Shark Bottom Longline Survey
PROJECT LEAD: J. MARCUS DRYMON, PH.D., PRINCIPAL INVESTIGATOR
Background: Declines in shark populations have sparked researchers and fishery managers to investigate more prudent approaches for the conservation of these fishes. As managers strive to improve data collection for stock assessment, fisheries-independent surveys have expanded to include data-deficient areas such as coastal regions. In 2006, we initiated a nearshore, fisheries-independent bottom longline survey in the northern Gulf of Mexico to capture seasonal variation in the distribution and abundance of sharks and other finfish in coastal areas. The goal of this survey is to provide a long-term, robust, fisheries-independent time series of value for stock assessments of multiple regional species.
Objectives: The objectives of the Shark Bottom Longline Survey are to (1) conduct standardized bottom longline surveys in the northern Gulf of Mexico (2) collect abiotic data (temperature, salinity, DO, etc) that can be used as potential predictors of species relative abundance, (3) use the survey platform to apply advanced (acoustic and satellite) tags to investigate movement and migration, and (4) provide samples (vertebrae, gonads, tissues, etc.) in support of ongoing life history studies for these fishes.
The Atlantic Sharpnose Shark, Rhizoprionodon terraenovae
Approach: To facilitate comparisons among other time series, we use the gear and deployment methods introduced by NMFS in 1995. These include 2km of monofilament mainline (4.0mm, or ~950 lb test), fished with100 gangions, the individual fishing units. Each gangion is 4 meters long, and terminates in a 15/0 circle hook baited with Atlantic mackerel (Scomber scombrus). Bottom longlines are soaked for one hour. Most sharks will be tagged and released, while a subset will be retained for ongoing studies.
Results to Date: The primary objective of this survey is to provide time series data that is useful for stock assessment. To that end, data from this survey have been used in the stock assessments (SEDAR assessments) for Blacknose (2010), Blacktip (2012) and Atlantic Sharpnose (2013) (Figure 1) sharks. Further, these data have been used in publications describing the across shelf distribution of coastal sharks in the northern Gulf of Mexico (Drymon et al. 2010), the trophic role of the Atlantic Sharpnose Shark (Drymon et al. 2012), the stock structure of Red Drum (Powers et al. 2012), and the factors affecting the distribution of coastal sharks at different scales (Drymon et al. 2013).
Funding Sources: NOAA SEAMAP, NOAA MARFIN, ALMRD, DISL, and NFWF Wildlife and Sportfish Restoration Fund.
Acoustic and Satellite Telemetry to Track Movements of Alabama’s State Saltwater Fish
Background: The recent collapse of many estuarine and marine fisheries has been widely recognized and is particularly acute for fishes that are long lived, slow growing, and reach sexual maturity at a late age. Several of these fishes have life histories that include ontogenetic movements across estuarine habitats and knowing how much area an individual uses during their residency in a marine habitat is vital to understanding the life history of a species; however, shifts in habitat with ontogeny can make evaluating habitat utilization and seasonal distribution difficult to assess. Atlantic tarpon are a highly migratory and highly prized sport fish throughout the Gulf of Mexico (GOM). Tarpon make seasonal and regional migrations along the GOM as part of their complex life history and exemplify the life history characteristics that exacerbate population declines. Given the paucity of information on tarpon ecology, there is a clear need to investigate and understand movement patterns and habitat use of this large fish.
Objectives: The objective of this study is to apply advanced telemetry to adult tarpon in Mobile Bay and the surrounding coastal waters of Alabama to investigate fine-scale (acoustic telemetry) and large-scale (satellite telemetry) movement patterns.
Approach: Telemetry is a valuable tool used to collect data from mobile marine organisms. Acoustic telemetry allows for fine-scale movement patterns to be assessed when a tagged fish is within range of an acoustic receiver array while satellite telemetry (specifically, pop-off archival transmitting (PAT) tags) allows for large-scale movement patterns to be assessed. Both acoustic and PAT tags were applied to tarpon in this study to track their movements around the coastal waters of Alabama.
Results to Date: Three satellite and PAT tags were successfully deployed on adult tarpon in the summer of 2014. We received data from the satellite tags and preliminary data show tarpon movements along the coastal waters of Orange Beach, AL where they then move into Mobile Bay, AL before making long-distance movements offshore towards Louisiana!
Funding Sources: This project is funded through the Mississippi-Alabama Sea Grant Consortium with additional funding from the Coastal Conservation Association of Alabama and from NFWF Wildlife and Sport Fish Restoration.
Coastal Alabama Acoustic Monitoring Program
There is an array of 40 listening stations with hydrophones strategically placed around Mobile Bay and Mississippi Sound.
“The hydrophones were placed around the bay to cover the entry and exit points of fish, and in this instance, we’re talking about a red drum or speckled trout,” Dr. Sean Powers explained. “We have all the rivers covered in the (Mobile/Tensaw) Delta. We have a string of them along the Causeway, at Fowl River and Dog River. We also have them in Mississippi Sound.
The hydrophones are designed to pick up acoustic signals with unique codes that identify individual fish. The acoustic tag sends a series of sound pulses in a few seconds. The hydrophone interprets that signal and identifies the fish. If it was a fish from Alabama, the identification of the fish gives researchers data on where the fish was tagged and where it was located when the signal was picked up at different times. If the hydrophone identifies an unknown code, the other states involved in the program are notified.
Each fish in the study is caught by researchers or other anglers and the small tag is attached.
In the News: Surgery on a paddleboard: Fish scientist investigates why some fish roam