Dolphin NJ05, in the Navesink River on Monday October 20, an adult animal that is part of the original group of 16 residing in the estuary since June. Credit: Emma Jugovich, NOAA
NOAA’s Fisheries Service today announced a monitoring plan for 12 bottlenose dolphins in the Shrewsbury and Navesink rivers. The agency also announced that there will be no effort to force the dolphins out of the area at this time.
Monitoring by NOAA dolphin researchers over the past week revealed no indications of stress, illness, or feeding problems. They identified 12 individuals moving easily from the Navesink to the Shrewsbury in two groups.
“These animals are in typical habitat, food is present, and we have no reason to believe they are stressed,” said Teri Rowles, director of NOAA’s National Marine Mammal Health and Stranding Program. “We’re not going to interfere in what appears to be a completely natural phenomenon, especially when doing so carries a high risk of harming healthy animals.”
NOAA consulted with a number of experts on the condition and behavior of these animals in this habitat and determined the conditions of the estuary are well within those tolerated by bottlenose dolphins.
There is also general agreement that efforts to move the animals from the area by luring, chasing, or catching them for relocation would be difficult, potentially dangerous for the animals and people, and not likely to succeed.
“Migratory bottlenose dolphins likely expand and contract their range in response to changes in environmental conditions, and this may well be what we are seeing,” said Larry Hansen, a NOAA researcher who studies the northern coastal stock of bottlenose dolphins to which this group most likely belongs. “They can spend the winter in colder water and even endure icy conditions, as long as there is enough to eat.”
“The appearance of a larger group after several years of sighting smaller numbers is consistent with the behavior of dolphins as they find new areas to occupy,” said Randall Wells, a senior conservation scientist with the Chicago Zoological Society who was consulted by the agency. “This group has been residing in the area for nearly four months and recent reports indicate that the remaining individuals appear to be behaving normally.”
“Based on our experiences, herding is unlikely to be effective here given the small number of animals and the distance to the ocean,” said Katie Touhey, who manages stranding responses for the Cape Cod Stranding Network. Her group was consulted by NOAA because it has used herding with a variety of species to prevent or to mitigate mass strandings.
NOAA’s monitoring plan is intended to better understand conditions that can trigger the dolphins to leave the estuary. “We hypothesize that they will leave when there is not food in sufficient quantity. We are collecting data to help us understand when and why that happens,” said NOAA’s Hansen.
Observers will be watching the dolphins and their prey several times a week, and the animals will be re-evaluated by dolphin researchers every two weeks. NOAA-approved observers are to be at the Route 36 Highlands Bridge construction site if dolphins are present, and high acoustic activities will be stopped if dolphins are within 500 meters of the bridge.
The agency will also be collecting data on noise levels around the bridge construction project.
“The observations and measurements are intended to provide data on acoustic signals and dolphin behavior around the site,” said Brandon Southall, director of NOAA’s Ocean Acoustic Program. “It might help us better understand what, if any, barrier the construction may pose to dolphin transit,” he said.
Smaller groups of dolphins appeared in the estuary in both 1993 and 2000, and NOAA did try to move them. In both cases, all the animals perished.
In the Northeast, there is no documented attempt to move this number of bottlenose dolphins as much as 8 miles as would be required. Luring with sounds has never been tried with this species. Herding has been tried with other species with mixed results. In most successful cases these animals were in poor habitats or otherwise distressed, and nearer to safer waters. Herding raises the stress level of animals considerably, and in some cases causes dolphins to strand, which is often lethal.
The two animals that were found dead in September and October were juveniles that died from pneumonia and infections common among young dolphins in the wild.
If you see a stranded or injured dolphin or other marine mammal in the area, contact the Marine Mammal Stranding Center at 609-266-0538.
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