Bangley, C. W.  2012.  Food and feeding habits of the spiny dogfish Squalus acanthias overwintering off the coast of North Carolina and the effects on the marine community.  Master’s Thesis.  East Carolina University, Greenville, NC.

Rather than summarize all the findings and dive into the nitty-gritty of the procedures (which you can get by actually reading the document), I’ll be giving the “behind the thesis” tour of this big paper I spent two and a half years writing.  With any luck, it’ll be somewhat entertaining.  It will also serve as a sort of retrospective before I start ramping up the blog to cover my dissertation work this summer.

The NOAA R/V Henry B. Bigelow, my home for over three weeks in March 2010.

Introduction – The dirty little secret of this introduction is that it’s about 90 % the same paper I wrote up as my thesis proposal.  I finished writing it in early 2010 and defended it about a week before heading up to my old stomping grounds of Rhode Island to catch the NOAA R/V Henry B. Bigelow.  The drive from Greenville, NC to Newport, RI is 12 hours with perfect traffic and leeway for speeding, and it was after 9 p.m. by the time I got up there.  Unfortunately, the Bigelow was docked at the Newport naval base and I would need to clearance to get aboard.  The office I’d need to go through was closed until the next morning, and my name wasn’t on the list left with the gate guard.  After some tense moments during which I was afraid I was about to get shot or hauled off by the Military Police before I could even set foot on the boat, I was told to come back in the morning.  Fortunately, I still have some friends in Newport and was able to secure a couch for the night.

The details of the cruise, where I got about half of my data (the other half graciously collected by Dr. Rulifson and Coley Hughes aboard the R/V Cape Hatteras), can be found in the series of posts beginning with this one.  In short, I spent an entire day more seasick than I’ve ever been, saw marine life I’d only dreamed of seeing as a kid, made over 160 dogfish vomit up their latest meals, and grew the most disappointing field work beard ever (though my beard-growing speed has increased rapidly since then.  Maybe this trip let my facial hair know it’s okay to occasionally grow out).  Definitely a great experience.

In the end, some of the proposed methods outlined in the Introduction worked out, while others proved way too ambitious.  Not bad for a project that only squeaked approval in just before jumping aboard the boat.

I sympathized with this dogfish both during my seasickness and while trying to get this chapter published.

Chapter 1: Nonlethal Puking -  One of my goals for this thesis work was to experiment with a nonlethal technique of collecting stomach contents from dogfish-sized sharks.  This particular technique, called “stomach tube lavage,” involves shoving a tube down the shark’s throat, flushing it with water, and letting everything tumble out.  Highly unpleasant for the shark, but it has to beat getting killed and cut open right?

Dogfish are an ideal subject for this sort of thing because a.) they’re numerous enough to be readily available, b.) they’re almost ridiculously hardy, and c.) they’ve been used as a “model” shark for testing different sampling and lab methods that can then be adapted to other species.  Overall, I felt pretty good about myself for trying it out, figuring that even if the only successful publication I’d get out of this thesis was how to nonlethally sample stomach contents, then at least I’d save a few sharks.  So in a prime example of “breaking eggs to make an omelet,” I humanely sacrificed some of the tubed sharks to see how much food was successfully removed.

This chapter went over well at my thesis defense, but upon trying to get it published it became clear that there were a couple glaring errors that ensured that no, this chapter would never be published on its own.  The efficiency was good but not great during sampling, but I hypothesized that the larger dogfish needed one more tube size up to retrieve the optimum amount of puke.  The reviewers read this in the first draft and said, “okay, go try the next tube size up.”  I got some extra lavages in while helping out with field work off of Cape Cod, and using the next tube size up found that it was very possible to get the entire contents of the stomach out using tube lavage.  “Awesome,” I thought, and sent out a revision.  The reviewers then asked if I’d recorded the number of flushes and the individual handling time for each shark, things that any rational thinking human being should be recording for this kind of paper.  Well, I blew that part.  I tried to write my way around it by estimating the individual handling time using the time between tows on the Bigelow and dividing it by the number of sharks lavaged, but the reviewers saw through my b.s. and rightfully rejected the paper.  Peer review works.

