Habitat Loss: Growth & Survival

Globally, habitat degradation and loss have been linked to negative effects on elasmobranchs, including decreased condition, increased pollutant-loading and even population declines.  Declines in growth rates of some fish taxa have also been shown to be indicators of broader ecosystem changes.  Therefore, it is important to follow the fates of these top predators as juveniles because they are potential indicators of overall ecosystem health. The study used long-term mark-recapture data and a before-after control-impact (BACI) design to study the effects of large-scale habitat degradation and loss on survival and growth of juvenile lemon sharks in a threatened nursery. 

  1. Have there been any changes in juvenile lemon shark growth rate after habitat loss?
  2. What factors are most important in determining juvenile lemon shark survival?

In 2011, The Bahamas established a shark sanctuary, banning shark-fishing throughout the country’s Exclusive Economic Zone.  While it is a measure aimed at protecting older lemon sharks, a species listed by the International Union for the Conservation of Nature (IUCN) as near-threatened, it may not be enough to maintain stable populations if important nursery habitats are degraded to the point that they cannot produce enough viable recruits to adult populations.  Habitat loss, particularly from anthropogenic disturbances, is likely one of the most significant threats to lemon shark populations. The protection of essential nursery habitat for juvenile lemon sharks in Bimini should be strongly considered in conservation and management efforts for the species, and the importance of Bimini’s lagoons as essential fish habitat in a nursery capacity should be weighed against future development plans.

1. Have there been any changes in juvenile lemon shark growth rate after habitat loss?

Yes.  There were significant declines in growth rates in both the North Sound and the nearby Easter Cay (also known as Sharkland) after mangrove deforestation in the North Sound. 

2. What factors are most important in determining juvenile lemon shark survival?

A comparison of survival models showed that survival is highly dependent on which nursery the shark is in, as well as its age.  The mangrove deforestation in the North Sound in 2005 had a drastic effect on newborns, reducing their survival to only 26%. 

Principal Investigator:

Dr. Kristine Stump – University of Miami

 

Collaborators

Dr. Samuel Gruber – Bimini Biological Field Station

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