Commercial Fishing Pressure: Bycatch

Commercial fishing pressure is an indicator of how the large-scale harvesting of free-ranging fish from coastal waters and high seas can impact the success of future catches of wild fish. This includes catch and bycatch (both high and low) of fish, other seafood and marine wildlife.

While global fishery resources supply humans with a significant portion of their protein needs, they may also inflict pressure on the environment through overfishing, the catch of unintended species, and the use of destructive or unregulated fishing methods that can result in high levels of bycatch, i.e. the catch of unintended species or undersized/underaged specimens of a target species.  

Commercial Fishing Bycatch
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Which Goals Does This Affect?


How Was It Measured?

Commercial Fishing, High Bycatch

Modeled demersal and pelagic high bycatch fishing pressure.

This Pressure represents fish caught using high bycatch gear, which includes demersal destructive (e.g. trawl), demersal non-destructive (e.g. pots, traps) and pelagic (e.g. long-lines) gear. Spatially-explicit global estimates of catch by five different gear types aassociated with high bycatch and the two associated with low bycatch were then calculated for each region. Pressure per gear class per region was calculated as the mean of all 1km pixel values within the region.  The maximum possible score (which is used to rescale all values 0-1) was set at 110% of the maximum regional score from previous years. High bycatch commercial fishing was then measured as the average of demersal destructive (e.g., trawl), demersal non-destructive high bycatch (e.g., pots, traps) and pelagic high bycatch (e.g., long-line) gear.

All pressures have different affects on different goals. For each goal, the affect of each pressure is weighted 'low' (1), 'medium' (2) or 'high' (3). The actual data-derived value of the pressure is then multiplied by the weight assigned to it for that goal. That process is repeated for each pressure-goal combination.  The sum of those values divided by 3 (the maximum pressure-goal value) expresses the total affect of that pressure on the goal.

Commercial Fishing (High Bycatch) has a high effect (weight = 3) on Food Provision (Fishing), Livelihoods and Economies (Commercial Fishing), and Biodiversity (Habitats: Soft Botton, and Species). It has a medium effect (weight = 2) on Artisanal Fishing Opportunity, and Sense of Place (Iconic Species). It has a low effect (weight = 1) on Livelihoods and Economies (Marine Cetacean Watching). 

Commercial Fishing, Low Bycatch

Modeled demersal and pelagic low bycatch fishing pressure.

Methods for this Pressure were identical to those for Commercial Fishing, high bycatch, but calculating the area exposed to fisheries using demersal non-destructive (e.g. hook and line) and pelagic (e.g. purse seine) gear. 

Commercial Fishing (Low Bycatch) has a medium (weight = 2) on Natural Products (Fish Oil). It has a low effect (weight = 1) on Food Provision (Fishing), Artisanal Opportunity, Livelihoods and Economies (Commercial Fishing), and Biodiversity (Habitats: Soft Bottom, and Species).

Full details for this data layer are provided in Halpern et al. (2008) and Halpern et al. (2015).


What Are The Impacts?

Impacts of Unsustainable Fishing Pressure
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ECOLOGICAL IMPACT
Increasingly intense large-scale fishing has spread throughout the ocean. Fishing pressure and destructive fishing techniques have led to the depletion, or even collapse, of major fish stocks.

Though declining exploitation rates have contributed to the rebuilding of some depleted stocks, on average, fish stocks are still well below maximum sustainable yield (maintaining the population size at the point of maximum growth rate) in most regions (Worm et al. 2009).

Overfishing can affect the population size of threatened or endangered species as well as the potential future catch of targeted fish stocks.

At least 32% of assessed commercial species are overexploited or depleted and a further 53% are already exploited to their maximum capacity (FAO 2010).

Unsustainable fishing pressure alters marine ecosystem structure and can have a significant impact upon biodiversity, productivity, and overall food web dynamics.

Destructive fishing practices result in bycatch, which is the catch of unintended species or undersized/underaged specimens of the target species. Bycatch of non-target species can harm the ecological structure of an ecosystem, affecting existing populations as well as potential future catch. Species other than fish, including whales, sharks, dolphins, sea turtles and sea birds die as bycatch from the use of nets and longlines (Davies et al. 2009).

Although some countries utilize bycatch for food and/or fishmeal, non-target species are usually returned to the water when they are dying or already dead. 
HUMAN HEALTH IMPACT
Oceans provide food for billions of people worldwide. Fish are highly nutritious, rich in essential minerals, micronutrients, essential fatty acids and proteins.

Fish provide more than 3 billion people, particularly in low-income, food deficient countries, with 15 percent of their average per capita intake of animal protein (FAO 2010).

If overfishing did not exist, global fisheries could have prevented malnourishment for nearly 20 million people and total catch in the waters of low-income, food deficit, nations might have been up to 17% greater than the tonnage actually landed there (Srinivasan et al. 2010).

The global demand for seafood continues to rise, while 40% of fisheries are actually decreasing in production and overfishing remains a major threat to seafood availability (Peterson and Fronc 2007).
ECONOMIC IMPACT
While there are tremendous economic and social benefits from fishing, overfishing can have significant adverse socioeconomic effects. The depletion of global fish stocks constitutes a loss of global natural capital and when fish stocks are fully exploited physically, associated fisheries are almost invariably performing below their economic optimum (World Bank 2008).

Net losses to the global economy from unsustainable exploitation of living marine resources are calculated to substantially exceed US $50 billion per year- equivalent to more than half the value of the global seafood trade (World Bank 2009).

Fisheries and aquaculture (both marine and freshwater) together employ about 44.9 million people worldwide. Each of these jobs produces approximately three secondary jobs, leading to a total of approximately 180 million people employed in the sector.

On average, each job holder supports three dependents or family members, so the livelihoods of about 540 million people worldwide--8 percent of the world population in 2008—were dependent on fisheries and aquaculture (FAO 2010).

Wild fisheries contributed between US $ 225-240 billion to the global economy in 2003 (Dyck and Sumaila 2010). 


What Has Been Done?


Get More Information

Consortium for Wildlife: Bycatch Reduction
A database of collaborative research between the fishing industry and the scientific community that aims to reduce bycatch for endangered species.

World Wildlife Fund (WWF): Smart Gear Competition
Created in partnership with industry leaders, scientists, and fishers, the competition encourages fishers to reduce the incidental catch of non-target species in fishing gear.

Sustainable Fisheries Partnership (SFP)
FishSource is a global fisheries online database created for seafood buyers and contributors.

Food and Agriculture Organization of the United Nations: Fisheries and Aquaculture Department
An index of fisheries’ global information networks.    

WorldFish Center
An international publication database dedicated to reducing poverty and hunger by improving fisheries and aquaculture.

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References




PHOTO(S): © Keith A. Ellenbogen
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