One of the reviewers made a comment after the first draft that the results of this chapter would be best served by folding them into a larger paper on the rest of the thesis.  Turns out if I’d listened to reviewer #3 in the first place, I’d have saved myself almost a year of bouncing revisions back and forth.  So that’s the strategy I’ll be taking to get my lavage efficiency estimates out.  I bear the reviewers and journal no ill will and hope to submit something more deserving to them in the future.  In the meantime, I’m still pretty proud of how well I got this method to work, so feel free to cite the thesis if you need an example of nonlethal methods, and know that it’s the product of lot of hard work, if not quite enough data to make its own paper.

Obligatory dogfish predation picture. Photo by Andy Murch (elasmodiver.com).

Chapter 2: Boys and Girls – This thesis quickly became a tale of two data sets.  The data collected aboard the Cape Hatteras was comprised almost entirely of large adult dogfish, which tend to have the most impressive stomach contents, but I wanted to try and break the sharks down into demographics to see if there were any shifts in diet with size or sex.  This chapter used data from the Bigelow only, since that cruise covered a variety of depths and shark sizes.  Unfortunately, there weren’t as many dogfish sampled in this survey so I had to really stretch to make some of the connections.  Ultimately, I had a lot of cool results in this chapter from some unfortunately-sized sample sizes.  As cool as it was that I was able to tentatively identify the size range at which my dogfish switched from krill to fish, there just weren’t many samples on the smaller side of that cut-off.

Breaking the diet up by sex was a lot more conclusive, and produced some nice pieces of data that I hope to get out somewhere.  The sex-diet-habitat connection I was able to make is, as far as I’ve been able to tell, the first time anyone’s tried to make that connection for dogfish.  The results impressed one of my labmates enough that he’s planning to cite my thesis in a paper he wants to get published.  If someone else gets published referencing my unpublished data, that makes me a published author, right?  Maybe my thesis will become a citation classic.

One of my favorite examples of dogfish-inflicted carnage. Photo by Ben Bangley.

Chapter 3: Nom Nom Nom – This chapter was really the point of the entire thesis, which was to document and try to quantify just how many of our favorite fish end up in the jaws of spiny dogfish.  The Bigelow data proved to be hodgepodge of whatever was available as prey, but the Cape Hatteras data suggested something rather interesting going on with dogfish feeding in February.  Atlantic menhaden (the most important fish in sea due to being eaten by just about everything) dominated the dogfish diet in the Cape Hatteras samples.  This may be important because menhaden have been in decline due to overfishing and habitat degradation, so there is a lot of interest among fisheries managers in finding out what the level of natural mortality is for these fish.  Again, everything eats them, so that’s tough to quantify, but I was at least able to get a decent estimate for the dogfish part of the equation.  Also interesting, dogfish apparently use their impressive teeth to chop up not just large fish being scavenged out of nets, but also large fish that they’re actively pursuing.  Maybe there is something to dogfish being part piranha…

One stumbling block for finding out how much dogfish eat is that the current estimate for spiny dogfish daily ration is based on the population in the North Pacific, which in 2010 was recognized as a separate species and has always been noted for being larger and slower growing than our Atlantic dogfish.  This has created a need for someone to figure out how fast Atlantic dogfish digest their prey, which in turn tells us how much food they need and how much fish they can eat.  Don’t worry guys, I’m on it.  More info on that in my next post.

They're so cute when they're killing. Photo by Andy Murch (elasmodiver.com).

