In a recent study, we found that our Hawaiian Monk Seal Research Program’s translocation efforts from 2012 to 2014 proved highly successful. Translocation is “the deliberate movement of organisms from one site for release in another.” It has been broadly applied to manage and conserve terrestrial wildlife since the 1800s. But it is far less common in the marine world, and is rarely applied to marine mammals. However, our team’s efforts buck that trend—about 400 monk seals have been translocated since the 1980s.
Most of these actions were taken to reduce immediate risks associated with the seals’ location:
- Predatory sharks
- Aggressive male seals
- Dangerous interactions with people in the main Hawaiian Islands
Previous studies have shown that the more fat the pups have when their mothers wean them, the better their chances of surviving the critical transition to independence. These pups have a greater weaning girth, and therefore a larger blubber reserve. Moreover, the specific relationship between girth and survival varies over time and among subpopulations. This is most likely due to the type and magnitude of risks faced by the young seals. The expected survival of a pup 41 inches (105 cm) in girth at French Frigate Shoals was only about 8 percent. The expected survival of the same size pup born at Laysan Island would be 73 percent!
Measuring the Success of Translocations
To test whether the translocations conducted during 2012–2014 were successful, our researchers had to account for the strong influence that weaning girth has on survival. Failing to do that could result in false and misleading conclusions. For example, if only the girthiest pups had been translocated, they would have had a very high chance of surviving no matter where they were. If we didn’t account for their plump condition, we might incorrectly conclude the translocations were a smashing success. As it turns out, the translocated pups we measured tended to be smaller than average. This means they would have been expected to have lower than average survival chances just because of their size.
This study clearly demonstrated that the translocations conducted during 2012–2014 had a statistically significant positive effect on the survival of the pups involved. As a result of our monitoring program, we were able to conduct robust analyses and confidently determine the success of this project.
After 2014, differences in survival of young monk seals in the Northwestern Hawaiian Islands subpopulations have been either too small or inconsistent to continue translocations. But this proven tool will remain in NOAA’s quiver and may be used in the future in situations when seal pups could benefit from translocations.