.
In essence, it comes to the conclusion that Reef Shark populations in populated areas in the Pacific have plummeted by 90%, as reported e.g.
here,
here,
here and
here. Apparently, Julia Baum asserts that the decline is
principally due to fishing and incidental bycatch.
Probably true - and yet, I am not totally convinced.
Now mind you, I am not a sufficiently trained researcher and may have missed some of the finer points in the paper - but then again, I was intrigued by
this really interesting post by
Para_Sight who points out that the causal connection may not be quite so direct, and I cite.
A binary relationship between the abundance of sharks and that of people is effectively saying that they are mutually exclusive: people = no sharks, no people = sharks. That’s a pretty disappointing thought. Of course it doesn’t tell us the mechanism, or even if the relationship is causal in any way, but I don’t think it’s a huge leap to suggest that human impacts on reef diversity and function in general, especially overfishing, are likely to put a pretty negative pressure on reef shark populations. If this proves true then it may not be that humans are doing anything to the sharks per se, just not looking after the reef generally, and that is being reflected at the top trophic level.
However you slice it, their results are more grist to the mill that we need to be doing a better job with the conservation of both reefs and sharks, because sometimes those two things are inextricably intertwined.I could not agree more!
If we want to preserve a species we must preserve its habitat,
#5, and this not only including the reefs but all of the hot spots like seasonal aggregation sites and above all, the nurseries!
But that's not where I want to go with this.
Let me elaborate.
1. Propensity to approach Divers and Boats.
Intuitively, I feel that the 90% number may be too high, and this due to the chosen survey method, i.e.
"towed-dive surveys" where paired SCUBA divers record shark sightings while being towed behind a small boat.
From the paper.
During each survey, a diver being towed behind a small boat recorded the identity and size of all fishes larger than 50 cm total length (nose to longest caudal fin lobe) encountered in a 10-mwide belt (Richards et al. 2011). To ensure surveys represented a near-instantaneous snapshot, divers counted only individual fish in a 10 × 10 m area in front of them and were careful not to record the same fish more than once.All observers were experienced scientific divers with extensive training in fish identification. Divers were towed for 50 minutes on each survey at approximately 45 m/min, which is much faster than the swimming speed of divers conducting belt transects (typically 8 m/min).We used a global-positioning-system unit on the tow boat to calculate transect lengths. Average tow length was 2.2 km. Surveys followed fixed isobaths (generally 15–20 m depths) and were positioned evenly around an island, with the aim of covering most of the circumference of each island at the targeted isobaths (tows around small islands were closer to each other than those around large islands).We analyzed only the towed-diver surveys that were conducted on forereefs (seaward slope of a reef) between 2004 and 2010 (n = 1607).Very compelling - and yet...
Check this out.
This is
Bikini Atoll in 2003.
I hear that the Sharks have alas been fished away, but here is a
report from 2000, and I cite.
After a few hours of casting along the reef, we approached a quarter-mile wide channel separating two idyllic tropical islands festooned with palm trees. The crew was smiling as Maddison said, "Watch this."Within minutes an armada of shadows appeared, heading our way. The dark shapes turned out to be hundreds of gray reef sharks, which began swimming around the boat, their aggressive mood indicated by arched body postures. The scary part was that we hadn't put any chum in the water!Totally
déjà vu!Having been around for a while and done quite a bit of exploration several decades ago, I distinctly remember witnessing this behavior whenever we did visit remote and pristine locations. We would get to the reef with the dinghy and within minutes, the Sharks (often Grey Reefs that are 71% of the Sharks counted in the surveys discussed in the paper) would be rushing to the craft.
Moreover, once in the water, the Sharks would actively approach the divers, sometimes in a quite assertive way. However as time went by and those dive sites would become more popular and thus more crowded, I remember witnessing a gradual retreating of the Sharks.
As an example, when I first dived Cocos in the early 80ies, Chatham Bay was full of Hammerheads all the way to the surf line, and the seaward side of Cascara and Pajara would always yield a lot of Hammers, Silvertips and Marbled Rays that would easily approach the divers. Now, those high traffic areas feature very few Sharks that appear to have retreated to the more remote locations like Dirty Rock, Shark Fin and Alcyone where they are also generally much more skittish.
And what about the small boats?
Reason would have it that in their majority, small boats around populated islands would be engaged in fishing.
In fact, the paper states
We assumed human population was a reasonable measure of human effects in this region because most of the surveyed populated islands (including all population centers) have been settled for centuries, have broadly comparable levels of fisheries development (including widespread use of motorized boats and modern fishing gear) and reef fisheries with a mix of recreational, subsistence, and commercial fishing activities.Reason would also have it that those Sharks who would have most readily approached those boats would have been the first to get killed either as proper catch or in retribution for being a nuisance like what has apparently happened in the GBR - whereas more timid Sharks would have had a higher chance of surviving and thus passing on their propensity to avoid boats to the next generation.
