Fall 2015 – GoMRI Researcher Interview with Dr. Debra Murie

Dr. Debra Murie. Photo provided by Dr Murie.

Dr. Debra Murie. Photo provided by Dr Murie.

(From Summer 2015 Newsletter) Dr. Debra Murie from the University of Florida answered a few questions about her RFP- II project, Spatial and Temporal Effects of the Deepwater Horizon Oil Spill on Growth and Productivity of Recreational and Commercial Fisheries in the Gulf of Mexico.

The PIs on the project, in addition to Dr. Murie, are Dr. Daryl Parkyn and Dr. Robert Ahrens.

1. Thank you so much for talking with us! Tell us a bit about your What are the goals of your project?

Our overall goal is to model the potential spatial and temporal effects of the Deepwater Horizon oil spill and associated events (i.e., dispersants) on the growth and productivity of representative recreationally and commercially important fish species in the Gulf of Mexico. Representative fish species associated with estuarine (spotted seatrout, red drum, mullet, sheepshead), reef (red snapper), sand/mud (flounder), and pelagic habitats (king mackerel, greater amberjack) within and outside of the areas directly impacted by the Deepwater Horizon oil spill have been targeted for these analyses (Louisiana versus the west coast of Florida, respectively). Changes in growth and productivity of these fishes will be estimated by measuring the annual growth patterns captured in their ear stones (otoliths), which work as natural chronometers just like tree rings. The potential impact of the Deepwater Horizon oil spill at a fisheries production level is being modeled using stock assessments that take into account the potential changes in the growth of these fishes at specific ages. At an ecosystem level, we are using a time-series analysis of the annual growth increments from older red drum and red snapper, a process known as sclerochronology, in combination with ARIMA models in an intervention/impact analysis.

2. What is your background and how did you get involved in this kind of work?

My background is in fisheries ecology and I am an Associate Professor in the Program of Fisheries and Aquatic Sciences in the School of Forest Resources and Conservation at the University of Florida. I have been involved in marine ecology since my earlier years as an undergraduate, studying anything from sponges to grey whales, and the underwater world continues to fascinate me to this day. I am particularly interested in sustainable resource use, including recreational and commercial fisheries and conservation of threatened and endangered fish species.

3. What are some of the most significant or exciting findings so far in your work?

We are still processing and measuring otoliths for most of the target species because our study depends on a time series ranging from 2005 to 2015 for the growth analysis, and the ability to measure previous annual increments in the otoliths lags by about 1 year. However, we have focused on spotted seatrout and red drum because these species use the estuaries extensively, especially when young. We have measured and aged over 20,000 individual fish to date. For seatrout, our model species, we have not observed any decrease in growth of fish that are 1 to 4 years of age before and after the oil spill. In fact, there appears to have been a marginal increase in the growth rate of spotted seatrout, although we still need to add one more year of data to our analysis. We think the increase in growth may be due to the release of the fish from density-dependent growth that could have occurred due to the mortality of various fishes observed immediately following the oil spill (i.e., reduced density of fish, so more food available to the remaining fish). Our analysis is continuing on with all of our target species.

4. You mention using sclerochronology in performing your time-series analysis, which ranges from 2005-2015, pre- and post-spill. Can you talk more about how this process works and how you are using it in your study? Are you able to “see” growth patterns in otoliths from before the spill, even if the samples were collected after the spill, using this technique?

For sclerochronology, we are actually using a much older time series for the fish, for example the red drum we are using range in age from 12 to 37 years. We are measuring the growth increment for each year of the fish’s life and then we “assign” each increment to a specific calendar year based on going backwards from the year of capture of the fish. When you have dozens of these older fish with their growth increments associated with specific calendar years, then you can see whether 2010 was associated with a smaller than average growth increment. This is also allowing us to examine, for example, if Hurricane Katrina in 2005 (or other major environmental events) impacted the growth of the fish more or less than the Deepwater Horizon oil spill.

5. Is there are particular species and/or habitat from your target species that may have been impacted more than the others?

We predicted that estuarine environments would be the most susceptible because the oil was physically present in those environments to a large degree. Based on that, we also predicted that seatrout, in particular, would be impacted through significant loss in what it usually feeds on, which is shrimp and other fishes mostly. Seatrout are also known through tagging studies to stay very close to their “home” estuary and seagrass beds, so their growth can be specific to an estuary. To date, we haven’t seen this decrease in growth rate. From some of our other complementary studies, however, we have seen more sublethal effects in red snapper fecundity, or egg production, off the coast of Louisiana. We are currently measuring red snapper otoliths for growth increments, so it will be very interesting if we see any decrease in growth of the fish in the post-spill years.

6. Can you tell us more about your collaborations with your fellow GoMRI researchers and/or state agencies?

Our project absolutely could not have been done without the collaboration of the Louisiana Department of Wildlife and Fisheries and the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute. These agencies have long-term, ongoing monitoring programs for the species that we are studying, and therefore they were able to provide us with a time series of biological information that was necessary for our study. These agencies collect location and fishing information, and a suite of biological information, on individual fish of our target species, including the collection of their otoliths. The greatest deficit in understanding the effects of the Deepwater Horizon oil spill, or any other potential disaster, rests with having data prior to the event for comparison. Based on our experience, it is critical to continue these ongoing monitoring programs in the state and federal agencies in order to assess the potential impacts of any future environmental disasters.

7. If funding were not an issue, what would you add to your project?

More funding and more time are always issues with research because as we go along in the planned research we observe other important avenues that have to be left unexplored. However, if we could add a component to our project then we would have added a study on the inter- relationships among the growth that we are measuring in the otoliths of the fish, the location of these fish within a potential impacted versus non-impacted area, and any changes in their trophic pathways. Fish can only grow by taking in energy through consuming prey, so that connection is very important.

[Back to the Fall 2015 Newsletter]