response of grey nurse sharks to rec lures and baited lines

[murf]

Behavioural response of grey nurse sharks to recreational lures and baited lines

from ecofishers

Investigating the behavioural response of grey nurse sharks to recreational lures and baited lines.
Drs Will Robbins & Vic Peddemors, Cronulla Fisheries Research Centre of Excellence

Project background

Grey nurse sharks, Carcharias taurus, typically inhabit the bottom of rocky gutters and caves on inshore reefs. Unfortunately these habitats are often targeted by line fishers seeking species such as snapper and kingfish, placing grey nurse sharks at risk of incidental hooking. The East Australian population of grey nurse sharks has steadily declined since mid last century, raising serious concerns about their future vitality. Low population estimates resulted in this population being listed as Critically Endangered since 2001.

Historical catch data, combined with observations of hooks and wounds on many grey nurse sharks off NSW have provided evidence of ongoing interactions with commercial and recreational line fishing gears. However, the underlying mechanisms associated with these interactions remained unclear. Specifically, it was unknown whether grey nurse sharks are more vulnerable to particular types of fishing gears or techniques, and at what rate interactions occur.

Project objective

To investigate the behavioural responses of grey nurse sharks to various recreational line-fishing gears. This involved examining interaction rates with bottom-set baited lines, towed lures and vertical jigs when deployed close to grey nurse shark aggregations. Research was focused at Fish Rock, South West Rocks, a NSW Critical habitat where year-round aggregations of grey nurse sharks occur.

Methodology

Gear types used in this research were commonly used by recreational fishers at the study site. Sampling was undertaken from a runabout, with all areas of Fish Rock sampled. Hooks were disabled on all gear types, with fish and shark interactions monitored using underwater video cameras which fed a signal directly back to the boat. Previous studies have found these cameras have no effects on the behaviour of sharks.

Sampling was conducted as three discrete experiments looking at bottom-set baits, trolled lures and jigs. Experiments consisted of

1. 800 bait trials of four different baits
2. 625 lure tows (537 km) of 16 different lures
3. 861 jig drops of eight jig types

Bait trials

Baits were fished using a modified paternoster rig, where the baits were positioned ~70 cm above the substratum. Sampling consisted of 5 minute replicates typically conducted in sandy gutters within ~40 m of grey nurse shark aggregations. Sampling was conducted at dawn, morning, afternoon, dusk and night. Night sampling was undertaken within 50 m of the position where sharks had aggregated that day and used red-filtered lights to illuminate the area around the baits. Four bait types were tested - whole and slabbed blue mackerel, whole pilchard and whole squid. A strike was recorded when a shark or fish took the bait, or completely engulfed the bait in its mouth.

The 800 bait trials were distributed equally across the five times of day (i.e. 40 replicates per bait per time of day). Baits were taken by sharks, by fishes targeted by local anglers, and by smaller, non-target fishes. Key findings from the bait trials were:

1. Grey nurse sharks took 22% of all baits deployed.
2. Larger baits of slabbed and whole blue mackerel were taken most by grey nurse sharks, with 34-35% of baits taken.
3. Smaller baits of pilchard and squid were also taken by grey nurse sharks, at a lower, but persistent rate of 10%.
4. Grey nurse sharks took all bait types at all times of day, with no consistent time-of-day preference.
5. The vast majority of bait takes by grey nurse sharks occurred by the shark approaching the bait, rather than the bait drifting onto the shark.
6. Grey nurse sharks were the only takers of baits at night. Fish took baits only between dawn and dusk.
7. Pilchard and squid baits were taken more often by fish species targeted by anglers.

Towed attractant trials

Trolling was conducted at dawn, morning and afternoon, at both shallow (1-2 m) and deep (7-10 m) depths. Fifteen different large and small artificial lures and one fish bait type were trolled 24 m behind the boat at 5 -7 kts, as per manufacturer recommendations. Trolling was conducted as circuits around the Fish Rock complex to ensure the maximum number of habitat types and area were exposed to the lures.

Gears tested were:

* Hard plastic lures (blue/white, red/white, yellow/green, yellow/red)
* Hard plastic rattling lures (blue, blue/silver, green/blue, silver)
* Metal lures (silver)
* Soft plastics (white, green/orange)
* Plastic poppers (red/white, blue/silver)
* Feather jigs (red/white, purple/black)
* Whole fish (blue mackerel)

The 625 lure tows around the Fish Rock complex allowed us to draw the following conclusions:

1. Fish strikes were most prevalent during dawn (42%) and afternoon (33%), with fewer interactions (25%) during morning sampling.
2. Over 18,000 sightings of fish were recorded.
3. Over 3,600 fish reactions to lures were recorded.
4. Over 100 fish strikes were recorded on the lures.
5. Only one grey nurse shark was seen during the lure tows.
6. No grey nurse interactions were recorded in 537 km of lure towing.

