Plastics and other marine debris have been found in the gastrointestinal tracts of cetaceans, including instances where large quantities of material have been found that are likely to cause impairment to digestive processes and other examples, where other morbidity and even death have resulted. In some instances, debris may have been ingested as a result of the stranding process and, in others, it may have been ingested when feeding. Those species that are suction or “ram” feeders may be most at risk. There is also evidence of entanglement of cetaceans in marine debris. However, it is usually difficult to distinguish entanglement in active fishing gear from that in lost or discarded gear. The overall significance of the threat from ingested plastics and other debris remains unclear for any population or species of cetaceans, although there are concerns for some taxa, including at the population level, and marine debris in the oceans continues to grow. Further research including the compilation of unpublished material and the investigation of important habitat areas is strongly recommended.
Marine litter has been characterized as an environmental, economic, human health and aesthetic problem, posing a complex and multidimensional challenge with significant implications for the marine environment and human activities all over the world [
Thirty-one species of marine mammals have previously been reported to have ingested marine debris [
“Microplastics” are a related concern and defined by the United States’ National Oceanic and Atmospheric Administration (NOAA) Marine Debris Program as plastic debris pieces in the size range of 0.3–5 mm. “Primary microplastics” are either intentionally produced for direct use, such as scrubbers in cleaning products, or as precursors to other products, such as preproduction plastic pellets. “Secondary microplastics” are formed from the breakdown of larger plastic materials. These small pieces of plastic are difficult to remove from the environment, and, because they have the potential to be ingested by a wider range of organisms than larger pieces microplastics may clog the feeding apparatuses or the digestive systems of a variety of species. Microscopic pieces may also be taken up from the gut into other body tissues [
In 2003, UNEP established a “Global Initiative on Marine Litter” to facilitate international cooperation on marine litter. This is coordinated by UNEP’s Regional Seas Programme (RSP) and the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities (GPA). Most recently, in March 2011, UNEP and NOAA organized the Fifth International Marine Debris Conference in Honolulu, Hawai’i. This meeting, which brought together440 participants representing38 countries, agreed the Honolulu Commitment, which outlines 12 actions to reduce marine debris and also produced the
An investigation was made of the published scientific and other literature in order to assess the current state of knowledge with respect to cetaceans. This review focuses on incidents recorded after the review authored by Laist in 1987, when he first raised substantive concerns about this threat for marine wildlife [
Many studies have been carried out across the world to try to quantify marine debris, and most of these have focused on large (macro) debris. These studies show that marine debris is ubiquitous in the world’s oceans and on its shorelines [
Higher quantities are found in the mid-latitudes and tropics, with particular concentrations associated with shipping lanes, fishing areas, and ocean convergence zones. About 2000 items of anthropogenic debris are found on north Atlantic shores per linear km per year and 500 per linear km per year on south Atlantic shores. More than half of this debris is plastic. By comparison, more than six times as much plastic has been reported washing ashore annually in the Mediterranean Sea. Observed global trends include a sustained and considerable increase over time and an increase in the associations of macroplastics with some wildlife (e.g., in bird nests and stomachs, and entangling seals) [
Some plastics sink when they first enter the water column, and others do so after accumulating a layer of fouling organisms and sediment. Considerable spatial variability affects plastic debris below the sea surface, and distribution is strongly affected by hydrodynamics, geomorphology, and human factors [
Concentrations of marine debris may occur in areas that are important for cetaceans, such as convergence zones where prey may be abundant. For example, in 1997 and 2000, surveys were conducted on the floating debris in the Ligurian Sea, a subbasin of the Mediterranean Sea which includes the Ligurian Cetacean Sanctuary [
Williams et al. [
There are two primary types of impact for marine wildlife: entanglement and ingestion and whilst cetaceans, pinnipeds, turtles and seabirds are all known to suffer from entanglement, it has been suggested that pinnipeds are particularly affected [
