Dolphin death in Florida highlights bycatch concerns

A female bottlenose dolphin that was less than a year old died after being entangled in what is believed to be heavy-weight monofilament fishing line, Mote scientists said recently. The death highlights concerns about the number of dolphins dying each year from human-relateimpacts and offers a chance to remind Florida residents and visitors on the best ways to help protect the state's marine animals.

The dead dolphin, nearly 5 feet long and weighing just under 90 pounds, was found floating in the Gulf of Mexico about 1.5 miles off Englewood, in northern Charlotte Harbour, USA. The animal was brought to Mote by the lab's Stranding Investigations Programme for a necropsy. The cause of death was obvious.

"The fishing line got wrapped around this dolphin's tail fluke and cut through the skin, blubber and even the bone, making it impossible for the animal to survive," said Mote veterinarian Dr. Deborah Fauquier, deputy manager of the Stranding Investigations Programme. Dolphins use their tails to propel themselves through the water and cannot survive without them.

The young dolphin's tail was cut almost completely off at the caudal peduncle (the area of the body just above the tail) and small portions of the skin around the wound showed signs that it was beginning to heal, even as the line continued to cut deeper into the dolphin's skin."The healing means that the line has been there at least several weeks," Fauquier said.

The line around the dolphin's tail had formed a slip knot and as algae and other plant material got caught in it as the dolphin swam, the line dragged, the slip knot continued to tighten, and it cut deeper.According to Mote's vice president of Marine Operations, Pete Hull, the 60-80 lb test line is probably used in offshore fishing for grouper or tarpon. The brittle condition of the line and the amount of attached vegetation suggest that it may have been discarded at sea for some time.This incident was similar to one recorded by Mote in 2000, said Dr. Nélio Barros, manager of the Stranding Investigations Program.

"But in that case, we were called while the young dolphin was still alive and we were able to remove the line that had wrapped around it," he said. "That was a good outcome because we were able to intervene and the animal survived. That was a happy ending. This was not." In that incident, fisheries experts were able to identify the line as 90 pound monofilament. They said at that time that the line likely came from a rod and reel.

Between 1985 and 2005, Mote's Stranding Investigations Programme recorded 16 dolphin deaths that were related to human interaction - from either fishing gear entanglement or boat strikes. "And it's likely those numbers don't reflect the full number of dolphins that die in similar incidents," Barros said. "Often, the animals that are brought here for necropsy are too decomposed for us to determine a cause of death. We also know that there are dolphins that die in the wild that no one ever sees or reports, so their causes of death can't be evaluated."

The director of Mote's Centre for Marine Mammal and Sea Turtle Research, Dr. Randall Wells, has studied bottlenose dolphins for 36 years and has seen an increase in human impacts on dolphins over that time."This dolphin's death is especially sad because this animal was otherwise healthy - she was the right size and weight for her age, so it's likely that her mother was doing a good job feeding and protecting her. This is a female dolphin that could have grown to adulthood and reproduced, thereby helping sustain the population. In Sarasota Bay, we have now documented the existence of five generations of resident dolphins - it's a shame that this one won't be contributing to future generations in the Gulf population."

According to Barros, remains of curdled milk were found in the young dolphin's stomach, which indicates that it was nursing from its mother until recently. Given the condition of her tail, there is no way that the dolphin could have captured fish on its own.The unfortunate death of this animal should help remind people who enjoy spending time on the water of several simple things they can do to keep dolphins safe and healthy.

"No one wants to harm the very animals they go out on the water to enjoy, so people just need to be vigilant about protecting them," Wells said.

source: Tampa Bay Newspapers