The Myth of “Mid-Water” in the Alaska Pollock Fishery


The following is a summarized version of a scientific paper written by Marissa Wilson, executive director, and Michelle Stratton, fisheries scientist, of the Alaska Marine Conservation Council. For a deeper dive into the impacts of pelagic trawl gear in the pollock fishery, read AMCC’s more in-depth scientific paper on the issue.

Fisheries management in Alaska is often referred to as the “gold star” standard. Sustainability is written into Alaska’s constitution and the identity of its diverse and productive fisheries. But how sound is this designation when it comes to the use of mid-water trawl gear in the pollock fishery?

Government, industry, and certification institutions have consistently described pelagic (or open ocean) trawl gear as fished off the bottom, or “mid-water,” with minimal or no interaction with seafloor habitat and benthic (or sea bottom) animals. Therefore, pelagic trawl fishing gear has traditionally been seen as more sustainable than bottom trawling gear, which scrapes the ocean seafloor in order to target fish species that are found at those depths.

Analysis recently highlighted at the North Pacific Fisheries Management Council (NPFMC), however, indicates that mid-water trawl gear in the pollock fishery — the largest food fishery on the planet — contacts the seafloor on average from 40 to 80 percent of the time, with rates up to 100 percent on factory ships. Unlike bottom trawl gear, pelagic trawl gear does not have any gear modifications, such as rollers or bobbins, to prevent damage to benthic habitat and infauna. These contact rates, however, call into focus the need for gear modification if the gear continues to be fished how and where it currently is.

Pelagic Trawl Gear

Pelagic Trawl Gear

Flawed Performance Standard for Mid-Water Trawl Gear

Currently, the legal definition of pelagic trawl gear actively prohibits meshes smaller than 20 inches between knots in the forward part of the net, and 15 inches between knots in the aft part of the net, with the intent of allowing animals to swim into and out of the net from the seafloor. In addition, a “performance standard” was developed for pelagic or mid-water gear to determine adherence to the intent of the gear definition. The definition of “pelagic trawl,” which differentiates the gear from “non-pelagic trawl” or bottom trawl, which is generally prohibited from use for the Bering Sea and Aleutian Islands (BSAI) pollock fishery, has changed in recent decades in response to restrictions in the catch of prohibited species, and currently rests upon a performance standard which prohibits having more than 20 crab (described also as infauna) on board at any one time. The regulation states that “crabs were chosen for the standard because they inhabit the seabed and, if caught with trawl gear, indicate that the trawl has been in contact with the bottom.”

Relying on the performance standard, however, is a flawed management practice. Some, if not most, crab mortality is not observable and is not currently reported directly in mortality rates which inform stock assessments, though it is known that not all crabs that encounter trawl gear are captured or avoided. Crab can be injured or killed by contact with any section of trawl gear: doors, sweeps, footropes (thick steel chains or cables), footrope gear, and net. Aside from contact, they can also be affected by the silt cloud stirred up by trawl gear dragging across the ocean floor.

Rose et. al 2012 provided a limited study of unobserved mortality of tanner, snow, and red king crabs from interaction with bottom trawl gear. Recapture nets were used to retain crab that interacted with the gear but did not end up in the primary net. They found that mortality rates of tanner and snow crab ranged from 4 to 15 percent, and red king crab mortality rates ranging from 9 to 32 percent. It could be estimated that those rates could be higher for pelagic trawl nets considering their lack of contact mitigation gear, and the substantial “smoothing” capacity of the steel footrope. Regardless, this demonstrates confidence in a range of statistically significant numbers that could and should be associated with unobserved crab mortality by pelagic trawl gear. However, the current rate of unobserved mortality accounted for in crab stock assessments and considered in pelagic trawl management standards is zero.

Decline of Iconic Crab Populations in the Bering Sea

Parallel to this, iconic bottom dwelling species, in particular snow crab and red king crab, are in dramatic decline in the Bering Sea, which could indicate a broader benthic ecosystem collapse. Consequences of the continued downward trend of crab stocks and subsequent fishery closures affect crab fishermen and crew, their communities, and communities adjacent to that fishery that provide processing services. The North Pacific Fishery Management Council has recently documented declining abundance rates of snow crab and red king crab that have alarmed fisheries participants to the point of soliciting emergency action. Considering the footprint of the pollock fishery, and decades of unmitigated seafloor contact, it is likely that long-term damage to sensitive habitat and sea-floor dwelling species, including crab prey, are contributing to the degradation of the ecosystem and the decline of these economically important crab fisheries.

To corroborate evidence of pelagic trawl contact with the seafloor, the NPFMC December 2022 Red King Crab Savings Area discussion paper reported the rate of metal pots used in other fisheries that were caught with pelagic trawl gear during the past 10 years in the Red King Crab Savings Area (RKCSA), a 4,000-square-mile area west of Bristol Bay in the Eastern Bering Sea designated since 1996 as a haven for red king crabs. Observer data shows that 9 to 21 percent of pelagic trawl tows in the Catcher Processor (CP) sector (vessels that catch and process onboard) and zero to 21 percent of tows in the Catcher Vessel (CV) sector (vessels that catch only) intercepted pot gear, which sits on the seafloor when deployed. Comparatively, the rates for bottom trawl gear ranged from two to 12 percent of tows in the CP sector and an annual average of zero percent of tows in the CV sector. On average, one out of every 11 pelagic trawl tows captures at least one pot, a rate that is greater than bottom trawling pot captures rates.