Jig trials

Vertical jigs were deployed using rod and reel, with results captured by an underwater video camera attached inline ~ 1 m above the jig. The camera allowed the lure to maintain a constant position in the camera?s field of view as it was jigged upwards. Two metal knife jigs (pink and green), and four types of soft plastics (blue, brown/white, green/orange and white) were tested in a series of five minute replicates. Two benthic jigs were also tested using the live-feed video cameras.

Vertical jigs were dropped and retrieved over 800 times in the presence of sharks. Over 92% of these drops landed in the gutter where sharks were located (proximate drops), with the jig passing within a body-length of a grey nurse shark in over 50% of these occasions. Key findings from the jig experiments are as follows:

1. One in 20 proximate jig drops (5%) hit a grey nurse shark. 62% of hits occurred on the way down, 38% on retrieval. These may have snagged grey nurse sharks had the gear possessed working hooks.
2. A further 6% of proximate drops were ?line hits? or ?near misses? passing within millimetres of sharks.
Grey nurse sharks attempted to bite the jig on only 6 occasions.
3. All interactions occurred when the jig was close to the substratum, with grey nurse sharks not seen to actively chase any jigs.
4. Grey nurse sharks interacted with benthic-oriented jigs in 55% of replicates. This usually involved sharks rubbing up alongside the jig, or the jig drifting onto the shark.

Conclusions of this study

Grey nurse sharks clearly interact with static baits deployed close to their aggregations. All bait types were taken at all times of day, and grey nurse sharks were the only bait-takers after dusk. Even the least taken bait types resulted in frequent (10%) shark interactions, demonstrating that bottom-set baits pose a high interaction risk when deployed around grey nurse shark aggregations.

None of the trolled attractants (lures and bait) elicited any reaction from grey nurse sharks. Although there may be indirect effects of sharks targeting fish that have been caught by lures, the lack of any interactions with trolled lures, and the low number of sharks recorded carrying lures suggests that trolling represents minimal direct risk to grey nurse sharks.

Knife jigs and soft plastic jigs pose risks to grey nurse sharks while fished close to the substratum. Most interactions occur through jigs hitting the shark, resulting in foul hooking. This can occur relatively frequently when fishing in close proximity to grey nurse shark aggregations. Benthic-oriented jigs had higher interaction rates than vertical jigs as they are deployed close to the substratum for longer periods of time.

[Black_Rat]

Surprise a labor gov mob is not tweaking the resultts !!!!!!???????
Damo.

[warrigul]

wow what a great study
when are they going to study divers in wet suits 6 at a time touching patting these rare endangrerd sharks
putting their bodys into the protected breeding lounge rooms while blowing bubbles like figgin god know what and coming back the next day and doing it all over again with a diffrent bunch off money paying frog men.
oh thats right of coarse it has no adverse affects on them its the 5/0 hook with a 6 inch soft plastic
fished on 10kg line that killed 100kg plus sharks and caused the depletion of grey nurse numbers not divers with power heads.
naughty fishermen look what you've done!!

[Lucky_Phill]

Now that is what I call research.

murf, are you able to link me to the paper, as I'd like to find out more.


Funny thing is, 99.99% of fishermen knew that GNS do not take trolled lures etc. Just needed to get this qualified so the powers that be can go back to " the backroom dealer-drome " and tell the " others ", that closing down these areas totally was wrong.

LP.
.
.
.
.

[NAGG]

Ah , the benefits of having funded research ........ via a licence.

Funnily - the first closures at fish rock only involved bait fishing ....... which made sense ! - Then more recently they locked out all forms of fishing

Anyhow , its good to see some decent research being done


Chris

[Angla]

Ah , the benefits of having funded research ........ via a licence.

Funnily - the first closures at fish rock only involved bait fishing ....... which made sense ! - Then more recently they locked out all forms of fishing

Anyhow , its good to see some decent research being done


Chris

Ditto that

Cheers
Chris

[PADDLES]

if this same research was also conducted at a numer of other known??? grey nurse sites it'd have even more clout.

[FNQCairns]

Interesting, was this research conducted on only already closed areas? The large shark rats of the sea (grey nurse sharks) probably behave like any other potential hook-line taker and will be far more interested in any bait after closed periods rob them of the caution they acquire when effort is applied to their territory.

if so guaranteed if this exact same research was conducted before the grey nurse con job became legislation....the baited drops conclusion in the article above would have shown a statistically different result.

none the less it was an interesting read, some practical real world contained within, still one local fisherman already knew from experience.

i caught a GNS once when I was 10 yo, was only like 4 foot long offshore down the NSW coast...my mom still says it was the best tasting fish she ever ate, i was to young to remember how it tasted.

