Understanding Coastal Ecosystems Room 201D
Jan 25, 2023 01:40 PM - 02:40 PM(America/Chicago)
20230125T1340 20230125T1440 America/Chicago Understanding Coastal Ecosystems Room 201D 2023 Bays and Bayous Symposium mbnep@mobilebaynep.com
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Marine Connectivity in the Mississippi Bight: Whose Larval Fish and Crabs Are They?
01:55 PM - 02:10 PM (America/Chicago) 2023/01/25 19:55:00 UTC - 2023/01/25 20:10:00 UTC
Fishery management requires an understanding of the variables that influence year-class strength, particularly those responsible for the year-to-year fluctuations in larval recruitment. This is especially difficult for species whose life history includes a lengthy planktonic larval duration that allows for wide dispersal through transport mechanisms set by seasonal meteorological and oceanographic conditions. Recruitment success is determined by these basin-scale hydrological processes that respond to variations in climatic wind stress patterns during larval development at sea. The emerging science of marine connectivity addresses the questions of timing of spawn, duration of larval stage, distance of travel, mechanics of transport and the eventual settlement on juvenile nursery grounds. Studies of red Snapper (Lutjanus campechanus) on the continental shelf and crossing the deep basin will be discussed as illustration. But because of its complexity, determining connectivity within the Mississippi Bight in the north central Gulf of Mexico has been uncertain especially in the western portion of the Bight involving the Mississippi Sound. In shallow waters, neither the present operational models nor drifter observations are sufficient to describe transport from Coastal Boundary waters to nursery grounds in the Sound. Blue Crab (Callinectes sapidus) and Atlantic Tarpon (Megalops atlanticus) are used to illustrate gaps in our understanding of nearshore transport. The authors have access to extensive biological databases and are testing inexpensive surface drifters that can be used to track nearshore currents. We are hopeful of attracting a regional interest in improving operational models for use in shallow water marine connectivity.


Presenters
DJ
Donald Johnson
GCRL, USM
Co-Authors
HP
Harriet Perry
University Of Southern Mississippi, Center For Fisheries Research And Development
JF
Jim Franks
University Of Southern Mississippi, Gulf Coast Research Lab's Fisheries Center
Responses of Juvenile Spotted Seatrout Cynoscion nebulosus to Experimental Acute and Chronic Low Salinity Exposure
02:10 PM - 02:25 PM (America/Chicago) 2023/01/25 20:10:00 UTC - 2023/01/25 20:25:00 UTC
Spotted seatrout are a highly important fishery species. Alabama's stock is declining, and a recent stock assessment identified factors regulating juvenile survival as critical for future recruitment success. State monitoring data suggests juvenile habitat may be limited by salinity. To evaluate the tolerance of juvenile trout, we exposed hatchery-reared juveniles (35-60 mm TL) to acute and chronic low salinities. For acute exposure, we acclimated individuals to 10 or 20 ppt salinity before reducing salinity at a rate of ca. 1.5 ppt/hr to reach ≤1 ppt in 6 (10 ppt tanks) to 13 hours (20 ppt tanks). Fish in all tanks exhibited reduced feeding rates, most likely due to disturbance from the manual water changes during salinity reduction, while none showed signs of stress related to salinity treatment. For the chronic experiment, fish were acclimated to 10 ppt before half the tanks were reduced to near 0 ppt over a 2-day period, and monitored over the next 8 days. Fish at 10 ppt continued feeding vigorously throughout the experiment, and none lost equilibrium. Fish in near 0 salinity declined in feeding rates from day 4 onwards, and 54% of individuals lost of equilibrium between day 8 and 11. Our findings show that post-settlement trout can survive brief periods of low salinity exposure, but probably cannot tolerate it for more than a few days. Future changes in salinity regimes in coastal Alabama may alter the amount of suitable juvenile habitat, with subsequent impacts to the population.
Presenters
RB
Ronald Baker
University Of South Alabama, Dauphin Island Sea Lab
Co-Authors Jonathan Chapman
Dauphin Island Sea Lab
Dietary Evidence of Facultative Cleaning by Juvenile Leatherjackets from Coastal Alabama
02:25 PM - 02:40 PM (America/Chicago) 2023/01/25 20:25:00 UTC - 2023/01/25 20:40:00 UTC
Carangidae is a family of carnivorous fish that, at maturity, primarily feeds on fish and mobile invertebrates. Juvenile Leatherjackets (Carangidae, Oligoplites saurus), feed on a variety of prey items, such as mysids, shrimp, and fish, and also consume fish skin, scales, and ectoparasites. There is conflicting evidence in the literature as to if these juveniles are incidentally consuming ectoparasites, or if they are in fact engaging in facultative cleaning behavior, specifically targeting these parasites. To determine if O. saurus are targeting scales or ectoparasites as a food source, the gut content of 130 juvenile leatherjackets, 21 - 100 mm TL, opportunistically collected throughout coastal Alabama were analyzed. 109 individuals had some food in the stomachs, and of these, scales were the most abundant food type, occurring in the stomachs of 66 individuals (61 %). Ectoparasites, the second most abundant prey item, were found in 52 stomachs (48 %). The high occurrence of ectoparasites relative to scales suggests that this species is actively targeting these parasites. Although cleaning behaviors are well studied on coral reefs, little is known about their potential importance in fish communities in turbid coastal environments. Monitoring the diets of these common fish could potentially provide an indicator of the parasite load and general health of coastal fish communities. 
Presenters
KH
Kelsey Hofheinz
Dauphin Island Sea Lab
Co-Authors Alex Rodriguez
Dauphin Island Sea Lab
RB
Ronald Baker
University Of South Alabama, Dauphin Island Sea Lab
University of Southern Mississippi
University of South Alabama, Dauphin Island Sea Lab
Dauphin Island Sea Lab
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