Skip to main content
Ocean Networks Canada

Ocean Networks Canada

Search form

Facebook iconTwitter iconLinkedIn iconYouTube iconFlickr iconInstagram icon

Menu

  • About Us
    • About Us
    • Jobs & Opportunities
    • Events & Workshops
    • Contact Us
    • Support Us
    • Annual Report 2019-2020
    • Organization
      • Leadership
      • Staff
      • Boards
      • Committees
    • Funders, Associate Members & Partners
      • Funders
      • Associate Members
      • Partners
  • Science
    • Science
    • Active Research
    • Highlights
    • Science Plan
      • Summary
      • Science Themes
    • Publications
      • General Interest
      • Academic
    • Getting Involved
      • Proposals
  • Innovation Centre
    • Innovation Centre
    • About the Innovation Centre
    • Success Stories
    • Contact Us
    • Smart Ocean™ Systems
      • Sensors and Instruments
      • Technology Demos
      • Ocean Observing Systems
      • Earthquake Early Warning
    • Partners & Networks
      • Industry Network
      • Global Partnerships
      • R&D Support
      • Students in Industry
    • Atlantic Partners
  • Learning
    • Learning
    • Learning Highlights
    • Learning Events
    • Partnerships
    • Contact Us
    • Ocean Sense
      • Community Observatories
        • Cambridge Bay
        • Campbell River
        • Kitamaat Village
        • Prince Rupert
      • Teacher Info
      • Student Info
      • Resources & Lessons
    • Get Involved
      • For Students
        • For Undergrads & Grads
      • For Educators
        • Educator Opportunities
      • For Communities
      • Ship2Shore
      • Citizen Science
        • Coastbuster
        • Digital Fishers
      • Youth Science Ambassador
    • Resources
      • Learning at Home
      • Educator Resources
      • Ocean Alive!
      • Oceanography 101
      • About the Observatories
      • Research Ideas
      • Student Reports
  • Observatories
    • Observatories
    • Arctic
    • Atlantic
    • Pacific
    • Mobile Platforms
    • Infrastructure
      • Data Facilities
      • Platforms
      • Devices & Sensors
      • Cables & Connectors
    • Expeditions
      • Wiring the Abyss
      • Expedition Logs
      • Maintenance Processes
    • Notices
      • Information for Mariners
      • Alerts and System Status
  • Data & Tools
    • Data & Tools
    • Highlights
    • Data Quality
    • Preview & Download
      • Preview & Visualize
      • Data Download Tools
      • State of the Ocean Plots
      • Ocean Report Card
    • Apps & Services
      • Mobile Apps
      • OPeNDAP Web Services
      • Related Sources
      • Earthquake Data Dashboard
    • Data Help
      • Usage Policy
      • Tutorials & Help Pages
      • Request Help
  • Sights & Sounds
    • Sights & Sounds
    • Terms of Use
    • Video
      • Live Video
      • Video Highlights
      • Video Archives
    • Images
      • Maps
    • Audio
      • Audio Highlights
      • Audio Archive
  • News
    • News
    • Stories
    • Newsletters
    • Calendar
    • Media Relations
      • Backgrounders
      • Downloads
      • In the News
      • News Releases
      • Media Contacts

About Us

You are here

  1. Home
Jan 30, 2017

The cumulative effects of bottom trawling and low oxygen on marine life

In November 2016, Ocean Networks Canada (ONC) scientists co-authored a publication in Deep-Sea Research II on the effects of deep-sea bottom trawling on seafloor marine life, already stressed by the naturally low oxygen waters of the north Pacific. This is the first study to measure the effects on the fauna living on the soft-sediment seabed of Vancouver Island’s continental shelf and slope. Previous scientific research has focused on by-catch (species accidentally caught in the fishing net), particularly in areas where deep-water coral and sponge reefs occur.

This article is based on a University of Victoria Master’s thesis by Maéva Gauthier. The data originates from remotely operated vehicle surveys along the cable route for ONC’s NEPTUNE observatory in 2007, prior to the installation of the observatory.

