Analysis of: Dealing with Mediterranean Bluefin tuna: A study in international environmental management

By Molly Rickles, SRC intern

Bluefin tuna is a highly migratory species that can live up to 30 years, currently are listed as endangered under the International Union for the conservation of nature (IUCN; Collette et al. 2011). This is due to the fact that the demand for Bluefin tuna has risen dramatically since 1980, when sushi and sashimi became increasingly popular in Japan. In the 1990’s, catches increased from 9,000 to 40,000 tons per year, and eventually leveled out around 24,000 tons per year.

This graph shows how catches of Bluefin tuna have increased rapidly beginning in 1980 (Sumaila & Huang, 2012).

Bluefin tuna are caught using purse sein nets and are often held there for weeks to months to fatten them up, in a practice called tuna ranching. This is done since tuna cannot be easily farmed, due to the fact that they need specific habitats for different life stages. Due to all of these factors, Bluefin tuna stocks have been severely depleted and there has been little success in managing their stocks.

A main issue with Bluefin tuna fishing is that it has been difficult to set quotas and enforce regulations due to the fact that they are highly migratory, and constitute as a straddling stock, meaning that the area they cover is over two or more nation’s exclusive economic zone (Heffernan, 2014). Under UNCLOS, this means that the nations must coordinate management efforts, but this has been ineffective. Since the UN has done little to protect tuna, since they are unwilling to compromise the value it brings to the world trade, the ICCAT, or the International Convention for the Conservation of Atlantic Tuna, was formed. This organization has 48 member nations, and its main objective is to provide quotas to each nation with fleets to fish Bluefin tuna. However, it has been found that the quotas set by ICCAT in 2010 were 70% higher than scientific recommendation (Sumaila & Huang, 2012). Many nations see this as a failure to conserve the threatened stocks. It has also been observed that dividing the quotas for Bluefin tuna may also be an ineffective way to manage the stocks, since there has been reported of stock trading, or nations without quotas fishing under a different flag. This is harmful to the stocks since regulations cannot be decided by one or two nations, but instead must be coordinated between the dozens that receive quotas (Heffernan, 2014).

In addition to nations constantly exceeding their quotas, there is another issue of illegal, unregulated and unreported fishing. This fishing is not included in the annual catch statistics because it is not reported to the ICCAT. This fishing has been estimated to exceed the quotas of all member nations by 62% (Heffernan, 2014). The issue of illegal fishing is so prevalent for Bluefin tuna because of its immense value. Another issue lies within the UN and ICCAT, since there are no strong enforcement measures in place to deal with the illegal fishing. A main policy tool suggested by Sumaila was to increase the penalties for illegal fishing and exceeding quotas. If there are stronger enforcement measures for Bluefin tuna fishing, fishers will be less willing to exceed their quotas. Currently, it is more economically beneficial for the fishermen to exceed their quotas even if the ICCAT finds out than to fish sustainably due to the lack of punishment as well as the high value of Bluefin tuna.

It has been made clear that Bluefin tuna management needs improvements in order to conserve the endangered population. Sumaila & Huang proposed many policy options that would help to regulate fishing, including at-sea inspections sites. This would prevent fishermen from lying about their catch numbers. These could be enforced by the ICCAT. However, it is noted that ICCAT does not have control over non-member nations, which creates an issue. It is suggested that the ICCAT should seek legal rights to manage the world’s tuna populations, in order to prevent non-member nations from continuing to overfish. Another suggested policy option would be to implement marine protected areas (MPA) in known tuna spawning grounds. This would be especially useful for Bluefin tuna, since they aggregate in specific areas to spawn, making them easy targets for fisheries. If their spawning grounds were protected, their population numbers would increase since they would be able to reproduce without the pressures of fishing (Sumaila & Huang, 2012).

Bluefin tuna stocks have been drastically declining, and this is heightened by the fact that their reproduction rates have also slowed, due to declining stock biomass (Sumaila & Huang, 2012).

One of the most surprising policy recommendations has recently been proposed for Bluefin tuna management. Their numbers have dropped so low that it has been proposed to add the species to CITES (Convention on International Trade in Endangered Species of Flora and Fauna). This is extremely rare for a commercially important species, since this protects against fishing pressures. However, this has been opposed by Japan, the highest importer of Bluefin tuna (Webster, 2011). When this was proposed, the fact that ICCAT is an ineffective manager of Bluefin tuna came into the spotlight. Due to this pressure, ICCAT lowered their quotas to scientific recommendations and enforced stricter regulations on catch limits (Webster, 2011).

Since Bluefin tuna became commercially important, their management has been handled poorly. In order to conserve Bluefin tuna, the ICCAT must become a more powerful management organization. Stricter regulations must be implemented and penalties for overfishing need to be enforced. If these changes are made in the management strategy, Bluefin tuna populations can be sustainable without completely collapsing, which is currently a very real possibility.

Works Cited

Collette, B., Amorim, A.F., Boustany, A., Carpenter, K.E., de Oliveira Leite Jr., N., Di Natale, A., Die, D., Fox, W., Fredou, F.L., Graves, J., Viera Hazin, F.H., Hinton, M., Juan Jorda, M., Kada, O., Minte Vera, C., Miyabe, N., Nelson, R., Oxenford, H., Pollard, D., Restrepo, V., Schratwieser, J., Teixeira Lessa, R.P., Pires Ferreira Travassos, P.E. & Uozumi, Y. 2011.Thunnus thynnus. The IUCN Red List of Threatened Species 2011: e.T21860A9331546.

