Rhythmic clicks, grunts and roars fill the Año Nuevo Island Reserve in California, home to a large breeding colony of northern elephant seals (Mirounga angustirostris). For nearly 60 years, scientists at the University of California Santa Cruz (UCSC) have studied the seals here. Lately, they have used Fitbit-like biomonitors on the seals to understand where they migrate to each year and what they eat. In 2022, one of the students attending a 10-week-long undergraduate field course at the reserve wondered how oceanographic conditions, such as surface temperature and pressure, affect the elephant seals. That curious question led scientists to connect oceanographic conditions in the northern Pacific Ocean to fish abundance in its deep twilight zone by measuring how successfully elephant seals foraged and reproduced. Their study, published in February in Science, analyzes this connection to estimate fish abundance in the twilight zone five decades in the past and predict it two years into the future. The study also shows how marine predators like elephant seals act as sentinels that can tell us about changes in the ocean’s inaccessible depths — if only we can learn how to decipher their reports. The twilight, or mesopelagic, zone — the layer of ocean water that extends 200–1000 meters (656–3280 feet) deep — is an inhospitable place. “It’s completely dark, it’s extremely cold, there’s this crushing pressure,” says study co-author Allison Payne, a graduate student in the UCSC lab of lead author Roxanne Beltran. “It’s kind of like another planet.” “We don’t know exactly…This article was originally published on Mongabay
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