Michael Grant does fascinating research with mysterious elasmobranchs in remote places. Basically, it's a job many people wish they had. Interested in marine biology from an early age, his love only blossomed on the beaches of Sydney and landed him in Papua New Guinea. How? Read on!
The Fins United Initiative: Thank you for your time, Michael! To kick this interview off, we'll ask you the "first question" we ask a lot of guest scientists here at TFUI... what got you interested in marine biology?
Michael Grant: My interest in marine biology developed from an early age. I grew up in Cronulla in South Sydney where I spent a lot of time at the beach. My dad was a mad fishermen and I always tagged along when ever I could. We spent a lot of time looking for the best places to fish examining currents, depth, wave action and whether the substrate was sandy, rocky, weedy or reef. During these fishing trips my dad had me questioning from a young age why particular spots were better than others and how physical factors in the environment dictated where the fish would be. This thought process was the beginning of my interest in the biology of all things marine.
TFUI: That sounds like an amazing introduction to science! What are you currently studying?
MG: I’m currently studying sharks and rays caught by remote artisanal fishing communities in Papua New Guinea. Specifically, I’m looking at euryhaline elasmobranchs and how they use different salinities throughout their life. There are a few species of very endangered euryhaline sharks and rays in Papua New Guinea including sawfishes and river sharks. It is important that we understand the habitat use of these species to help conserve their populations.
TFUI: And what led you to study shark life histories?
MG: I began studying shark life histories largely by chance as my supervisor Prof. Colin Simpfendorfer offered me the opportunity to examine the life history of the silky shark for my honours. This was part of a larger project run by Dr. William White, to study the life histories of various species of shark commonly caught by commercial fishing operations in Papua New Guinea.
TFUI: Can you explain what a "shark life history" is to TFUI readers?
MG: The life history of an animal is essentially the story of its growth from birth to death and its reproductive cycle within its life. For sharks and rays, we can calculate their age by examining their vertebrae. They deposit growth bands in their vertebrae, similar to growth rings found in a tree. Generally, broad opaque bands are deposited in summer months when resources are abundant and higher water temperatures facilitate faster growth. Conversely, in winter months, growth is thought to slow and this is reflected by the presence of narrow translucent bands. So in order to calculate the ages of sharks and rays, the number of opaque and translucent band pairs can be counted within their vertebrae and from this, we can estimate age.
TFUI: That is jawsome!
MG: To thoroughly examine the growth rate of a species, we collect specimens of all length classes and count the growth bands in each individual’s vertebrae. When we plot the ages of each individual against its length, we can fit a growth curve to the data. From this curve, we can estimate the size of birth, the rate of growth throughout its life and the maximum size the species might reach. We also look at the sexual maturity status of individuals collected and this helps us identify the length and age when sexual maturity is reached. Where females are pregnant, the number of embryos in uteri are counted which indicates litter size. From all this information we can then estimate population growth rates and generation times. This is all life history information and vital to fisheries management to ensure populations are not being caught at a faster than they can replenish themselves through reproduction.
TFUI: This all so fascinating! And, we haven't talked to a scientist yet who studies freshwater and euryhaline elasmobranchs. Why are these animals so special?
MG: Well did you know that around 40% of known teleost species occur in freshwater while only ~5% of sharks and rays can penetrate into freshwater?
TFUI: WOAH! No way!
MG: This is due to sharks and rays unique osmoregulatory physiology and their protracted life histories, which is a bit of a long complicated story I won’t get into here – but the bottom line is that the few species that can survive in freshwater are quite unique and special. Most of these species live full time in freshwater, the majority of which
belong to the neotropical stingray family Potamotrygonidae. These neotropical stingrays are all found in South America and no longer have a necessity to excrete excess salts. They are the only chondricthyan species with a vestigial rectal gland. Only a few species that can be found in freshwater also occur in marine waters. These species have the remarkable ability to alter their blood chemistry and the activity of organs such as the rectal gland and kidneys in response to their ambient environment.
TFUI: What kind of dangers do these animals face?