Heffernan, J. P. (2014). Dealing with Mediterranean bluefin tuna: A study in international environmental management. Marine Policy, 50, 81-88. doi:10.1016/j.marpol.2014.05.014

Sumaila, U. R., & Huang, L. (2012). Managing Bluefin Tuna in the Mediterranean Sea. Marine Policy, 36(2), 502-511. doi:10.1016/j.marpol.2011.08.010

Webster, D.g. “The irony and the exclusivity of Atlantic bluefin tuna management.” Marine Policy, vol. 35, no. 2, 2011, pp. 249–251., doi:10.1016/j.marpol.2010.08.004.

Spatial Dynamics as an Approach to Fisheries Management

By Casey Dresbach, SRC intern

In the last half of the century alone, industrial fisheries have witnessed a global increase in total fishing efforts (Anticamara et al., 2011). Fishing efforts include, but are not limited to: the number of organisms caught, the type of gear used, and the areas in which fish are extracted. Implementation of spatial dynamics into fisheries management will afford us a greater comprehension of the direction of the global fishing sector from the perspective of sustainability. It involves the understanding of fishing effort in space and time.

The success of spatial dynamics can be seen in industrial fisheries, specifically those in developed countries. Utilization of vessel monitoring systems, a fairly recent technological advancement, permits the tracking of fishers through live space and time. Spatial information can help managers discern areas of overlap, where fishing practices may be too high in a vulnerable area important to threatened marine species (Rosenberg, 2000).

It is critical to take small-scale fisheries around the world into account when estimating a total global catch. In the developing world, small-scale fisheries are the driving force of the economy and, because of this, have significant impact on the total number of fish caught each year. Nearly removing close to 22 million tonnes, (48.5 billion pounds) per year. Unfortunately, unlike the technology that is readily available in the United States, these decentralized countries are limited. They tend to be spread along the coastline, occur in regions with limited funds or stable governance, and overall have data-poor knowledge with regards to estimating long-term fishing efforts (FAO, 2015).

These small-scale fisheries implement almost an “inherited sense of knowledge,” using what is called local-ecological knowledge (LEK) to support proper management in these fisheries, which is not entirely beneficial in terms of adapting with the rest of the world’s technological advancements.

In a recent study, spatial dynamics were used to assess a small-scale fishery in the Philippines (Selgrath, J. C., Gergel, S. E., and Vincent, A. C. J. 2017). A defined location was chosen, as well as a specified time frame from 1960-2010. The Danajon Bank ecosystem in the Central Visayas, Philippines houses an important double barrier coral reef ecosystem. The study quantified spatial and temporal changes there, in a province with extreme poverty and poor infrastructure. Their small-scale fishery is of vital importance to the highly-populated area. Through participatory mapping and interviews, researchers analyzed the direction of fishing practices and the dramatic shift from fishermen and members of the community who have been exposed to it for the past several years.

Figure 1. Danajon Bank, a double barrier reef located off the northwest coast of Bohol, Philippines.  (The Fisheries and Coastal Resource Management Interpretive Center (FCRMIC))

From these 391 interviews, information was systematically collected about the spatial history of the study area in six specific steps: personal history, fishing history, gear history, orienting fishers to the map, mapping fishing grounds, and fishing ground history. This approach combined historical experience and expertise to create multifaceted timelines and maps of local practices or environments, as shown in Figure 2.  The study also established the evolution of fishing gear practices and further classification of them as destructive or non-destructive, relative to the time. For example, in 1960 this spatial dynamic approach was able to discern that hook-and-line fishing was the predominant fishing gear, used in about 10% of the study area. While at the same time, traps were less than 5% of the study area until the 1970s, when the gear became more prolific.

Figure 2. Along the Danajon Bank Ecosystem in the Philippines, residents were interviewed and asked to map the history of their fishing practices inside of a mapped area. (Selgrath, J. C., Gergel, S. E., and Vincent, A. C. J. 2017)

​The multifaceted participatory mapping of the area over the past fifty years showed in great detail how small-scale fisheries have changed drastically. The study demonstrates how spatial dynamics and historical maps can lead to better-informed policies in data-poor systems (Selgrath, J. C., et al., 2017). A supporting study stated while “scaling up management interventions can make both biological and institutional sense, there is a point at which institutional capacity is exceeded.” (Christie, Pollnac, Oracion, Sabonsolin, Diaz, & Pietri, 2009). The need to immediate policy implementation is important, but deeper evaluations and historical mapping prior can help create a stronger framework of conservatory policy.

​Moving forward, more research is needed to analyze the importance of historical mapping and to better understand a fishery’s status. “The match between the spatial range of the ecosystem and the governance system is the most important consideration and will play an important role in scaling up of fisheries management initiatives.” (Armada, White, et. al 2009). A collaborative method among small-scale fisheries and larger industrial industries should be established in order to optimize an accurate estimate of long term fishing efforts on the global scale; gathering knowledge from a more personal level to better understand the broader impacts.

