Estuarine habitats serve as important nurseries for many species of juvenile fishes and invertebrates. Due to concerns about declining fishery stocks and habitat degradation, it is critical that the value of different habitats be evaluated, so that areas that are most important can be prioritized for habitat conservation and restoration. This dissertation used Atlantic croaker (Micropogonias undulatus) as a model species to quantitatively examine patterns of early juvenile nursery habitat use, factors influencing growth and mortality, and to test the widely held assumption that ?growth is a valid indicator of habitat quality?. A unique aspect of this study was consideration of how growth and survival of juvenile Atlantic croaker were influenced by the joint effects of individual (larval and juvenile growth) and cohort (density-dependent) characteristics, as well as biotic and abiotic characteristics of the nursery. Late-larval and early juvenile Atlantic croaker were collected weekly, using a 1-m beam trawl in river, upper-estuary, and creek habitats of two estuaries (White Oak River estuary and Newport River estuary, North Carolina, USA), sampled during two seasons (fall and spring) of two recruitment years (2001-2002 and 2002-2003). Subsequent analysis of otolith microstructure was used to provide estimates of growth rates, population age structure, and mortality. Juvenile Atlantic croaker were most abundant in oligohaline river nursery areas (primary nursery area), with the upper-estuary serving as an important ?refuge? habitat following periods of high freshwater outflow that forced fish down-estuary. In addition to management implications (i.e., time and area closures of shrimp trawling), such flood events have important implications for growth-based assessment of habitat quality: A positive covariance between larval and juvenile growth was found only after periods in which croaker were displaced from river nursery areas, when food was apparently in short supply. Atlantic croaker cohorts from both estuaries also exhibited evidence for selective mortality favoring survival of individuals that were faster growing as larvae and early juveniles, as well as evidence for density-dependent growth (i.e., slower average cohort growth rates at higher conspecific density). The results of this study indicate that growth is not a robust indicator of habitat quality. Unless factors such as previous environmental history, density-dependence, and selective mortality are accounted for, growth-based assessment of habitat quality may reach incorrect conclusions regarding the value of different habitats.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-11032005-100512 |
| Date | 08 December 2005 |
| Creators | Searcy, Steven Philip |
| Contributors | John Miller, Jon Hare, Jim Rice, David Eggleston |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-11032005-100512/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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