MG: Freshwater and euryhaline elasmobranchs face several additional dangers not found in marine environments. While fishing pressure, habitat modification and pollution are sincere threats across all aquatic and marine systems, they also have to contend with far less stability in physical factors of the environment. Seasonal rainfall patterns can heavily influence turbidity, pH, and dissolved oxygen levels as well as currents and depth. In estuarine areas, these factors may also be subject to change from daily tidal action. Unlike marine species, a major constraint to freshwater and euryhaline species is the small volume of their habitat.
TFUI: How so?
MG: Species occupying freshwater habits may be spatially confined by natural barriers including rapids, waterfalls and low water levels or additionally by dams and other infrastructure. This means that these species cannot always readily escape negative pressures to their environment unlike their marine counterparts. For this reason they require special conservation attention.
TFUI: On twitter, we've seen you show others how to measure and take genetic samples from dried fins. Why this is important and what can be accomplished from it?
MG: Fins are a great way to quickly gather a snap shot of shark catch within a fishery. Working in very remote areas such as Papua New Guinea, field work is expensive, resources are limited and time is often constricted. In many fishing communities sharks are incidentally caught in fishing nets targeting prawns or fish. When caught, they are sometimes retained and the meat is either consumed or sold. For some Papua New Guinea communities, fishing is an important part of their livelihoods so many villagers may additionally keep the fins from shark catch for sale. Because fins are dried and may be stored for a long time (weeks, months or even years), when we sample a villages catch we can get an idea of the range of species being caught in the fishery. Some fins however are more valuable than others, such as those from shark like rays or larger individuals, so we have to be careful when interpreting relative abundance. To identify species present, we take a small genetic sample from each first dorsal fin within the batch. We can also get an estimate of the length and weight for some species where a relationship between fin dimensions (length, height etc.) and body size is available.
TFUI: Any fin guides you recommend?
MG: I can highly recommend “Sharks and Rays of PNG” which contains one of the best available I.D. guides.
TFUI: So what do you think is the best way to get the general public interested in elasmobranchs? How can we create more awareness about the special species you study?
MG: I think it largely comes down to getting information about sharks and rays out to the general public. For me, I think if people understood the magnitude of shark and ray by-catch in commercial fisheries for example, a more compassionate interest would develop in the imperative of their conservation. Furthermore, how many people know how slow some species grow? How long it takes for them to reach maturity? How few young they produce?
TFUI: I'm guessing not many.
MG: When I visit villages in Papua New Guinea while conducting sawfish surveys, people are always fascinated
when I tell them that some sawfish species take around 15 years to reach maturity, can live for 30 plus years and only produce a few young every other year. They immediately realise the importance of regulating overfishing and how important the larger breeding members of the population are. So I think that more awareness can be created through educational outreach. Avenues such as documentaries, blogs, social media, school-based education and dedicated platforms such as The Fins United Initiative are a great way to garner interest and create this awareness.
TFUI: What is your whackiest "in the field" story?
MG: Well working in Papua New Guinea there are always plenty of interesting situations. One that particularly stands out came about during my time at the Sepik River mouth. We woke up at about 7 00am to inspect the catch in a gillnet that had been set over night. By the time we got to the beach where they butcher the catch, eight bull sharks were lined up on the bank. We were all ready to take our measurements and genetic samples when a cassowary showed up on the beach.
TFUI: Oh my gosh, no way!
MG: The cassowary held us up for about 20 minutes as it had a good look at the catch and a quick lie down. It was definitely an ‘only in PNG’ moment.
TFUI: [laughs] What’s next for you?
MG: I’m only in the first year of my PhD so I’m pretty locked down for the next 3 years. Eventually I’d like to be an academic and work with my own students but right now I’m really enjoying working in Papua New Guinea and the
TFUI: And we have to ask- what is your favourite Chondrichthyan species and why?
MG: The bull shark is my favourite chondrichthyan as they are one of the most ecologically successful species. They are euryhaline and are commonly found in rivers and lakes, even Lake Nicaragua. Unlike other euryhaline species though, bull sharks are also found throughout a wide range of marine environments, even in coral reefs and remote islands such as Fiji – I think that’s pretty cool!
TFUI: We couldn't agree with you more!
THE FINS UNITED INITIATIVE WOULD LIKE TO THANK michael FOR HIS TIME AND
TFUI Founder Melissa C. Marquez is author of all animal bios and "Behind the Fins" segments.
SEE MELISSA'S TEDx TALK HERE:
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