Equipped with a new 36-foot research vessel and summer weather, scientists at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University-Corpus Christi are getting back to work documenting marine life around artificial reef sites off the Texas Gulf Coast.
Last year, HRI launched a two-year study, funded by the Texas Parks and Wildlife Department, to analyze 15 artificial reef sites off the Texas coast and definitively answer the question of whether these reefs create new, self-sustaining habitat. I reported why that’s an important question, along with details of the study plans, in an earlier post. While boat availability and weather played some havoc with plans for dive and ROV surveys last summer, researchers did get some nice video of abundant fish around the study sites, and collected measurements and tissue samples via longlines.
This summer, says Jennifer Wetz, HRI fisheries project manager, effort will focus on three artificial reef sites – MI-A-7, BA-A-132, and MU-A-85 (see map) – all cut-off platforms 45 to 55 miles offshore. “We hope to regularly visit those sites and do ROV and dive surveys and vertical longline sampling. We’ll also be sampling some natural banks in that same area. That will allow us to look at differences between artificial reefs and natural hard bottom in terms of the biological characteristics of fish – their age, growth, and reproductive potential. We’ll be looking at whether the artificial and natural sites function similarly or are different.” Comparative surveys will also be done at standing platforms in the same area. Most artificial reefs contain platforms that have been cut off 85 feet below the surface, while standing platforms extend the height of the water column from sea bottom to surface, providing continuous structure for habitat.
This work will also answer another question: how do ROV surveys and diver-based surveys differ? “What are we missing doing one versus the other?” Wetz explains. “ROV work produces archived data that we can bring back to the lab to look at what species are there and in what abundance. But do you see more diversity as a diver with more freedom to look around?” While their field of vision is more limited, ROVs can go deeper than human divers, so can potentially survey all the way to the bottom, typically 200 or 250 feet at these sites. One of the drawbacks of ROV surveys, though is the sheer volume of data, which requires a lot of staff time to analyze.
The Texas Parks and Wildlife Department is working on collecting data on species and abundance at all of its reef sites, and HRI’s dive surveys will be conducted using the same protocol TPWD uses: five minutes at the top of the structure (typically 90 to 100 feet deep), noting all species and their abundance, from single to few (2 to 10), many (11 to 100), or abundant (more than 100). That way, the data can be combined with TPWD’s.
Last year, ROV surveys conducted at all the study sites yielded a total of 52 identified fish species. One site alone, BAA 132, had 30 species.
During June, the researchers have been conducted longline sampling at all the study sites. This involves dropping vertical longlines, set with ten hooks of various sizes to target a variety of fish sizes, to the bottom for five minutes. The vast majority of the catch so far, Wetz says, is red snapper, a commercially important species in the Gulf. The stomach contents, reproductive organs, and otoliths of these fish are examined (otoliths, or ear bones, indicate the age of an individual fish).
July and August will be devoted to ROV and dive surveys. The team is meeting this week to work out a dive plan – which sites, which teams, and when – and to update training as needed. Having their own boat makes a huge difference; last year, the researchers sometimes couldn’t get out to sites because charter boats were all booked.
In addition, the team is monitoring a near-shore reef site off Port Aransas in about 70 feet of water (MU775 on the map) prior to reef material being placed there in early fall. Surveys will be conducted shortly after the materials are placed, then on a regular basis, most likely monthly. That will allow comparison of marine life present at the natural site to what is recruited to the reef, something that has not been documented before. Wetz hopes to also do pre- and post-surveys of a standing platform (PN-A-42 on the map), which will be reefed in place, to document how that fish community changes.
I plan to accompany the team into the field in the next couple of weeks. Watch for a report here.
Previously in this series:
Counting Fish: Gulf of Mexico Artificial Reef Survey
Counting Fish: on the artificial reefs
Counting Fish: well, thanks Isaac, no counting fish this week
Counting Fish: Longlines, Lionfish and Liberty Ships