Abstract
To understand the distribution of deep diving odontocetes, it is important to investigate the relationship between the foraging whales and their prey. Short-finned pilot whales mainly feed on squid and occasionally fish. Foraging short-finned pilot whales off the Island of Hawaii were located using trained visual observers and a passive acoustic hydrophone or a hydrophone array. A 500 meter by 500-meter survey box was set up over the foraging sites. A two-frequency split-beam echosounder collected micronekton backscatter over foraging and non-foraging control sites of the same location and similar time of day. Nautical Area Scattering Coefficient (NASC) (m2nmi−2) profiles were compared over the water column between foraging and non-foraging populations to analyze the relationship between micronekton density and short-finned pilot whale foraging. Using a generalized additive mixed model and a generalized linear mixed model, it was determined that short-finned pilot whales were able to exploit the daily variation of micronekton preferring to forage when the relative biomass was higher, and the deep scattering layer was found at shallower depths suggesting that there was more prey at accessible depths for the whales to feed on.
Highlights
The term “patch dynamics” was first quantified by Thompson [1], describing the dynamics of a system’s heterogeneity [2]
Using a generalized additive mixed model and a generalized linear mixed model, it was determined that short-finned pilot whales were able to exploit the daily variation of micronekton preferring to forage when the relative biomass was higher, and the deep scattering layer was found at shallower depths suggesting that there was more prey at accessible depths for the whales to feed on
Myctophids are the major component of the micronekton [39,40], that make up the diet of the prey of pilot whales which consists mostly of cephalopods [19,20,41,42,43,44]
Summary
The term “patch dynamics” was first quantified by Thompson [1], describing the dynamics of a system’s heterogeneity (patches) [2]. As seen in terrestrial systems, biological variability can persist on a multitude of spatial and temporal scales [3] This patchiness has been documented in marine environments and can exist on a diversity of spatial scales from meters to thousands of kilometers and time scales from hours to years [4], with the implications affecting organisms ranging from small plankton to larger marine mammals [5,6]. Spatial variability in the marine environment with patchiness of primary productivity and prey abundance in pelagic waters can lead to the heterogeneous distribution and aggregations of higher trophic level predators [5,6]. Patches due to eddies have been documented to aggregate top predators including melon-headed whales, Peponocephala electra, off the Hawaiian Islands with whale tracks being focused toward the outer edge of the cyclonic eddies [6], providing further evidence of a link between primary producers and high-level consumers, with the melon headed whales foraging mostly on pelagic and mesopelagic squid and fish [9,10,11]
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