by Chloe Mayne
Marine debris has become an extensive problem in the oceans today. Plastics and other debris affect over 250 species of marine organisms by entanglement and ingestion. Current studies have shown large marine mammals to be affected by entanglement, but few studies exist on the affects of ingestion of plastic debris. There have been three recorded standings of sperm whales with large amounts of plastic and marine debris in their stomachs. In the Mediterranean Sea, the population of sperm whales is considered to be a separate species and has had a decline in population over the past 20 years. This decline has been attributed mostly to boat strikes and entanglement, with no knowledge of the affects of plastic ingestion. Stephanis et al. (2013) examined a stranded sperm whale in the Mediterranean Sea that had ingested a large amount of marine debris. They discuss the results in terms of the spatial distribution of sperm whales and the anthropogenic activities in the area. In the Mediterranean Sea, the species is found near Almería and the Strait of Gibraltar. This study found that the whales feed in an area with lots of debris from the greenhouse industry. In the sperm whale examined, the cause of death was determined to be gastric rupture from the build up of debris.
On March 28th, 2012, a male sperm whale stranded near Castell De Ferro, Granada. The whale was weighed and measured. The abdominal cavity was also opened and the contents of the stomach were recovered. They were taken to the Estación Biológica de Doñana-CSIC in Spain where they were labeled, weighed, and measured. For pieces of anthropogenic material greater than 4 cm2, type of material, diameter, color, and origin were determined. This helped to categorize the items into either greenhouse debris or general debris. Items less than 4 cm2 were put together and considered small plastics. The sperm whale’s fluke was compared with a catalogue of sperm whale flukes assembled by Carpinelli et al.
Data about the spatial distribution of sperm whales were collected through surveys from research projects of the NGO Alnitak from 1992 to 2009. Over the survey period, 74,187 km were sailed and 34 groups of sperm whales were recorded with 55 individual whales. The Alboran Sea was the study area and it was characterized by spatial and environmental variables such as depth, slope, sea surface temperature, and primary production.
This study found the stranded whale to be 10.0 m long and weigh 4500 kg. The sperm whale was extremely emaciated but there was no evidence of other injuries. The abdominal cavity of the animal was opened for inspection. The stomach contained squid beaks and a large mass of compacted plastics that ruptured through the first stomach compartment. There were squid beaks on the outside of the small intestine but nothing was found to be inside the intestines. Gastric rupture was considered the cause of death. The stomach contents that were recovered were mostly greenhouse and general debris. The most common debris found was the cover material of greenhouses. There were 64 pieces of greenhouse debris and 21 pieces of general debris. The sperm whale’s fluke had not been photographically matched in the Mediterranean Sea.
While marine debris has been encountered in sperm whale stomachs throughout the 20th century, none of the debris has been attributed to greenhouse activities. In the Mediterranean Basin, greenhouse agriculture has expanded rapidly as people are able to grow year-round. These greenhouses require many plastic materials in their construction. The most common debris found in the sperm whale was the plastic cover of the greenhouses. There were also two flowerpots and seven bits of burlap plastic bags found in the whale’s abdominal cavity.
There was a bimodal sperm whale distribution based on longitude, with a high density toward the Straight of Gibraltar and another small peak around Almería. The model for group sizes showed that they increased in density towards shallower waters and it can be seen that the animals are feeding in waters near an area with a large greenhouse industry. There are no data of floating debris in the Mediterranean Sea, making it difficult to know where the debris resides in the water column and how much plastic is in the ocean, but it is likely that it came from greenhouses on shore.
This study only examined one stranded sperm whale since it is quite difficult to recover a sperm whale carcass unless it is washed to shore and hasn’t fully decayed. While there may be few other studies, it is obvious that addressing the issue of plastics from greenhouse agriculture in the sea is important.
Stephanis, R., Gimenez, J., Carpinelli, E., Gutierrez-Exposito, C., Cañadas, A., 2013. As main meal for sperm whales: Plastics debris. Marine Pollution Bulletin 69, 206–214 http://bit.ly/1yhegFs