In the first installment of this two-part epistle, I described the detrimental impacts on benthic ecosystems caused by traps (or pots) used by commercial fishermen. Most of those impacts are caused when the traps are dragged across seafloor habitats during recovery, or by wind and storms. In this episode, I will address the impact of trap and buoy lines on pelagic ecosystems.
Lobster traps on the dock in Stonington, Maine (B. Stevens)
In contrast to the lack of attention paid to the impacts of trap fishing on benthic habitats, impacts to pelagic species, including pinnipeds, cetaceans, and turtles has received much attention. This has led to many proposals for reducing or mitigating such impacts. The diamondback terrapin Malaclemys terrapin is such an iconic creature of the Chesapeake Bay that it has become the mascot for the University of Maryland. Juvenile terrapins are often captured in traps for blue crab, another iconic Chesapeake Bay species. Estimates of mortality of terrapins due to crab trap bycatch range from 15 to 78% of the population. Fortunately, bycatch reduction devices (BRDs) can reduce the entrapment of terrapins by a factor of 20 while simultaneously increasing the size range of trapped crabs.
Whale entangled in trap buoy lines (NOAA)
But the larger problem is due to the entanglement of whales in buoy lines or floating trap lines. The International Whaling commission estimated (in 2015) that over 300,000 whales and dolphins were killed each year due to entanglement in fishing gear. Entanglement with fishing gear, primarily lobster and crab trap lines, causes 82% of overall whale mortalities. The North Atlantic Right Whale is endangered, with a population estimated at less than 400 total, including fewer than 70 reproductive females. According to NOAA, vessel strikes and entanglement are the leading causes of mortality for NARW. The Atlantic Large Whale Take Reduction Team estimated that 85% of NARW have suffered entanglement at least once, and 26% of the population is entangled each year. The problem is not limited to the US east coast; entanglement is also an issue in the New Zealand fishery for western rock lobster, and Dungeness crab traps are a major source of entanglement for grey whales in Northern California.
Whale entanglements have led to the requirement for weak links in buoy lines, but these have not been proven to be effective. This is especially true in the deep water lobster fishery where 50 traps may be connected to a groundline up to 1 km in length; when retrieved, the weight of suspended line and traps can exceed that of a small car. Fishers compensate for accidental breakage of weak links by increasing the strength of buoy lines. Furthermore, when effective, weak links may result in allowing the whale to go free while still entangled, which makes it much harder to disentangle.
To address this problem, the Atlantic States Marine Fisheries Council voted to require reductions in vertical lobster buoy lines of 20-40%, whereas the Atlantic Large Whale Take Reduction Team has recommended a 50% reduction would be required in the Maine lobster fishery, and 30% in Massachusetts. Despite the protestations of fishermen, effort reductions would probably not result in reduced catches of lobster, since Maine lobster are heavily overexploited, and might actually increase profits, because fishers could probably catch just as many lobsters with 10% of the current effort.
Using fewer trap lines can be achieved by fishing traps in strings, with one buoy line on each end. This is standard procedure for the black sea bass and deep water crab fisheries, but creates the associated problem of trap dragging as discussed previously. In addition, in highly competitive fisheries such as lobster, fishers could end up setting trap lines across each other’s gear, causing gear conflicts. Norwegian crab fishermen have solved this problem cooperatively, by sharing the positions of their gear publicly. But that idea is anathema to American fishers, who don’t want their competitors knowing where they fish.
Some fisheries, such as those for American Lobster or Dungeness crab, will continue to depend on individually buoyed crab traps. For those fisheries, the best solution is the development of rope-less traps (RLTs). RLTs can range from simple devices that deploy a buoy after the decomposition of a galvanic timed release (GTR, commonly a short piece of zinc that degrades after a specified time period), to complicated systems using acoustic releases.
The Ropeless Consortium at Woods Hole Oceanographic Institute (WHOI) has pioneered the approach to creating rope-less traps. Such traps store the buoy and lines within the trap or an adjacent device using a lift bag, pop-up buoy, or buoyant spool. Buoy lines would only be released when the trap was being recovered, thus preventing them from entangling whales. They have also developed prototypes of underwater modems that can be used by fishing vessels to locate traps and release the buoy mechanisms. It can also encode encrypted information that can be provided in response to an authorized query.
