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

Paper by Lindsay N K Davidson, Meg A Krawchuk, Nicholas K Dulvy

 

By Pat Goebel, SRC Intern

A drop in shark and ray landings may 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. Unfortunately, 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. The demand for shark products is relatively new concept, as their commercial value has increased with the decline of other valuable fisheries. As on could assume with supply and demand, the high demand of shark products leads to an increase in fishing pressure. The increase in fishing pressure combined with the lack of laws regulating the shark and ray fishery, lead to the depletion of shark and ray populations. 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 overfishing.

Figure 1 - Shark_fins_Taiwan

Shark and ray landings peaked in 2003 and have declined by about 20% in the past decade. Davidson et al. (2015), noted that the decrease is more likely related to overfishing than management implementations. The official harvest number used in this study is possibly two to three times below the actual number of sharks and rays being caught. This study highlights the fact that sharks and rays are being harvested at an unsustainable rate. Moreover, Davidson et al (2015), stressed several countries that warrant prioritization for conservation and management action. The greatest declines were reported in Pakistan and Sri Lanka, both of which have little to no management or enforcement. If new management strategies are not implemented into these countries, elasmobranch populations will continue to be harvest at a detrimental scale.

Figure 2. 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 2. 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 Tagging with University of Miami’s President’s Council

By Patrick Goebel, RJD Intern

It is always pleasant waking up to your alarm on a shark tagging day. My alarm went off at 5:30am and in no time I was on my way to Miami. I met the team around 7:30 am at Diver’s Paradise. We loaded the boat and set off to pick up our participants for the day. We picked up our citizen scientists, a group of Miami Alumni as part of the President’s Council at the Miami Seaquarium.

Before heading out, the group fueled up with some breakfast and coffee. We didn’t know it at the time, but we would need all the energy we could get. During this time, Dr. Neil Hammerschlag, our program’s director, gave a brief introduction about the importance of our research and why we use our research methods. He mentioned it is estimated over 100 million sharks are killed each year. This got the attention of our guests and set us up for a great day of shark research and conservation.

After a short ride out, we quickly deployed our first set of ten drumlines with the help of our citizen scientist from the President’s Council. The next step in was deploying our new platform, which weighs a good 100+ lbs. We slipped the platform into the water, attached it to the boat via 3 poles, to hold it in place. Our team was surprised it was a piece of a cake. Once in place, we took turns standing and talking about the logistics of the platform. Since this was the first time we had ever used the platform, no one was sure if and how it would work. It is like getting a new toy or car, we could not wait to try it out.

The team inserts our new platform into the water (1)

The team inserts our new platform into the water.

 

We were hoping to catch a smaller shark first so we could test our platform and get the hang of it. However, as you know nothing goes as planned. I started to pull up our first drumline and noticed that the 40lb drumline felt a little heavier than normal. I quietly noted to a few members of the team that “we got something big on.” After a couple of minutes, we got the shark close enough to the boat to tell we had an 8+ bull shark on. The team quickly jumped into action ready to bring this big girl up onto the platform. Again to our surprise, we quickly and easily brought the shark onto the platform and began our workup. Our citizen scientists from the President’s Council took three measurements: precadual length, fork length, and total length, followed by a finclip, muscle biopsy. We then released and happily enjoyed, for a few minutes, how well the platform did.

A member of the

A member of the President’s Council assists with measurements.

It wasn’t long before we had another test for the platform. The next two lines each had on a 7+ ft nurse shark. These sharks are like armored tanks packed with muscle. If you have ever been on the boat with us before, you know nurse sharks don’t really cooperate with us, so this would be another great test for our platform. However, two nurse sharks later the platform yet again exceeded our expectations.

The day continued to get better and better. On our 18th drumline we caught another 8+ ft bull shark. This was exciting because we placed the first satellite tag of 2014 on this shark, which you can track here, https://sharkresearch.rsmas.miami.edu/education/virtual-learning/tracking-sharks.

The first satellite tagged shark of 2014 (1)

The first satellite tagged shark of 2014.

 

We really killed it in our third set. In this set alone, we caught 6 sharks of 4 species in the following order: nurse, bull, nurse, blacktip, and lemon. I have never caught a lemon shark out of Miami so this was a unique experience for me. These sharks can be quite feisty and have a very unique pale yellow/brown coloring. Also, their two dorsal fins are very similar in size, which makes them very distinguishable.

This trip on February 20th will likely be a trip none of us will forget. Our guests from the President’s Council were a great help and showed a passion for our research. We left them with a plethora of new knowledge about the importance of the ocean, which hopefully they will share with others. Sharing our knowledge about ocean conservation is truly a remarkable experience, one in which we believe is a great way to help conserve the ocean for future generations. Thanks to all who participated today and our team for an excellent day on the water.

Can MPAs help tropical sharks?

By Christina Marmet,
Marine conservation student

Sharks have been around for 450 million years, and have survived every extinction episode that our Earth has known since then (Litman 1996). However, human beings may be the biggest threat they have ever faced.

