Paper: Stelfox, M., et al., A review of ghost gear entanglement amongst marine mammals, reptiles and elasmobranchs, Marine Pollution Bulletin (2016), http://dx.doi.org/10.1016/j.marpolbul.2016.06.034
What is more “Halloween-y” than graveyards and ghosts? Not too much. There are very creepy graveyards floating throughout the ocean created by ghost fishing gear. When lost or tossed-off fishing gear still catches wildlife, we say the gear is “ghost fishing”.
Even though people have been fishing for ages, there has been a rise in the number of traps and nets accumulating in the ocean. Gear is lost for a variety of reasons: storms or bad weather, damage, improper use, snagging on bottom, lack of disposal facilities or high cost of proper disposal, lack of space on board the vessel, and/or difficulty in retrieving it. On top of that, newer fishing technology utilizes materials that do not biodegrade as their natural predecessors did. This ALDFG (abandoned, lost, or discarded fishing gear) accounts for an estimated 10% of marine debris – adding 640,000 tons annually! It’s a global concern to a number of species, especially those already in decline.
I’m not the first oceanbites writer to cover underwater graveyards: a few previous oceanbites writers have covered derelict fishing gear, in the form of crab traps. But it isn’t just traps; it’s also line and nets. To look at how entanglement in ghost gear impacts marine megafauna, Stelfox, Hudgins, and Sweet reviewed all the published literature on the issue.
Quantifying mortality due to ghost fishing is very difficult to estimate and it changes with the amount of time the gear spends in the water. Plus, many nets fragment and drift with the ocean’s currents, making studying their true impact difficult. Megafauna like whales and dolphins can become entangled in line (including line associated with traps) and nets, and may even be attracted to them if the debris aggregates their prey. Many studies lump entanglement in any type of marine debris (including plastic bags, clothing, tires, etc.) together, making it hard to conclude anything about ghost fishing gear.
The authors waded through the literature and identified 40 species of megafauna recorded as entangled in ALDFG. Marine mammals were the most common with 70% of the reported entanglements. Of those mammals, humpback whales and North Atlantic right whales had the highest records of entanglement (670 and 648, respectively). A high percentage of individuals of those species (~50% and 83%, respectively) shows evidence of some entanglement in the past. When these animals are entangled on their tails, they may eventually shake lose and live – but scars of their previous entanglement often remain. Antarctic fur seals and California sea lions follow whales with 492 and 443 individuals on record. Only one paper discussed manatee entanglement, but recorded 375 entangled. Reptiles (sea turtles and the saltwater crocodile) account for 27% of total entanglements, with the majority being Olive Ridley sea turtles (68%). Only 2% of entangled megafauna were elasmobranchs like sharks and rays.
What type of gear were these creatures entangled in? 55% were entangled in ghost fishing nets and 35% were entangled in monofilament fishing line. The other 10% included ropes from traps or crab pots, or unknown, or a combination of net and line. Rope and monofilament line were the types of gear with the highest impact on whales, whereas ghost nets are the major gear type affecting sea turtles and pinnipeds (seals and sea lions). Turtles unfortunately encounter this gear in three habitat areas—reefs, open ocean, and nesting beaches—making them vulnerable at all life stages. Manatees appear to be most affected by monofilament lines and hooks through both entanglement and ingestion, but more research is necessary.
This review identified several gaps in knowledge, hopefully to be addressed in future research! For example, the Indian, Southern and Arctic Oceans have little representation in this literature. More studies should examine certain species that appear to be at risk, such as manatees and sharks. Sharks were recorded in low numbers but that may be because few studies have addressed their entanglement in ghost gear. Species of concern need some extra study as well. Finally, more studies focused on ghost fishing gear specifically as the entangling agent are required to better understand the impact. Creating regional databases to document incidences of ghost fishing would be useful in improving knowledge and ensuring consistency in collection.
Halloween is the time of year we get to celebrate the creepy, crawly, gruesome, morbid, dark, and scary things in the world! It’s also the time of year for jokes, dressing up, tricks, and treats. One of the most disturbing and gruesome marine conservation issues, in my opinion, is ghost fishing. My favorite part of Halloween has always been designing a costume. Now these two things may not seem related, but they are. What do ghost fishing and designing a Halloween costume have in common? Well, you could go to the easy answer and say “creating ghosts”, but I challenge you to look further. Both are problems that require ingenuity to solve. Efforts to minimize ghost fishing impacts include clean-ups. In a clean-up, deep sea nets are removed with “creepers” (long bars with dredges attached that are dragged behind a boat) that grab nets from the seafloor. Gear lost in shallower waters can be retrieved by divers. Preventing gear from becoming ghost gear can be accomplished with fisher incentive programs and education within the community. It is also important to know locations of lost gear for removal purposes because imaging technologies are progressing to allow location with drone or satellite imagery. To end on a positive note, some humans have exhibited ingenuity and have developed initiatives to collect derelict fishing gear and turn it into carpet and clothing whose sale, in some cases, benefits the communities who collect that gear!