Chapter 4: Two Predators – In North Carolina fisheries management, very few people get by without having to deal with striped bass.  Sometimes it’s tough to tell that there are any other fish in the sea at all.  I had hoped to find evidence of predation on some larger fish while I was going through my shark puke, but imagine my glee when, of all fish, stripers started showing up in dismembered chunks.  Granted I didn’t find many, but I’m not the only person to find stripers in the bellies of these ferocious little sharks: they show up in dogfish guts in both the NEAMAP and ChesMMAP surveys, and you can look up the data yourself on VIMS’ website if you don’t believe me.

Using the same technique from Chapter 3, I estimated the quite low level of predation on striped bass.  I wanted to explore this relationship further because, as largeish fish-eating predators, these two species are very evenly-matched ecologically.  I looked at dietary and spatial overlap, and even delved into a little predator/prey interaction theory in attempting to explain how dogs and stripers might get along in the wild.  Interestingly, menhaden are a very important shared prey item, suggesting that the stability of dogfish/striped bass interactions might depend on a readily available supply of those tasty little fish.

Writing this chapter was a blast and I’m looking at tweaking it, adding some more data, and publishing it (I’ve also been speaking about it at ECU, Tidewater, and later this summer at the AES meeting in Vancouver).  This chapter also got me really into predator/prey theory, which is a research interest I’d like to stick with (and has definitely influenced the content of this blog).

The Future – So that wraps up my Master’s thesis retrospective.  My dissertation work will likely be taking me beyond spiny dogfish, but I’m sure they will play a big role (along with their smooth cousins).  I also have a dogfish-specific project or two coming down the pipeline.  My next post will detail some of the projects I’ll be working on in the next year.  Expect the blog to take on a bit more of a “project log” format this summer, though there will definitely still be room for profiles of other people’s research and fishery management issues.  It’s been a wild ride for the first part of my grad school experience.  Thanks for reading and commenting, and remember to never underestimate the little guys.

In the meantime, I’ll leave this up as an open thread for those who would like to share their best shark stories.  Leave your most awesome, humorous, bizarre, gnarly, or interesting shark encounters in the comments.  All species welcome.

Check the date of this posting.

This has all been made possible by a sudden and seemingly unrealistic increase in dogfish biomass in the late 2000s.  One interesting theory for how this may have happened was presented at the AFS Southern Division Meeting (unfortunately, I couldn’t make it this year) by Ryan Knotek (check out the podcast of his talk).  Basically, not all spiny dogfish are breeding at the same time, which may have staggered the reproductive output of the species and helped mitigate the effects of overfishing.  It’s one of many shark talks (and other worthwhile fisheries science talks) available on SDAFS’ podcast page.

Taylor et al. (2012) documented four confirmed attacks, three of them fatal, on Northern right whale calves by white sharks along the U.S. east coast.  These potential whale killers are members of my favorite white shark population.  It should be noted that none of these attacks were directly observed (the ocean is a big place, even for animals as large as great whites and right whales) and had to be inferred using rather clever means.  For other large, mobile, mammalian prey, predation rate by sharks is estimated by the appearance of bite scars on the individuals that got away (this method had been used to estimate the risk of shark attacks on dolphins).  Sharks, especially great whites, have very distinctive bites.  The stereotypical half-moon shape seen on plenty of surfboards during Shark Week specials are also found on young whales, and are easily distinguished from orca bites, which look more like rows of straight lines (from the orca’ teeth raking across the whale’s flesh… gruesome).  At least four right whale calves have been found with those “surfboard bites” on their flanks and tails.

The smoking gun. White shark bites on a whale calf that survived the attack. From Taylor et al. (2012).

Bites on live whale are obvious proof that sharks are willing to attack young right whales while they’re still alive.  Granted, an attack on a vulnerable, inexperienced calf is not quite as badass as an attack on a fully-grown adult, but considering that right whales are born around the average size at maturity for great whites (10-15 feet), these sharks are making solo attacks on prey that is the same size as them or possibly larger.  Never let it be said that white sharks are cowards.