Today, there are about 500 species of sharks in the ocean, with more being discovered regularly. However, according to the IUCN Red List, more than one-third of all oceanic shark species are at risk of extinction. They are endangered mostly because of overfishing and the increased loss and degradation of coastal habitats (Stevens et al. 2000, Ferretti et al. 2010).

One of many possible solutions to help protect sharks is to create marine protected areas (MPAs), especially in coastal areas where sharks are most vulnerable to human impacts. However, in most cases, lack of knowledge regarding the movement patterns of sharks hinders the establishment of specific shark protected areas.

The National Oceanic and Atmospheric Administration MPA Center defines marine protected areas as “any area of the marine environment that has been reserved by federal, state, territorial, tribal, or local laws or regulations to provide lasting protection for part or all of the natural and cultural resources therein” (NOAA MPA Center www.mpa.gov accessed Nov. 1, 2012).

Hypothetical example of a marine protected area, a marine reserve, and a no-take marine reserve. Source: Pacific Fishery Management Council (www.pcouncil.org)

Hypothetical example of a marine protected area, a marine reserve, and a no-take marine reserve. Source: Pacific Fishery Management Council (www.pcouncil.org)

 

MPAs are put in place mostly for the protection and conservation of rare and endangered marine species and habitats, as well as to maintain the biodiversity of a specific area (Agardy 1997). MPAs can also help preserve the socio-economic value of a marine area for human use through fisheries or recreation. They are thought to be most effective at protecting sedentary species – animals who have very little movement or are attached to something – as most MPAs are small in size, and the benefits from the protection diminishes once individuals move outside the boundaries (Bonfil 1999).

Many MPAs have been put in place without prior knowledge of how they will function due to the urgent need for protection of marine environments (Roberts, 2000). In Knip et al. (2012), the aim of the study was to evaluate the possible degree to which existing MPAs may shelter shark populations by tracking the movements of two tropical coastal species within two MPA regions in the Great Barrier Reef Marine Park, Australia. Their hypothesis was that coastal sharks received conservation benefits from the MPAs by staying inside the boundaries (Knip et al. 2012).
The research was conducted from 2009 to 2010 in Cleveland Bay, within which there are two Conservation Park (CP) zones with strict fishing restrictions (Knip et al. 2012). During the course of the study, 37 pigeye sharks (Carcharhinus amboinensis) and 20 spottail sharks (Carcharhinus sorrah) were fitted with acoustic transmitters. Receivers were deployed throughout the two CP zones to monitor shark movement and residency inside the MPA (Knip et al 2012).

Acoustic transmitters allow scientists to know the location of tagged animals and time at which they pass within the range of the receivers (Welch 2005). Downloading of receiver data occurred every 6-8 weeks (Knip et al. 2012). The acoustic receivers were placed only inside the CP zones. Consequently, the interval between all detections was calculated for each individual shark to determine the length of time outside the protected area. The scientists concluded that the longer the interval between detections, the more likely the shark had exited the MPA (Knip et al. 2012).
The acoustic tagging led to the findings that pigeye sharks spent a mean of 23% of their time inside the MPA, while spottail spent a mean of 32% (Knip et. Al 2012). They also discovered seasonal variations: pigeye sharks spent twice as long in the MPAs in summer than winter, and the opposite pattern was apparent among spottail sharks (Knip et al. 2012). All individuals made excursions outside of MPAs, but the number and duration of the excursions varied among individuals of both species (Knip et al. 2012).
The authors recognized that these results lead us to believe that these two species of sharks are beneficiaries of the marine protected areas. It undeniably shows a certain degree of protection for the sharks, as they were found spending a noteworthy amount of time in the MPAs. However, the percentages also show that the sharks are out of the reserve 70 to 80% of the time, suggesting that MPAs in this region provide only limited protections for these two species, and potentially for all mobile species.
Indeed, the authors suggested that the degree of MPA effectiveness would in part depend on the seasonality of the nearby fishery industry, with respect to the seasonality and timing of excursions of sharks from MPAs (Knip et al. 2012). It would have been interesting to look at precise bycatch data, such as how many fishermen incidentally catch and release sharks, and where and when exactly they catch them. The authors mention that the location where the sharks exit the MPAs is of critical importance for conservation. Most fishing effort in this region occurs in the intertidal zone, which is where the pigeye sharks prefer to cross out of the CP zones (Knip et al. 2012). The effects of fishing pressure were obvious: fishers in this region removed 21% of the pigeye shark population, while there was no capture of spottail sharks (Knip et al. 2012), thus suggesting the need for fisheries regulations in and around the MPAs. Unfortunately, there was no discussion of fishermen sample size, and it is thus hard to determine the significance of this catch, which may represent only a fraction of total fishing threat.
This paper demonstrates the importance of knowing the movement patterns of sharks and other mobile species in order to create better conservation areas. Undeniably, it would be worth spending more time looking at the reasons for the crossing patterns in and out of the MPAs for these two species of sharks. Besides, if the area adjacent to an MPA boundary is heavily fished, the risk of capture for an individual will remain high even if it spends most of its time inside the MPA (Knip et al. 2012).
This study was among the first to evaluate the efficacy of MPAs for shark conservation (Knip et al. 2012). Consequently, it proved that not only the creation of MPAs could be an important contributor to shark conservation, but also that better knowledge of shark behavior would most likely encourage the development of more specific and effective fisheries-management plans. The authors suggest an ‘onion-ring’ type approach to MPA design, where core areas would be buffered by outer zones that exclude potentially high impact fisheries (Knip et al. 2012). It can be concluded that the effectiveness of MPAs for sharks is dramatically decreased by certain fishing activities nearby, and that there is a need for better MPA regulations in and around protected areas.
The authors came to the conclusion that this study demonstrated that individual MPAs may generate benefits for multiple shark species, and thus did not need to follow a species specific initiative (Knip et al. 2012). Although this study demonstrates that MPAs are a good first step to protecting even highly mobile species, it is crucial to remember the great diversity of shark species. These findings can really only be generalized to other shark species with similar life history and behavioral characteristics. Consequently, more research into the potential for MPAs to contribute to shark conservation is needed in different ecosystems worldwide.

