The Impact and Epidemic of Overexploitation on Chambered Nautilus Populations

By Sianna Raquel Vacca, SRC intern

The era of one of the cephalopod’s oldest family members and elusive living fossil, the chambered nautilus, may be coming to an end. This prehistoric species has remained unchanged for over 400 million years and is a native of the tropical, deep-water habitats in the Indo-Pacific region. They are closely related to the other cephalopods such as octopus, squid, and cuttlefish and shares various distinguishing characteristics with its’ modern relatives such as jet propulsion (which allows them to attain speeds of about two knots) and the use of their strong beaks to prey on and crush crustaceans. Chambered nautiluses have retractable tentacles in numbers far surpassing 90, which suitably equip them to be deep-sea scavengers and opportunistic predators. While their eye-sight is poor and merely permits them to discern varying light concentrations, this species is greatly dependent upon their sense of smell while hunting.

Figure 1: Chambered nautiluses can extend their tentacles deep into various substrates to search for small, dead marine organisms, such as shrimp. (Source: Flickr).

Although they are biologically similar to other living cephalopods in a handful of ways, the nautilus is a specifically unique species with distinguishable features setting them apart from their relatives. “Most obvious, nautiluses possess the ancestral trait of an external shell; a shell that has protected them for hundreds of millions of year but is dooming them today” (Barord 2015).

Despite the nautilus species’ historical resilience, proven by their survival through all five major mass extinctions, marine conservationists are fearful that they will not fare as well through the sixth global extinction episode. The crudely unregulated and poorly managed nautilus shell harvest industry is depleting Pacific populations at alarming and consequential rates, further exacerbating the biotic threats posed by overexploitation. Their distinctive coiled and patterned shells are internationally sold as souvenirs, jewelry pieces, and home décor items, to name just a few uses. Since there is no evidence or indication that nautilus fishing is part of a cultural practice or stems from historical relevance, it appears that the demand for these shells is superfluous. While habitat destruction and climate change has been used as part of the argument construct to explain the declining nautilus populations, the shell harvest industry, most prominent in the Philippines and western Indonesia, has proven to be the most influential culprit.

Figure 2: Ornamental nautilus shells are considered to be an international commodity because of their unique, coiled design. The chambers within their shells, as pictured above, actually serve the nautiluses a great physical function by allowing them to either fill or empty these compartments with water to adjust their density. (Source: Pixabay).

DeAngelis (2011) investigated the changes in catch per unit effort (CPUE) in nautilus fishery regions in comparison to an unexploited nautilus population, further proved the impact of overfishing. The paper reports that while an unexploited chambered nautilus population at Osprey Reef, Coral Sea in Australia has remained stable throughout the past twelve years, results from the Philippines show up to 80% declines in reported CPUE from 1980 to the present. This time span consists of fewer than three nautilus generations, indicating that because they are hindered by a slow growth-rate and gradual reproductive output, the chambered nautilus seems to have a low likelihood of recovery or repopulation.

It may seem that this precious, ancient species is doomed to an inevitable extinction within the foreseeable future, however, domestic efforts to starve the shelling industry can have notable impacts. While the United States has historically participated in the nautilus shell trade, a recent recommendation has been submitted to the U.S. Congress from the National Marine Fisheries Service (NMFS) and National Oceanic and Atmospheric Administration (NOAA) to list the chambered nautilus as ‘threatened’ under the Endangered Species Act (ESA). The factual substantiation offered in the aforementioned proposal demonstrates that the survival of this species is in dire need of human intervention, and the protections granted in the Endangered Species Act could potentially reverse the chambered nautilus’ path towards extinction. Defenses for listing the nautilus species as ‘threatened’ under the ESA include:

1) The chambered nautilus serves a greater function alive than that of its hollowed shell.

Chambered nautiluses are part of the complex ecosystem that makes up coral reefs. To avoid predation in the open ocean, these small marine mollusks dwell in reefs for protection. As both an active predator and scavenger, they play a valuable role in their environment.

Additionally, this animal is being harvested for ultimately futile purposes. Unlike some species which are hunted for their meat and act as the primary food source for undeveloped countries, chambered nautiluses are captured for their shells. These shells are then internationally traded and used for aesthetic and nostalgic purposes. The harvest of this species would perhaps be more justifiable if they were being used to prevent some sort of starvation epidemic, but seeing as that is not the case, their current use is unnecessary.

2) This species has already experienced significant population declines.