Walker and Coe made an extensive survey of foreign body ingestion by odontocetes [
Summary of incidents of ingestion by cetaceans of plastics and other debris reported in Walker and Coe between 1963 and 1986 with notes indicating where ingestion was indicated to be of significance [
Species | Number of incidents | Locations | Notes |
---|---|---|---|
Sperm whale, |
3 | Florence, OR, New Jersey and Newfoundland | One animal of 38 examined from a mass stranding in Oregon had one liter of tightly packed trawl net in its stomach |
Dwarf sperm whale, |
1 | Corolla, NC | |
Pygmy sperm whale, |
3 | Sullivan’s Island, SC, Galveston, TX, and Brevard Co., Florida | The Texas animal had “pounds of plastic bags clogging its stomach chambers” |
Cuvier’s beaked whale, |
3 | San Diego, CA, Assawoman, VA and Seaford, VA | |
Blainville’s beaked whale, |
1 | East Hampton, NY | |
Gervais’ beaked whale, |
2 | Hatteras Island, NC and Cape May, NJ | The NJ animal had its stomach full of plastic |
Short-finned pilot whale, |
1 | Corolla, NC | |
Rough-toothed dolphin, |
3 | Maui, HI and 2 from Sandbridge, VA | |
Pacific white-sided dolphin, |
4 | Three from Santa Monica, CA, one from Long Beach, CA | The forestomach of the Long Beach animal was half full of four plastic bags, two plastic bottle caps, and various organic materials |
Common dolphin, |
4 | Two from Los Angeles County, CA, one from Malibu, CA, and the other from Hermosa Beach, CA | The LA County animal had one partial red balloon ( |
Bottlenose dolphin, |
9 | All from the California coastal population—stranded on various CA shores | Along with other organic and plastic debris, three of the animals contained hooks |
Risso’s dolphin, |
2 | Martha’s Vineyard, MA and Manhattan Beach, CA | The animal from MA was recorded as having a plastic bag in its throat |
Striped dolphin, |
1 | Cape Point, NC | |
Northern right whale dolphin, |
2 | Los Angeles County, CA and Santa Monica, CA | |
Harbour porpoise, |
1 | Corolla, NC | |
Dall’s porpoise, |
3 | Venice Beach, CA, and two from Santa Barbara, CA | The Venice Beach animal had its stomach “jammed with debris” including 13 pieces of clear plastic sheet, 3 heavy clear plastic bags, 2 plastic bread bags, and two plastic sandwich bags |
Walker and Coe concluded that odontocete cetaceans were affected to an unknown degree by the ingestion of oceanic debris but that the sperm whale,
A number of other authors have reported more recently on incidents of ingestion. For example, the first account of ingestion causing mortality in sperm whales was recently published: in 2008, two male sperm whales stranded along the northern California coast with large amounts of fishing net scraps, rope, and other plastic debris in their stomachs [
In November 1993, an emaciated juvenile female pygmy sperm whale was found stranded in Great Inlet, Longport, New Jersey, and taken into a rehabilitation facility [
In December 2009, a pod of seven male sperm whales stranded on the Adriatic Coast of southern Italy [
Beaked whales have also been suggested to be especially vulnerable [
An immature male Cuvier’s beaked whale that stranded at Biscarrosse, Landes, France, on January 29, 1999 was found to be emaciated, with a blubber layer almost half that expected for an animal of its age, sex, and size [
Santos et al. report on the stomach contents of three Cuvier’s beaked whales, two of which stranded in Galicia, northwest Spain, in 1990 and 1995 and the other in North Uist, Scotland, in 1999 [
Santos et al. [
The stomach contents of 23 cetaceans stranded in the Canary Islands between 1996 and 2006 were examined, and five of the animals examined had plastic debris in their stomachs with big plastic items being taken by deep diving teuthopagus whales [
A North Atlantic bottlenose whale,
Accounts of plastic ingestion by beaked whales outside of the North Atlantic also exist. For example, there is a published report on a Blainville’s beaked whale washed ashore in Brazil with a blueish bundle of plastic threads occupying a large part of its main stomach chamber [
There are scattered reports of ingestion of marine debris by other odontocete cetaceans. For example, in September 1997, a small harbour porpoise,
The stomach contents of 42 harbour porpoises that were either bycaught or stranded between April and June in 2002 and 2003, on the Turkish western Black Sea coast, were examined [
An adult male rough-toothed dolphin,
CSIP has also reported marine litter ingestion by 3 out of a sample of 128 short beaked common dolphins stranded in the UK [
Plastic debris ingestion was examined in a large sample of Franciscana,
In 2000, a Bryde’s whale,
In April 2002, a dead minke whale,
CSIP has not reported ingestion of plastic in any of the 13 baleen whales examined in the UK between 2005 and 2010 [
The first comprehensive review of the impacts of marine debris globally was undertaken by Laist [
Overview of entanglement and ingestion in cetaceans.