Works Cited

Armada, N., White, A. T., Christie, P., & Global Marine Time, T. N. (2009, April 17). Managing Fisheries Resources in Danajon Bank, Bohol, Philippines: An Ecosystem-Based Approach. Coastal Management , 308-330.

Anticamara, J. A., Watson, R., Gelchu, A., and Pauly, D. 2011. Global fishing effort (1950–2010): trends, gaps, and implications. Fisheries Research, 107: 131–136. Elsevier B.V.

FAO. 2015. Voluntary guidelines for securing sustainable small-scale fisheries in the context of food security and poverty eradication. FAO, Rome.

Christie, P., Pollnac, R. B., Oracion, E. G., Sabonsolin, A., Diaz, R., & Pietri, D. (2009, April 17). Back to Basics: An Empirical Study Demonstrating the Importance of Local-Level Dynamics for the Success of Tropical Marine Ecosystem-Based Management. Coastal Management , 349-373.

Selgrath, J. C., Gergel, S. E., and Vincent, A. C. J. 2017. Incorporating spatial dynamics greatly increases estimates of long-term fishing effort: a participatory mapping approach. – ICES Journal of Marine Science, doi:10.1093/icesjms/fsx108.

The Fisheries and Coastal Resource Management Interpretive Center (FCRMIC). (n.d.). Danajon Bank. Philippines.

Expanding fisheries management and marine conservation across borders

By Mitchell Rider, SRC master’s student

In 2006, the U.S. Congress reformed the Magnuson-Stevens Fishery Conservation and Management Act (MSA) – an act that directs marine fisheries management – by amending the High Seas Driftnet Fishing Moratorium Protection Act. This new amendment directed Secretary of Commerce to recognize foreign nations identified as participating in the bycatch of protected living marine resources (PLMRs) by including them in a biennial report presented to Congress. The responsibility of identifying participating foreign nations was delegated to NOAA Fisheries. The procedure for identification was delineated as follows: Once participation in bycatch is confirmed, NOAA must consult with the participating nation to inform them about the MRA, define the requirements of meeting positive certification, offer help in meeting that certification, and outline the consequences of receiving negative certification. Positive certification is met when a management plan to regulate bycatch is implemented and yields results comparable to that of the U.S. Negative certification is received when the participating nation fails to do so, and this is met with U.S. sanctions.

Image of a loggerhead turtle escaping a net equipped with a turtle excluder device (TED). [By NOAA –, Public Domain,]

Mexico was the first nation to be recognized for PLMR bycatch and was recognized specifically for the bycatch of an internationally shared PLMR, the North Pacific loggerhead turtle in 2013. In their paper, Senko et al. (2017) illustrates the effects of identifying Mexico for bycatch of the North Pacific loggerhead turtle and potential recommendations for improving management and its implementation.

Loggerheads nest along the coast of Japan, but perform developmental migrations taking them into the North Pacific basin where a proportion of the population recruits into the Gulf of Ulloa along the Pacific coast of Baja California Sur. It is in this location off the coast of Mexico loggerheads are subjected to high rates of bycatch by bottom-set nets targeting commercially important species like halibut. Mexico was identified after the concurrent discovery of >1,000 beached loggerhead carcasses and 88 loggerheads captured in bottom-set nets.

Upon identification, Mexico initially denied the bycatch of loggerheads even though they had agreed to reduce bycatch rates. At this point, the Mexican government disregarded its collaboration with the U.S. to test turtle friendly fishing gear, and instead proposed a plan to establish a protected area for the loggerhead within the Gulf of Ulloa. In response, the U.S. decided, as a compromise, to grant Mexico more time to establish this protected area. Instead, Mexico utilized this time to establish a partial fishing reserve. Since Mexico did not comply with U.S. regulation standards, the U.S. gave Mexico a negative certification. Almost a year later, Mexico established new loggerhead bycatch control measures, which ultimately lead the U.S. to grant a positive certification.

A map of Mexico where the Baja California Sur (BCS) is shaded in with green.[CC BY-SA 3.0,]

From this case, Senko et al. proposed policy recommendations to improve the processes of identification and consultation of the new amendment. Because of the Gulf of Ulloa closure and the trade sanctions, thousands of fishermen did not receive an income for one summer. Therefore, the U.S. should consider the potential socioeconomic and political effects that result from these threatened trade sanctions. In addition, there should be a universal form of reporting bycatch data from each country so fewer countries that do report their data are not as dissected as ones that do not do this. Finally, the authors suggested NOAA Fisheries be provided with more resources to create better collaborative relationship with the identified nation. In this case, a better relationship with Mexico may have prevented them from denying allegations initially, thus delaying the process of management implication. If these recommendations are implemented into the identification and consultations processes, the U.S. could avoid creating socioeconomic and political hardships.

Works cited

Senko, J., L. D. Jenkins, and S. H. Peckham. 2017. At loggerheads over international bycatch: Initial effects of a unilaterally imposed bycatch reduction policy. Marine Policy 76:200-209.

Local taboos could help conserve marine fisheries in Tanzania

By Jess Daly, SRC Intern

In developing nations it is often difficult to effectively enforce marine conservation laws because of a lack of staff and funding. With so little government intervention, it may be unclear to what extent the rules are being followed. A 2017 study by Shalli et al. examined how alternative methods of management might be affecting fisheries in Tanzania.

