Date of Award

Spring 5-5-2023

Document Type

Thesis

Degree Name

Bachelor of Science (BS)

Department

Marine Science

College

College of Science

First Advisor

Juliana M. Harding

Abstract/Description

Intertidal estuaries are key nursery habitats for juvenile marine fish species. Post-larval spot (Leiostomus xanthurus) enter southeastern estuaries in pulses corresponding to offshore spawning events during the late winter/early spring months as light and temperature are increasing. As they enter the estuaries they develop into juveniles. Juvenile spot have high fidelity for specific intertidal creek pools that provide protection from predators and access to food. Spot annual growth rates have been determined using length-frequency distributions but rarely have cohorts within the same year been analyzed for differences. Spot seasonal trends in standard length (mm), biomass (g dry tissue), and growth rates (mm/day) were quantified in Crabhaul Creek, North Inlet estuary, SC in relation to water temperature during 2021. Spot were collected approximately bi-weekly from January to December 2021 using seines or cast nets. Standard length (mm), total length (mm), and biomass (g dry weight) were measured for at least 20 individuals from each collection. Fish were grouped into 8 categories based on collection water temperature prior to analyses. Standard length demographics (2 mm length bins) were evaluated using FiSAT II to identify cohorts across temperature categories. An ANCOVA was used to determine differences in length-based growth rates between cohorts. Crabhaul Creek water temperature and salinity during 2021 ranged from 6 to 35 oC and from 5 to 37 ppt, respectively. During 2021, spot standard lengths ranged from 19 to 102 mm with corresponding biomass from 0.013 to 3.135 g. For the first cohort the ingress date was January 15th while the assumed spawning date was December 1st . This January cohort was seen in the temperature categories of 10 to 15oC (mean standard length = 23 mm), 15 to 20oC (33 mm), 30 to 35oC (54 mm), 30 to 25oC (68 mm), and 15 to 10oC (75 mm). For cohort 2 the ingress date was March 21st, and the spawning date was assumed to be January 16th. The March cohort was seen at 20 to 25 oC (mean standard length = 34 mm), 35 to 30oC (50 mm), and 25 to 20oC (64 mm). The third cohort arrived in mid-April and was likely spawned on March 1st. The April cohort was seen in the temperature categories for 25 to 30oC (mean standard length = 37 mm), 30 to 35oC (40 mm), 30 to 25oC (55 mm), 20 to 15oC (63 mm). Growth rates for January, March, and April cohorts were 0.24 mm/day, 0.22 mm/day, and 0.19 mm/day, respectively. Spot transitioned from isometric to allometric growth between 58 and 62 mm standard length in July (January cohort) through November (April cohort). Biomass at this transition was 0.7 g, 0.8 g, and 1.1 g for January, March, and April cohorts, respectively. These data potentially document reasons for interannual differences in young of the year survival rates and resulting year class strength assuming faster growing fishes that move into deeper or offshore habitats have advantage(s) over slower growing fishes with longer estuarine residency. Future habitat management strategies for related fisheries that promote food availability in estuarine nursery habitats should be explored.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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Available for download on Friday, December 31, 2027

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