Publication Date

2013-07-30

Availability

Open access

Embargo Period

2013-07-30

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Fisheries (Marine)

Date of Defense

2013-07-08

First Committee Member

John W. McManus

Second Committee Member

Elizabeth A. Babcock

Third Committee Member

Donald L. DeAngelis

Fourth Committee Member

Joseph E. Serafy

Fifth Committee Member

R. Dean Grubbs

Abstract

The lemon shark, Negaprion brevirostris, is a large coastal elasmobranch that relies on shallow nearshore nursery areas for increased juvenile survival throughout its range. Habitat loss due to anthropogenic development has occurred globally at large scales, particularly in the coastal zone. In Bimini, Bahamas, where lemon sharks use mangrove-fringed lagoons and creeks as nurseries, the construction of a large resort and marina complex has altered the natural environment through mangrove removal, seabed dredging and the filling of wetlands. The Bimini system is one of the most well-studied in all elasmobranch literature. Given the wealth of pre-disturbance data, this study was a unique opportunity to quantify potential changes in lemon shark survival, growth, movement and prey resource availability in response to habitat loss. A telemetry study showed that despite the disturbance, juvenile lemon sharks continued to show strong site fidelity to the degraded nursery. However, a before-after control-impact (BACI) analysis of the marine faunal community showed that since the disturbance, there have been significant changes in overall community structure, as well as significant declines in multiple taxa. Mojarra, the most important prey item for juvenile lemon sharks within the nursery, experienced one of the most dramatic declines. A BACI analysis showed that post-disturbance, juvenile lemon shark annual growth rate within the degraded nursery declined. In addition, survival models suggested that the disturbance negatively affected annual survival, particularly for the young-of-year, driving estimates to values which indicate that the anthropogenic disturbance lowered the nursery’s ability to provide ample recruits to adult populations. With the threat of continued development within Bimini’s lemon shark nurseries, it is important to consider precautionary management principles. Because many marine species rely on coastal habitats at some or even all life stages, the loss or degradation of these areas can have significant negative consequences on biodiversity. As one of the top predators within the system, lemon sharks are an important indicator of overall ecosystem health. In Bimini, juvenile lemon sharks are obligate residents of a nursery that has been degraded in terms of quality, complexity and resources, and these changes have had negative effects on their growth and survival. Habitat loss, particularly from anthropogenic disturbances, is likely one of the most significant threats to lemon shark populations. The protection of essential nursery habitats in Bimini may be critical to effective conservation and management of this species, and the importance of Bimini’s lagoons as essential fish habitat in a nursery capacity should be weighed against future development plans.

Keywords

habitat loss; anthropogenic disturbance; Bimini Bahamas; mangrove; lemon shark; BACI

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