MarSci 202 PSet 2

Problem 1 §

A. §

The major factors leading to the decline of sea turtles over the past 500 years include over-exploitation, habitat loss, and bycatch. Historically, sea turtles were heavily hunted for their meat, eggs, and shells, which severely reduced their populations. In modern times, incidental capture in fisheries, coastal development affecting nesting sites, and climate change have compounded these pressures. These factors, coupled with pollution and illegal poaching, have caused significant declines in sea turtle numbers (Houtan & Bass, 2007).

B. §

The loggerhead sea turtle (Caretta caretta) population has seen declines of around 43% in some regions, particularly in Florida, over the 18-year period from 1989 to 2006 (Witherington et al., 2009). The green sea turtle (Chelonia mydas) populations in certain regions, such as Peninsular Malaysia, have declined by more than 80% since the 1950s, largely due to egg harvesting and other human activities (Tibbetts, 2009).

C. §

Five current threats to sea turtles include:

1. Bycatch in fisheries
2. Habitat destruction due to coastal development
3. Climate change affecting nesting sites
4. Illegal poaching of eggs and adults
5. Pollution, particularly plastic waste and marine debris (Fiedler et al., 2012)

The most critical threat to address is bycatch, as this causes significant mortality in both adult and juvenile sea turtles, leading to population declines. Reducing bycatch through the implementation of turtle-excluder devices (TEDs) and improved fishing practices can have an immediate and measurable impact on sea turtle conservation (Heppell et al., 1996)

Problem 2 §

A §

• $x$: age
• $N_x$: population at age $x$
• $d_x$: deaths during age $x$
• $l_x$: percentage alive wrt $x=0$
• $q_x$: percentage dead during age $x$

B & C §

D §

Conservation biologists should focus their efforts on the life stages corresponding to ages 8 and 9, where the highest mortality rates are observed ($q_8=0.5090$ and $q_9=0.3664$). These ages likely represent critical developmental stages, such as when turtles transition to new habitats or face increased threats from predators and human activities like bycatch in fisheries. While deaths right after hatching do contribute a noticeable amount of deaths, it is overshadowed by the dropoff in pupulation between ages 8 and 9, implying that money spent on saving sea turtle nests is not the most efficient use of resources.

Problem 3 §

A & B §

C §

As opposed to the general survivorship of green sea turtles, the population in Bahamas do experience a steep dropoff just after aging ($q_0=0.3965$) implying that spending money on this early stage i.e. protecting hatchlings would have the biggest impact.

Bibliography §

Houtan, K., & Bass, O. (2007). Stormy oceans are associated with declines in sea turtle hatching. Current Biology, 17, R590-R591. https://doi.org/10.1016/j.cub.2007.06.021.

Fiedler, F., Sales, G., Giffoni, B., Monteiro‐Filho, E., Secchi, E., & Bugoni, L. (2012). Driftnet fishery threats sea turtles in the Atlantic Ocean. Biodiversity and Conservation, 21, 915 - 931. https://doi.org/10.1007/s10531-012-0227-0.

Witherington, B., Kubilis, P., Brost, B., & Meylan, A. (2009). Decreasing annual nest counts in a globally important loggerhead sea turtle population.. Ecological applications: a publication of the Ecological Society of America, 19 1, 30-54. https://doi.org/10.1890/08-0434.1.

Tibbetts, J. (2009). Dangerous Delicacy: Contaminated Sea Turtle Eggs Pose a Potential Health Threat. Environmental Health Perspectives, 117, A407 - A407. https://doi.org/10.1289/EHP.117-A407B.