Monday, January 19, 2009
The cracked bay scallop shell indicates crab predation.
Over-fishing is a relatively hot topic these days. One group of fishes that are particularly threatened are sharks - because they are large, long lived, and have relatively few offspring. Here an excerpt from a recent article online:
"GENEVA – More than a quarter of sharks in the northeast Atlantic Ocean face extinction with some species already wiped out in certain areas due to over-fishing, a conservation group said on Monday.
Twenty-six percent of sharks, rays and chimaeras are threatened with extinction and another 20 percent are in the 'near threatened' category, the Switzerland-based International Union for the Conservation of Nature (IUCN) said in a statement."
This has the potential to be devastating to bay scallops. With the loss of sharks, which are large apex predators, their prey is released from a predation pressure. This, in turn, allows populations of shark prey to expand - these include smaller sharks, skates, and rays, which are typically benthic feeders which eat shellfish. One species in particular has increased to such numbers, the cownose ray, that it has devastated the bay scallop fishery in North Carolina. This has been documented by scientists for the past 8 years, and recently made Science magazine in 2007. Luckily, we don't have the large feeding aggregations of cownose rays here in New York, and as far as I can tell, we haven't seen large increases in skates, at least not in areas where we have bay scallop populations.
Although it is possible that we are seeing other trophic cascade-type effects, some of which I plan to investigate in my thesis research. I don't want to get into too many details until I know if I am doing this for sure, but its possible that loss of some local fishes has released crabs from predation pressure, allowing them to forage more freely on their prey, juvenile bay scallops included. By the way, I am working on my proposal right now and it is killing me! Can't wait until it is all over!
Thursday, January 15, 2009
Most bay scallops live less than 2 years, and so a concentric growth ring is usually only laid down once. Typically seed scallops reach a size threshold, 35-55mm by the end of their first growing season. However, some scallops are less than 20mm when the growth ring is set. These could be the product of fall spawns, and there is some thought that these scallops don't spawn before they are large enough for their first harvest, that is, they are likely to live into and spawn in a 2nd year. Some populations consist of more than 50% of these "nub" scallops. This has been a particular problem in places like Nantucket, where large portions of scallops have small growth rings. In order to harvest a bay scallop, it must have a clear growth ring, however, "nub" scallops have such small rings, they often appear as ringless adults. This has drastically shrunk the harvest of scallops in this area. That is, until this year, when an emergency regulation was passed to save the harvest. The legislation stated that now scallops could be harvested if they were greater than 2.5 inches in shell height OR if they had a 10mm growth ring - this means that ringless adults (nub scallops) can be harvested if they are greater than 2.5 inches. I don't know if I agree about this legislation, mostly because very little is known about nub scallops and their potential importance for spawning in the 2nd year. I did think it was interesting that bay scallops have been in the news recently.
The photos were taken by Steve Tettelbach and borrowed from a poster presented at last year's 100th annual National Shellfish Association meeting.
Monday, January 12, 2009
I can't believe it has been so long since I last posted. I had a busier than anticipated end of the season. I was still diving the week before christmas, and luckily the season ended then, because on my last dive day, the neck seal on my drysuit broke. It was weird, usually the seal might crack or tear, but when I was suiting up, a chunk came off the neck, almost like a cookie cutter was used. But anyway, that was the last day, and it should hopefully be fixed before the season starts again in March-April. Otherwise, we planted ~200,000 scallops at a couple sites this year. We tried 2 new sites because we had a macroalgae overgrowth problem last winter, which led to anoxia at the sediment surface and likely decimated our scallop plantings there (>90% loss). This time of year is slow, but I am still very busy. I am working on a new draft of my last manuscript, hoping to address all the issues brought up by the previous reviewers. I am also trying to put together my PhD dissertation committee and write my proposal. Ideally, I will finish writing and defend my proposal before May, this way I can make adjustments for the next field season. So we shall see. Right now all I have is an outline, but at least thats a start. I am also trying to finish processing my samples from the summer, but still have over 100 scallops left to go. That doesn't seem like much, true, but I can only do about 30 scallops at a time - there is limited space in our drying oven - and I have to wait 2 days to finish the processing, so it takes some time. I am also going to make more grass mats for this summer, so that should start to consume my time as well. To top it off, I am registered for 2 classes in the spring, so I can honestly admit I have a full schedule in the spring. But its not too bad, and I am looking forward to taking the next step toward attaining my PhD.