The sea is undeniable in its power and awe. It has a calling that we are drawn to. In 2010, it was estimated that nearly 60% of the world’s population lived within 100 kilometers of a coast. By 2020, it is suspected that number will increase to nearly 75% (Knip, Heupel, & Simpfendorfer, 2010). With the increase in population size comes an ever increasing need for the urbanization of the coastlines. Acts such as deforestation, construction, and dredging for coastal development are detrimental to nearshore areas (Knip, et al., 2010).
Mangrove habitats worldwide have decreased by almost 35% in the last 25 years due to cutting for lumber and clearing for development (Valiela, Bowen, & York, 2001). While the characteristics that define shark nursery habitats are not entirely understood by scientists, as shark populations continue to decline, the need to identify these nursery habitats has increased over the last several decades (Heupel, Carlson, & Simpfendorfer, 2007). It is known, however, that for many species of nearshore sharks, mangroves are utilized by juveniles as nurseries, providing safety from predators and an abundance of food (Knip, et al., 2010).
In the Bahamas, around Bimini island, juvenile lemon sharks (Negaprion brevirostris) have long utilized mangroves to perfect their hunting skills and evade capture by other predators (Jennings, Gruber, Franks, Kessel, & Robertson, 2008). Recently, the mangroves have been greatly reduced to make way for a resort in the area. As the available mangrove and sea grass (Thalassia testudinum) decreased, there was also a directly correlated decrease in the survival rates in the juvenile lemon sharks (Jennings, et al., 2008). As I discussed in my previous post, Consequences of Elasmobranch Population Decline, sharks exhibit slow life history characteristics and low fecundity. This means that they have long gestation periods and produce few pups at a time (Chin, Kyne, Walker, & McAuley, 2010). It is crucial that these pups survive in order to maintain a healthy, stable population.
You can help protect threatened areas like mangroves by getting involved with restoration projects. Check out
- Mangrove Action Project are taking a truly grassroots, bottom-up approach to mangrove conservation and restoration issues. Their approach involves and includes the voices of the global South, local communities, and their partner non-governmental organizations (NGOs).
- The Nature Conservancy is working with the Grenada Fund for Conservation Inc., the Grenada Red Cross Society, and community members to look closely at climate adaptation strategies for Grenville, a fishing community on the northeast side of Grenada.
- Grenville is vulnerable to even the smallest of storm surges, and is witnessing erosion and loss of natural habitat every day. In the past, healthy corals, and mangroves slowed waves before hitting Grenville’s beaches, providing a natural barrier for the community and important coastal resources.
- Now, with the reefs degraded and the mangroves largely missing, the beaches have eroded, and important fisheries habitat has been lost, and coastal infrastructure and people are more vulnerable to impacts from the sea.
Next time I will continue my examination of declining shark populations due to human influences by looking into how human coastal development can effect sharks through terrestrial runoff.
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Featured Image Source
Gross, S. (Photographer). (2013). Baby Lemon Shark in Mangrove [Digital Image] Retrieved from http://cdn.c.photoshelter.com/img-get2/I0000bztSHVOOCoE/fit=1000×750/2013-06-03-HI258.jpg
Chin, A., Kyne, P. M., Walker, T. I., & McAuley, R. B. (2010). An integrated risk assessment for climate change: Analysing the vulnerability of sharks and rays on Australia’s Great Barrier Reef. Global Change Biology, 16(7), 1936–1953.
Heupel, M. R., Carlson, J. K., & Simpfendorfer, C. A. (2007). Shark nursery areas: Concepts, definition, characterization and assumptions. Marine Ecology Progress Series, 337, 287–297.
Jennings, D. E., Gruber, S. H., Franks, B. R., Kessel, S. T., & Robertson, A. L. (2008). Effects of large-scale anthropogenic development on juvenile lemon shark (Negaprion brevirostris) populations of Bimini, Bahamas. Environmental Biology of Fishes, 83(4), 369–377.
Knip, D. M., Heupel, M. R., & Simpfendorfer, C. A. (2010). Sharks in nearshore environments: models, importance, and consequences. Marine Ecology Progress Series, 402, 1–11.
Valiela, I., Bowen, J. L., & York, J. K. (2001). Mangrove forests: One of the world’s threatened major tropical environments. BioScience, 51(10), 807.