Due to the excessive chambered nautilus shelling industry in the Philippines, Pacific nautilus populations have notably decreased. While not much is known about these organisms because of how deep in the ocean they live, enough data has been collected to statistically prove that if they continue to be extracted at current rates, they will experience extinction within the foreseeable future.

3) Efforts taken as part of U.S. policy will hopefully encourage other countries to follow suit.

As a global superpower, many nations look to the United States as a model for policy and legislative procedure. While harvesting chambered nautiluses isn’t nearly as prominent of an industry in the U.S. as it is in southeast Asia, formally recognizing that this species is threatened could bring international awareness to this ecological concern. It could encourage other nation-states to institute various policy instruments to protect nautilus populations and promote lasting, world-wide conservation efforts.

This classification could save the chambered nautilus from extinction, albeit directly or indirectly by slowing the rate at which their population declines and allowing for additional measures to be taken.

Works cited

De Angelis, Patricia. “Assessing the Impact of International Trade on Chambered Nautilus.” Geobios, vol. 45, no. 1, 2012, pp. 5–11., doi:10.1016/j.geobios.2011.11.005.

Barord, Gregory Jeff. “On the biology, behavior, and conservation of the chambered nautilus, Nautilus sp.” 

Dunstan, A., et al. “Nautilus Pompilius Fishing and Population Decline in the Philippines: A Comparison with an Unexploited Australian Nautilus Population.” Fisheries Research, vol. 106, no. 2, 2010, pp. 239–247., doi:10.1016/j.fishres.2010.06.015.

Dunstan, Andrew, et al. “Nautilus at Risk,Estimating Population Size and Demography of Nautilus Pompilius.” PLoS ONE, vol. 6, no. 2, Oct. 2011, doi:10.1371/journal.pone.0016716.

Skate Overfishing: Studying and Protecting Data-Poor Fish Stocks

By Timothy Hogan, SRC Intern

In response to overfishing, scientifically-derived annual catch limits and other regulations were developed to protect many declining species. Despite this, some understudied organisms could not receive the same improvements, where minimum data and low resolution made their abundance relatively unclear. Catch limitations became relatively difficult to set, as the population trends of many species could not be analyzed with confidence. Recent studies have managed to develop approximate regulations despite the lack of data (Newman et al 2015). However, a lack of coordination and data review continues to leave gaps in our understanding of these organisms.

Skates, cartilaginous fish closely related to rays and sharks, are one of these data-poor species. Because of their low economic benefit, and the lack of understanding behind their aging and population dynamics, the aging and regulations behind these organisms become difficult to set with confidence (Miller et al 2009). As important predators that control the populations of many crabs, scallops, and other organisms on the seabed, they remain important to control and protect as some of the more data-rich species.

 Figure 1: A long-nose skate found off the coast of Washington. While similar to rays, skates are generally distinguished from their relatives due to their longer snout, two dorsal fins along their thicker tail, and thorn-like scales along their middle back

Figure 1: A long-nose skate found off the coast of Washington. While similar to rays, skates are generally distinguished from their relatives due to their longer snout, two dorsal fins along their thicker tail, and thorn-like scales along their middle back

The northeast skate complex, composed of the seven species of skates found along the Northwest Atlantic shelf system, remains to be relatively well-studied and monitored compared to some other skate groups. While recent reports state that all but one species are not experiencing overfishing (Miller et al 2009), the low resolution of the data makes these results more inconclusive. Regulations are therefore generally set on the life history of these species, since species size and growth rate are common indicators of an organism’s resilience to fishing pressures (Frisk et al 2001). Studies by Kelly and Hanson (2013) show that the maturity age of two particular species, the winter skate and the little skate, is relatively late compared to most other commercial fish. These types of organisms, known as K-strategists, are put under careful monitoring by many regulation groups, as they tend to be the most susceptible to overfishing. Figure 1 showcases the overall population declines that have been observed from these effects (Kelly and Hanson 2013). The majority of individuals are not able to survive to maturity from fishing pressures, causing overall population declines over time. While this may also simply be due to the low catch and landing rates of skates, it is still important to consider the potential population decline and lengthened recovery time.