The deep-sea video and sonar data from the surveys reveals a decline in invertebrate and fish populations, and a reduced biodiversity in the oxygen minimum zone—where oxygen saturation is at its lowest—off Vancouver Island (depth 600-1100 m). This coincides with the most heavily trawled areas primarily targeting thornyhead fishes (Sebastolobus alascanus and S. altivelis).

Thornyheads captured on left, bottom trawl scar mark on seafloor on the right.​

Figure 1: Left, thornyheads (Sebastolobus spp.) captured during the study’s video surveys. Right, bottom trawl scar mark on the seafloor near Clayoquot slope, 30 miles offshore Vancouver Island (depth 1100 m).

Commercial bottom trawling off the coast of British Columbia began in the 1990’s in response to growing market demands. It is still economically important, despite scientific evidence and public concern about the risks to seafloor habitats and marine life.

After the first 15 years, Fisheries and Oceans Canada estimated that the bottom-trawling fishery footprint impacted an area larger than Vancouver Island; specifically 38,000 km2 along Canada's Pacific coast, at depths ranging from 115 to 1100 m. In its latest yearly assessment, the estimated economic value of British Columbia’s groundfish fishery—which combines bottom trawls and other fishing gear—is $146 million (87,049 tonnes). This represents 40% of Canada’s entire market: $362 million (169 tonnes).

Catch and monetary value of British Columbia’s Groundfish fishery 1985-2015

Figure 2: Catch and monetary value of British Columbia’s groundfish fishery, 1985-2015. (Data source: Department of Fisheries and Oceans)

Bottom trawling represents the most pervasive human impact on the world’s continental margins, even when compared to oil and gas exploration, waste and litter disposal, and mining. As fish stocks become depleted in coastal areas, its footprint is steadily descending into deeper waters. Direct effects of bottom trawling have been extensively reviewed in scientific literature and include scraping and ploughing of the seafloor, sediment resuspension with a smothering impact on the seafloor fauna (benthos), destruction of non-target species, and organic loading from the dumping of waste from at-sea processing. Indirect effects include post-fishing mortality and long-term, trawl-induced changes in the benthos, such as reduced diversity and biomass, and changes in ecosystem structure and habitat heterogeneity.

Extent of deep-sea red shrimp fishery off the coast of Spain

Figure 3: Left, extent of the deep-sea red shrimp (Aristeus antenatus) fishery off the coast of Spain. The map highlights (in yellow) the fishing vessel tracks from GPS positioning data, showing the target fishing areas near the La Fornera submarine canyon. Right, the fishing activity in this region is so intensive that its negative effects are compared to the effect of plowing farmlands, exterminating entire seafloor communities and leaving behind a barren seafloor. (Map and image: Puig et al 2012).

Despite this grim picture, recent positive changes in bottom trawling policy aim to prevent its expansion into deeper waters. In 2016, the European Commission agreed to ban bottom trawling below 800 m in European Union waters; also, it established measures to prevent bottom trawling in vulnerable marine ecosystems, such as deep-water corals and sponge reefs.

Similar measures have also been implemented in British Columbia since 2012, in an unprecedented agreement reached between British Columbia’s Deep Sea Trawlers Association and key non-government organizations such as the David Suzuki Foundation, Living Oceans, and SeaChoice. In a move towards reducing the impacts on deep-sea habitats, the voluntary agreement put the following key fisheries management strategies into effect: 1) the fisheries footprint has been reduced by 8,000 km2 through limiting the maximum bottom trawling depth to 800 m and banning trawling from areas where corals and sponge reefs are known to occur in high densities; 2) a habitat quota means that vessels can retrieve no more than 4,500 kg of corals and sponges annually; 3) a habitat encounter protocol requires vessels to immediately report if they retrieve over 20 kg of corals and sponges combined; and 4) a habitat review committee conducts ongoing evaluations of fisheries impacts on the ecosystem. As a result of these and other measures worldwide, a once overexploited fishery is now moving toward sustainability.

