Ecological contexts of diving behavior in Hawaiian false killer whales

TL;DR

This study explores how environmental and biological factors influence the diving behavior of false killer whales in Hawaii, revealing patterns linked to ocean conditions and prey.

Contribution

The first comprehensive analysis of diving behavior in false killer whales, highlighting their variable patterns and ecological adaptability.

Findings

False killer whales frequently dive in the epipelagic zone and exhibit deep dives exceeding 1000 meters.

Dive depth and frequency are influenced by oceanographic variables like current magnitude and chlorophyll-a concentration.

Larger individuals tend to dive deeper, though with significant variation across demographic groups.

Abstract

Predator movements vary across different ecological contexts, offering valuable insights into their foraging strategies. However, studying these contexts in marine predators is challenging due to the difficulty of observing them and their prey over sufficient spatiotemporal scales. Using bio-loggers and detailed life history information, we investigated abiotic and biotic factors shaping the diving behavior of a highly social apex predator—the false killer whale (Pseudorca crassidens)—around the Hawaiian Archipelago where three partially sympatric, genetically differentiated populations coexist.

We deployed time-depth recorders (n = 5) and depth-transmitting satellite tags (n = 16) on false killer whales between 1999 and 2025 to describe diving at multiple spatiotemporal scales and ecological contexts. We fit generalized additive mixed-effects models to examine relationships between dive metrics and temporal and spatial proxies of prey distribution. Dive metrics were compared across demographic traits (sex, population, relative size) to assess potential drivers of behavioral variability.

False killer whales spent most of their time in near-surface waters and frequently dove within the epipelagic zone. Individuals exhibited various dive types within and among different habitats, including near-seafloor and deep ( > 1000 m; record maximum of 1424 m) diving behavior. Dive rates and depths were highest during daylight hours and full moons, although with significant inter-individual variation. Dive depth increased with current magnitude and mixed layer depth and decreased with lagged surface chlorophyll-a concentration. Larger individuals tended to dive deeper, although with high variation across demographic groups. These findings offer key insights into potential drivers of diving behavior, albeit with small effect sizes.

We present the first comprehensive description of diving behavior for this species, which was characterized by variable temporal patterns, in contrast to sympatric species that are known to exploit diel vertically migrating prey. The diversity of dive types across habitats, along with trends between dive metrics and oceanographic variables, suggests that false killer whales may adjust their vertical movements to target different prey and environmental conditions.

ʻOkoʻa ka holo ʻana o ke poʻiiʻa ma nā ʻano honua kaiaola like ʻole, a hiki nō ke ʻike ʻia kā lākou kaʻakālai ʻai. Paʻakikī naʻe ke kilo ʻana i kēia mau honua o nā poʻiiʻa kai ʻoiai, paʻakikī ka nānā ʻana iā lākou me kā lākou ʻai ma nā pālākiō henua kaime. Ma o ka hoʻohana ʻana aku i nā lēpili ola a me nā ʻikepili ola kikoʻī, noiʻi mākou i hiki i nā mea ʻōnaeao a me nā mea ola kino ke pā i ke ʻano o ka luʻu ʻana o ke poʻiiʻa keu ma ka lauana ʻana - ke koholā ʻāhuka iwi poʻo like (Pseudorca crassidens) - a puni ka paeʻāina Hawaiʻi i noho pū ʻekolu pūʻuo ʻano pili a ʻokoʻa ma ke ōewe hoʻi.

Ua hoʻopaʻa mākou i nā mīkini ana kaime a hohonu (n=5) a me nā pepili hoʻoili ukali hohonu (n=16) ma nā koholā ʻāhuka iwi poʻo like mai nā makahiki 1999–2025 i mea e wehewehe aku ai i kaluʻu ʻana ma nā pālākiō henua kaime a me nā pōʻaiapii kaiaola. Ua hoʻohana mākou i nā ana pilina kaulike a me nā ana kaulele no ke kālailai ʻana aku i ka pilina wa ma waena o nā ʻikepili luʻu a me nā mea kaime a henua hoʻi o ka hoʻomalele ʻana o ka ʻai. Hoʻohālikelike ʻia nā ʻikepili luʻu ma nā waeʻanona ʻano (ke keka, ka pūʻuo, ka nui) i mea e kālailai ai i nā mea e hiki ke pā aku i nā ʻokoʻa o ka lawena.

I ka hapanui o ko lākou ola, noho pinepine nā koholā ʻāhuka iwi poʻo like i ka ʻili kai a luʻu lākou i loko o ka wao mālamalama. Ma ka hoʻokahi, hōʻike ʻia nā ʻano luʻu like ʻole i loko o nā kaianoho ʻokoʻa, e like hoʻi me ka pili papakū a hohonu (>1,000m; ma ka hohonu loa 1,424m) lawena luʻu. ʻO ka pinepine a me ka hohonu o ka luʻu ʻana, ua kiʻekiʻe loa ma nā hola ao a me nā wā mahina poepoe, me ka loaʻa pū naʻe o ka ʻokoʻa o kēlā me kēia. Ua piʻi ka hohonu o ka luʻu ʻana i ka nui o ke au a me ka hohonu o ka wao pā lewa a ua iho i ka lohi o ka aea ʻana o ke kolopila-ʻā. ʻOi aʻe ka hohonu o ka piʻi ʻana o nā mea ʻoi aku o kona nui, eia naʻe, me ka nui o ka loli ʻana ma nā pūʻuo ʻano. Ma o kēia mau hua, loaʻa nō nā ʻike koʻikoʻi no nā e pā ana i ke ʻano o ka luʻu, i loko nō naʻe o ka liʻiliʻi o ka hopena.

Hōʻike aku mākou ka wehewehena piha mua o ka hana luʻu o kēia ʻano lāhui, i kuhikuhi ʻia ma nā lauana kaime ʻokoʻa, i hoʻohālikelike ʻia me ka lāhui ʻano pili a ʻokoʻa ma ke ōewe hoʻi, kekahi lāhui i ʻike ʻia e luʻu a piʻi e ʻai i ka ʻai neʻena. Ma o ka ʻokoʻa o nā ʻano luʻu ma nā kaiaola, a me ke ʻano o nā ʻikepili luʻu a me nā ʻano mea kai, hoʻololi paha nā koholā ʻāhuka iwi poʻo like i ko lākou neʻena kū i mea e loaʻa ʻai kekahi ʻano ʻai ma nā ʻano pōʻaiapili kaiapuni like ʻole.

The online version contains supplementary material available at 10.1186/s40462-026-00630-4.

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