Specifically, the focus of this project was how traditional knowledge and local taboos alter the behavior of local fisherman. Traditional knowledge is wisdom that is passed down through generations, and taboos are a subcategory that includes the belief that certain actions are either too immoral or too sacred to be done in good conscience. The study examined six different Tanzanian fishing communities (4 rural and 2 urban), and used a wide variety of survey methods to gather information, including observation of fishing practices, a questionnaire given to fishers, and interviews with village leaders.

Figure 1

A fisherman goes out with his boat in the waters off of Dar-es-Salaam, Tanzania. [Grant, Milton. “Fishing in Tanzania.” United Nations Photo. 01 May 1991. /un_photo/34848229512]

Those who were given the questionnaire were also asked to provide their ages, genders, education levels, and lengths of residency. Across all of the villages, the majority of fishers were men who were between the ages of 30-40 and had a primary school education or less. However, when asked about local taboos, it was the uneducated elders who were able to provide the most information.

It was discovered that a wide variety of taboos exist within the Tanzanian fishing communities. The first is that certain fish species should not be eaten; reasons given for non-consumption included religious beliefs and fear of toxicity. Specific species and explanations of the taboos varied in the different villages, but all of them discussed dietary restrictions in one way or another. While the trend was present, however, the study found that nearly 50% of respondents did not comply with this taboo. A second class of taboos includes several actions involving the creation and deployment of fishing gear (such as women not touching new nets). These rules were more closely followed, with 44% of respondents claiming that they stringently complied with them, partially because of fear of social backlash. Almost 77% of fishers admitted noncompliance with taboos related to restrictions before or during fishing. More than 97% did not adhere to local taboos that prohibit fishing on certain sacred reefs, and nearly 47% claimed that they fished on certain prohibited days (such as religious holidays).

Figure 2

A graph depicting the levels of compliance to six different “categories” of taboos by different groups of fisherman as either strong, weak, or none. [Shalli et al. /sh/iyrngyxjy05qhm5/ AACAfkJqi4aOBqumSsEb0cZNa? dl=0&preview=shalli+et+al+2017.pdf]

Many of the local taboos, if they were widely followed, would aid in marine conversation by limiting things like fishing days, target species, fishing in sensitive reef areas, and catch size. While it appears that the majority of taboos are ignored in practice due to growing village populations and an increased demand for fish, it is believed that if local fishermen were educated in how these taboos actually affect population sizes, they would be more likely to observe them. In addition, local conservation laws should be aligned with existing taboos to highlight just how much they could aid in successful fisheries management.

Work Cited

Shalli, Mwanahija Salehe, et all. 2017. The role of local taboos in management of marine fisheries resources in Tanzania. Marine Policy 85: 71-78.

Analysis of a drop chain trawl as a method of bycatch reduction with squid, skates, and flatfish

By Brenna Bales, SRC Intern

It is no secret that bycatch is a huge problem threatening the health of the oceans. Gillnets, longlines, and trawl nets often capture many more unintended species than what is originally sought after. In order to reduce this extremely wasteful practice, it is imperative that new systems and new technologies be created to find a solution. Here, Bayse et al. (2016) tested the viability of drop-chain trawls as a tool to reduce bycatch.

The ground-gear rigged to the trawl net included rubber disks and rollers, designed to prevent the catch of any unintended benthic species.

The ground-gear rigged to the trawl net included rubber disks and rollers, designed to prevent the catch of any unintended benthic species.

Drop-chain groundgear, configured beneath a trawl net for this experiment, was determined to be effective at reducing bycatch in the Nantucket sound squid fishery off of Cape Cod, Massachusetts, USA. Longfin inshore squid (Doryteuthis pealeii) are the intended catch in the surrounding waters, however summer flounder (Paralichthys dentatus) and skates (family Rajidae) are two species that often find their way into the trawls as bycatch. Concerns have been raised throughout the area’s other fisheries that the use of this new system’s heightened foot-ropes will result in a lower catch due to squid escaping underneath the fishing line. However, this system is designed to take advantage of the benthic behaviors of the bycatch species during the trawling process (Ryer, 2008; Winger et al., 2010), without compromising the ability to capture squid.


On the 16th and 17th of June, 2012, four tows were conducted aboard the F/V Atlantic Prince. Underwater video was recorded using an HD GoPro in shallow, clear water during daylight hours. The camera was placed in the trawl at the top of the net, facing forward and slightly down towards the mouth of the trawl. From the recordings, the following events were quantified: entrance into the trawl or escape underneath the fishing line and between drop-chains, contact/impingement between animals and ground gear, swimming behaviors, positions, orientations and time in trawl mouth. These behaviors were subsequently assessed as to whether the capture or escape of the animal resulted.

Hundreds of fish accidentally caught in the net of a shrimp fishery, June 1969. Source: Wikimedia Commons.

Hundreds of fish accidentally caught in the net of a shrimp fishery, June 1969. Source: Wikimedia Commons.


A total of 2,532 individual squid were observed, of which zero escaped. 99.0% of squid were oriented with their mantle in the direction of towing. As for summer flounder, 87 total were observed, however 44 had an unknown capture outcome. Of the 43 whose capture outcome was known, 26 entered the trawl and 17 escaped. 76.7% of the flounder changed direction as they were swimming, subsequently entering the trawl. Last but not least, 197 skates were observed at the mouth of the trawl, of which 175 escaped. 91.8% of all skates were oriented in the same direction as the trawl.