Damage to Ocean Bottom Habitat

While pelagic trawl gear is distinguished from bottom trawl gear in regulation, it is known that in practice both have substantial bottom contact – with pelagic trawl gear absent mitigation measures that address its impact. Even though the design of pelagic trawl gear is purported to benefit species like crab by allowing them to fall through the meshes, it is clear that the gear has a leveling effect on critical ocean bottom habitats and species such as coral. The Bering Sea Aleutian Island Fishery Management Plan (FMP) for groundfish describes the leveling effect of pelagic trawl fishing on benthic habitat (emphasis added):

Sessile organisms that create structural habitat may be uprooted or pass under pelagic
trawl footropes, while those that are more mobile or attached to light substrates may
pass over the footrope, with less resulting damage. Non-living structures may be more
affected by pelagic trawl footropes than by bottom trawl footropes because of the
continuous contact and smaller, more concentrated, surfaces over which weight and
towing force are applied.
In contrast, bottom trawls may capture and remove more of
the large organisms that provide structural habitat than pelagic trawls because of their
smaller mesh sizes. The bottom trawl doors and footropes could add complexity to
sedimentary bedforms as mentioned previously, while pelagic trawls have an almost
entirely smoothing effect.

Infauna, including crabs, bivalves, and marine worms, are considered to be engineers of the seafloor, all of which are important for nutrient exchange and essential cycles of sediment stabilization and destabilization. In addition to infauna, benthic habitat in the Bering Sea also includes slow-growing octocorals, sponges, and more. These species provide greater ecosystem benefits than protective shelter alone. They also provide medicinal nutrients when consumed, which is increasingly important for species at greater risk of disease with changing water temperatures; and biogeochemical cycling, or pathways by which matter is circulated, which contributes to benthic-pelagic coupling (the exchange of energy, nutrients, and organisms from one habitat to the other), considered a distinct biological feature of the Bering Sea ecosystem, which is broadly regarded as the natal grounds for many juvenile species. As changing ocean temperatures affect benthic-pelagic coupling resulting from melting sea ice, it is increasingly important to protect species that contribute to biogeochemical cycling.

New Regulations Needed for Pelagic Trawl Gear

While the sustainability of the pollock fishery as a single species fishery has been globally celebrated, the ecosystem around this fishery is in peril. Red king crab and snow crab, both in dramatic decline in the Bering Sea, may be indicator species of broader benthic collapse resulting from human activity. Failing to fully consider the significant bottom contact of pelagic trawl gear means ignoring long-term damage to important habitat features that underpin a complex and increasingly fragile ecosystem, and provide irreplaceable resources for resilience and recovery at times of ecosystem stress. Habitat loss and climate change are influencing biodiversity in ways that are difficult to anticipate. Even without considering the ongoing impacts of climate change, improvements are warranted in this fishery considering habitat impacts alone. However, particularly in a time of climate change, due diligence in assessing habitat damage is needed to protect food web integrity, resources that support ocean life, and perhaps most importantly the integrity of ocean biodiversity inextricably linked to intact, healthy habitat. These are the most critical, baseline tools of resilience in the ocean.

The Alaska Marine Conservation Council is dedicated to protecting the long-term health of Alaska’s marine ecosystems which sustain vibrant fishery-dependent communities. We call for pollock industry participants, including fishermen, managers, and sustainability proponents, to reconsider the accuracy of calculations of habitat disturbance and to enforce a prohibition on seafloor contact of the doors, footrope, net, and other components of the pelagic trawl gear used in the pollock fishery. If pelagic trawl gear incorporated bottom sensors and was fished at least three meters off the seafloor, we may begin the century-long process of healing benthic habitat to return functionality to the entire ecosystem. Absent these modifications, the only appropriate alternative to mitigate damage to seafloor habitat is to enact the same fishing area closures for pelagic trawl gear as bottom trawl gear and to require similar gear modifications to raise various components off the seafloor.

We recognize the concerns from industry that change can constrain the fleet, and potentially increase costs or decrease revenue. Those impacts are challenging; however, it is recognized across time and space that healthy habitat is essential to biodiversity, which supports the greater marine ecosystem. Skillful, evolving stewardship is of the utmost importance, especially considering the increasing stressors these ecosystems are experiencing.

Continuous review of current fishing impacts on stock health, and comprehensive ecological analysis to support responsible decision-making, is critical to maintain a viable ocean commons.

About Marissa Wilson

Marissa Wilson is the executive director of the Alaska Marine Conservation Council.

3 comments on “The Myth of “Mid-Water” in the Alaska Pollock Fishery

  1. No mention of the possible rippling effects of this massive ecosytem disruption on the food chains which sustain Alaska’s dwindling king and chum salmon populations. Factory trawling is the most destructive form of fishing yet devised by Man. It must be banned outright!

  2. I fished,I regret. What is a real practical solution?
    Who is implementing it?
    How can I help?

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