Fisheries and aquaculture are confronted with continuing problems such as climate change, growing human populations, low income of small scale fishers and fish farmers, and competitive production and trading conditions. People should be confronting and discussing the challenges in order to come up with solutions on how we can respond; and the community should be resilient and adaptive in combatting the challenges. We cannot immediately solve some problems, such as overfishing, illegal fishing, depletion of marine resources, as they have deep root causes, but we are learning how to address them. Governments do their best to manage fishery resources to meet these challenges. Decision makers and the public also need to continually listen to new information so that they are equipped with knowledge for sustaining marine and aquaculture resources and protecting people who depend on them for nutrition, livelihood and business. Research is an important information gathering tool that contributes to policy and decision-making. The Asian Fisheries Society and its partners are taking a lead in making new information accessible through its platform AsiaPacific-FishWatch providing essential information on fish harvested or farmed for food in Asia-Pacific. I am pleased that AsiaPacific-FishWatch gives attention in its profiles and posts to the critical social, economic and market character of the value chains. The Asian Fisheries Society emphasises equally social and economic knowledge and biological, physical and technical knowledge.

Prof. Alice Joan G. Ferrer, PhD, President, Asian Fisheries Society

 
 
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ASIAPACIFIC-FISHWATCH

All fishing gears have some level of environmental effect. Under the FAO Code of Conduct for Responsible Fishing, the fishing sector is expected to reduce its effects to the minimum possible in ways that are also compatible with its own sustained existence. For yellowfin tuna caught in surface and deep waters by a wide variety of fishing methods, bycatch is one of the most observable effects of fishing on the environment. This is especially the case when yellowfin tuna are caught by longline, gillnet and by purse seining on floating objects, including fish aggregating devices (FADs). Air and water pollution from fishing vessels and fish processing are other environmental concerns.

Environmental variation also has an effect on the abundance and distribution of yellowfin tuna. As the ocean warms and becomes more acidic due to increased emissions of carbon dioxide (CO2), the distribution and catchability of yellowfin tuna stocks are expected to become even more variable.

EFFECTS OF YELLOWFIN FISHING ON OTHER SPECIES

Yellowfin tuna are caught by purse-seine nets, longline, pole-and-line and troll line in the Western and Central Pacific Ocean (WCPO), and by gill nets, longline, purse seine, pole-and-line, handline and troll line in the Indian Ocean (IO) (see Production). These gears do not come into contact with the seafloor and so do not directly affect the benthic environment.

Nevertheless, longline fishing for yellowfin, albacore and bigeye tuna has a substantial bycatch of non-tuna species. Varying by area of the WCPO, the main fish bycatch species include sharks (especially blue shark which may be a target species), billfish, pelagic stingrays, and moonfish or opah (Lampris guttatus).

Sharks are not always caught as bycatch. Sometimes, they are targeted for their fins and meat because longline crews often take the opportunity to top up their incomes through sales of shark fins. Tens of thousands of sharks are caught (and usually finned) each year in the WCPO and IO. As a result, catches of many shark species have experienced steep declines in recent years, most likely due to high fishing mortality.

In the WCPO about a dozen species of shark have been identified as common bycatch: blue shark (Prionace glauca), silky shark (Carcharhinus falciformis), oceanic whitetip shark (Carcharhinus longimanus), mako sharks (Isurus spp), thresher sharks (Alopias spp), porbeagle shark (Lamna nasus), winghead hammerhead (Eusphyra blochii), scalloped hammerhead (Sphyrna corona), great hammerhead (Sphyrna mokarran) and smooth hammerhead (Sphyrna zygaena). In the IO, shark catches have been recorded only recently and refer mainly to retained catch.

Conversely, sharks cause considerable damage to tuna on hooks in the longline fishery, and reduce the value of the tuna catch.

Changing the types of hooks used on longlines and their positions in the water column, replacing wire traces with nylon leaders, and improved shark handling practices, are being used or investigated to 1) reduce the catch of sharks, 2) improve condition of sharks on landing and survival upon release, and 3) enhance the catch of target species.

Longline catches of seabirds, marine mammals and turtles are significant in some areas.

Gill nets, which are used extensively in the IO, are of greatest concern for bycatch among the surface fisheries for yellowfin tuna. Gillnet fishing is poorly monitored. The proportion of non-tuna species in the purse-seine catch is relatively low, whether the nets are set around FADs (1.6%) or on free-swimming schools not associated with FADs (0.4%). In the WCPO surface fisheries, the bycatch of non-tuna species includes mainly silky shark, mackerel scad, mahi mahi, frigate mackerel, oceanic triggerfish and rainbow runner. The bycatch of juvenile bigeye tuna is of concern in the tropical purse-seine fishery. The bycatch from pole-and-line and troll fisheries is minimal. However, when pole-and-line fishing was much more common than it is today, localized depletion of stocks of the small pelagic fish species used as live bait was of concern to some Pacific countries.

