Tagging Mako and Blue Sharks
Oct 26, 2024
How do scientists keep track of large pelagic species like the mako shark and blue shark? Suzy Kohin from the Southeast Fisheries Science Center explains the science behind satellite tagging and how her office uses this information to inform management decisions.
[ music and rushing water ]
[ music ]
I'm Suzy Kohin,
and I've been working here at the Southwest Fishery Science Center since 2002.
And I'm working mostly on the large pelagic fish,
the tunas, billfish, and sharks,
and the blue shark and the mako shark are both important species
from a fisheries management perspective.
We have both longline and drift gillnet fisheries that target large pelagic fish,
like swordfish or tunas, here off the West Coast,
and both blue sharks and mako sharks are caught in those fisheries.
Therefore, they've been included in a federal fishery management plan
for highly migratory species here on the West Coast.
And one of the reasons we're trying to understand their movement patterns
is so that if there is a vulnerable life history stage,
like where you might always find pregnant females or a nursery area,
where you may want to protect those areas to allow the females to come in and pup,
and then wait until they depart before you start your fisheries or things like that.
[ music ]
One of the cool projects that I've been involved with since I started is
tracking sharks, the large sharks, with satellite tags.
And so we use a range of tags,
like this is a pop-off archival tag that stores
temperature and depth and light level information,
and we can actually get vertical use of the water column
as well as from the light level we can estimate the locations.
We also use these other tags.
They're called SPOTs, or Smart Position and Temperature tags.
And they transmit, ah, it's a radio signal to satellites.
And we can get a signal almost in real time of the approximate location within one kilometer.
And we've tagged over 90 shortfin mako sharks
with either one of these tags or a combination of both.
And both is nice because we get really good horizontal movement information
from the radio positioning tags,
and we get very good vertical movement data from the pop-off tags.
[ music ]
So before this tagging study,
we didn't know their range, how deep they go in the water column.
We're also studying their feeding habits.
And one of the interesting things is because we've been
conducting these studies since 2002 on several of these species,
we've been able to observe some interannual variation as well in their movement patterns.
And you can see that the animals that were tagged in 2003
are shown in the red lines,
in 2004 in the yellow lines,
and in 2005 in the green lines.
And in general, they like to use this California Current region,
which is an area very abundant in prey,
and it has upwelling during the summer.
And what's interesting is in 2004,
those animals ranged a lot farther than they did in the other two years.
And that's a pattern that was also observed with sea lions that were tagged that year.
And we believe that the prey availability in the California Current closer to the coast
was not as high, which is why these animals had to range farther.
And sometimes if you recover one of these tags,
then you actually get the minute-by-minute depth and temperature data.
And you'll see these just, in the middle of the track,
there might be a 900-meter dive or something.
And you wonder, was it being chased by a predator?
Or was it chasing a yummy squid? Or I don't know.
So it's sort of the mystery that these tags reveal.
And at the same time, we learn a lot about their behaviors.