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The Decline of Seagrass Meadows

Zostera! Eelgrass, Zostera marina, is a flowering, marine vascular plant that remains submerged all the time. This is quite a feat for vascular flowering plants, and only a few dozen species world wide are capable of growing completely submerged in a marine environment. Eelgrass creates and extremely important habitat, its upright structures and complex root system create a 3-D living space for many different types of animals. It is (or was) the dominant habitat forming SAV (submerged aquatic vegetation) throughout much of the coastal waters in the northeastern United States. Unfortunately, for various reasons, eelgrass meadows have seen drastic declines, and in many locations eelgrass only exists in a mosaic of small patches. This is extremely bad news as many of the important, and formerly important, commercial and recreational fisheries of the northeast US are dependent on Zostera at some part of their life cycle as a nursery and foraging ground. Some of the species are finfish like tautog, bluefish, fluke, winter flounder, porgies, while others are shellfish such as blue mussels, hard clams, oysters, bay scallops, and blue crabs. Many of the aforementioned species support or once supported vibrant fisheries. Many of those fisheries have collapsed, also for various reasons. However, is it possible there is a link between the crash of the fisheries, the decline of Zostera and the failure for recovery on both ends?

Bay Scallop on Eelgrass

Argopecten on Zostera! Bay Scallops, Argopecten irradians , have developed a very close relationship with eelgrass, Zostera marina. As larvae, they are passively transported, and tend to settle in eelgrass meadows when the current is dampened by the 3D structure of the seagrass. This same 3D structure provides post-set juvenile scallops a spatial refuge from predation. Even as larger juveniles and adults, scallops are capable of, and have been shown to, actively select eelgrass habitats.

Other species also use eelgrass

grass shrimp A number of other species utilize eelgrass as a habitat. Included are grass shrimp, like the Palaemonetes pugio, other decapods such as blue crabs, bivalves such as hard clams, gastropods (snails), and numerous fish species, including winter flounder, tautog and cod.

Lionfish Increasing in the Keys? Derby nets same number with less effort

Well, since all I have been doing all week is field prep, I don’t yet have pretty (or interesting pictures) nor have I had much time to dive into the literature.  But I did notice that lionfish were in the news again, as the 2011′s first Lionfish Derby in the Florida Keys happened this week.  Those who follow Chronicles know that I have blogged about lionfish quite a bit.  Last fall I did a post about lionfish derbies in Florida.  More recently, I did a fairly popular post about invasive lionfish, and had a celebrity post by a labmate of mine who does sponge research in Jamaica and is now an avid lionfish hunter. Heck, I even posted about lionfish on my first blogsite !

So this shouldn’t come as any surprise that I am doing yet another lionfish post.  By this point you know the story.  They are a Pacific reef predator that has been introduced to the Atlantic. They can now be found in great numbers throughout Caribbean and Florida reefs, but can also be found as far up the east coast of the US as Long Island!  There are many potential problems of having this novel reef predator on already impacted reefs in the Atlantic, so its a situation people have been monitoring for quite some time.  And their ever increasing numbers have led to attempts at eradication.

2011 will be no different.  The first of three Florida Keys lionfish derbies was held earlier this week.  Considerable cash and other prizes were offered to teams with the highest catch, and both the largest and smallest fish.  Over 500 specimens were hunted and killed.  That’s the good news.  The bad news? It only required 10 teams of between 2-4 people showed up to catch the 531 lionfish.  Last year, the same derby had 27 teams catch 534 fish.  While one could argue that this year’s teams were more skilled lionfish finders, it is also likely that this is an indication of more lionfish.  A catch per unit effort type thing.

Fisheries researchers often use catch per unit effort – CPUE – because sampling effort may vary from one time to another, or from one place to another, and so CPUE standardizes the individuals caught to the effort exerted. Not knowing anything about the actual number of total participants, if we use “teams” as the effort, this year’s CPUE was 53.1, over two and a half times more than last year’s CPUE of 19.8.  So what does that mean? Now I am not a fisheries biologist by any means, and so I might be giving a totally oversimplified explanation, or I might be wrong altogether (and hope someone corrects me), but while CPUE is not a direct measure of fish population abundance, it is an oft-used proxy.  The increase in CPUE this year from last year likely indicates an increase in population.

CPUE is itself problematic because it is typically fisheries-dependent data.  Its value as an estimate of abundance varies with the catchability of the particular fish species surveyed and the efficiency of the gear being used.  A major assumption of CPUE as a proxy for abundance is that the relationship between catch and abundance is linear, ie, the more fish, the higher the CPUE (you can learn more about estimates of abundance from this UNCW lecture)  This is the assumption I am making with the lionfish population in the Florida Keys based on my simple, back of the envelope calculations.  Again, there are problems using fisheries CPUE since it is often not proportional to abundance – fishers become more efficient over time and don’t fish randomly.  But for the sake of this argument, it is probably safe to say that lionfish populations in the Florida Keys are on the rise.  Stay tuned for more after the final 2 derbies.

Check back as I am sure I will make edits when more fisheries minded people read and comment.

EDIT: A follower sent me this video of a new tool being used to capture lionfish which may be more efficient than a typical spear gun.  Plus I like the soundtrack.

Edit 2: A new blog has jumped into the fray of lionfish blogging, with this post of a very good video on the subject.  The blog is SeaMonster – started by Jon Bruno and Emmett Duffy.  It is really good, so you should definitely check it out. 

2 comments to Lionfish Increasing in the Keys? Derby nets same number with less effort

  • I’m certainly not a fisheries biologist, but having followed this story for a few years I think you’ll probably need some more data before drawing conclusions about the population. The fishing techniques for lionfish are evolving rapidly. Five years ago, nobody was hunting these things. Now it’s an organized sport complete with specialized products, training manuals, and PR campaigns.

    For example, consider this gadget. I haven’t tried it, but it looks like it would be much more efficient than a standard spear gun, and it apparently comes with a catch bag that’s designed specifically for this sharp-spined quarry.

    In any case, thanks for keeping up the great coverage. I’m hoping to get back to diving soon, and lionfish hunting is high on my list of new things to try underwater.

    • Alan,
      Thanks for the comment. I realize that my understanding is rough and my interpretation is probably lacking. I just found it very interesting that less than half the number of teams caught the same amount of fish, and tried to equate that to something I learned in fisheries biology, oh, probably 10 years ago now. Obviously there are lots of assumptions, but the idea behind it was that effort seemed to decrease while catch remained the same. Obviously, if the gear is that much better, that might explain it.

      I haven’t had the pleasure of shooting a lionfish yet, but I hope to get to the Caribbean this winter to give it a whirl.

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