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American lobster on ocean bottom American lobster (Homarus americanus) spotted during the recent lobster habitat survey of Alvin Canyon using NEFSC's HabCam. Photo credit: NOAA Fisheries/NEFSC
HabCam on ship deck HabCam on deck May 26, 2016, after recovery from the ocean floor. Photo credit: NOAA Fisheries/Robert Johnston
map showing Alvin Canyon location Google Earth view of Alvin Canyon, showing lobster habitat survey transects.

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June 20, 2017
Contact: Heather Soulen

Diving Deep in Search of Juvenile Lobster Habitat

Burton Shank is a research fishery biologist on the Invertebrate Task Team in NEFSC's Population Dynamics Branch. In honor of Massachusetts Lobster Day, he answered a few questions about the NEFSC's lobster surveys.

When and where was your recent lobster habitat survey?

It was May 29th through the 30th and we ended up working at the head of Alvin Canyon (see map). We did a habitat survey from 125 meters down to 275 meters. We used the HabCam vehicle that was designed with the capacity to work at these sorts of depths. We use it primarily for the Scallop Survey which means we usually work down to 100 meters and maybe as deep as 125 meters, but not deeper than that because that’s where the scallops stop. Most of the other work that’s along the lines of habitat surveys is done with something like the ROPOS that’s out on the Bigelow right now. They don’t work shallower than 550 meters to 600 meters so there’s this gap in the middle between 125 meters and 600 meters where nobody’s surveying which is actually an awful lot of habitat.

Why did you conduct the lobster habitat survey?

This survey was originally funded by the Office of Sustainable Fisheries. They had a short RFP (request for proposals) out for those who had small projects that could improve stock assessments. The question was whether or not there is habitat out there that juvenile lobsters can potentially settle into, grow up on and be independent of what’s going on in the inshore areas where we’re losing lobster habitat primarily due to increasing water temperatures. A lot of the inshore areas in southern New England are reaching the physiological limits that lobsters can tolerate. Over the last 30 years or so, you can see a lot of the inshore lobster fishery has declined, moving south to north. You saw the inshore fishery off of New Jersey go down first, then Long Island sound went down, then Rhode Island and then Massachusetts has been going down. So you can see this wave moving from the south to north through the inshore habitat where it seems a lot of the lobster productivity has been dropping off.

What kind of data were you collecting and what will the data be used for?

With the HabCam vehicle we have downward facing stereo cameras taking pictures of the bottom of the ocean. Coupled with that, we have a 3D side-scan sonar on the vehicle which is collecting an acoustic swath about 100 meters wide, 50 meters on either side of the vehicle which allows us to render a three dimensional image of what the bottom topography looks like. On top of this, we’re using a multi-beam sonar on the research vessel to map a much wider swath of habitat. That’s where most of the area coverage comes from. At the end of the day, you take the imagery and the side-scan and match that up with the multi-beam to get a sense for what the larger-scale habitat map looks like. And finally, we’ve got the oceanographic sensors on the vehicle collecting temperature, salinity, oxygen, dissolved organic carbon, particulate matter (sediment in the water) and chlorophyll. These are useful for this survey because we know the thermal (temperature) tolerance of juvenile lobster and if we can get a high resolution map of both the bottom thermal habitat and the physical habitat for juvenile lobster, it becomes really useful for identifying appropriate habitats for juvenile lobster settlement.

To hear about how HabCam's images and side-scan sonar work together to tell scientists what the habitat is like, listen to this audio clip:

What did you find?

We didn’t know what we were going to see when we headed into this area. Down to 275 meters, it was essentially all soft bottom. We saw very little hard bottom, but as we started to get closer to where the canyon really starts to slope off into the deeper water, we started passing individual patches of cobble or individual boulders. So what is shallower than 275 meters is going to be soft bottom habitat of one sort or another, fairly soft sediment, some clay formations, that sort of thing. There was a lot of temperature variation down in the canyon, which was surprising. It was a little bit warmer than I expected it to be, warmer than a lot of the areas up on the bank in the shallower areas. This may be largely driven by current patterns and upwelling events going on out there. We found that half of the canyon is already at 12ºC at the end of May, warm enough for juvenile lobsters to settle. We were concerned that the water in the canyons may only be warm enough for settlement for a short part of the year and not match up with when larvae are settling. However, if it is 12ºC now, there may be a larger settlement window than we originally thought.

To hear what kinds of temperatures Shank was expecting based off of conversations with other scientists, listen to this audio clip:

Why is this information/data important?

Within the context of lobsters and the lobster habitat question, it sort of becomes a question of whether you treat the offshore lobster fishery differently than the inshore fishery if they essentially have different sources of larvae that are recruiting into the fishery. It’s an interesting question because you certainly have adult lobsters that are moving back and forth between the inshore and offshore areas, so you’ve got this exchange of adults, but you potentially have these separate sources of larvae for the two areas. And if we are getting recruitment of larvae into these deeper habitats, the larvae are potentially coming from other canyons on Georges Bank which means they’re coming from outside of the stock. This is important because right now we treat southern New England as a single stock, but are inshore and offshore areas actually functioning ecologically as different stocks? And if they are, how are they connected? These are all open systems so there’s exchange to some degree. When the inshore populations were healthy, the offshore populations may have been largely subsidized by adult lobsters that settled inshore and then migrated offshore. The question now is have offshore habitats changed from a dependency on adult lobsters migrating from inshore areas to being more dependent juvenile settlement from other offshore areas where we see lobster populations increasing. This is largely conjecture right now, but a question we’re pursuing with this and other research.

To hear what kinds of bottom substrate juvenile lobsters prefer, listen to this audio clip:

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