Unlike standard lobster traps (1), the on-call-buoy concept developed by the Ropeless Consortium (2) would not entangle whales (WHOI).
The Edgetech Model 5112 Ropeless Fishing System incorporates an acoustic release mechanism, rope that is stored in a chamber of the trap, and a buoy that can be triggered from the surface by an ultrasonic signal. The system is controlled by tracking software that can be run from an iPhone or Android device. In 2020, these listed for about $3500 each, and would require one for each trap. Fiobuoy has also developed a similar system using rope attached to a buoyant spool.
The Edgetech Ropeless Fishing System (Edgetech Corp., Wareham, MA, USA).
At present, ropeless systems are too expensive for widespread adoption. But they are highly supported by conservation organizations and will probably be required in the Northeast US lobster fishery within 5-10 years. Both NOAA and the Massachusetts Department of Marine Fisheries are working with the fishing industry to encourage the development, improval, and ultimate adoption of RLTs.
Although the whaling industry is essentially extinct, the recreational whale watching industry is worth $2 Billion per annum, and this has brought whale conservation to the forefront of public interest. Conservation groups are already calling for changes in fishing methods to reduce whale entanglement. Due to whale entanglements in the Maine lobster fishery, the Marine Stewardship Council recently suspended its certificate of compliance for that fishery, Seafood Watch placed them on its “Red list”, and Whole Foods (owned by Amazon) has phased out Maine Lobster from its stores. This pressure will eventually force fishers to adopt new fishing gear and methods.
The incorporation of electronics onto traps opens a Pandora’s box-like door to much more innovation. In the future, “Smart traps” equipped with such technology could provide information beyond just location and ownership. They could also incorporate a range of sensors that measure local water temperature and detect trap fullness, including sector-scanning sonar to detect the presence of other crabs or fish nearby. Encrypted information would only be provided to the owners or enforcement agencies and could be detected by shipboard systems or robotic gliders. Location and movement of traps could be monitored remotely, and any change in position or status reported to the owners. This would lead to reductions in lost gear, ghost fishing, entanglements, gear conflict, and impacts on benthic ecosystems.
In this hypothetical future scenario, each fishing boat would deploy a fleet of independent “smart” traps, along with additional “master” units, containing a suite of environmental sensors. After deployment, instruments on the master unit would measure the water temperature, current speed and direction, and determine tidal timing and velocity. Sensors on each trap would relay catch information to the master unit. When catch rates had levelled off, sonar on the master unit could detect the distance and direction to more crabs and better fishing conditions (Yes, sonar can detect the presence of crabs). The master unit would then signal the entire fleet of traps to inflate buoyancy bladders, lifting them off bottom just enough to drift with the tide to the new location, passing over epibenthic organisms without disturbing them, before settling to the bottom. When sensors detected optimal fullness, the master unit would signal the ship to come retrieve them. Individual traps would be triggered to surface in sequence, arriving in time to be recovered sequentially. This process would result in greatly improved economic and fuel efficiency, reduced contact with benthic ecosystems, and virtually no impact to marine mammals. Such a system would be a great improvement over current fishing methods.
I admit that my vision of future fishing methods may be somewhat rosy. I always told my students that “Anything that goes in the water is expendable. Except you”. The marine environment is extremely harsh, and any piece of equipment used in it is subject to forces and events out of our control. And there is a high probability that you won’t get it back. For this reason, fishers have tried to keep their fishing gear simple; anything complicated will not last long. So it seems counter-intuitive to suggest that the simple crab/lobster/fish trap should undergo a profound transformation into a high-tech device in the near future. But that is the direction we are headed.
The trouble with traps is that, despite their efficiency, they are destructive of the marine environment. If we want to continue to consume sustainably caught fish and shellfish, we as a society will have to enforce adoption of improved fishing methods. Replacing simple traps with ropeless traps is one way to do it, and this may lead to future “smart” traps that will bring even greater improvement and less environmental impact. I’m betting on it.