Course:CONS200/2021/Effectiveness and use of descending devices to mitigate rockfish bycatch

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This article contains a brief overview on the immediate effects of descending devices used to release a common bycatch fish called 'rockfish' (Sebastes), which is commonly caught during commercial fishing operations off the coast of North America and many other parts of the world.

Rockfish are an endangered species of fish often caught as bycatch, primarily off the western coast of North America. However unlike shallow dwelling fish, deep dwelling fish such as rockfish suffer from an immediate effect known as barotrauma, which is caused by the sudden pressure difference created when the fish is brought from deep waters to the surface during fishing operations. As a result, traditional catch-and-release methods for bycatch cannot be used to release rockfish, as survival is not guaranteed, thus, alternate methods must be considered.

To mitigate rockfish mortality due to barotrauma during bycatch, and to maintain rockfish populations, new types of descending devices can be potentially employed on a large scale to help ensure healthy individuals are released back into the population. These new devices can not only prevent the decline of rockfish populations but could also potentially increase fishing efficiency by reducing bycatch altogether.

There are 39 species of rockfish in British Columbia, the image above shows the yelloweye rockfish, wich is one of many inshore species found off of North America's West Coast.[1]

Rockfish (Sebastes) Information


There are 102 identified species of rockfish (Sebastes) worldwide, with at least 72 species residing in the Northeastern Pacific.[2]

Rockfish are a unique kind of coastal organism as most rockfish species have long lifespans, often exceeding 50 years.[3] Some species, such as the Yelloweye rockfish can live up to 100 or more years, making it one of the oldest fish off the North America's West Coast and the oldest ground feeding fish in Canada. Rockfish live along many coastline habitats, from shallow kelp forests to deep submarine canyons.[3]


Rockfish are at the center of conservation on North America's West Coast because they are a very slow maturing and reproducing fish. It will take 12 years for a female rockfish to mature and become a reproductive member of her population. Rockfish are an organism that have specific seasonal spawning seasons, usually through winter to spring. The most fertile stage of a female rockfishes lifespan develops has she matures into old age, usually halfway through a rockfishes average lifespan or older;[4] this can be a huge factor in determining a population or species survivorship and overall fitness, as overfishing typically causes the oldest, and largest, rockfish to become extinct.

Due to their seasonal reproductive cycle, the preservation of new generations, after overfishing or natural disaster, is difficult.[3] The late maturing female reproductive system, fertility range and the annual spawning seasons can hugely impact a rockfish population in a fishing zone, thus, causing many populations to become endangered in very little time.

Population History

Rockfish have always been a target of human consumption, initially mostly by indigenous populations.[3] However in the early 1980s due to technological improvement and attitude change towards the species, rockfish became a primary year-round target for commercial and recreational fishing causing them to suffer intense exploitation.[3] Over the past 30 years in a survey conducted in Puget Sound, United States, it is shown that numerous species of rockfish have undergone population decline due to growing consumer demands and overfishing.[3] As a result of severe rockfish population decline and potential ecological damages, many species of rockfish in the United States became listed as endangered and are under the protection of the National Marine Fisheries Services and US Endangered Species Act.[3]

Overfishing and Bycatch

Due to the rockfish’s characteristics such as large size and slow maturation rate, rockfish are “intrinsically more vulnerable to overfishing”[4] as their slow reproduction will amplify the consequences of population loss due to commercial fishing. Another danger of fishing can affect the smaller rockfish populations, as they are often unintentionally caught as a result of fishing due to their limited range and behavior[5], which means that they can very likely unintentionally end up in shellfish traps and other fishing gear.

Rockfish bycatch in commercial fishing


One major concern regarding rockfish bycatch lies within the prawning industry, as many juvenile rockfish are reported to have been captured within prawn traps.[6] However, research using traps replicating similar designs of those employed in commercial fishing have demonstrated small amounts of rockfish bycatch yielding around 0.015 rockfish per replicated trap.[6] However, the research concludes that this may be a complete representation of the magnitude of impact of prawn traps on rockfish population and states that it should be done directly by commercial fishing industries.[6]

Derelict Fishing Gear

Derelict fishing gear, are traps, lines and netting abandoned by fishing boats or destroyed during storms that can continue trapping fish and other marine life forms.[7] This poses a threat to local rockfish populations, as numerous live and dead rockfish specimens have been found within traps during derelict fishing gear removal operations in Washington.[8] It is estimated that 653 traps were lost in the Salish sea during the years 2012-2013.[8]


Barotrauma is the result of the pressure difference in deep sea fish when brought to the surface, usually via angling and netting and can be fatal depending on the species. As rockfish are deep sea species that live 300m below the surface. They suffer from health complications related to this pressure difference such as ruptured swim bladder[5] and compromised reproductive capabilities.[9] Furthermore, severe barotrauma will result in emboli within the pharyngo-cleithral membrane, esophageal eversion, exophthalmia and ocular emphysema and can cause buoyancy problems that may result in death.[10] As a result of the apparent effects of barotrauma, traditional catch-and-release methods must be reconsidered for rockfish conservation efforts to reduce rockfish mortality.