The Western and Central Pacific Fisheries Commission (WCPFC) and the Indian Ocean Tuna Commission (IOTC) have conservation measures for bycatch mitigation and monitoring. Specific conservation and management measures address bycatch issues for sea turtles, sharks (including finning), sea birds, cetaceans, other finfish and reporting provisions to support bycatch research and monitoring. The International Seafood Sustainability Foundation (ISSF) conducts regionally specific bycatch mitigation training workshops for purse-seine vessel skippers and publishes guidebooks for purse-seine skippers and observers, and for longline skippers (http://www.issfguidebooks.org/downloadable-guides/)

IMPACTS ON AIR AND WATER

Purse-seine and longline vessels rely on fossil fuel and thus their exhaust fumes and refrigerant gases contribute to greenhouse gas (GHG) emissions and global warming. The estimated total carbon footprint of tuna caught by purse seine (all species) was approximately 1,530 kg CO2 per tonne of tuna landed (2009 estimate). The GHG emissions associated with catching tuna by purse-seine vessels, storing the fish on board, and delivering whole fish to processing plants are three times greater than the emissions stemming from the processing, packaging and transport of the resulting products. The amount of fuel used to catch a tonne of tuna is greater for longline vessels than for purse-seine vessels. The carbon footprint of longline tuna products is increased further if air freight is used to deliver sashimi-grade tuna and other fresh tuna products to markets because GHG emissions are much higher for airfreight than for sea freight.

The most significant environmental effects from catching juvenile yellowfin tuna in surface fisheries are point-source impacts from canning. Many of the countries that process and export canned tuna are developing countries: Thailand, Seychelles, Mauritius, Kenya, Indonesia (IO) and Philippines, Indonesia, Papua New Guinea, Fiji, American Samoa (WCPO). In these low-cost countries, the processing (‘canning’ or ‘loining’) facilities undertake the labour-intensive activities while the actual canning may also be done there or in higher-cost countries such as Spain and Germany. The amount of factory waste has increased significantly in low-cost countries, which generally have less capacity to regulate environmental impacts. As a result, in the vicinity of the factories, local access to coastal food resources, and quality of life, may be affected.

Another environmental effect of fish processing is the high consumption of water for transporting fish and offal around the plant in flume systems, for cleaning plant and equipment, for washing raw materials and product, and for de-icing and thawing.

EFFECTS OF ENVIRONMENT ON YELLOWFIN

Ocean conditions have pronounced effects on the distribution and abundance of tropical tuna. While these effects are best documented for skipjack tuna, they also occur for yellowfin tuna.

In the WCPO, the most conspicuous of these effects are due to the El Niño Southern Oscillation (ENSO) in the WCPO. ENSO is a swing between warmer (El Niño) and cooler (La Niña) ocean conditions across much of the tropical Pacific, that also affects the depth of the thermocline and the extent of the upper mixed layer. It occurs on irregular cycles (2-7 years) due to interactions between the atmosphere and the ocean. Changes in ocean currents and temperatures linked to ENSO are likely to influence where and when yellowfin tuna spawn, and how larvae, juveniles and their prey are dispersed or retained in areas conducive to their growth and survival. El Niño events appear to be favourable to yellowfin tuna recruitment because the main yellowfin tuna spawning grounds in the WCPO are associated with the warm pool, which expands during such events.

Annually, the IO has two distinct monsoon seasons that cause seasonal changes to oceanic and coastal waters, including in the depth of the thermocline and position of convergence zones. In turn, these changes affect the distribution of yellowfin tuna and its vulnerability to fishing gears. Yellowfin tuna is caught in greater numbers where the thermocline is shallow. In addition, year to year variation in the seasonal pattern of changes is large and associated with the Indian Ocean Dipole, a climate oscillation (on irregular cycles of 4-5 years) between a warmer (positive) and a cooler (negative) state. Indices measuring the state of the Indian Ocean Dipole are better predictors of warm and cold events in the Western Indian Ocean than are ENSO events, although ENSO events also appear to have an influence, especially if intense.

