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COROMANDEL LIFE
SUMMER 2014
Blue Shark Satellite Tagging:
Assessment of Migration and Critical Habitat Use: NZ & Beyond
This map from Feb,
2013 shows swim routes
of seven of the Blues
tracked by Riley Elliott.
Bromy swam north
2000km for New
Caledonia.
Hanna is the lone
female in the study.
Riley tracked her north
(to mate?) then she
returned to NZ, perhaps
to give birth. He plans
to examine her this
summer.
THREE MONTHS SINCE THE FIRST BLUE WAS TAGGED:
WHERE ARE THEY NOW?
May 16, 2013
Huge distances have been covered by several of the mature blue
sharks tagged, yet some have stayed much closer to shore.
Bromy has made a straight journey to the tropical waters south of
New Caledonia, over 2000km! Bluey has also decided on a tropical
holiday. Perhaps they realize that the Pacific Island nations have begun
establishing shark sanctuaries in these tropical waters, banning shark
fishing and finning. Unfortunate for the other 6 sharks still in NZ waters
where it is still LEGAL to FIN sharks! Seems ridiculous that NZ has not
joined the 98 other countries worldwide in the ban of shark finning!
Nonetheless, the remaining 6 are still relaying locations most days.
Trooper and Bodhi have remained in the waters around the Three
Kings Islands, renowned for its large schools of fish. Theory is, these
two, like many other apex predators, will hang here until the East
Australian Current, resides north as winter approaches. They will feed
up as much as possible, before venturing north to tropical waters for
winter, where however less food is present.
Cheech, Riley and Mike have all remained within the BOP area, moving
in and out from the coastal waters, to shelf waters >2000m deep. Here
they will be following the last of the warm water patches, foraging on
schools of skippies, pilchard and deep for squid.
Hannah, the only female (2.2m mature), has made a round trip up past
the Kermadec Islands, suggested as a female birthing site, before
returning back to the offshore waters of BOP.
EXPECT MALES TO START RETURNING FOR SUMMER
Nov. 1, 2013
As summer approaches Riley Elliott is gearing up for another season
of blue shark tagging in NZ waters. This summer, he is more prepared
than ever thanks to the amazing tracks of last year’s sharks. Clear
age/gender segregation has been observed, with mature males
migrating north, nearly to the equator! As summer nears, and the
East Australian/Auckland current begins to flow south, the male blues
are following. All 7 males (2-2.7m long) have resided in warmer, deep
oceanic waters for the NZ winter.
Contrary to this, Hannah, the NZUA tagged blue shark, and only female,
continues to show preference for NZ coastal waters. Riley’s hypothesis
is that mature females move north with males at the end of summer, to
the Kermadecs, intercepting departing males for mating, leaving them
on their journey north, and returning to NZ coastal waters to maintain
sexual segregation (a behavior used by many sharks to reduce breeding
pressures – which in sharks can kill females) as they grow their young
ready for birth in the following summer.
Riley hopes to track down Hannah this summer, in person, to see
how she is fairing and whether she is heavily pregnant! Note: For blue
sharks, gestation is speculated to take 8-10 months. Blue sharks are
born live in litters of varying numbers from 50-100+
This is a tracking map, taken a few months after sharks received their tracking
devices. Riley Elliott’s blue sharks all have names: Bodhi, Bromy, Mike, Riley,
Cheech, Kelly, Trooper, Bluey and Hannah, the lone female. Generally, sharks
swim for warmer waters during the New Zealand winter months. And if they
swim deep, they are probably chasing squid, their main food source.
See up-to-date maps of locations of Riley’s tagged Blue sharks at
sharkwatch.org.au/
At the Shark Watch website, click on the individual shark’s name to show
its migratory pattern. Each dot represents a dated position; click on the
dot to see the date. Here, one of Riley’s sharks, Hannah, ranged far out to
sea, perhaps to mate, but prefers to stick close to the north island shore.
Compare recent map to Hannah’s early pattern on the map above.
Riley and Mike are scouting the Coromandel waters this month and
Riley sent us this update early January.
From Riley Elliott’s Shark Watch website and blog
Latest news!
NE NZ SUMMER BIRTHING GROUNDS
Jan. 4, 2014
I just did my first trip last week for this summer, off Great Barrier
Island. I got amazing results, confirming my theory that NE NZ
waters are a definite breeding and birthing ground for the South
Pacific Blue shark. Evidence was gathered in the form of 10
new born Blues (30-50cm long, all with umbilical scars and skin
folds). Had a mature male, that we tagged (named Kalmar) and
then we had and tagged a mature female 2.5m long with fresh mating scars all over
her, showing that they are breeding here; she had placenta hanging from her, proof
that she had recently pupped here (the new borns we saw being possibly hers). I
tagged a juvenile Blue inshore of Barrier and the tracks so far from them (see map)
are helping cement my theories of critical habitat use and migration:
1) NE NZ is a breeding, nursery and birthing ground for the South Pacific Blue shark
= thus a critical habitat.
2) Pregnant females reside within NE waters for gestation and pup before intercepting
migration males as they move north through the kermadec region, where the males
continue north and the females return to coastal NZ waters to gestate.
This means that unregulated impacts from the removal of 150,000 blue sharks a year
in NE NZ waters, just for fins, may be dire for the south Pacific Blue shark population,
and the related ecosystem these creatures control.
We were shocked to see this arrive from Riley just before press time.
“All males tagged in the first year, moved outside NZ waters (where they
are often protected from finning), and upon returning in July to NZ waters,
where shark finning is legal, ALL disappeared!!! This timing coincided with
the peak Tuna fishing season – so they were likely finned! A horrible fate
for the sharks and a waste of $30,000 worth of scientific equipment.
“The NZ Government is implementing a shark fin ban over the next 3
years, however blue sharks, who are finned the most, have been unjus-
tifiably left till 2016 for protection! Will I lose the ten new sharks I have
tagged to this horrible practice?”
To follow all Riley’s sharks visit
d new action at
Note: Sharks occur as bycatch in all tuna surface longline fisheries which has increased with the
reduction of tuna populations being overfished. The NZ surface longline tuna fisheries combined
total catch is composed of 33% albacore, 17% swordfish, 16% Blue sharks, 8% southern bluefin
tuna, 8% bigeye tuna and the rest as other species. Clearly Blue sharks outweigh most of the
targeted tuna species. If you combine all shark species caught (mainly Blue, Mako and Porbeagle)
they make up 30% of the total tuna fishery catch!