Barotrauma is a direct result from sudden changes of water pressure on the rockfish's gallbladder and internal organs. A clear indication of a rockfish affected by barotrauma is a swollen stomach and bulging eyes as shown in the image above.

Specifications regarding the effects of barotrauma on rockfish reproduction capabilities

A study on yelloweye rockfish (S. ruberrimus) has shown: that those who have survived the effects of barotrauma without proper recompression, although still reproductively capable, may have suffered a compromise to reproductive capabilities due to factors such as energy cost of recovery.[9] This cost may "negatively affect reproductive fitness through reduced embryo condition."[9] Embryos of females who have undergone the effects of barotrauma and released without recompression have reduced embryo oil globule volume (OGV), compared to those released with a deepwater-release mechanism (DRM).[9] The long term effects of this ultimately means reduced chances of successful embryo development and amount of offspring developed per spawning batch.

Solutions to mitigating bycatch effects on rockfish populations

Descending Devices

A descending device is an underwater instrument joined to a weight, minimum of 1 pound, 16 ounces, that is used to release caught fish back into the aquatic environment.[11] A deep sea descending device is typically made up of a line, pulley, weight and a barbless hook or clasp and is mandatory for fishing boats in case a bottom feeding fish is caught during fishing. The hook or clasp is attached to the jaw of the fish and is a cruelty free way of releasing fish into required depth.

Effects on rockfish

Without the usage of descending devices to lower rockfish down, 90% of rockfish are assumed to be killed off by the effects of barotrauma.[10] However with the usage of various types of descending devices, the survival rate of rockfish is estimated to be 91.4% when descended to appropriate depths.[10]

List of Descending Devices

1. Barbless inverted weighted hook
  • The "Shelton Fish Descender™"[12] - a barbless hook that gets inserted inside rockfish’s mouth or jaw. Once the fish is at a certain depth, the hook or clasp releases by quickly yanking the fishing line. This descender is good for deeper depth spaces as it has a line attached, custom to the buyer
  • 9% reported mortality rates for rockfish released[10]
2. Spring-loaded clamp
  • The "Fish Grip"[13] - a clasp used for handling fish on boats or areas where fish are extracted from aquatic habitat. It is a hand held device used to protect the enzymes surrounding fish as well as a tolerant approach to handling fish. Good for surface level or shallow depth use
  • The "SeaQualizer™"[12] - This is a more efficient line as it already has a specified depth that can be customized or kept automated as packaged. Due to the pre-specified depth, the user does not need to yank line to release fish, like the The Shelton Fish Descender, which is a more basic model. This descender is good for shallow, medium or deep depths. It also has multiple clamps, allowing for more than one fish to descend
  • 4.3% reported mortality rate for rockfish released[10]
3. Pressure-release clamp[12]
  • The "RokLees™ Fish Descender"[13] - Very similar descending device as the The Shelton Fish Descender, but it is a more cruelty free model as it is a jaw clasp and it has a rubber tab(s) to ensure less injury to fish during release. The clasp will release with a yank at the fishing line
  • 11.3% reported mortality rate for rockfish released[10]

Bycatch reduction device (BRD)

Commercial bycatch is a danger to many aquatic species such as the rockfish.

Employing bycatch reduction devices on traps and nets allow non-target catch a chance to escape, which would help mitigate bycatch and increase fishing efficiency overall. One study notes two designs which include an 'open escape window' bycatch reduction device designed to reduce bycatch of Chinook salmon and Widow rockfish, and noted that there was 'potential' for reducing bycatch rates within the traps.[14] This could be further enhanced with artificial lighting, as the light was noted to have a great influence on the behavior of fish while reducing escape time.[14]

Rockfish Conservation Areas

The government of Canada has implemented conservation areas across British Columbia’s coasts. These areas make fishing of rockfish illegal under conservation initiatives to repopulate shorelines where Rockfish have become critically endangered. Inshore rockfish populations are at most risk due to commercial and recreational fishing using unsustainable methods such as hook and line and trapping.[15] Establishing protected areas can allow the rockfish to mature under conditions that do not involve human impacts that can hinder population growth. In BC, Canada, over 4800 square kilometers are reserved as 'rockfish conservation areas'.[11]

However, although in action, current BC conservation areas have shown to have little effects on recovering rockfish population, which is potentially due to the inadequate level of protection and other factors such as compliance and enforcement.[16] This could also be due to the fact that rockfish repopulation could take much longer than the 7 years since the area was established.


