//
you're reading...

Ecology

Little fish, big fish… which one poses the bigger threat?

Article:

Biton-Porsmoguer, S., Bǎnaru, D., Boudouresque, C. F., Dekeyser, I., Bouchoucha, M., Marco-Miralles, F., … & Harmelin-Vivien, M. (2018). Mercury in blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) from north-eastern Atlantic: Implication for fishery management. Marine Pollution Bulletin127, 131-138.

Have you ever heard the term mercury poisoning? It may not be as common as other types of poisoning but it is much closer to us than we think. Mercury is a naturally-occurring element whose emissions and deposits have increased exponentially with human activity (such as fossil fuel burning). Exposure to mercury can have toxic effects on our brain, kidney, and lungs.

Fig. 1 Sources of Mercury in the open ocean (Top). Mercury interaction in the ocean, from source to seafood (Bottom). Source: Coastal and Marine Mercury Ecosystem Research Collaborative.

 So, how are we exposed to it? In general, it is an element that naturally incorporates itself in many food webs that we take part in. Take ocean ecosystems for example: mercury is ingested by many fish and Invertebrates (prey) which are then eaten by larger fish (predators). Now, those predators (shark, swordfish, king mackerel, bluefish tuna, groupers, albacore tuna, and tilefish) continue to ingest prey throughout their lives while the Mercury in those preys accumulates in their muscle tissues. By the time we buy fish at the grocery store or fish market, we are eating a big, fat, tasty fish that may contain high Mercury content.

Fig. 2 Bioaccumulation is the increase of a pollutant in an organism (Top)  and Biomagnification is the increase of a pollutant in a food chain (Botton). Source: wethinklink

 So, how do we avoid this? The U.S. Food and Drug Administration (FDA) has established regulations in the market to control for mercury content. No fish sold may contain more than 1 mg of Mercury per kg of fish. The Environmental Protection Agency (EPA) in the other hand, recommends not consuming more than 0.3 mg of Mercury per kg of fish and not to exceed total 0.0175kg of total fish per day.

 Does that mean that every fish is tested for Mercury levels? The answer is no! That’s a bit unnerving, so you may ask: Then how can they tell us that the fish you are about to consume is safe??  We depend on scientists to study the life history traits of important commercial species, which reveal an important measurement, the fish size to mercury level ratio. This ratio helps scientists recommend the maximum size a fish can reach without crossing into unsafe mercury levels.

 The Study

 Spanish and Portuguese commercial fishing fleets in the Northeast Atlantic capture a wide variety of shark species, using long-line fishing. Sharks captured are not size regulated and there is no knowledge of a mercury level content to size ratio across life history traits. Scientists sampled muscle tissues and stomach content of 48 shortfin mako (Isurus oxyrinchus) and 40 blue shark (Prionace glauca) from the Vigo Fish Market in Spain for Mercury concentrations.

Fig. 3 Blue Shark. Source: ARKive

Fig. 4 Shortfin Mako. Source: swfsc.noaa.gov

 Results

 Scientist found that Mercury levels in the shark’s muscle tissue increased with size and weight for both shortfin mako and blue shark. When sex, age, and season were taken into account, they found no difference in Mercury levels, meaning these variables cannot help predict mercury content in the sharks. However, the researchers noted that for blue sharks, mercury levels were higher if they were found North of the Azorean archipelago. The scientists also observed that shortfin mako mercury levels were within accepted standards, but the individuals captured were juveniles. Shark individuals larger than 190cm for shortfin mako and 250cm for blue shark in total length showed higher mercury content than considered safe by the European Union (1 mg kg1 wet weight).

 

Fig. 5 This graph shows Mercury levels on the y-axis and total body length on the x-axis. The trend we see is as body length increases, mercury levels in the sharks increases. Grey dots and line represent shortfin mako and black dots and line represent blue shark. Source: Biton-Porsmoguer et al, 2017

What does this mean?

 Using fish/shark size to mercury level ratio may continue to be a good management practice for this species. The scientists recommend captures of shark individuals to not exceed 200 to 250 cm for the blue shark and from 150 to 190 cm for the shortfin mako. However, this also presents a new challenge; capturing juveniles who have not reached sexual maturity or have not had the chance to reproduce will greatly decrease the population with time. Mercury content must be considered for public health safety as well as regulating shark captures to ensure sustainable fishing of the species. Lastly, this study continues to highlight the importance of research on life history traits for important commercial species and their implication on best management practices to conserve the species.

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 6 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 9 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 11 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 11 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com