Could it be that over the many years, this would have led to more boat-wary Sharks in populated areas due to the selective extirpation of the bolder gene pool?
Long story short?
- Maybe when sampling remote islands, the small boat towing the observers did attract Sharks (in the case of the Grey Reefs, possibly even out from the passes where they usually reside and to the forereefs that were being monitored), thus leading to a positive bias when establishing the baseline count.
- Maybe when sampling inhabited islands, the boat noise did repel Sharks and thus lead to a negative bias.
The consequence of the above would lead to a double observation bias and result in an exaggerated rate of decline and confirm my purely intuitive
caveat.Yes at this stage, this is highly speculative.
But is this plausible and if so, would it be worth testing, and how?
2. Human Effect - only negative?Reefs surveyed by towed divers 2004–2010 in the Pacific Ocean (triangles, survey reefs; white stars, large human population centers; PRIA, Pacific Remote Island Areas).This is the area that has been surveyed.
I'm sure that the observations are generally accurate, albeit maybe biased as per the above - and yet, they may not be the whole story.
Take French Polynesia.
It features highly populated islands where Shark populations are however healthy. My interpretation is that there is a vibrant Shark tourism industry that has provided for an economic incentive for
not fishing for Sharks, this even before the current Shark protection measures. Also, due to the tests in
Mururoa and Fangataufa, the archipelago has been heavily patrolled which has likely kept potential poachers at bay,
And here's another personal observation.
In 2002, I organized a 13-month exploratory
diving expedition throughout Micronesia and Melanesia aboard a large roving liveaboard vessel.
Here is the itinerary, click for detail.
In essence, we started in Bali and then did Kupang, Irian Jaya, Palau, Yap, Chuuk then down to New Ireland, over to Manus and Wewak, back to New Britain, then Bougainville all the way past Ghizo to Honiara, then back to Milne Bay.
Always in search of the most pristine environments and of Sharks, we did target the most remote and least populated locations between the principal islands where we would stop to re-supply. Especially in the Micronesian atolls, we specifically dove the likely hotspots, i.e. the reef passes where we would attract scores of Grey Reef and Silvertip Sharks with the
infamous bottle. When close to the principal islands, we would co-operate with chosen local dive operators and visit their flagship dive sites, like e.g. Blue Corner in Palau.
Our findings were completely counter-intuitive.
To my great dismay, the most remote and least populated reefs had been completely fished out. Several of the Micronesian atolls featured wrecks of long liners and those reefs were covered in fishing gear, mainly long lines and ghost nets. Conversely, moderately populated islands had no Sharks right in front of the villages but plenty just a short distance away, and many of the principal islands did feature surprisingly healthy stocks.
My interpretation is that there is no such thing as
"remote and pristine" anymore.
The fishing fleets have the resources, the technology and the willingness to go looking for Fish anywhere, and will wreak utter havoc when and where nobody is watching.
Conversely, especially Melanesia has a strong tradition of reef tenure where the traditional owners will vigorously, and often violently defend their fishing grounds against any intrusion.
Finally, like in French Polynesia, many of the principal island have well established Shark viewing tourism operations.
For me, this was a seminal observation.
Ever since that voyage I'm of the conviction that the only way to conserve biodiversity is to abandon the utopian vision of there being anything "natural" left. Instead, we must recognize that our influence extends to everywhere and that instead of bemoaning a past that will never come back, we must concentrate on
managing what is left. Check out the
current definition of wilderness & you will discover that this has now very much become a relative concept and a managed space.
But I'm digressing as usual.
The paper says this about protection.
We did not include protection level in our analyses because the region’s large marine protected areas were established only recently (e.g., 2006 in the northwestern Hawaiian Islands) and because protected areas cover only small percentages of the total coastline in populated areas (e.g., 5% around the main Hawaiian Islands). There is also some evidence that only areas that are strictly off limits to humans effectively protect reef sharks (Robbins et al. 2006). Moreover, in the larger, more isolated protected areas (e.g., northwestern Hawaiian Islands), remoteness rather than formal protection is probably the main factor limiting fishing because enforcement is generally light.Maybe the above is just too narrow.
From my personal observations, there are other mechanisms that may well confer a substantive degree of protection and where the presence of humans is more of a positive than not.
But those are just nuances - the general gist of the paper is certainly correct.
Anyway, just a bit of food for thought.
Bon appétit!PS more evidence for Reef Shark population declines
here!