Monday, 16 September 2019

Cetacean sightings within the Great Pacific Garbage Patch.

The Great Pacific Garbage Patch is an area of the Pacific Ocean between Hawai'i and California, and is one of a series of patches where an ocean gyre (rotating current) tends to trap floating plastics, resulting in an ever growing patch of discarded nets, ropes, lighters, toothbrushes, water bottles, pens, baby bottles, cell phones, plastic bags, and microplastics. The area is known to be on one of the major sea routes used by migrating Whales, and a variety of Whale species have washed up dead on the Californian coast with plastics in their stomachs, leading to concerns that the debris may be causing Whale fatalities, both through ingestion and entanglement, though there has to date been no direct studies of the impact of the garbage patches on Whales.

In a paper published in the journal Marine Biodiversity on 9 April 2019, Susan Gibbs of the Ocean Cleanup Foundation, Chandra Salgado Kent of the Centre for Marine Science and Technology at Curtin University, Oceans Blueprint, and the Centre for Marine Ecosystems Research at Edith Cowan University, Boyan Slat, also of the Ocean Cleanup Foundation, Damien Morales, again of the Ocean Cleanup Foundation, and of Blue Planet Marine, Leila Fouda, once again of the Ocean Cleanup Foundation, and of the School of Biological and Chemical Studies at Queen Mary University of London, and Julia Reisser of the Minderoo Foundation, and the Oceans Institute at the University of Western Australia, describe the results of an aerial survey of the Great Pacific Garbage Patch, which specifically targeted Whales present within the area.

Gibbs et al. made two survey flights over the Great Pacific Garbage Patch using a Hercules C-130 aircraft flying out of Moffett Airfield in California, during October 2016, during each of which a series of transects of the patch were made. During each flight eight people were used to record Whale sightings, working in pairs from each of the plane's paratroop doors, with one person acting as a spotter and the other a recorder. Where possible Whales were also photographed.

A total of 14 Whales were spotted in seven groups, plus 1280 large plastic items (fishing nets etc.). The Whales were not evenly distributed across the patch, five of the seven sighting having occured in a brief period of time, large items of plastic were quite often seen in close proximity to Whales.

The first sighting comprised a group of four small Toothed Whales, Odontocetes, of an unknown species. The second sighting was of three Sperm Whales, Physeter macrocephalus, a mother, calf and an escort; the calf was about four and a half metres in length, suggesting it was vert young (Sperm Whale Calves are about four metres long when born, and grow very rapidly). The third sighting was of a large dark Whale of uncertain species, possibly another Sperm Whale. The fourth sighting was of a single 'relatively large' Whale.the fifth sighting was of two large Baleen Whales, Mysticeti, identified by the observation of two large blows with shapes consistent with those produced by the double blowholes of Baleen Whales. The sixth sighting was of a single Beaked Whale, Ziphiidae, of uncertain species. The seventh sighting was of two further Beaked Whales. The final three Whales were probably Cuvier’s Beaked Whales, Ziphius calvirostris, but could not be confidently identified, and may not all have been of the same species.

Cetaceans and ocean plastics within the Great Pacific Garbage Patch. In the map, background colour levels represent predicted plastic pollution gradient (red = highest levels, blue = lowest levels); grey lines show the survey transects (~665 km each) and black dots indicate locations of the seven Cetacean sightings. Photographs above the map show some of the Cetaceans observed in this study: Sperm Whales (sighting 2, and sighting 3) and Beaked Whales (sighting 6, and sighting 7); red circles in sighting 3 indicate debris locations. Photographs in the right side of the figure give examples of debris types sighted: ‘ghostnets’, ropes, crates and buoys. Gibbs et al. (2019).

The most common identifiable large items of plastic were abandoned fishing nets, followed by containers, buoys, lids, and ropes. Only three of the Whales could be identified to species level, but the observed specimens included Sperm Whales, Beaked Whales and Baleen Whales, all of which have been found washed up on Californian beaches with plastics in their stomachs, implying that they are affected by the plastic waste in the garbage patch.

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