The ghost of fishers past

The folks you see out on their boats on the bay are not the only ones fishing; those who came before them still get a slice of the action, as this recent article about the retrieval of "ghost gear" from the Chesapeake Bay illustrates.  In many trap-based fishing industries, like lobsters and crabs, a significant number of traps are lost during the course of regular fishing efforts.  In addition, when a fishery turns bad, as happened in the Long Island Sound lobster fishery in 1999, some fishers cut their losses, and their marker floats, quit the fishery and just leave their gear where it is on the bottom of the bay.

The problem is, ghost gear like this keeps on fishing, long after the fisher has moved on to other endeavours.  The design of the trap continues to attract animals, even without bait, because the trap is basically a refuge or cave.  Those that enter are unable to leave and as they die they may act as bait to attract yet more animals to feed on their body.  In this way, the trap becomes a sort of "biomass black hole", sucking in animals from all around, for as long as the trap holds together.  Nets can ghost fish too, especially gillnets or any kind of trawl that can trap fish or strangle a reef

We used to trawl up ghost lobster gear all the time when I was working in Long Island Sound.  Indeed, few days on the water went by without snagging someone's old gear at some point, which speaks to the density of gear that's out there in some inshore waters.  I'm glad the fishers and the resource management agencies are working together to address the problem, because its one of those awful chronic out-of-sight, out-of-mind issues that can erode a fishery despite everyone's best efforts to manage things properly.  If you find ghost gear, call your local DEP or DEC, even the EPA, and let them know so they can come and retrieve it.

Picture of ghost gear on a coral reef from NOAA

Fish as filters?

There's been a bit of press lately (see for example) surrounding a new paper from VIMS that concludes that the Atlantic menhaden or Bunker (Brevoortia tyrannus) is not very good at cleaning the Chesapeake Bay.  This seems an odd sort of paper but its actually not that crazy an idea.  Its turns out that lots of bivalve species like hard clams and soft clams actually pump enough water through their gills, sifting food as they go, that they can actually have a significant impact on the water clarity and nutrient content of the water.  Indeed, the zebra and quagga mussels that have invaded the Great Lakes have changed the entire ecosystem by doing exactly that.  With clearer water, there's less plankton productivity in the water column and more macrophytic plants and algae growing on the bottom.  Menhaden are filter feeders too, and they can occur in large schools, so perhaps its logical to think that they might be able to do the same sort of thing as the clams.  Alas, based on the VIMS experiments, it seems that they can't.

This is an interesting example of a negative result publication.  Often times you'll hear folks say we shouldn't publish negative results because, technically, you failed to prove that they clean the water, which is not the same as proving that they don't.  Well, as long as everybody is aware of that distinction, I still think negative results like that are useful to know, for two reasons.  One, its likely that they don't; if they do, then the effect is so minor that it was difficult to detect.  And two, it might save someone else from having the same idea and trying the same futile experiment.

The Chesapeake has some sporadic problems with hypoxia, which is ultimately a nutrient pollution issue, so I applaud the researchers for looking at a biological solution for what is otherwise a pretty intractable problem.