REFERENCES

Agardy, T.S. (1997) Marine Protected Areas and Ocean Conservation. Academic Press, San Diego.
Ferretti, F., Worm, B., Britten, G.L., Heithaus M.R. & Lotze H.K. (2010) Patterns and ecosystem consequences of shark declines in the ocean. Ecology Letters, 13, 1055-1071
IUCN Red List. (2012) Accessed 1 Nov. http://www.iucnredlist.org
Litman, G.W. (1996) Sharks and the origins of vertebrate immunity. Scientific American, 275, 67.
National Oceanic and Atmospheric Administration (NOAA) – National Marine Protected Area (MPA) Center. Accessed 1 Nov. 2012 http://www.mpa.gov/aboutmpas/definition/
Pacific Fishery Management Council. (2012) Habitat and Communities: Marine Reserves and Marine Protected Areas. Accessed 1 Nov. http://www.pcouncil.org/habitat-and-communities/marine-protected-areas/
Roberts, C.M. (2000) Selecting Marine Reserve Locations: optimality versus opportunism. Bull. Mar. Sci. 66, 581-592.
Stevens, J.D., Bonfil, R., Dulvy, N.K., Walker, P.A. (2000) The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES J, Mar. Sci. 57, 476-494.
Welch, D. (2005) Tiny Acoustic Transmitters Help Map Salmon Tracks in the Ocean. Accessed 1 Nov. 2012 http://www.aip.org/149th/tsang.html
Wildlife Extra News. 2008 http://www.wildlifeextra.com/go/news/shark-tagging546.html#cr

New Educational Activity: Mercury & Sharks

Bioaccumulation of Mercury in Sharks: Part 1With great excitement, we would like to announce a brand-new educational activity now offered here on the RJD website! Utilizing a subset of data from RJD shark research trips, you can investigate the bioaccumulation of methyl mercury in South Florida shark populations.

Broken down into two worksheets, the first part will provide you with a strong background knowledge of what bioaccumulation is and how methyl mercury affects human health.

Bioaccumulation of Mercury in Sharks: Part 2The second part will walk you through a color-coded Microsoft Excel spreadsheet, organizing and analyzing mercury values found in shark muscle tissue. Then, you will be asked to draw conclusions based on your findings.

As a note, the curriculum is geared toward high school students and above, but anyone is welcome to give it a try! We hope that you will enjoy this new activity, and share your feedback with us. Also, feel free to explore our opportunities for participation in the field, collecting data just like what is used in this worksheet.

New Educational Activity: Mercury & Sharks

Bioaccumulation of Mercury in Sharks: Part 1With great excitement, we would like to announce a brand-new educational activity now offered here on the RJD website! Utilizing a subset of data from RJD shark research trips, you can investigate the bioaccumulation of methyl mercury in South Florida shark populations.

Broken down into two worksheets, the first part will provide you with a strong background knowledge of what bioaccumulation is and how methyl mercury affects human health.

Bioaccumulation of Mercury in Sharks: Part 2The second part will walk you through a color-coded Microsoft Excel spreadsheet, organizing and analyzing mercury values found in shark muscle tissue. Then, you will be asked to draw conclusions based on your findings.

As a note, the curriculum is geared toward high school students and above, but anyone is welcome to give it a try! We hope that you will enjoy this new activity, and share your feedback with us. Also, feel free to explore our opportunities for participation in the field, collecting data just like what is used in this worksheet.

Shark Research Featured on Animal Planet – Wild Recon (March 9 @ 8 pm)

Dear All

Our research was featured on a special episode of Wild Recon on Animal Planet:

You can Watch the Full Episode Here (Click here to download)

Our segment is occurs between the following times: 18:48 – 32:33

Wild Recon Episode:
Ocean Killers

Hunted for their fins, shark populations are plummeting across the globe. Animal adventurer Donald Schultz joins scientists in a race against time to save these fearsome predators from extinction.

http://animal.discovery.com/videos/wild-recon-ocean-killers-full-episode.html

Our segment is between the following times: 18:48 – 32:33

Filming for Wild Recon with Donald Shultz (Click to Enlarge)

Sampling a hammerhead – filmed during Wild Recon on Animal Planet (Click to Enlarge)