Only one case study analyzed by Taylor et al. (2012) involved a still-living whale.  On a whale found dead, it can be tricky distinguishing the fatal bites made while the whale was alive from the bites of the army of sharks and other creatures scavenging the carcass.  In one case, a necropsy revealed no other trauma or possible causes of death other than a deep shark bite on the tail that severed a major artery.  The other two cases involved a combination of entanglement in fishing gear and shark attack, but at least a few of the bites on these unfortunate whales occurred before they were dead.  But how did the researchers tell which bites occurred before death?

The answer lies in a method that would make Al proud.  Like many large marine creatures, right whales are absolutely crawling with parasites.  One in particular, the orange cyamid (a species of whale louse), colonizes wounds very quickly.  The amount of louse coverage can give an estimation of when the wound occurred.  In the three fatal cases at least a few of the shark bites had louse coverage that suggests the bites occurred while the whale was still kicking.  This is an awesomely gross and effective method, analogous to the use of maggots to estimate time of death on land.

So aside from the overwhelming badassery of sharks attacking large whales, there are some rather serious implications of the findings of this paper.  The most obvious is that North Atlantic right whales are among the most critically endangered marine species on earth.  Whaling hit this species hard, and in the early-mid 20th century the population may have been below 100 individuals.  The right whale population has shown evidence of recovery in the last few years, with a record 39 calves born in 2008-2009 (yes, this species is so endangered that almost 40 births is a huge deal).  Two of the four cases analyzed by Taylor et al. (2012) occurred during this period, meaning that at least 5% of the right whale calf population was subject to shark attacks.  This may seem like a bad thing, but sharks and other predators tend to preferentially attack prey that is abundant.  An increase in shark attacks on whale calves is actually a good sign, since it means there are now enough calves being born to represent a worthwhile food source for their predators.

Why right whales?  Right whales were named by whalers for being the “right” whale to hunt due to their behavior: they tend to stay on the surface, move slowly, and float when dead.  Behavior also makes right whale calves the “right” whale for sharks to hunt: unlike other whales such as humpbacks that travel in large pods, mother and calf right whales travel in pairs, meaning there is only one angry adult for a shark to get past to get to the calf.  The authors theorize that most shark attacks on whales occur at or shortly after birth, when the calf is most vulnerable and inexperienced and the mother is somewhat incapacitated by, well, giving birth.  Never let it be said that white sharks are dumb.

This paper is hot off the presses (as far as I know, this blog might be the first coverage it’s gotten) but it presents evidence of a predatory relationship with huge implications for both whale and shark conservation.  That said, this paper, unlike other papers on shark predation, doesn’t pretend to cover more ground than it does.  It doesn’t need to.  Here we have evidence that Carcharodon carcharias may still have a little bit of Carcharodon megalodon in it.

Taylor, J., Mandelman, J., McLellan, W., Moore, M., Skomal, G., Rotstein, D., & Kraus, S. (2012). Shark predation on North Atlantic right whales (Eubalaena glacialis) in the southeastern United States calving ground Marine Mammal Science DOI: 10.1111/j.1748-7692.2011.00542.x

In case you haven’t been following, filmmaker and ocean enthusiast (seriously, have you seen The Abyss?) James Cameron has made it to the Challenger Deep, also known as the bottom of the Marianas Trench, also known as the deepest point of the ocean on the planet.  Congrats to James and the entire Deep Sea Challenge team.  I can’t wait to see the footage and photos of what they see down there (first tangible evidence of Cthulhu?).

A maximum-size mako clocks in at about 12-15 feet, which is pretty impressive in general fish terms, but isn’t quite up to the 18-21 feet documented for the big, dangerous sharks like whites and tigers.  A 10-foot mako would be considered rather large for the species, and an average-sized adult is probably somewhere between 6-8 feet.  However, makos are not well-known for their size, but their speed and agility.  The maximum speed attained by a charging mako has yet to be reliably recorded, with potential bursts of up to 46 mph.  This makes it certainly the fastest shark, and possibly the third-fastest fish in the ocean, behind only the sailfish and bluefin tuna.  In fact, other large, fast pelagic fish make up a decent chunk of the mako’s diet, especially when they can be picked off after being hooked.  Makos are probably a fisherman’s favorite shark to have on the end of a line, both because the meat tastes like swordfish but better and because they put up spectacular fights, leaping in the air and occasionally turning around to attack the boat.  This is one shark that really lives up to its reputation.

