Overfishing, CPUE, and Commercially Extinct Species. 

Overfishing, CPUE, and Commercially Extinct Species. 
February, 17, 2019. By Megan Lorino

University of Port Elizabeth published an article in 1981 on the topic of catch per unit effort using gill-nets in the Sundays River estuary of South Africa. Their data was obtained from 55 catches using gill-nets. Nets were positioned in lower, middle, and upper reaches of the estuary. Each site was selected with avoidance of boat traffic in mind. Measurements were taken of salinity as well as (surface) water temperature of each site. CPUE was recorder for each caught species on a monthly basis and always included number per species as well as weight of each given species.

The most abundantly caught species was the sea catfish Tachysurus feliceps which totaled 226 individual fish, followed by the flathead mullet Mugil cephalus with a total of 191 individual fish, the souther mullet Liza richardsoni with a total of 185 individual fish, and the kob Argyrosomus hololepidotus with a total of 175 individual fish. The Argyrosomus hololepidotus (kob) was the  dominant catch in terms of weight, weighing 315kg, followed by the spotted grunter Pomadasys commersonni weighing 165kg. This particular study was to evaluate the abundance of varying species within the communities of the Eastern Cape estuaries. Gill-nets were set up between 1976 and 1979. 1,258 total fish were caught during this study. The CPUE (catch per unit effort) was 21kg/standard net.

 

References
Marais, J. (1981) African Journals Online. African Zoology. Seasonal abundance, distribution, and catch per unit effort using gill-nets, of fishes in the Sundays estuary. Retrieved from https://www.ajol.info/index.php/az/article/view/152270/141866

 

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Commercial extinction (of fish) is determined when a particular species of fish has become too rare to be caught for profit any longer. This occurs after a process of depletion – the reduction of that particular species due to overfishing. Recovery from overfishing causing an oceanic fishery to collapse can be combatted in several ways. One way is to create stronger regulations and plans of action toward illegal fishing in order to give stocks a chance to recover. More aggressive fisheries management, the increased use of aquaculture, and better law enforcement of catch-governing laws could all help to reduce overfishing and restore populations. Illegal fishing and unsustainable harvesting of fish is still one of the biggest issues causing overfishing that needs to be managed more diligently in order to really save our fish populations and truly reduce overfishing.

 

References
Doyle, A. (2015) Reuters. Ocean fish numbers on ‘brink of collapse’: WWF. Retrieved from https://www.reuters.com/article/us-environment-oceans/ocean-fish-numbers-on-brink-of-collapse-wwf-idUSKCN0RG1JW20150916

National Geographic (2010) Overfishing. Retrieved from https://www.nationalgeographic.com/environment/oceans/critical-issues-overfishing/

Dredge Fisheries Analysis

Dredge Fisheries Analysis by Megan Lorino.
February, 7, 2019.

Dredge fishing involves dragging a dredge across the sea floor in order to collect targeted fish species. There are many targeted species for dredge fishing practices including clams, oysters, mussels, scallops, sea urchins, sea cucumbers, conch, and crabs. There is a known risk of significant amounts of bycatch – the undesired catch of species other than those being targeted. There is also a great risk of harming other marine life with dredge fishing, one of the most harmed marine species being sea turtles. While the dredges are being pulled along the sea floor turtles are often crushed or captured in collection bags. Many other marine animals endure this risk including whales and dolphins, which may become entangled by the tow lines.

There are two types of dredges, scraping dredges and penetrating dredges. The scraping dredges have teeth or sharp bars that dig into the bottom of the sediment in order to pick up and collect marine animals which live on the sea floor. Penetrating dredges, which are also called hydraulic dredges, shoot jets of water into the sea floor in order to chase out the animals which live deeper in the sea floor out into collection bags. Dredges can weigh 2,600 pounds or more. Dredges have actively been called the most damaging gear to bottom ocean habitats. When dredges are dragged along the sea floor they also kill many smaller species including snails and worms. Areas abundant in seagrass can be damaged by destruction of the grass roots. This negatively impacts species of fish and other marine animals that rely on seagrass for food supply, habitat and protection from predators.

Proper management of dredge fisheries can help reduce the habitat destruction, bycatch, and harm to marine species during dredge fishing. Using lighter weight dredges where possible can lower the risk of crushing marine animals. Protecting certain habitats to allow some areas to remain untouched from dredges can also help protect many species. Regulating the allowance or minimum size requirements between teeth or bars on dredges can allow smaller species to pass through and avoid becoming injured while the dredges pass through their habitats. Remaining areas that have not been disturbed by dredging should be protected.

Policy decisions should be based on science where it is often proved how damaging certain fishing methods are. It is the responsibility of fisheries managers to maintain ethical policies to protect our natural ecosystems and maintain appropriate regulations to help lessen the risks of harming marine species while capturing those for commercial use. Scientific method now addresses what types of impacts from fishery practices are considered most harmful. There is enough scientific evidence present day to consciously make an effort to manage fisheries while reducing the number of marine species being harmed or resulting in population declines. “The time has come for fishery managers and conservation organizations to add fishing selectively, avoiding habitat damage, and protecting marine biodiversity as important components in maintaining ocean ecosystems and healthy fisheries.” (MCBI, vi)

Resources
NOAA Fisheries. Fishing Gear: Dredges. Retrieved from https://www.fisheries.noaa.gov/national/bycatch/fishing-gear-dredges

Safina Center. Fishing Gear 101: Dredges. Retrieved from http://safinacenter.org/2015/05/fishing-gear-101-dredges-the-bottom-scrapers/

MCBI Marine Conservation. Shifting Gears. Retrieved from https://mcbi.marine-conservation.org/publications/pub_pdfs/ShiftingGears.pdf