A complex relationship exists between the Indian Ocean Dipole and the yellowfin-tuna catches of purse-seines and longlines, including differences across sub-regions of the IO. In the western IO, the distribution and longline catches of yellowfin tuna are influenced by the Indian Ocean Dipole. With a period of about 4 years. High sea surface temperatures (>29.5 °C) tend to be related to low primary production and decreased catch rates during positive Indian Ocean Dipole events. Especially in the Arabian Sea and around Madagascar, increased yellowfin tuna catch rates occur in association with negative Indian Ocean Dipole events, along with lower sea surface temperature and high primary production.

EFFECTS OF CLIMATE CHANGE ON YELLOWFIN

Increased GHG emissions are expected to increase sea surface temperatures (SST), stratification of the water column and the pH of seawater, and alter the strength of major currents and counter currents. In the WCPO, SST and the average extent of the warm pool are expected to progressively resemble present-day El Niño conditions. Modelling of the projected effects of changes to the WCPO on yellowfin tuna has yet to be completed. However, such effects are expected to be somewhat similar to the projections that have been made for skipjack tuna. In the shorter term (by 2035), increases in catches may occur in the central and eastern areas of the region. However, by the end of the century, decreased catches are expected in the EEZs of all Pacific Island countries and territories except French Polynesia and Cook Islands.

In the WCPO, the prime yellowfin tuna fishing grounds are expected to move progressively eastward along the equator, and towards higher latitudes. Where yellowfin tuna remains within its preferred temperature range, catch rates of surface schools may increase as the water column becomes more stratified due to increasing SST and decreasing salinity resulting from the projected increases in in rainfall in equatorial regions.

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GUIDE TO FURTHER READING

Note: Details of all sources are given in References below.

For preliminary estimates of the impact of tuna fishing on non-tuna species, see Ana Justel-Rubio & Victor Restrepo (2015). For bycatch of longlines, see Victor Restrepo and colleagues (2014. For bycatch on longlines in the WCPO, see Shelton Harley and colleagues (2010).

For sharks and longline fishing, see Mike McCoy & Robert Gillett (2005), Shelley Clarke, (2011), Shelley Clarke and colleagues (2011) and (2014) and Tim Lawson (2011) for the WCPO, David Ardill and colleagues (2011) for the IO. Makoto Peter Miyake and others (2010) reported on shark damage to tuna on longlines. The WCPFC’s Conservation and Management Measure (CMM) 2010-07 lists shark species of concern. For information on fishing gear modifications to reduce longline shark catch and bycatch see Don Bromhead and others (2013), Pew Marine Environment Group (2011), and Peter Ward and others (2007).

For longline catches of seabirds, mammals and sea turtles, see Shelley Clarke and colleagues (2014). For remarks on surface fisheries for yellowfin tuna catches and gill nets, see ISSF (2014a). For purse-seine catch information for the WCPO, see Shelton Harley and colleagues (2010). On baitfish for pole and line fishing in Solomon Islands and Fiji, see Steve Blaber and others (1993); for Maldives see R. Charles Anderson (1997). For bycatch conservation and monitoring measures of the WCPFC, see https://www.wcpfc.int/conservation-and-management-measures, for IOTC see http://www.iotc.org/cmms; for a recent compendium of measures, see ISSF (2014b). For ISSF skippers' and observers' guides, see http://www.issfguidebooks.org/downloadable-guides/.

Peter Tyedmers and Robert Parker (2011) provide a preliminary assessment of the impacts of bigeye tuna fishing and supply chain on air and water. The report from UNEP (2000) provided information on the environment impacts of tuna processing.

For information on tuna fish processing, see Makoto Peter Miyake and others (2010), Amanda Hamilton and others (2011), Elizabeth Havice & Kristen Reed (2012), Patricia Tuara (2006), Nancy Sullivan & Vina Ram-Bidesi (2007), Kate Barclay & Ian Cartwright (2007), and UNEP (2000).

For the effects of the environment and oceanography (including the ENSO in the WCPO) on yellowfin tuna distribution and biology, see Patrick Lehodey and others (2003), (1997) and (2011), Janice Lough and others (2011), Alexandre Ganachaud and others (2011) for the WCPO; and, for the IO, Francis Marsac (2001, 2014), Frederic Ménard and others (2007), Kathleen Miller (2007), and Ana Corbineau and others (2008), and Kuo-Wei Lan and colleagues (2013).

For the effects of climate change on yellowfin tuna stocks and the supporting ecosystem in the WCPO see Alexandre Ganachaud and others (2011), Patrick Lehodey and others (2011), (2013), Johann Bell and others (2013), Janice Lough and others (2011), and Robert Le Borgne and others (2011).

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