Anything dolphins can do sharks can do better. Except maybe breathe air. Image from newenglandsharks.com.

If a predator can be judged by its prey, then makos are among the elites in the shark world.  Stillwell and Kohler (1982) identified blue sharks, swordfish, large tuna, and sea mammal remains among the stomach contents of mako sharks along the U.S. east coast, but the diet was dominated by bluefish (Pomatomus saltatrix).  Bluefish are among the most voracious predators in Atlantic coastal waters, attacking in large schools and chopping up menhaden and herring nearly as large as themselves.  According to Stillwell and Kohler (1982), the Atlantic mako population consumes about 14.5 % of the entire bluefish stock per year.  Bluefish remained extremely important to the mako diet when it was updated by Wood et al. (2009).  Using updated estimates of the metabolic needs of these warm-bodied sharks, Wood et al. (2009) found that an average-sized mako needs to consume about 4.5 % of its body weight per day.  This leads to an annual consumption of 500 kg (1,102 lbs for the non-metrically inclined) of bluefish per shark.  The importance of bluefish in the diet has remained constant despite fluctuations in bluefish abundance, suggesting that makos in the Atlantic seem to have a particular affinity for these vicious prey.

In the Pacific, makos may be an important regulator of the infamous Humboldt squid (Doscidicus gigas).  Humboldt squid are the third-largest cephalopod on the planet and occur in much greater numbers much closer to shore than either giant or colossal squid.  They’ve also recently shown significant increases in population and expansions in range.  In the past few years, Humboldt squid have occurred as far north as Alaska, where they may pose a threat to valuable Pacific salmon stocks.  It’s thought that a combination of climate change and declining predator populations have lead to this explosion of squid.  Fortunately, the Pacific mako population is on it.

Like sperm whales, shortfin makos show scars from battles with large squid. From Vetter et al. (2008).

Vetter et al. (2008) used data from just about every research technique available to study interactions between the mako and Humboldt squid populations in the California current.  These included gut content analysis, identification of squid scars on makos, archival satellite tagging to compare the horizontal and vertical movements of both predators, and even plankton surveys to check patterns of recruitment for shared fish prey.

They found that Humboldt squid make up about a third of the mako diet, and that there is some dietary overlap between the two.  The sharks they tracked made a few dives into the Oxygen Minimum Zone (OMZ), where Humboldt squid lurk when they’re not hunting, but didn’t stick around for very long.  Since something as large and fast as a mako needs a lot of oxygen, the OMZ probably presents a refuge area for Humboldt squid.  Vetter et al. (2008) suggested that most mako/squid interactions probably happen when the Humboldts rise out of the OMZ to feed.  Perhaps most badass of all, Pacific makos are frequently covered in battle scars from the last moments of those tasty squid, which means the titanic battles between sperm whales and giant squid have a smaller, faster counterpart.

In conclusion, makos are voracious predators of voracious predators.  The only chink on the mako’s badassery is that they’re occasionally preyed upon by orcas, which you could read as “it takes an orca to take down a mako.”  When the cephalopds finally invade land and depose humanity, it will be because they were trying to escape from the sharks.

