Evaluation of the Captive Care, Post-Release Behavior and Survival of Seven Juvenile Female Hawaiian Monk Seals

Extremely poor juvenile survival in the endangered Hawaiian monk seal (Monachus schauinslandi) is primarily caused by prey limitation and continues to drive the population decrease in the Northwestern Hawaiian Islands (NWHI).

In 2006-2007, a pilot project was conducted to determine whether temporarily providing nutritional supplementation and protection from predation would enhance the survival of juvenile monk seals.

Seven female seals, two of which were rare fraternal twins, were included in the captive care (CC) project.

Six weanling seals gained weight commensurate with their duration in captivity, 89 to 297 d, with weight gains of 31 to 143% initial body weight, and were released at Midway Atoll. The seventh seal, a female yearling, died 23 d after being admitted from complications associated with malnutrition and stress.

The CC and three control seals were instrumented with satellite-linked GPS dive recorders to monitor post-release behavior and survival as part of an assessment of the project’s success. Satellite tags transmitted between 37 and 311 d. Initially, the CC seals foraged closer to shore, used less of the atoll, and dove to shallower depths (< 20 m) and for shorter durations (< 4 min) relative to the controls (> 60 m and > 4 min). Over the course of several weeks, most of the CC and control seals were foraging in a similar fashion.

These results demonstrate that following a brief acclimation period, captive-fed monk seals are capable of foraging normally post-release. However, none of the CC seals were alive as 2-y-olds, whereas two of the control seals were alive in 2010 as 4-y-olds.

Although post-release survival was poor in the current study, with a more suitable release location, an expanded captive-feeding program could be a useful tool to salvage the reproductive potential of Hawaiian monk seals in the future.

Norris TA, Littnan CL, Gulland FMD. 2011. Evaluation of the captive care and post-release behavior and survival of seven juvenile female Hawaiian monk seals (Monachus schauinslandi) Aquatic Mammals 37(3): 342-353. DOI: 10.1578/am.37.3.2011.342