Sharks and Global Norming in North Carolina

On January 1, 2016, the Southern Fried Science central server began uploading blog posts apparently circa 2041. Due to a related corruption of the contemporary database, we are, at this time, unable to remove these Field Notes from the Future or prevent the uploading of additional posts. Please enjoy this glimpse into the ocean future while we attempt to rectify the situation.

I’ve been posting very sporadically due to spending the past month or so compiling all the data from the Marine Species Distribution Survey’s Cape Lookout leg.  This was an exciting part of the survey for me because it brought me back to the waters I worked in while earning my PhD, so it a lot of ways it was like coming home.  I happily took the lead on the apex predator portion of the survey so that’s mostly what I’ll be recapping first, but future posts will have more details on the trap, core, and genetic surveys.

Of course a lot has changed since then.  For one thing, the ocean was two meters shallower, though parts of Beaufort and Morehead City used to flood at high tide even back in 2015.  The biggest change may be the collapse and migration of many of North Carolina’s barrier islands, especially after Hurricane Monty rolled through ten years ago.  In my mind I still picture Cape Lookout, now an island sitting by itself southeast of the Down East Banks, as part of a chain of barrier islands that once outlined all the North Carolina sounds.  Core and Shackleford Banks are still on the map, but as shallow subsurface shoals that have a nasty habit of grounding whatever daring (or foolish) freighters still land cargo in Morehead City.  They do draw in a lot of fish though, and still act as a sort of sill that allows Back and Core Sounds to function pretty much as shallow lagoons.  If rumors of coral growth on some of the banks are true, it’s possible that the shoals could become fixed in place again.

As with many coastal communities, evacuation and adaptation have left their mark on the Cape Lookout region.  The bottom is littered with the remnants of whatever anthropogenic structures weren’t moved or lifted in time to escape the inevitable march of the tide (which also makes navigating in the sound interesting).  Carteret County is also somewhat unique in that many of its residents continued to stay and adapt rather than migrate inland as many other coastal residents did.  These lifted communities (or stiltsvilles, as the locals call them), combined with the sunken remains of the parts of town that didn’t make it, have potentially created a lot of structured habitat.  One of the goals of the Cape Lookout leg of the survey was to determine whether all this new structure was having any affect on marine life, especially those species targeted by fisheries.

So what are sharks doing now that they’ve moved into a lot of place where humans used to live?  To figure that out, we used loop traps to catch, identify, and tag individual sharks with transmitter/accelerometer/camera tags (referred to as TACs).  These tags transmit an ultrasonic signal that gets picked up by roving receiver drones maintained by the Duke and UNC marine labs.  These drones maintain a position close enough to the surface to send live data feeds from up to six tagged animals within detection range to the microsatellite network.  It can get messy and there can be a lot of interference from other transmitters such as navigation buoys and military drones, but we’ve partnered up with the DIT Digital Observatory program to launch another fifty microsats dedicated just to the MSD survey, which should really smooth out our data feeds.  We’re still working out a way to keep the drones themselves, which somewhat resemble sea turtles, from occasionally being attacked by tiger sharks.

The catch data from this past season show that sharks continue to be a presence in North Carolina’s estuarine waters, though again things have changed since the last time I was chasing sharks around here.  The most common sharks continue to be Atlantic sharpnose sharks, though a fair number of my old friends the spiny dogfish migrate inshore during the winter and early spring to take advantage of the big hickory shad spawning runs, and even occasionally show up on cooler-than-average days in the summer if menhaden are running (remember when we thought these were a just a cold water species?).  Only a handful of smooth dogfish were caught, which is unsurprising given the northward shift of their nursery habitat.  Sandbar sharks are present year-round, and preliminary tagging and genetic analysis has pretty much confirmed that these sharks are from the southern population that pups from Chesapeake Bay to Florida, and not the northern population with nurseries from New Jersey to Cape Cod.  The embayments along the Down East Banks have become quite a productive nursery for blacktip sharks, and juveniles have actually become somewhat of a nuisance for the flounder ranchers in the area due to their ability to get into the pens and wreak havoc on the captive fish.