References

Stillwell, C. E., & Kohler, N. E. (1982). Food, Feeding Habits, and Estimates of Daily Ration of the Shortfn Mako (Isurus oxyrinchus) in the Northwest Atlantic Canadian Journal of Fisheries and Aquatic Science, 39, 407-414

Vetter, R., Kohin, S., Preti, A., McClatchie, S., & Dewar, H. (2008). PREDATORY INTERACTIONS AND NICHE OVERLAP BETWEEN MAKO SHARK, ISURUS OXYRINCHUS, AND JUMBO SQUID, DOSIDICUS GIGAS, IN THE CALIFORNIA CURRENT California Cooperative Oceanic Fisheries Investigations Reports, 49, 142-156

Wood, A. D., Wetherbee, B. M., Juanes, F., Kohler, N. E., & Wilga, C. (2009). Recalculated diet and daily ration of the shortfin mako (Isurus oxyrinchus), with a focus on quantifying predation on bluefish (Pomatomus saltatrix) in the northwest Atlantic Ocean Fishery Bulletin, 107, 76-88

One of the biggest issues in fisheries management is discarded catch.  Discards are frustrating for fishermen and managers alike because they represent fish that were likely wasted after being caught in the gear.  Most discards result from regulations (think size limits, prohibited species, etc.), but some are perfectly marketable fish that have to be tossed because they’ve been partially eaten.  Gillnets are especially problematic for scavenging because the captured fish are immobile in the net until they’re brought up by the fishermen, and present an irresistible target for scavengers (just look at what happened to some fish we caught when the hagfish got to them).  Dogfish and seals also present unique issues if they get caught in the process of scavenging: dogfish have an amazing ability to totally wrap themselves up in the net, and accidentally drowning a seal can get a fisherman in a boatload of trouble.

Rafferty et al. (2012) don’t really address the capture issue with scavenging dogfish and seals, and instead focus on the direct impact of the actual scavenging.  With plenty of other nibblers out there aside from dogfish and harbor seals, it’s important to be able to separate which scavenger is at fault.  Fortunately, both spiny dogfish and harbor seals have very distinctive bites.

The signature bite patterns of a.) harbor seals and b.) spiny dogfish. From Rafferty et al. (2012).

Seals tend to like to tear out the juicy bits of their fish prey, taking out the innards (especially the liver) and often leaving the rest of the fish behind.  Dogfish, on the other hand, are there for the delicious fishmeat, and leave clean bites in the fillet areas (or skeletonize the fish altogether).  Either way, a fisherman won’t be able to sell fish that damaged.

Once it was possible to identify how much damage to could be attributed to which scavenger, it was a simple matter for Rafferty et al. (2012) to put a monetary value to it.  In their sampling period they found that dogfish accounted for 1.98% of the catch and seal munched 0.40%, for a total of 2.38% of the catch discarded due to scavenging damage.  The total catch observed by Rafferty et al. (2012) during their sampling period was worth $61,800, and they estimated that dogfish and seals ate $2,250 worth of it.  The paper concludes that at the current market price for haddock (at the time of the study), scavenging by these to animals would cost fishermen 3.64% of the market value of their catch.  This may not seem like much, but Rafferty et al. (2012) do note that the populations of both scavengers are continuing to increase, so this represents a baseline estimate.

While dogfish and seal scavenging is certainly annoying to deal with (and Rafferty et al. (2012) never even touch on the joys of removing these animals from the net) it seems to pale in comparison to other issues facing fishermen when it comes to making a decent buck.  That said, every little bit helps.  The paper recommends shorter soak times to allow scavengers less time to get at the catch, but this may carry its own pitfalls as longer soak times usually mean a bigger catch (even if not all of it is in the best shape).  Shorter soak times do carry the benefit of a lower mortality rate for the scavengers.  Ultimately, both dogfish and seals have been hunting and scavenging fish for far longer than humans have even been around, so it’s up to us to adapt to them.

RAFFERTY, A., BRAZER, E., & REINA, R. (2012). Depredation by harbor seal and spiny dogfish in a Georges Bank gillnet fishery Fisheries Management and Ecology DOI: 10.1111/j.1365-2400.2011.00837.x

The NC Maritime Museum, the venue for this year's Tidewater.