[Aussie123]

The worst part about the GNS population at Fish Rock is over the years not one gov department has ever asked or consulted the local fisherman about the sharks.
Everything is done through the greedy divers who for many years have been trying to get Fish Rock totally closed to all forms of fishing.
The local dive shops have been pushing for a marine park there with only them having the permits to dive the rock and that instantly gives them a million dollar business that comes with an Internationally recognized dive site.
Years ago they tried to get full closures using the Loggerhead Turtles as part of the Hat Head National Park and after a long battle they lost so now its the GNS that they are using to get the closures for themselves.
Years ago there were so many GNS at the Rock but very few divers.
These days there is 50 plus divers a day go down and annoy the sharks and this has dispersed the GNS population there.
Many divers rode on the backs of these sharks and many still do it today and years ago many were shot by spearos as well.
We had some fantastic ground NE of the rock in 28-32 fathom where at night we handlined a lot of Jews and other reefies but these days you cannot fish it after dark as its so lousy with the GNS that steer clear of Fish Rock because of the diving fraternity that annoy them on a daily basis.
A lot of these sharks also moved north to the top end of Trial Bay.
The top of the mud hole holds a reasonable population of GNS these days as well as the inshore reefs off Grassy and these 3 areas historically had no GNS populations there ever.
The sad fact is these sharks have been pushed out of there homes from the large amount of diving activities happening there on a daily basis but the fishermen are being blamed for killing them off.
If the relevant parties would consult all user groups when doing their studies they may just find where the GNS populations really are these days along that part of the coastline.
Rocks in Line is the first port of call as there is more GNS there these days than what is at Fish Rock.

[cormorant]

The worst part about the GNS population at Fish Rock is over the years not one gov department has ever asked or consulted the local fisherman about the sharks.
Everything is done through the greedy divers who for many years have been trying to get Fish Rock totally closed to all forms of fishing.
The local dive shops have been pushing for a marine park there with only them having the permits to dive the rock and that instantly gives them a million dollar business that comes with an Internationally recognized dive site.
Years ago they tried to get full closures using the Loggerhead Turtles as part of the Hat Head National Park and after a long battle they lost so now its the GNS that they are using to get the closures for themselves.
Years ago there were so many GNS at the Rock but very few divers.
These days there is 50 plus divers a day go down and annoy the sharks and this has dispersed the GNS population there.
Many divers rode on the backs of these sharks and many still do it today and years ago many were shot by spearos as well.
We had some fantastic ground NE of the rock in 28-32 fathom where at night we handlined a lot of Jews and other reefies but these days you cannot fish it after dark as its so lousy with the GNS that steer clear of Fish Rock because of the diving fraternity that annoy them on a daily basis.
A lot of these sharks also moved north to the top end of Trial Bay.
The top of the mud hole holds a reasonable population of GNS these days as well as the inshore reefs off Grassy and these 3 areas historically had no GNS populations there ever.
The sad fact is these sharks have been pushed out of there homes from the large amount of diving activities happening there on a daily basis but the fishermen are being blamed for killing them off.
If the relevant parties would consult all user groups when doing their studies they may just find where the GNS populations really are these days along that part of the coastline.
Rocks in Line is the first port of call as there is more GNS there these days than what is at Fish Rock.

Good to see real research. I'd be happy to read it even if the results were different as I want my fishing to be long term sustainanble. Just wish more real research was done instaed of the endless funds being handed out to small interst groups who do nothing physically good but spend it all keeping themselves employed campaining in the political sphere and creating media releases. Bloody leaches.

Amazing for the divers what a consistant well organised group locally and nationally can achieve. The fishing groups should heed the lesson . The Divers got the Adelaide sunk north of Sydney - Total cost multi multi millions you wouldn't believe and all this from a group of unlicensed, non fee paying unregulated people yet fee paying fishermen are pushing crap uphill all the time and their $ is spent on ramps, studies etc that help them access and restrict their sites from fishing . What a screwed up world we live in.

I see science friends constantly begging for grants and no long term funding unless they tow the political line in their fields of science and it makes me sick that true science , research and inovation is stuffed by people trying to pickwinners before the hard work is done. Current gov't narrow mind and short term budget objectives has stuffed research for years going forward. Clever country - my arse!

More money to independent science thoroughly peer reviewed and public so we can trust the results would be a better start than political knee jerk reactions.

[deepfried]

Thanks for the post. I think it reinforces what most knew already.

So when can we start dropping jigs again at some of the areas that have been closed. I am sick of reading old reports from Broughton Is spots that are now closed.