From these results, it was determined that the modified drop-chain trawl, specifically modified to accommodate the behaviors of the bycatch species, was effective in reducing the number of skates caught, but ineffective for reducing summer flounder bycatch. In addition, it did not compromise the ability of the net to catch squid. All in all, this is just one method of bycatch reduction that has proved successful. In combination with several other methods, such as larger trawl mesh sizes, or the use of grids, we can reduce the harmful impact of other commercial fisheries.


Bayse SM, Pol M V, He P (2016) Fish and squid behaviour at the mouth of a drop-chain trawl: Factors contributing to capture or escape. ICES Journal of Marine Science, 73, 1545–1556.

Ryer, C. H. 2008. A review of flatfish behaviour relative to trawls. Fisheries Research, 90: 138–146.

Winger, P. D., Eayrs, S., and Glass, C. W. 2010. Fish behaviour near bottom trawls. In Behaviour of Marine Fishes: Capture Processes and Conservation Challenges, pp. 67–103. Ed. by P. He. Willey-Blackwell, Ames, IA.

Why do Fishers Fish?

By Emily Rose Nelson, SRC Graduate Student

Humans have been fishing for over 40,000 years. Initially, the world’s waters were thought of as a resource with no bounds. However, intensification of fishing pressure over the last 100 years has decimated fish populations, forcing us to realize that the oceans’ resources indeed do have limits. Today, fish make up more than 16 percent of the global human protein intake, whether it is in the form of subsistence fishing in developing countries or extravagant restaurants in wealthy countries. As demand for marine resources continues to grow, pressure on fish populations is also increasing. Governments around the world have started making efforts to slow the decline of ocean resources, but in many cases the success of these initiatives is dependent on compliance of the fishermen. Essentially, conservation efforts are in direct conflict with fisher objectives. For this reason, it is important to understand why a fisher is fishing in the first place – knowledge of fishers’ motivations will help policy makers identify the most effective conservation methods.

Young et al. 2016 set out to answer the question, “Why do fishers fish?” using an ethnographic approach. They conducted semi-structured interviews of experienced male fishermen at two sites, Australia and the Solomon Islands. The interviews gathered information about their general background, fishing methods, motivations for fishing, and feelings upon return from a fishing trip.

The interviews identified an overwhelming split in motivation to fish between the two study sites. 100 percent of fishers in the Solomon Islands were motivated by food and 93 percent were motivated by income. In contrast, 96 percent of the fishers in Australia were motivated by a connection to the environment. Recognizing these differences in incentives can help managers to form the best conservation policy for each region. For example, one could not realistically set in place a no-take marine reserve throughout the Solomon Islands without providing the fishermen and their families with an alternate source of food and income.

Motivations for fishing in Australia (gray bars) and the Solomon Islands (black lines).

Motivations for fishing in Australia (gray bars) and the Solomon Islands (black lines).

Despite the drastic difference in ‘primary reason to fish’ between the Solomon Islands and Australia, interviews revealed that many other drivers were the same. When fishers in the Solomon’s were given a hypothetical situation in which they had secured an alternate income, 100 percent of interviewees indicated that they would still continue to fish whenever possible. This shows that the fishers are getting enjoyment out of their work and indicates the presence of a somewhat recreational mindset. Therefore, if economic conditions were to improve in the area there would likely be a growth in recreational fishing. In Australia, where recreation is the primary reason for fishing, 80 percent of fishers identified food as a secondary incentive. For those people, fishing provides an escape from their stressful day to day lives, with the added bonus of catching a fresh meal for a price much cheaper than what is available at local fish markets.

Young et al. were not only able to identify clear-cut cultural differences in fishing motivations, but also recognize that fishing may provide benefits to individuals and communities that transcend these traditional motivations. In both the Solomon Islands and Australia, mentions of social bonds with fellow fishers and camaraderie were widespread in interviews. Lastly, the interviews revealed that fishing might not be as far off from conservation as some may think. The values identified of many fishers in this study, such as “teach children to appreciate nature” and “foster respect for the environment” are very similar to those of conservationists. As said by an Australian fisher, “fishing provides environmental benefits because we like to protect things that are dear to us.”


Young, A.L., Foale, S., & Bellwood, D.R. (2016) Why do fishers fish? A cross-cultural examination of the motivations for fishing. Marine Policy, 66: 114-123.

Addressing knowledge gaps to utilize best practice management for bottom-trawling fisheries

By Grace Roskar, SRC Intern

Bottom-trawls are a type of fishing gear that can be destructive towards the seabed and its associated organisms. A fishing vessel tows large trawl nets that trap marine animals as they are dragged across the ocean floor. With heavy ropes, chains, or bars, the fishing gear disturbs the seabed while capturing nearly anything in its path. About 20% of fish and shellfish caught globally every year are caught using bottom-trawls, amounting to about sixteen million tons.

A typical bottom trawl. Source:

A typical bottom trawl. Source:

A meta-analysis by McConnaughey et al., in 2005 has shown that bottom trawling for benthic invertebrates may cause reductions in a decrease in biomass, the diversity of fish, and the body size of fish, among other ecological traits of fish communities. Some fish species use specific habitats for shelter or food, and it may be possible that trawling and dredging impact the productivity of these fish species. This is especially important to examine because wild-capture fisheries provide a substantial amount of food for the growing global population.