Map of British Columbia’s groundfish fishery footprint

Figure 4: British Columbia’s groundfish fishery footprint, highlighting areas removed from fishing grounds since the voluntary agreement came into effect in 2012. Image credit: Living Oceans Society.

Understanding how these remote ecosystems are impacted by human activities is the key to sustaining deep-sea fisheries. This ONC study provides the first evidence that natural stressors can exacerbate bottom trawling effects. In this case, the north Pacific oxygen minimum zone has a profound impact on marine life, reducing abundance and biodiversity. The worldwide expansion of oxygen minimum zones or “dead-zones” has been associated with climate change. Models predict a decline of 1 to 7% of the global ocean inventory of dissolved oxygen by the end of this century.

The study found that the deep-sea soft-bottom communities were adversely affected by both bottom trawling intensity (measured by a high-resolution sonar mounted in the remotely operated vehicle) and low dissolved oxygen waters (measured via Line P, Fisheries and Oceans Canada’s long time-series of oceanographic data). ONC will continue to investigate these synergistic interactions of human-induced impacts and natural ocean variability along British Columbia’s continental margin.

Scanning sonar image on right, ROPOS ROV initiating a dive on left​

Figure 5: Left, Scanning sonar image captured with remotely operated vehicle ROPOS and video surveys. Right, remotely operated vehicle ROPOS initiating a dive descent.

deep-sea | Research | bottom trawling | low oxygen | red shrimp | Sebastolobus | Aristeus antenatus | groundfish | human impact | trawlers

Printer-friendly versionPDF version

Related Stories

Expert Q&A on Canada’s growing blue economy
Feb 9, 2021

Oceans link to climate change
Jan 8, 2021

Rock solid climate solutions: Negative emissions technology
Sep 26, 2019

ONC and Schmidt Ocean Institute Team Up
Sep 5, 2013

China Trade Mission Showcases B.C. Ocean Technology
Sep 4, 2013

Saanich Inlet Hypoxia Paper Published
Sep 26, 2012

Digital Fishing Derby
Aug 1, 2012

Calendar of Events

February 2021

  • « Prev  
  •   Next »
S M T W T F S
31
1
2
3
4
5
6
 
 
 
 
 
 
 
7
8
9
10
11
12
13
 
 
 
 
 
 
 
14
15
16
17
18
19
20
 
 
 
 
 
 
 
21
22
23
24
25
26
27
 
 
 
 
 
 
 
28
1
2
3
4
5
6
 
 
 
 
 
 
 

Newsletter

Sign up for our monthly e-newsletter:

 

Tweets Follow @Ocean_Networks

 

 

Highlights

  • Audio
  • Data
  • Learning
  • Science
  • Video

Reading Room

  • Active Research
  • Backgrounders
  • FAQs
  • Glossary
  • News Briefs
  • News Stories
  • Newsletters
  • Publications

Cool Stuff

  • Apps
  • Digital Fishers
  • iBooks & e-Pubs
  • Live Video
  • Maps
  • Images
  • State of the Ocean

Data & Tools

  • Apps
  • Data Plots
  • Data Search
  • Data Policy
  • Data Help
  • OPeNDAP Web Services

Opportunities

  • Calendar
  • Educator Opportunities
  • Global Partnerships
  • Industry Network
  • Jobs
  • Staff List
  • Technology Services

Sites & Instruments

  • Arctic Sites
  • Northeast Pacific Sites
  • Salish Sea Sites
  • Notice to Mariners

Follow Us

Facebook iconTwitter iconLinkedIn iconYouTube iconFlickr iconInstagram icon

Sign up for our newsletter

Feedback

CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Image CAPTCHA
Enter the characters shown in the image.

                              

About Us | Contact Us | Media Relations | Legal Notices

©   Ocean Networks Canada. All rights reserved.  2474 Arbutus Road, Victoria, BC, V8N 1V8 | 1.250.472.5400