Figure 2: A frequency - size distribution of Little Skate specimens collected throughout various years. The solid gray line represents the year 2007, and shows a high peak below the age range of maturity, beginning at 32 cm. Samples from 2008 and 2009, the two dotted lines, are seen to be much lower. This could be due to a natural decrease from fishing pressures or a low catch number (Kelly and Hanson 2013)

Figure 2: A frequency – size distribution of Little Skate specimens collected throughout various years. The solid gray line represents the year 2007, and shows a high peak below the age range of maturity, beginning at 32 cm. Samples from 2008 and 2009, the two dotted lines, are seen to be much lower. This could be due to a natural decrease from fishing pressures or a low catch number (Kelly and Hanson 2013)

In the past, skates were targeted for their fins, which would primarily be used as lobster bait and occasionally food (Cavanagh and Damon-Randall 2009). However, because their slow reproduction rates increased their vulnerability, possession and landings of skates have been significantly reduced since 2003. Prior to this, the population conditions of the skates have been relatively unmonitored, making it difficult to tell the population state. Current regulations placed based on new data can hopefully encourage population rebuilding of these organisms, leading to an eventual recovery.

A more prominent and unmeasured cause of skate depletion both historically and currently has been bycatch. Because they are found throughout the deep waters of the coast, they can be unintentionally caught by fishing equipment that collect organisms from the seabed. Notably, haddock, an important commercial fish found in the Northeast Coast of the United States, were caught using trawling nets. While these could catch the target species relatively effectively, it was infamous for also taking many other organisms from the seabed, including crabs, flounders, and skates (Beutel et al 2008). In times of high fishing for these haddock, major effects can be observed on a variety of other organisms. The barndoor skate has been eradicated from specific geographic areas due to being caught in fishing gear alone (Cavanagh et al 2009).

Because of its effects and historical damage, it is crucial to take bycatch into account when developing regulations. For most organisms, it is difficult to quantify unintentional catches because of a lack of data. Most data-poor species do not have the same level of enforcement as some of the more commercially important species. When collecting numbers for fishing regulations, most data is collected on shore from samples present on the ship. When caught as bycatch, many skates and other organisms are simply discarded into the water before. Unfortunately, this leaves the most prominent source of population damage difficult to be measured.

Even without the necessary data, a variety of efforts have been made to reduce the potential bycatch on rays as well as other organisms. New technology is continuously developed to reduce bycatch, including an Eliminator TrawlTM which reduced skate by catch from 33.4% to 1.4% of the weight of the target haddock, allowing a significant amount of preservation (Beutal et al 2008). New regulations and methods are continuing to be established to these data-poor species, allowing more accurate fish stocks and subsequent to be developed for these species (Newman et al 2015). However, many of these elements remain in early development, and still require a significant amount of data before they can be used effectively.

In order to improve regulations on skate fisheries, it is imperative to put more effort into learning about skate dynamics. While there is limited information on many of these aspects, using more data-limited assessments to analyze these species may be used to collect data, though any conclusions should be monitored often. In the future, it is important for regional management offices to coordinate and pool their data, while also creating a standard set of regulations to maintain these organisms in multiple locations. The current best practices for protecting skates and other fish with minimal data are relatively unknown, but given communication and extensive studies, it remains possible for these organisms to be better preserved and understood in the future.


Newman, D., Berkson, J., and Suatoni, L (2015). Current methods for setting catch limits for data-limited fish stocks in the United States. Fisheries Research, 164, 86-93.

Phillips, S.RM, Scott, F., and Ellis, J.R (2015). Having confidence in productivity susceptibility analyses: A method for underpinning scientific advice on skate stocks? Fisheries Research, 171, 87-100.

Beutel, D., Skrobe, L., Kathleen, C., Rhule Sr., P, Rhule Jr., P, O’Grady, J., and Knight, J (2008). Bycatch reduction in the Northeast USA directed haddock bottom trawl fishery. Fisheries Research, 94(2), 190-198.

Frisk, M.G., Miller, T.J., and Fogarty, M.J (2001). Estimation and analysis of biological parameters in elasmobranch fishes: a comparative life history study. Can. J. Fish. Aquat. Sci., 58, 969-981.

Kelly, J.T. and Hanson, J.M. Maturity, size at age and predatory-prey relationship of winter skate Leucoraja ocellata in the southern Gulf of St. Lawrence: potentially an undescribed endemic facing extirpation. Journal of Fish Biology, 82, 959.

Millers, T., Muller, R., O’Boyle, B., and Rosenberg, A. (2009). Report by the peer review panel for the Northeast data poor stocks working group. Woods Hole (MA): Northeast Fisheries Science Center. Report for the Data Poor Assessment Working Group.