This study aimed to identify specific questions about bottom-trawling fisheries that key stakeholders feel need to be scrutinized in order to guide suitable policy and management measures. The research also sought out important gaps in global knowledge that, if taken into consideration, would help the advancement of best practice management for bottom-trawling fisheries, defined as ‘bottom trawling that would achieve sustainable fisheries production while minimizing adverse impacts on the environment’ (Kaiser et al 2015).

First, a group of 52 stakeholders from 11 different countries was selected. Stakeholders were categorized either as research scientists or practitioners, a group that comprised of people from fishing and processing industries, non-governmental organizations, or governmental organizations. The stakeholders composed a comprehensive list of ‘knowledge-needs’, which were then voted on and ranked in terms of priority. The underlying idea was that addressing these knowledge-needs would be necessary to support the development of best practice management. Through a one-day workshop, including discussion sessions and voting, a list of 25 top-priority knowledge-needs were finalized out of the original 108.

This flow diagram shows the methods of prioritizing knowledge-needs into a final list.

This flow diagram shows the methods of prioritizing knowledge-needs into a final list.

Several statistical tests were used to examine how the reasoning behind the rankings varied between practitioners and scientists. The median scores were positively correlated for each knowledge-need, showing high agreement levels between the scientists and practitioners of what was top priority. Knowledge-needs were organized into categories: direct effects, ecosystem and production, operational, and management and indicators. The management and indicators category was the most represented, with six knowledge-needs in the top ten. The highest-ranked knowledge need was ‘What is the extent and distribution of different seabed habitat types?’ Given the wide range of different stakeholders consulted, the agreement between the scientists and practitioners about the importance of this knowledge-need is encouraging. It shows the pressing need to better understand the relationship between bottom-trawling and the different habitat types affected. Furthermore, six other knowledge-needs were related to some extent to improving knowledge of the impacts of interactions between fishing gear and the seabed. The second most highly ranked question asked, ‘What level of trawl fishing impact on other ecosystem services is acceptable such that sustainable seafood production can be maintained?’ This question suggests that the environmental impacts of bottom trawling, such as changes in ecosystem structure and the fish population, need to be evaluated in comparison to the social and economic impacts of trawling.

A list of the top ten knowledge-needs, including what category each was placed in.

A list of the top ten knowledge-needs, including what category each was placed in.

The rest of the knowledge-needs addressed a range of topics, from the need for better understanding of where bottom trawling occurs and how much of it, to evaluating the ability of certain habitats to recover from the effects of trawling. Many knowledge-needs were additive, such that addressing one would help advancement to another. The study successfully identified specific questions that will be collaboratively discussed further to close knowledge gaps in the global fisheries industry. Future research would include continuing to examine collective knowledge and to use discussion to work towards closing knowledge gaps.



Kaiser, M. J., et al. (2015). “Prioritization of knowledge-needs to achieve best practices    for bottom trawling in relation to seabed habitats.” Fish and Fisheries.      doi: 10.1111/faf.12134

McConnaughey, R. A., and Syrjala, S. E. Short-term effects of bottom trawling and a storm event on soft-bottom benthos in the eastern Bering Sea. – ICES Journal of            Marine Science, 71: 2469–2483.

Integration of Indicator Alarm Signals for Ecosystem-Based Fishery Management

By Robert Roemer, SRC Intern

Taking into account different stakeholder’s priorities, while combining ecological, economic, and recreational indicators for managing sustainable fisheries have been a long-standing problem. While not a new issue, these quandaries are only compounded when opinions conflict within each ecological, socioeconomic, and recreational stakeholder class.

A recent study conducted by Duggan et al. 2015 aim to address this problem by utilizing a ‘signal detection” approach, by focusing on shifting issues of multiple indicators usually with inconsistent, conflicting units to a simpler state. In the researchers eyes, simplicity is vital to successfully managing fisheries stocks. By reducing conflicting management approaches and units to just two management options (reduce harvest rate or not reducing the harvest rate), researchers can calculate just one signal, termed the “Response Support Signal” (RSS). The Response Support Signal is derived from the complete range of indicators and opinions then quantifies the level of support to reduce, or not-reduce the harvest rate.

How did the researchers determine the RSS?

First, time series fisheries data was obtained from ICES reports for a total of nine Celtic Sea stocks. Then, 21 indicators were obtained from the literature that covered a variety of metrics like: average weight; discard rate; species evenness; and fuel costs over different time frames. From each indicator, a “status signal” was computed, with each status signal composed of two stages; (1) the indicator or “warning signal” which revealed if each indicator was beyond its threshold, and (2) if adjusting the indicator via a hypothetical change would align with the warning signal (i.e. reducing when indicator is beyond threshold and not reducing when within its threshold). From this, sets of indicator-stock combinations are formed with each having a respective status signal: Hit − (H −), Hit + (H +), Miss (M), and False Alarm (FA). From the frequency of status signals in each indicator, the true positive rate (TPR) and false positive rate (FPR) were calculated by:

TPR= N(H −) / N(H −) +N(M) and FPR= N(FA) / N(H +) + N(FA)

where N(x) denotes the frequency of occurrence of x. The TPR is then plotted against the FPR to determine the degree of alignment between decisions and the indicator values.