Tiger sharks regularly patrol the ocean side of the shoals and occasionally enter sounds themselves, but it’s the bull shark that is truly the apex predator of the sounds.  These highly adaptable sharks pup in the upper reaches of the Newport River and the patchwork of tidal creeks behind the Down East Shoals provide ample refuge habitat for the juveniles.  The adults rove throughout the system and it would probably make some Atlantic Beach residents nervous to know just how many bull sharks over 2.5 meters in length are hunting directly beneath their houses at night.

However, no shark has taken to the changed landscape of coastal North Carolina better than the scalloped hammerhead.  Schools of these sharks move in and out of the sounds with the tide and juveniles spend their first 2-3 years within the saltier parts of the Newport River.  With so many batoid species in severe decline (hunting cownose rays down to 0.5 % of their original population did not actually seem to “save the bay”), there was some debate over what prey species may be sustaining the rebuilt hammerhead population.  Based on our sonic lavage results, it looks like lionfish, and lots of them.  The hammerheads are eating the occasional sharpnose shark or juvenile blacktip shark as well as several larger bony fishes, but a full 75 % of the 104 hammerheads we lavaged had lionfish in their stomachs.  I guess it makes sense, since hammerheads seem to be fairly unaffected by stingray venom so may also have some capacity for shrugging off lionfish venom as well.  The TAC tags show a high amount of quick turning, burst swimming, head shaking, and other hunting/feeding behavior in the vicinity of structured habitats like the pilings under lifted houses, which are also the areas where the trap surveys have caught the most lionfish.  We also managed to get the holy grail of some actual hammerhead vs. lionfish video and are in the process of analyzing the hunting technique.  Interestingly, the trap and drone surveys have documented more juvenile reef-dwelling species like parrotfish, groupers, and snappers near structures that are visited more often by hammerheads.  Could shark predation on lionfish actually allow some of the other reef species room to settle in structured habitat?

One of the more surprising and encouraging findings from this survey is the presence of juvenile lemon sharks, especially among the tighter and more complex pilings supporting the larger lifted communities.  Lemon sharks have been hit especially hard by the catastrophic loss of mangrove habitats started by human development and continued by rising sea levels.  Ironically, human development may be the salvation of this species if the support structures are providing the same amount of protection as mangrove roots.  The thermal range of neonate lemon sharks has only reached North Carolina within the last decade, so it remains to be seen if this represents new nursery habitat for this endangered species.

As a group, apex predatory sharks seem to be adapting to the changing nearshore environment, though the prospects for colder-water species with ranges rapidly constricting around the poles are pretty grim.  North Carolina has not been spared the ravages of global norming, and many of its formerly iconic species such as spotted seatrout, striped bass, and alewife will likely never return, having been pushed out of the state’s waters either by environmental changes or invasive predators.  Many of the sharks that are now common around Cape Lookout were rare stragglers from the south when I was doing my dissertation work.  One bright spot is that some sharks appear to be adapting to feeding on lionfish.  Aside from scalloped hammerheads, lionfish were found in the stomachs of bull, blacktip, lemon, and even spiny dogfish sharks.  Which is good, because lionfish far outnumber just about every demersal bony fish in the system except pinfish.

It remains to be seen if residual pollutants left behind as coastal communities retreated inland will have any long term population-level effects, though bans on eating meat from sharks over the maximum safe size limit should remain in effect.  Though law now requires residents of lifted and shoreline communities to either recycle or convert 100 % of their waste to energy, there are still countless submerged septic tanks and sewer lines that are either currently leaking into the water or are about to burst.  Though the old waste of relatively low-population areas like Beaufort and Morehead City has been largely flushed out by increased tidal mixing (in fact, Newport and North Rivers reopened to shellfish harvest and culture earlier this year), it may take decades of actively cleaning the submerged portions of large cities to make their waters safe for seafood production.

On January 1, 2016, the Southern Fried Science central server began uploading blog posts apparently circa 2041. Due to a related corruption of the contemporary database, we are, at this time, unable to remove these Field Notes from the Future or prevent the uploading of additional posts. Please enjoy this glimpse into the ocean future while we attempt to rectify the situation.