Debris Is Killing Sharks And Rays

Human-caused debris in marine environments is on the rise, with the biggest culprit being plastic. In fact, plastic debris can be found from the bottom of the ocean to the surface. Our oceans are rife in plastic, and over 700 marine species have been compromised as a result. The most common threats to marine wildlife include ingestion and entanglement. As much as 12.7 million tons of plastic are estimated to exist within our oceans, and this estimate is expected to increase dramatically in the near future.

When considering the types of debris that exist within our marine environments, two broad categories emerge: fishing-based sources and land-based sources. Fishing-based sources tend to enter our oceans as a result of abandoned equipment, broken equipment, or inclement weather, while land-based debris exists primarily as a result of inadequate waste management practices. Unfortunately, shark and ray populations are particularly vulnerable to these types of debris given that they have a late onset of maturation coupled with low reproductive rates. To further compound the problem, it is estimated that between 63 and 273 million sharks are killed per year already through various fishing practices.  

Despite the critical nature of this phenomenon, the entanglement of marine wildlife is an understudied topic and a lack of data exists. However, with the increased availability of social media, the exchange of information on this topic has been greatly supported. In fact, various social media platforms (e.g., YouTube, Facebook, and Twitter) are serving as digital scientific databases. In this review of scientific literature and Twitter social media data, researchers synthesized information on entanglement to better understand the extent of the problem. In order to collect their data, they used search terms that aligned with marine species, coupled with marine debris terms such as plastic, marine debris, entanglement, entrapment, etc. In addition, sawfish were included despite not being classified as a marine species, given that they are highly susceptible to entanglement.  

Based on the selection and review of 26 research papers spanning from 1971 to 2019, there were 47 related entanglements representing 34 species and 16 different families across all three oceans affected. The most common cause of entanglement, representing 74% of cases, was ghost fishing gear followed by polypropylene strapping bands (11%). The entanglement cases were most likely to have occurred in the Pacific (49%) and Atlantic (46%) oceans, with the most common geographic region being the USA (44%) followed by the UK (30%) and South Africa (10%). Based on the Twitter results, 74 cases were identified representing 26 species and 14 families. Consistent with the literature, ghost fishing gear was the most common cause of entanglement (94.9%) with the majority of cases occurring in the Atlantic Ocean (89.4%).

The results of this study indicate that entanglement is a significant animal welfare issue, despite the fact that it does not impact marine wildlife to the same scale as does the marine fishery industry. The researchers also point out that while this study provides important information on the topic of marine wildlife entanglement, there continues to be insufficient data on this topic. As a result, the researchers recommend standardized reporting on this issue to more accurately identify and quantify the nature of the problem.