Figure 1: ROC plots where each point represents a fish stock time series. The further to the top left corner, the more often management actions were appropriate to indicator signal. Points below the line and right indicate inappropriate responses to indicator signal.

Figure 1: ROC plots where each point represents a fish stock time series. The further to the top left corner, the more often management actions were appropriate to indicator signal. Points below the line and right indicate inappropriate responses to indicator signal.


What has been concluded?

When data is pooled across stock and years, it shows historical management trends to be independent of indicator alarms. A higher occurrence of H + and M rather than H – and FA, indicates a bias of historical management practice to not reduce fishing mortality (64% of years analyzed). However, what is surprising is after investigating all eight stakeholder scenarios, it was found that all support a reduction in fishing mortality from 1980 to present, with special emphasis on the timeframe of 1990-2003.

The authors in this study identified the critical need for fisheries management to be scientifically objective, and have offered a framework that is both practical and effective for assessing a variety of indicators that are integral to the field of fisheries management. The defined RSS values include objective indicator information that harmonizes with stakeholder preferences, a valuable asset to be used for management decisions. One object of note, the authors acknowledge this tool is not necessarily intended to advise mangers to what course of action is best management, but to structure the communication and to facilitate discussion between various stakeholder groups to help achieve best practices.



Duggan, D. E., Farnsworth, K. D., Kraak, S., & Reid, D. G. (2015). Integration of Indicator Alarm Signals for Ecosystem‐Based Fishery Management. Conservation Letters8(6), 414-423.


Why have global shark and ray landings declined: improved management or overfishing?

By Patrick Goebel, SRC Intern

A decline in shark and ray landings could be thought of as a success for in improved management strategies. However, in the case of Davidson et al (2015), that is too good to be true. Sadly, the decline in global shark and ray landings has been attributed to overfishing and other ecosystem influencers.

Sharks and rays are commercially valuable for their fins, meat, liver, oil and skin with their fins and meat in the highest demand. The demand for shark products is relatively new, as their commercial value has only increased with the decline of other valuable fisheries. The increase in fishing pressure combined with the lack of laws regulating the shark and ray fishery has resulted in population declines.

The rapid decline in shark and ray populations resulted in new management strategies. Davidson et al (2015), investigated these new management strategies to determine if declines in shark and ray catches were a result of the fisheries management performance or over.

fishing. Figure 1. Global distribution of (a) country-specific shark and ray landings averaged between 2003 and 2011 and mapped as a percent of the total. (b) the difference between the averages of landings reported in 2001-2003 and 2009-2011

Figure 1. Global distribution of (a) country-specific shark and ray landings averaged between 2003 and 2011 and mapped as a percent of the total. (b) the difference between the averages of landings reported in 2001-2003 and 2009-2011

Shark, ray, skate, and chimaera landings from 1950 (earliest years of reporting) to 2013 were investigated. In total, 126 countries shark and ray landings were modeled against indirect and direct fishing measures and fisheries management performance.

The peak of shark and ray landings was 2003 and has declined by about 20% in the past decade. As stated in Davidson et al (2015), the reduction in shark and ray landings are related to indirect and direct measures of fishing pressure rather than management implementation. This shows that sharks and rays are being harvested at an unsustainable rate. Furthermore, Davidson et al (2015), highlighted several countries that deserve prioritization for conservation and management action. The greatest declines were reported in Pakistan and Sri Lanka, both of which have little to no management. If new management strategies are not implemented into these countries, sharks and rays will continue to be harvest at damaging rate.

Davidson, Lindsay NK, Meg A. Krawchuk, and Nicholas K. Dulvy. “Why have global shark and ray landings declined: improved management or overfishing?.” Fish and Fisheries (2015).

Atlantic Bluefin Tuna Fisheries: A Case of Mismanagement

By Hanover Matz, RJD Intern

While many fisheries around the world are currently being devastated by the overwhelming power and efficiency of modern fishing fleets, the Atlantic bluefin tuna fishery of the Atlantic and Mediterranean is one that has come to the forefront of marine conservation as an example of mismanagement and overexploitation. The bluefin tuna fishery in the Atlantic has traditionally been divided between the west Atlantic and the east Atlantic and Mediterranean stocks, with disagreements over the divisions of distinct populations (Sumaila and Huang 2012). Figure 1 shows the distribution of bluefin tuna in the Atlantic, with major spawning grounds (dark gray spotted areas) and migration routes (arrows). Tuna fishing in the Mediterranean can be traced back to ancient times, with hand lining and seine fishing practiced by peoples as early as the Phoenicians and the Romans. Fishing practices expanded into trap fishing and beach seine nets between the 16th and 19th centuries, and eventually were replaced by the modern industrial seine and longline fleets of the 20th century (Fromentin and Powers 2005). It is during the late 20th century that major changes in the total catches of bluefin tuna occurred.