Last weekend I attended the 26th Annual Meeting of the Tidewater Chapter of the American Fisheries Society, better known as AFS Tidewater or just plain Tidewater.  To recap, this conference encompasses fisheries academics, students, and managers from the so-called “tidewater region,” which is made up of the states of Delaware, Maryland, Virginia, and North Carolina.  This chapter emphasizes marine and estuarine topics, which can be a welcome change from the larger, more freshwater-dominated meetings.  This year the conference was in Beaufort, NC, which is well-covered by marine and fisheries research, with the NC State, UNC, and Duke marine labs, the main office of the NC Division of Marine Fisheries, and a good-sized NOAA lab all nearby.  Beaufort is also rich in ocean-related history, and the venue (The NC Maritime Museum) reflected this well.  As it turned out, the spring weather (mostly) broke out the day before the conference, making it a perfect time to be in Beaufort.  So how’d it go this year?

The ECU contingent typically rolls deep at Tidewater, and this year was no different, with ten students from the various fisheries biology labs presenting either posters or talks.  The whole shebang was also run by a recent ECU alumni, Jacob Boyd.  Other schools that regularly bring a crowd include NC State, VIMS, and the Maryland Chesapeake Bay Laboratory (CBL).  The local DMF and NOAA labs usually present some pretty interesting stuff as well.  Here’s a rundown of the stuff that I personally found interesting, and if I missed something worth mentioning feel free to recap it in the comments.

Poster Session

ECU had a few posters up.  Christina Booth recapped the findings of the Fisheries Techniques class in their assessment of whether some small ponds at one of ECU’s rec centers could support fishing.  Turns out they’d need a lot more shelter to keep the fish safe long enough to reach catchable size.  Coley Hughes and Jeff Dobbs showed their progress in different aspects of a large project using otolith microchemistry to figure out where striped bass were born and have been migrating.  Joey Powers identified habitat preferences in juvenile red drum and spotted seatrout, finding that detritus bottoms make better nurseries for red drum while submerged aquatic vegetation (think seagrass) is preferable for seatrout.

Other cool posters: Sam Binion (ECU alum, now at NC State) worked some stats magic to try and develop a method for predicting fish communities based on environmental factors.  Travis Richards (Florida State) looked at stable isotopes in spotted seatrout from different areas of an estuary, and found that the underlying water can influence isotope values enough to throw off the diet signature.  He stressed the importance of getting baseline values from the study area, which is something that some of the more isotope-crazy researchers working on highly migratory species (isotopes have really blown up in the shark world) should be worried about.

Talks – Day 1

The first day of talks included all of the student presentations.  Again, I’m just going to briefly describe the main points of those that I paid special attention to.

Andre Buchheister (VIMS) kicked things off with an overview of the fish community within Chesapeake Bay over time.  It looks like there’s been a major shift since 2007, with less croaker (formerly the highest biomass of any species in the bay) and more biomass of various elasmobranchs (particularly cownose rays, but the mighty spiny dogfish were in there too).

Andrea Dell’Apa (ECU) showed evidence for a shift in male-female ratio of spiny dogfish schools off of Cape Cod that seems to be based on time of day.  He suggested that fishermen can selectively target the less at-risk males by fishing early in the morning. 

Dan Zapf (ECU, whose blog The Endolymph came back from the dead this week – check it out for all your herring, otolith, and hockey needs) identified the Chowan River as the potential best nursery habitat for blueback herring, and showed through otolith chemistry that the fish will move between rivers to find optimum habitat.  Mike O’Brien (CBL) continued the nursery habitat theme by showing that juvenile fish in Maryland coastal bays are more affected by seasonal differences than their position in the bay with respect to the inlet.

River herring took the place of striped bass as the dominant species for the ECU talks.  Matt Butler found that three creeks in the Chowan River seem to produce the most herring larvae, and are characterized by high Chlorophyll a (a sign of primary production from algae), alkalinity, and relatively little human influence.  Annie Dowling compared these trends in juvenile abundance and found evidence for the first stages of a possible recovery of river herring populations in the Chowan River.

