Preserving Ecological Balance: Lemon Shark Conservation Policies for Bimini

By Erika Pietrzak, June 16, 2024

Overfishing, acidification, climate change, pollution, and habitat destruction threaten lemon sharks around the world. All of the lemon shark’s major threats are human-created and must be human-ended.

Background

Lemon sharks (Negaprion brevirostris), a near-threatened species growing up to ten feet long, are targeted by international fisheries, caught as bycatch, and harvested for their fins and meat. With a 30-year lifespan, lemon sharks have paroled the tropical and subtropical zones of the Atlantic and Pacific for millions of years. Lemon sharks get their name from their yellow hue which camouflages them against the seabed. These opportunistic feeders are pivotal to ecosystems as they shift food webs, leading to decreased planktivorous fish and increased mesopelagic fish. Additionally, by consuming large amounts of organic matter, lemon sharks reduce the amount of pollutants in the waters. Lemon sharks wield control over species abundance and distribution, fostering greater ecosystem diversity, and offering habitats for other species, thus bolstering the resilience and productivity of these ecosystems. In the Caribbean, specifically at Bimini Islands (a chain of islands in the Western Bahamas and home to the largest lemon shark nursery grounds), coastal development, overfishing, sea level rise, and habitat alterations threaten these populations. As an integral component of the food web, the dwindling number of lemon sharks poses a risk to entire ecosystems

Context

Lemon sharks have been fished on record since 300 BC in Peru. However, unsustainable and harmful fishing practices have left the species vulnerable. Gear entanglement and bycatch are two of the leading causes of harm and death to lemon sharks. For example, certain types of fishing gear and bait have been found to attract lemon sharks, but are being used to catch other fish, resulting in significant bycatch. Despite significant research into alternative habitats, lemon shark populations continue to dramatically decline.

The human population of the Bahamas has increased by 15 percent since 2000. As a result of increasingly rapid coastal development, coral reefs in the area “have dramatically declined over the last 50 years” and more than 70 percent of the Bahamas’ coral have high partial mortality rates. Such coastal expansions have resulted in escalated marine pollution, reduced oxygen levels, heightened sedimentation, and loss of crucial habitats. Moreover, noises from coastal activities stress lemon sharks and negatively impact their physiology. These impacts can displace prey and disrupt breeding, causing further population decline. Furthermore, slight temperature changes in the coastal water because of global warming can be detrimental to lemon sharks, especially juveniles, who have a limited temperature range.

More than 30 percent of Bimini’s mangroves were removed in the 2000s to build a hotel/casino. By 2007, 18 percent of seagrass and 750 thousand cubic meters of sand fill were removed. These mangroves are home to over 153 marine species, including a favorite prey of lemon sharks– yellowfin mojarra. As coastal development increases and urbanization destroys habitable areas for lemon sharks, their populations are increasingly threatened at this nursery. During dredging in 2001, North Bimini nursery seagrass and sharks experienced a 20–25 percent decline in survival, presumably due to trace metals. Analysis of lemon shark samples revealed trace amounts of zinc (Zn), manganese (Mn), selenium (Se), cadmium (Cd), and lead (Pb). Of particular concern are the elevated levels of manganese, known to induce Parkinson's Disease in humans and to diminish brain function in cows, mice, and fish. Furthermore, coastal development can decrease oxygen levels in the water and harm sensitive juvenile lemon sharks. 

Climate change and sea level rise endanger lemon sharks that “use shallow lagoons for both mating” and birthing. This is vital to lemon shark survival as juveniles use these shallow areas as protection from predators while providing sufficient feeding opportunities for three years. Preserving the integrity of Bimini, the only well-characterized lemon shark nursery in the Bahamas and the most well-studied in the Atlantic, is imperative since the potential reduction in neonate and juvenile survival due to environmental changes may severely limit the ability of lemon sharks to seek out new and suitable parturition grounds.

Current Policy and Governance

To ensure the species' thriving existence, the Bimini government must prioritize the protection of mangrove habitats, revise coastal development strategies, establish marine protected areas, and invest in community education initiatives. In 1993, the Bahamas banned long-line fishing, a practice that often resulted in sharks being caught as bycatch and suffering injuries or death. On July 5, 2011, the Bahamas banned “commercial shark fishing as well as the selling and trading of shark products.” Despite these measures, reports in 2014 indicated an upsurge in the discovery of long-line fishing gear—lines and hooks—washing ashore, suggesting a persistent issue of illicit fishing practices. This overfishing can not only be detrimental to lemon shark populations, but can harm mangroves and starve lemon sharks when their prey is drastically reduced.

In 2011, the Bahamas took action by declaring over 600 thousand square kilometers of its waters as a shark sanctuary, “prohibiting any commercial fishing of the animals as well as banning the possession, sale and trade of shark products.” This action makes it the only nation “to create a shark sanctuary out of the entire marine habitat that surrounds the island.” 

In 2000, the North Sound of the Bahamas was designated as a Marine Protected Area, and the North Bimini Marine Reserve (NBMR) was announced in 2009. Yet, as of 2022, the NBMR was not established and was not on any proposed legislation.

Recommendations

Protection of Mangrove Habitats: Mangroves are threatened by pollution, endangering lemon shark juveniles and making it harder for them to survive to adulthood. Where mangroves have been destroyed, mangrove planting initiatives should be led by the government to restore these areas. These can be made into educational initiatives to promote climate-friendly sentiments in the area. The government should also ban any future development projects that would destroy Bimini’s mangroves.

Coastal Development Management Plans: Plans should create buffer zones in which construction cannot occur within a certain distance from essential habitats, particularly mangroves. Plans should also include improved waste management systems to reduce pollution and improve noise reduction systems to limit noise pollution in known lemon shark areas. To limit the impacts of human-made climate change, the Bahamas must significantly regulate any materials and runoff around the coast.

Marine Protected Areas: Coastal Development Management Plan changes would work well with the establishment of marine protected areas (MPAs) to reduce human impacts on lemon sharks and lemon shark prey’s habitats. By designating the Bimini nursery as an MPA, overfishing would decline and the habitat could recover to allow this area to continue being used by juveniles. A first step in this process would be establishing the NBMR immediately.

Investment in Community Education: This species suffers from a lack of public support as they are seen as dangerous animals that pose a threat to human and marine life. Bimini should increase funding for community education to increase public interest in these animals and, consequently, increase public support. Alternatively, community education around protecting coral reefs and lemon shark habitats could improve lemon shark prey populations and decrease pollution and destruction. With more than 50 percent of the nation’s GDP coming from tourism and over $100 million annually coming from shark diving alone, these educational initiatives could also extend to tourists, creating a new possible economic sector.

Conclusion

Lemon sharks inhabit a unique role in marine ecosystems that humans are threatening to destroy, causing a cascading effect down the food chain. The direct inverse relationship between human and lemon shark populations in the Bahamas exposes the severity of this threat. Overfishing, acidification, climate change, pollution, and habitat destruction threaten lemon sharks around the world. All of the lemon shark’s major threats are human-created and must be human-ended.

Change The Chamber is a nonpartisan coalition of over 100 student groups, including undergraduates, graduate students and recent graduates.