Methods
Summary
To test the hypothesis that Hawaiian false killer whales (Pseudorca crassidens) alter their foraging behavior and prey selection in response to fishery activity, we will use a focused combination of passive acoustic monitoring and satellite tagging, supported by fisheries data correlation. These methods are chosen because they directly address key aspects of the hypothesis: where whales forage, how they forage (including group dynamics and communication), and how their behaviors overlap with fishing effort.
The study will target two categories of sites that differ in fishing pressure to provide a comparative framework:
1. High Fishery Activity Areas: Areas with intense commercial fishing, representing strong human-prey competition.
• Hawai‘i Deep-Set Longline Fishery: Offshore tuna and swordfish fisheries.
• Main Hawaiian Islands Handline and Gillnet Fisheries: Nearshore and seamount-associated fishing activities.
• Kona Crab & Lobster Trap Fisheries: Sandy-bottom and benthic fisheries that could impact prey bases.
2. Low Fishery Activity Areas: Areas with minimal commercial fishing, serving as ecological baselines.
• Northwestern Hawaiian Islands: Marine protected areas with strict fishery restrictions.
• Remote Pelagic Zones: Offshore areas beyond the reach of regular commercial fishing.
At each site, we will record foraging activity, movement patterns, and fishery interactions over several months, aiming to tag and monitor at least 10 individuals in each category.
Data Collection Methods:
1. Passive Acoustic Monitoring (PAM)
Purpose: Detect and characterize foraging behavior, communication patterns, and potential disturbances from fishery activity.
Equipment: Bottom-moored autonomous acoustic recorders (e.g., Ecological Acoustic Recorders (EARs), SoundTraps).
Essential Link to Hypothesis: Long-term acoustic recordings allow detection of foraging buzzes, echolocation clicks, and social vocalizations that may shift based on prey availability and noise disturbance from fisheries.
Key Variables:
• Vocalization types (foraging buzzes, social whistles, echolocation clicks)
• Vocalization rates (clicks per minute, buzz rates)
• Duration and frequency of foraging bouts
• Ambient noise levels associated with vessel presence
2. Satellite and Archival Tagging
Purpose: Track movement patterns, dive behavior, and proximity to fisheries.
Equipment: Suction-cup and dart-attached satellite-linked tags with depth sensors.
Essential Link to Hypothesis: Dive profiles and spatial movements reflect foraging strategies and potential prey shifts, especially near fishery activity.
Key Variables:
• Dive depth and duration
• Distance from active fishing vessels
• Time spent in high vs. low fishery zones
• Group size estimates during surface intervals
3. Fisheries Data Correlation
Purpose: Quantify overlap between whale foraging zones and active fisheries.
Equipment: Fisheries observer reports, automatic vessel tracking (AIS) data, and bycatch incident logs.
Essential Link to Hypothesis: Identifies depredation behavior and reduced prey availability linked to fishery operations.
Key Variables:
• Frequency of whale-fishery interactions
• Depredation rates (whales stealing fish from lines)
• Changes in targeted fish stock biomass over time
Challenges
Tracking false killer whales in low-fishery areas may result in under-sampling due to their broad habitat use. To mitigate this, we will concentrate tagging efforts early in the study on these regions until a minimum of 10 separate individuals are tagged, ensuring sufficient data for comparative analysis.
Pre Analysis Plan
We will create visualizations and conduct preliminary statistical analyses to compare whale behavior across sites:
• Heatmaps of whale movements relative to fishery zones.
• Dive profile comparisons (depth and duration) between high and low fishing areas.
• Sonograms of vocalization types and rates.
• Group size distributions by site type.
• Noise exposure analyses near active fisheries.
Protocols
This project has not yet shared any protocols.