Molly Taylor (Florida State) looked at patterns of spot feeding habits within a Florida estuary.  She found that seasonality and river flow are important, and that freshwater insects make up a decent amount of the diet for spot in the upper regions of the bay.  Chelsie Wagner (Florida State) also looked at trophic dynamics, this time for large predators (sharks, dolphins, rays) in relation to the Gulf of Mexico hypoxic zone using aerial surveys (pretty badass study if you ask me).  None of the predators or fish schools showed any predictable patterns in relation to the hypoxic zone, but this may have had to do with the fact that it’s largely confined to bottom water.  Cownose rays did hang out at the margins, and it was theorized that they may be dive-bombing benthic critters trying to escape from the zone.

I should give a specie mention to Danielle Zaveta (CBL) for being a good sport as I embarrassed myself spectacularly before her talk.  The fire alarm had gone off during Annie’s presentation, throwing the timing of the talks off and leading me to think it was my turn when actually it was hers.  This played out in front of the entire audience as I went to take the podium while everyone in the ECU crowd screamed that it wasn’t my turn.  Fortunately she was cool about it and gave a great talk on finding the appropriate models for blue crab stock assessments.

The next couple talks (separated by lunch break, appropriately enough) involved fish eating other fish.  For my talk, I focused on the interactions between spiny dogfish and striped bass off of North Carolina, where they chase the same prey and occasionally stripers end up in dogfish stomachs.  This allowed me to quote Mitch Hedberg during my talk.  In conclusion: stripers likely don’t have much to fear from dogfish unless both predators run out of other prey.  Nicole Mehaffie (CBL) followed up her quality talk from Seattle by expanding on the role of anadromous species (fish that run up rivers to spawn) in the diets of ocean-going predators.  For dogfish, cod, and monkfish, anadromous prey are relatively unimportant on a large scale but become very important near the actual river mouths.  Delicious.

Garry Wright (ECU) attempted to develop a model for just how many dogfish are actually present based on the catch in a gillnet.  Using an enclosed net containing a known number of dogfish (that I tried to help him set up last winter with nearly disastrous results), he found that a gillnet set will account for about 7.7 % of the dogfish in the general area.  He also used vertical gillnets to show that dogfish can be present anywhere in the water column, so bottom trawl surveys may not be getting the whole picture.

Friday concluded with a dinner social and afterparty at the awesome Backstreet Pub (a favorite haunt of ocean bloggers, salty fishermen, and wayward boaters) featuring the alt-country (good music, not the garbage you heard on country stations) musical stylings of Tobacco Roses.

Talks – Day 2

The second and final day of talks was made up entirely by professionals in fisheries fields, mainly from state and federal agencies.

James Morris (ECU alum, currently at NOAA) has become the invasive species guru in the Carolinas, and talked about a new (potentially tasty) invader, the Asian tiger shrimp.  These critters can grow up to a foot long, eat smaller fish and shrimp, and have been showing up in large numbers in shrimp trawls since last year.  They’re popular in aquaculture, and the invasive population growing off the southeast U.S. likely originates from shrimp farm escapees.  If you get one, do your part and eat it, then tell me what it tastes like.

Todd Kellison (NOAA) showed disturbing evidence that degradation of coral reef habitat is causing fish to show less site fidelity towards specific reefs.  This is true across all trophic guilds, from the top predators to the little herbivores, suggesting that it affects the entire reef fish community.

Julianne Harris (NC State) tagged striped bass with acoustic transmitters at spawning grounds in the Roanoke River and used receivers in the river and ocean to determine not only where the fish went, but how long they were resident in the river and even how they behaved after catch and release.  At least once a tag stopped moving from a site entirely and turned out to have been eaten by a turtle.  I’m looking at using acoustic telemetry in some way and this talk really illustrated the diversity of things you can find out from it.

And that wraps up my epic recap of Tidewater 2012.  Hope to see everyone next year in Maryland.