Cavanagh, M.F., and Damon-Randall, K (2009). Status of the barn door skate (Dipturus laevis). National Marine Fisheries Service Report, Northeast Regional Office.

Bowley, S. (2008, April 12). A long-nose skate. Washington, Olympic Coast NMS. Retrieved March 17, from Wikimedia Commons:

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).

Fishery Collapses Explained by Overfishing, Life-History Traits, and Climate Variability

By Christopher Brown, RJD Intern

Species around the world have experienced significant declines below fixed thresholds that indicate the risk of extinction. Evidence has suggested that the risk of extinction runs high in terrestrial species that maintain large body sizes, feed high in the food chain, and demonstrate slow population growth rates. However, within marine ecosystems, species that exhibit fast population growth rates have been found to be just as likely to face the risk of extinction as species with slower population growth rates. Population growth rates can be understood as one of several factors that determine the risk of extinction. Additional factors that may influence the risk of extinction include climate variability and harvest dynamics. Overfishing, especially in waters unregulated by governing bodies, may play a strong role in population collapse. Recent studies have suggested that fast growing marine species subject to climate variability are more sensitive to overfishing than slow growing marine species.

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Figure 1: Proportion of fish stocks that have ever collapsed (Gray regions represent large marine ecosystems without fish stock status information) (Pinksy and Byler, 2015).

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Figure 2: Seasonal climatic variability of large marine ecosystems (Pinksy and Byler, 2015).

Pinsky and Byler used boosted regression trees to analyze the effects harvesting, species traits, and climate variability had on one hundred and fifty-four fish populations located around the world. In regards to fish and fisheries data, population collapses were analyzed using the RAM Legacy Stock Assessment Database version 1.0. This large database withholds a time-series of both population biomass and fishing pressure dating from 1950 to 2008. A fish stock was defined as collapsed if the minimum annual biomass dropped below 20% of the biomass necessary to support a maximum sustainable yield (Pinsky and Byler, 2015). The climate variability of seventy large marine ecosystems (LME) was calculated using sea surface temperatures (SST) from an 1870-2014 HadISST dataset. The SSTs were averaged monthly within each LME and the time-series were de-trended by subtracting a linear regression from each set of values. Short-term climate variability was measured to analyze the seasonal cycles, in addition to long-term climate variability. The four main questions that were addressed included (Pinsky and Byler, 2015):

  • Do the interactions of fishing with rapid growth rates contribute to population collapses?
  • Are fishery collapses more likely in regions with more variable climates?
  • Do the interactions of climate and fishing contribute to collapses?
  • What are the relative influences of fishing, life history and climate on population collapses?

Pinsky and Byler found that LMEs that had the greatest seasonal climatic variability were either enclosed, coastal areas, or located at intermediate latitudes. The most depleted fish populations in these LMEs had the greatest overfishing durations, maintained faster growth rates, and experienced a significant amount of seasonal climatic variability. Fish populations that were subject to overfishing in LMEs with great climatic variability were determined to be about twice as likely to collapse than fish populations overfished in LMEs with less climatic variability. Even though overfishing was a dominant factor in the models used to analyze fish population collapse, it was determined that life-history characteristics and climate variability predispose fish populations to collapse and depletion (Pinsky and Byler, 2015). Fast growing species have short generation times, and slow growing species have longer generation times. Fish species with short life histories are more prone to collapse, especially if there is a long delay in reducing harvest rates after population growth declines. Fish species with long life histories are able to tolerate longer delays. Because fish species with short life histories are more difficult to incorporate into sustainable fishing practices, dynamic management is needed to rapidly reduce harvest rates when it appears that a fast-growing species is approaching a collapse. Population biomasses and fishing pressures must be monitored closely enough to detect the possibility of the collapse and depletion of global fish populations in order to keep fast growing species above the fixed thresholds that indicate the risk of extinction.


Pinsky, Malin L., and David Byler. “Fishing, fast growth and climate variability increase the risk of collapse.” Proc. R. Soc. B. Vol. 282. No. 1813. The Royal Society, 2015.

The use of spearfishing competition data in fisheries management

by Pat Goebel, RJD Intern

There are fewer fishes in the ocean today than there were 200, 100, and even 20 years ago. This fact is reiterated in the case study authored by Pita, which shows   decreases in the abundance and weight of coastal rocky reef fishes over the last 50 years in Galicia.