In conclusion, descending devices have a significant effect in mitigating the effects of rockfish bycatch due to the main benefits of reducing mortality and reproductive issues from barotrauma. Fish released with the assistance of descending devices have significantly improved survival rates and have shown to be more reproductively capable than those released without. With increasing industrial commercial fishing and recreational fishing, it is important to protect endangered rockfish species and prevent their extinction. New technologies such as descending devices can ethically catch, or release rockfish from coastal fishing zones without the dangers of extreme bodily trauma or overfishing. The use of descending devices are becoming more popular in the fishing industry due to their convenient, adaptable nature and their effectiveness to conserve and increase the survival rates of rockfish caught in bycatch.


Please use the Wikipedia reference style. Provide a citation for every sentence, statement, thought, or bit of data not your own, giving the author, year, AND page. For dictionary references for English-language terms, I strongly recommend you use the Oxford English Dictionary. You can reference foreign-language sources but please also provide translations into English in the reference list.

  1. Landis, B. Y. (2015, November 8). "Rockfishes (sebastes spp..)". Better Know a Fish!. Retrieved November 8, 2021. Check date values in: |date= (help)
  2. Kendall, A.W. (1991). "Systematics and identification of larvae and juveniles of the genus Sebastes. In: Boehlert G.W., Yamada J. (eds) Rockfishes of the genus Sebastes: Their reproduction and early life history". Developments in environmental biology of fishes. 11 – via Springer Link.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 Williams, Gregory D.; Levin, Phillip S.; Palsson, Wayne A. (2010). "Rockfish in Puget Sound: An ecological history of exploitation". Marine Policy. 34: 1010–1020 – via Science Direct.
  4. 4.0 4.1 Magnuson-Ford, Karen; Ingram, Travis; Redding, David W.; Mooers, Arne Ø (2009). "Rockfish (Sebastes) that are evolutionarily isolated are also large, morphologically distinctive and vulnerable to overfishing". Biological Conservation. 142: 1787–1796 – via Science Direct.
  5. 5.0 5.1 "Rockfish". Galiano Conservancy Association. June 8, 2021. Retrieved October 15, 2021.
  6. 6.0 6.1 6.2 Favaro, Brett; Rutherford, Dennis T.; Duff, Stefanie D.; Côté, Isabelle M. (2010). "Bycatch of rockfish and other species in British Columbia spot prawn traps: Preliminary assessment using research traps". Fisheries Research. 102: 199–206 – via Science Direct.
  7. "What is ghost fishing?". National Ocean Service. September 27, 2011. Retrieved December 10, 2021.
  8. 8.0 8.1 Antonelis, Kyle; Selleck, James; Drinkwin, Joan; Saltman, Annika; Tonnes, Dan; June, Jeffrey (2018). "Bycatch of rockfish in spot prawn traps and estimated magnitude of trap loss in Washington waters of the Salish Sea". Fisheries Research. 208: 105–115 – via Science Direct.
  9. 9.0 9.1 9.2 9.3 Blain-Roth, B. J.; Sutton, T. M (03/2019). "Effects of barotrauma and recompression events on subsequent embryo condition of yelloweye rockfish Elsevier". Fisheries Research. 211: 121–216 – via USDA. Check date values in: |date= (help)
  10. 10.0 10.1 10.2 10.3 10.4 10.5 Bellquist, Lyall; Beyer, Sabrina; Arrington, Morgan; Maeding, Jordan; Siddall, Alayna; Fischer,, Paul; Hyde, John; Wegner, Nicholas C. (2019). "Effectiveness of descending devices to mitigate the effects of barotrauma among rockfishes (Sebastes spp.) in California recreational fisheries". Fisheries Research. 215: 44–52 – via Science Direct.CS1 maint: extra punctuation (link)
  11. 11.0 11.1 "Protecting rockfish". Government of Canada. 2021-06-17. Retrieved December 9, 2021.
  12. 12.0 12.1 12.2 "Descending Devices". Englund Marine & Industrial Supply. 2017. Retrieved October 15, 2021.
  13. 13.0 13.1 Killer, Ed (June 12, 2020). "Snapper and grouper will better survive release with now-required descending device". TCPalm. Retrieved October 15, 2021.
  14. 14.0 14.1 Lomeli, Mark J.M.; Wakefield, W. Waldo (2012). "Efforts to reduce Chinook salmon (Oncorhynchus tshawytscha) and rockfish (Sebastes spp.) bycatch in the U.S. west coast Pacific hake (Merluccius productus) fishery". Fisheries Research. 119-120: 128–132 – via Science Direct.
  15. "Rockfish Conservation Areas". Government of Canada. 2021, February 10. Retrieved December 10, 2021. Check date values in: |date= (help)
  16. Haggarty, Dana R.; Shurin, Jonathan B.; Yamanaka, Lynne (2016). "Assessing population recovery inside British Columbia's Rockfish Conservation Areas with a remotely operated vehicle". Fisheries Research. 183: 165–179 – via Science Direct.

Seekiefer (Pinus halepensis) 9months-fromtop.jpg
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