Species | Laist 1987 [ |
Laist 1997 [ |
This review |
---|---|---|---|
Mysticete whales |
|
(Ingestion only) | |
|
I/E | ||
|
E* | E* | |
|
E* | ||
|
E* | E* | |
|
E* | ||
|
E* | ||
|
E* | I/E* | I |
|
I | ||
| |||
Odontocete whales |
|
||
|
I | I/E* | IM |
|
I | ||
|
I | I | I |
|
I | ||
|
I | I | I?M |
|
I | IM | |
|
I | I | |
|
I | I | |
|
I | ||
|
I | I | I |
|
I | ||
|
E* | ||
|
I | ||
|
I | I | |
|
I/E* | I | |
|
I | ||
|
I | I | |
|
I | ||
|
I/E* | I | |
|
I/E | ||
|
I | I | |
|
I | ||
|
I | ||
|
I | ||
|
I | ||
|
I |
Key: I: ingestion recorded; E: entanglement recorded; IM: mortality reported as associated with ingestion; I?M: mortality resulting from ingestion likely.
*Entanglement in fishing gear where it is not clear if it was in use or lost at the time of entanglement.
Lambertsen et al. commented on the “imperfect nature of our understanding of the impact of marine debris on mysticete species” whilst also theorizing that fouling of the baleen may prove lethal, as it could interfere with the particular feeding mechanism used by these animals [
As a means of trying to quantify entanglement, there have been a number of studies of nonlethal entanglements of whales using the pattern of scarification photographed on their bodies. For example, Neilson et al. found that 52–78% of humpback whales,
In a similar study to that of Neilsen et al., nine minke whales from a photo catalogue of 74 known individuals which were known to regularly return to the waters in the west of Scotland were observed entangled, or with scars suggesting previous entanglement in marine debris, including pieces of discarded or “ghost” net [
It has long been held that marine wildlife entanglement in and ingestion of synthetic marine debris are insidious and cryptic threats [
It is difficult to attribute any trends to the published literature because of differences in sampling procedures and other factors such as the changes over time and variations that may exist for difference regions and cetacean populations. Table
Nonetheless, it is clear that marine debris is an increasing problem, and there is growing evidence of impacts on cetaceans. There are now numerous recorded incidents where ingested debris has caused pathology and a growing concern especially for deep water suction feeders and arguably ram feeders as well, noting that marine debris has also been proposed as significant threat for the critically endangered northern right whale. Whilst it is strongly suggested in the literature that the small cetaceans living in surface waters are less likely to ingest harmful materials than other species, it is also apparent that this may change where there is substantial debris at the surface, as reported off northern Argentina.
However, apart from a small number of systematic surveys involving larger numbers of animals, the relevant data are generally scattered and rather scant. During research onto this topic, it became apparent that many cetologists and some institutions around the world hold some records of ingestion or entanglement in marine debris but, as these are frequently observations on one or just a few individual animals, they rarely bring them forward for publication. Nonetheless, if such records were compiled, they would probably help us better understand the scale and significance of this problem, and this may also help to pinpoint particular problem areas or populations that are being particularly impacted. The importance of appropriate pathology of stranded and bycaught cetaceans in order to investigate this issue is also apparent and likewise the desirability of developing approaches to determine if fishing gear was active or discarded when entanglement occurred.
Further consideration of where vulnerable cetaceans and marine debris may be converging—for example, the deep water canyons used as core habitat by beaked whales—is also recommended. Overall, in comparison to the level of understanding that exists for some other marine species such as turtles and albatrosses, the current level of understanding of the threat posed by marine debris to cetaceans is poor, and it is strongly recommended that this be addressed.
Grateful thanks to Paul Jepson, Rob Deaville, Colin MacLeod, Katie Dyke, M. B. Santos, Paul Johnston, Vicky James, Sue Fisher, Kate O’Connell, and Pine Eisfeld for their help in preparing this paper, and to two anonymous reviewers for helping to improve it. The UK Cetacean Strandings Investigation Programme (CSIP) is funded by Defra and the UK Devolved Administrations. The publication of this paper was sponsored by OceanCare and the World Society for the Protection of Animals.