Monk Seal Monday #2

PC: B. Becker

In September, two Hawaiian monk seals were outfitted with dive recording tags that not only capture the seals’ location but time spent hauled out, time at the surface of the sea, and time spent (and depth of ) diving. Data from the tags is transmitted whenever the seals come within range of a cell phone tower. The instruments tags were affixed to the middle of the seals’ backs using an epoxy. When the seals next molt, the tags will fall off.

This first graphic shows the movement of the two tagged seals. The yellowish-green dots represent R1KT, a male. The red dots represent R7AA, a female. The graphs give us a look into three week’s worth of these two seals’ lives.In the graph on the right, we see the depths of R7AA’s dives. She records several dives in excess of 150 meters, but the vast majority of her dives log at under 100 meters of depth.

On the other hand, the majority of R1KT’s dives record upwards of 150 meters. There are numerous factors that could explain the differences. One, age. R7AA is a juvenile; whereas, R1KT is older. Too, underwater topography may affect their dive depths. Generally, according to science, monk seals like to forage on or near the ocean floor. They are generalist feeders and their diet includes a variety of fishes (eels, wrasses, squirrelfish, soldierfish, triggerfish, parrotfish), cephalopods (octopus and squid), and crustaceans (crab, shrimp, and lobster). Diet studies indicate they prefer prey that hides in the sand or under rocks, unlike most of the locally popular game fish (e.g. ulua, papio and ʻoʻio) and the proportion and type of prey consumed varies significantly by island, year, age and sex.