Tuna Figure 1

Distribution of Atlantic bluefin tuna fisheries and migration routes (Fromentin and Powers 2005)

Catch data from the 1970s onward shows an increase in total catch beginning in the 1990s. Figure 2 shows bluefin tuna catches in the Atlantic from 1950 based on gear type. Bluefin tuna catches rose from levels between 5,000 to 8,000 tons in the 1970s to 40,000 tons in 1995. The International Commission for the Conservation of Atlantic Tunas (ICCAT) was established in 1969 to oversee the management of bluefin tuna, but this management has faced several issues with regards to limiting the overexploitation of tuna stocks (Sumaila and Huang 2012).  One significant error on the part of ICCAT was the setting of Total Allowable Catches (TAC) above the limits suggested by advisory scientific bodies. Fromentin et al. (2014) describe the various problems that have plagued the management of bluefin tuna by ICCAT. Along with a disregard for recommended scientific limits, tuna stocks have been overfished due to the frequency of Illegal, Unreported, and Unregulated (IUU) fishing. With bluefin tuna fishing occuring over such a large expanse of ocean in the Atlantic alone, crossing waters under the control of various nations and the high seas, it is difficult to effectively enforce management policies. The authors of the 2014 report also identify how uncertainties in stock assessment have contributed to the mismanagement of bluefin tuna.

Tuna Figure 2

Total catch of bluefin tuna in tons by gear type since 1950, showing significant increase since the 1990s (Sumaila and Huang 2012)

Three sources of uncertainty in bluefin tuna have contributed to difficulties in establishing management policies: uncertainity in the biology and populations of tuna, poor quality of data, and errors in the ability of models to predict tuna population dynamics. (Fromentin, Bonhommeau et al. 2014). Given the migratory nature of bluefin tuna and the expanse of ocean which they inhabit, it is difficult to conduct studies on their biology and development. Catch data has also been inaccurate in the past due to the levels of illegal and unreported fishing in the industry. Finally, uncertainties in the models used to predict population dynamics make it difficult for management bodies such as ICCAT to develop effective policies. Bluefin tuna cross the Exclusive Economic Zones (EEZs) of many different countries, contributing to further difficulties in managing fish stocks that may be subjugated to fishing regulations across multiple nations (Sumaila and Huang 2012). While a better understanding of how bluefin tuna populations may overlap and mix has been established in the past decades, more research still needs to be conducted (Fromentin and Powers 2005). Another indicator that Atlantic bluefin tuna stocks have declined is the measurement of spawning stock biomass, the portion of the stock population capable of reproducing. Data since 1970 up to 2005, including both reported and illegal, unreported, and unregulated fishing, shows a decrease in spawning stock biomass by 60% since 1974 (Sumaila and Huang 2012). This means that overfishing may not only be reducing current populations, but hindering their ability to reproduce by depleting the number of reproductive individuals.

In response to increased fishing pressure on bluefin tuna stocks and decreased catches, aquaculture of tuna now occurs in several regions. Figure 3 shows current locations of tuna aquaculture. Starting with the cultivation of Atlantic bluefin tuna in Canada and Pacific bluefin tuna in Japan in the 1960s, farming of tuna has spread to the Mediterranean and Australia. However, most of this farming consists of capturing wild tuna and fattening them in pens for later harvest, while it still remains incredibly difficult and costly to rear tuna from larvae to adults. This method of catching wild tuna in seine nets and fattening them most likely does not help contribute to alleviating fishing pressures on wild stocks (Metian, Pouil et al. 2014)

Tuna Figure 3

Global distribution of bluefin tuna farms (Metian, Pouil et al. 2014)

Given the current level of harvesting, better management of Atlantic bluefin tuna needs to be put in place. The capacities of the purse seine net fleet and longline fleet in the Atlantic already exceed the mean productivty of bluefin tuna (Fromentin and Powers 2005). Even if there are uncertaintities in the measurements of tuna productivity, the status of tuna populations is precarious enough that it would be risky to continue the current fishing effort. Sumalia and Huang (2012) make several policy recommendations to better manage Atlantic bluefin tuna stocks. First, the total allowable catch needs to be reduced to levels as recommended by scientific research. Second, a better detection and penalty system needs to be established in order to reduce illegal fishing. Finally, the establishment of Marine Protected Areas and the listing of Atlantic bluefin tuna as endangered on the Convention for International Trade in Endangered Species (CITES) would afford tuna some protection to allow populations to recover. However, the multinational fishing effort and policy formation process of ICCAT has made it difficult to come to reasonable agreements between nations to manage tuna. To protect this valuable species, action needs to be taken to reduce the current fishing effort and total allowable catch. Better scientific research will provide more effective management tools, but the current advice being given by scientific bodies needs to be headed when establishing catch limits. If Atlantic bluefin tuna stocks are to continue to provide a valuable resource of seafood to world markets, a more sustainable fishery needs to be established.



  1. Fromentin, J.-M., S. Bonhommeau, H. Arrizabalaga and L. T. Kell (2014). “The spectre of uncertainty in management of exploited fish stocks: The illustrative case of Atlantic bluefin tuna.” Marine Policy 47: 8-14.
  2. Fromentin, J.-M. and J. E. Powers (2005). “Atlantic bluefin tuna: population dynamics, ecology, fisheries and management.” Fish and Fisheries 6: 281-306.
  3. Metian, M., S. Pouil, A. Boustany and M. Troell (2014). “Farming of Bluefin Tuna–Reconsidering Global Estimates and Sustainability Concerns.” Reviews in Fisheries Science & Aquaculture 22(3): 184-192.
  4. Sumaila, U. R. and L. Huang (2012). “Managing Bluefin Tuna in the Mediterranean Sea.” Marine Policy 36(2): 502-511.