Derelict gear impacts extend beyond marine species to include habitat, human safety, the economic viability of Puget Sound’s fisheries, and the health of the Puget Sound ecosystem. Explore the links below to learn more about the impacts of derelict fishing gear.
Crab Pot Impacts
The vast majority of nets lost in Puget Sound are gillnets. Gillnets are made of a plastic monofilament and used to catch salmon. Gillnets can become snagged on rocky outcroppings and hung up on rocky ledges. The plastic material does not significantly degrade over time and marine life that becomes caught in the nets further attracts predators to the net and they become caught as well. The Northwest Straits Initiative has removed thousands of nets from Puget Sound waters, most of them gillnets. We use highly skilled commercial divers for this dangerous work and follow safety protocols that we designed in partnership with Washington State Department of Fish and Wildlife and Department of Natural Resources.
Our experience has shown that nets continue to catch marine life indiscriminately and can significantly smother and/or damage marine habitats. We record all animals that are found in derelict fishing gear and keep a database of these impacts. Click here to download a research report on mortality caused by derelict nets.
Commercial and sport crabbers are required to use a biodegradable cotton escape cord (also known as rot cord) on their pots so that if pots are lost, the cord will degrade and crabs can escape. Even with this cord properly attached, a pot lost in Puget Sound can continue to fish for four months, capturing crab continuously. Without escape cord, a lost pot can continue to fish for more than two years. On average, a derelict crab pot will kill about 22 harvestable crabs a year. Derelict crab pots mostly impact Dungeness crab, but also capture other crabs and some fish. Primarily, crab pots become derelict when their buoy line is clipped by a passing vessel or when they are deployed in water that is too deep for the length of the line on the pot. Sometimes pots are lost because they are moved by tides or currents and are swept into deeper areas. Pots are frequently found in vessel traffic lanes and boaters out after dark have a challenging time seeing crab pot buoys.
Both nets and pots harm marine habitat. When currents slow around crab pots on the bottom, the resulting turbulence can scour sediment and eelgrass, leaving holes and bare patches meters across. Nets are often found draped over rocky reef habitat and kelp, causing sedimentation, smothering habitat and cutting off access to valuable habitat for marine species. We have found nets draped across centuries-old cloud sponge reefs, the reef scraped bare beneath. The good news is that for the most part habitat recovers quickly once derelict gear is removed. Research by the Northwest Straits Foundation has found that a year after nets and pots are removed, most habitat is fully recovered.
Derelict nets and pots kill indiscriminately, beyond just the target species they were intended to catch. Marine mammals, seabirds, fish, and invertebrates are all commonly found trapped in derelict gear. Because it is difficult to estimate the overall ecosystem threat that derelict gear poses, a researcher at UC Davis developed a model that predicted total mortality caused by a given net based on entanglement data collected upon its removal. This peer-reviewed research model is updated each month as more data is collected. As of November 30, 2010, it predicted that the 3,829 gillnets removed by the Northwest Straits Initiative since 2002 have prevented the nearly-always lethal entanglement of 1,210 marine mammals, 21,364 birds, 67,934 fish and 2,291,335 invertebrates (of which about one half are killed) each year that the nets were derelict on the seabed. It has been said that Puget Sound is dying a death of 1,000 cuts; if that is the case derelict gear is a particular deep cut. Below are just a couple of examples of derelict gear ecosystem impacts.
• Each derelict pot removes an estimated 22 Dungeness crab from Puget Sound each year, and there are estimated to be 12,000 pots lost each year. Dungeness crab larvae are a critical component of juvenile salmon diets.
• In 2008, the Northwest Straits Initiative removed a gill net with 162 seabirds, 14 salmon, 42 dogfish, 1,400 Dungeness crab and 1 harbor seal. Factoring in decomposition rates, it is estimated that this single net in 23 weeks time killed 1,800 birds, 450 salmon, 1,300 spiny dogfish, 16,900 crab, and 11 harbor seals. In an ecologically rich area like Port Susan bay, derelict gear can be a tremendous stress on the ecosystem and source of mortality.
• Derelict gear blocks access to habitat, making certain species more vulnerable to predation.
Derelict nets and lines pose a threat to recreational divers, who have been caught and drowned in Puget Sound in the past. The Northwest Straits Initiative is working with divers and dive operators to raise awareness of the dangers of derelict gear.
Nets and lines can also foul ships’ props, causing a dangerous loss of steering or power. In 1993 the Korean Ferry the M/V Seo-Hae capsized when it turned sharply to the right after a 10mm derelict line coiled around its prop shaft. 292 people drowned.
Economic impacts of derelict crab pots
In 2009, the Foundation conducted a study of economic impacts of derelict crab pots in Puget Sound. Data was collected on simulated derelict crab pots in Dungeness Bay and combined with similar data from Port Susan, provided by the Stillaguamish Tribe. From that study, we now estimate that 12,000 pots are lost each year in Puget Sound, most by recreational crabbers. These pots capture and kill an estimated 178,874 harvestable crabs each year, costing the commercial crab fishery between $450,657 and $744,296 in lost revenue annually. This represents up to 4.5% of the value of recent annual commercial crab harvests in Puget Sound.
The cost of removing derelict crab pots varies considerably depending on the location and density of pots. A single day of removal operations costs about $4,200, not counting costs of surveys needed to locate pots. The Initiative removes an average of 22 pots per removal day, for a per pot removal cost of about $190.
Derelict net removal: habitat restoration costs and benefits
Derelict fishing nets negatively impact marine habitat in a number of ways. They collect sediment and smother habitat, making it inaccessible. They scrape and strum on hard surfaces, scouring away vegetation and sessile animals. They entangle and eventually uproot and kill aquatic vegetation. Removing derelict nets allows natural ocean processes to restore these damaged habitats over time. A recent research study conducted by the Foundation showed that kelp assemblages damaged by derelict nets are restored to 90% full service functions in just one growing season after net removal.
A single day of net removal can uncover about 0.3 acres of marine habitat at a cost of about $5,600. This translates to a per acre restoration cost of $18,667. Other estimates of the costs of restoring bull kelp forests in the San Juan archipelago put the price tag at over $100,000/acre.