The methods scientists use to determine estimates in abundance and size are criticized, especially when estimates are based on data from commercial fisheries. Commercial fisheries are always changing or shifting. New regulations and markets combined with more or less productive fishing grounds can misrepresent population estimates. A solution to this can be to use long-term data sets from recreational fisheries competitions. In the case study, The use of spearfishing competition data in fisheries management: evidence for a hidden near collapse of a coastal fish community of Galicia (NE Atlantic Ocean), a long-term data set (1953-2007) of recreational spear fishing was investigated to estimate local fish populations.

The results of the present study show a dramatic decrease in abundance (up to 76%) and body weight (76%) of coastal rocky reef fishes over the last 50 years. The decreases in population size and body weight are both critical factors, which will hamper the recovery of the coastal rocky reef fishes in Galicia.

Catch frequency f or 5 species of fish in Galicia

Catch frequency f or 5 species of fish in Galicia

Fishing along with global warming and pollution has nearly resulted in the collapse of the coastal rocky reef fish in Galicia. A management plan to help restore the depleted fish stock is eminent. A solution to the problem may lie in the paper as the size of the catch and the size of the fish tended to be bigger in the least fished zone.  So, stopping or reducing fishing in heavily fished areas may help restore the abundance and size of fishes within this important ecosystem.

Pita, P., and J. Freire. “The use of spearfishing competition data in fisheries management: evidence for a hidden near collapse of a coastal fish community of Galicia (NE Atlantic Ocean).” Fisheries Management and Ecology 21.6 (2014): 454-469.

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.


The effects of human population density on coral reef fish

By Brittany Bartlett, RJD Intern

Coral reef fisheries are extremely important to the livelihoods of millions of people. Unfortunately, habitat degradation and unsustainable fishing practices have resulted in a decline in these fisheries. Therefore, a recently published article by T.D Brewer et al. entitled “Effects of Human Population Density and Proximity to Markets on Coral Reef Fishes Vulnerable to Extinction by Fishing” seeks to understand the social and economic issues behind this depletion in order to improve management.

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The Overfishing of Mediterranean Bluefin Tuna

by Dani Escontrela, RJD Intern

Bluefin tuna is the most valuable fish species in the world. Their numbers, however, have greatly decreased in recent years due to their high demand. In fact, in 2001 “one 202 kilogram bluefin tuna caught off the northern coast of Oma, Japan sold at the Tsukiji market for 862 USD/kg” (Shamshak et al 2009). The bluefin tuna has life history traits that make it more susceptible to overfishing: they reproduce at a later age, they reproduce when they are of larger size, and they aggregate when they are going to spawn (Longo et al 2012). In addition, like many other species in the ocean, they are susceptible to industrial pollution. As the fishing of this species has continued without many regulations to protect them, their numbers have greatly declined. In fact the International Commission for the Conservation of Atlantic Tuna (ICAAT) predicts that a collapse in the fish stock in the near future is inevitable (Longo et al 2012).

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RJD Twitter teach-ins start Monday at 1 with overfishing

We will be hosting a series of Twitter teach-ins on marine biology and conservation topics. Each teach-in will cover a topic in a series of Tweets, including links to photos and videos, as well as NGO reports, blog posts, and scientific papers which people can read to find more information. These will take place on our Twitter account, @RJ_Dunlap, and will include hashtag #RJDTeachIn.

We encourage anyone interested in participating in the teach-in to follow (and encourage your friends, colleagues, and Twitter followers to follow) @RJ_Dunlap. We also encourage people to RT important points for their own followers.

Each teach-in will take approximately 20-30 minutes. Following each teach-in, there will be an opportunity for anyone to ask us questions. We will answer any question that people ask us.

The topic of the first RJD teach-in, which will take place Monday at 1:00 EST, will be overfishing. Future topics will include invasive species, bycatch, seafood sustanability,  marine protected areas, shark biology and conservation, sea turtle biology and conservation, ecotourism, and more- stay tuned! Additionally, if you have a topic you’d like to hear more about, let us know in the comments section of this post and we may host a teach-in about it.

The mission of the RJ Dunlap Marine Conservation Program is to “advance STEM (Science, Technology, Engineering and Math) literacy and marine conservation by combining cutting edge research and outreach activities”, and we hope that these Twitter teach-ins will help us to advance that mission. We hope that you’ll follow along with the first teach-in Monday at 1 EST, and we hope that you’ll encourage your followers to do the same.