ceti
"We ran a wide range of routine tests on the samples we had stored from all eight of the bottlenose dolphins, including the test for Brucella ceti. What really surprised us was that half of the bottlenose dolphins we tested carried Brucella, which is a rare thing to find in this species and in this region. In fact, no other isolations of Brucella species were found in 15 bottlenose dolphins from the rest of England and Wales between 1989 and 2008, and only one out of 36 dolphins examined in
Scotland during the same period. We also discovered that the levels of Brucella in the Cornwall dolphins were much higher than in the other species we'd examined."
PCBs
The second shock for the researchers was the very high levels of polychlorinated biphenyls (known as PCBs) in the blubber of two of the dolphins. One of them had the highest level of PCBs recorded in this species in the UK in the last 20 years.
PCBs are toxic chemicals that used to be added to paints and cements, fire retardants, adhesives and hydraulic fluids. Because of their toxicity, they were banned about 20 years ago, but they still persist in the marine environment, particularly in coastal waters. They get into the fish the dolphins eat and are readily absorbed into fat, so the dolphins' blubber is an ideal reservoir.
High exposure to PCBs may increase susceptibility of the bottlenose dolphins to infections, including Brucella ceti. PCBs have also been linked to fertility and reproductive issues in dolphins and can affect the immune system, exposing the dolphins to a number of serious diseases and conditions such as meningitis swelling of the brain.
Scientists now think that chemical pollutants such as PCBs may be one of the possible causes of the decline of the local bottlenose dolphins.
Jan Loveridge, Coordinator of the Strandings Network says,"Strandings and sightings data suggest that UK bottlenose dolphin populations, including ours in Cornwall, have declined markedly from historic levels and the loss of any individuals from such a small population will have a strong impact on its ability to survive. We're so fortunate to have this local laboratory to help us find out what's killing our dolphins."
"The bottlenoses are such a local icon; they're part of Cornwall's heritage and one of the reasons that people visit the county. It would be a tragedy if we lost those precious moments when we see them leap and flip in the air and I'd hate to think that our children and grandchildren might be denied that pleasure. We need to keep monitoring how they're doing, and do whatever we can to protect them. Research like this by Nick Davison is crucial if we're to understand what's going on in our marine environment."
Although Brucella can be passed to humans, the risk from dolphins is very small indeed. Nevertheless, the AHVLA recommends that people don't swim with dolphins or touch any bodies they find on the beach, just in case. Instead, they urge the public to call the Trust's Marine Strandings Network on 0845 201 2626 if they find a stranded dolphin.
The publication describing the findings of this research can be read on the Marine Strandings Network's website www.cwtstrandings.org/publications.htm.
http://www.wildlifeextra.com/go/news/dolphins-pcb.html
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