California Current Integrated Ecosystem Assessment

Ecosystem Context for Reducing West Coast Whale Entanglements

The number of large whale entanglements confirmed by NOAA Fisheries has increased off the U.S. West Coast in recent years. This alarming pattern has mobilized efforts to understand and address factors that contribute to whale entanglement in fishing gear. NOAA Fisheries is responsible for recovering and protecting these whales under the Marine Mammal Protection Act and Endangered Species Act. The states are responsible for managing many of the fisheries that interact with these whales.

In part, the increase was spurred by a unique combination of variables: environmental conditions, distribution of fishing effort, distributions of important whale prey, and public awareness (Figure 1). In response, multiple government agencies, fishermen, and environmental organizations are actively engaged and committed to finding solutions that reduce the number of entanglements while continuing to support economically valuable fisheries.

goal of Integrated Ecosystem Assessment (IEA) scientists is to provide science support for Ecosystem Based Management. On this page, we compile timely, relevant, spatially explicit information that can help managers, industry, and other stakeholders better understand and mitigate the causes of large whale entanglements in marine waters of the California Current.


Research by NOAA scientists and partners has shed light on conditions that may cause increases in whale entanglements. The Data Dashboard has a suite of customizable plots that describe environmental conditions, whale and prey populations, and fishing activity along the West Coast in recent decades:

Whale Entanglement Data Dashboard

Alternatively, access a complete list of the Full Indicator Suite below, with detailed descriptions, maps, and plots with links to downloadable data.

Habitat Compression

A spatial time series that tracks the area of coastal upwelling habitat, the Habitat Compression Index (HCI) is a regional indicator used to assess the likelihood of ecosystem shifts and shoreward distribution patterns of top marine predators like whales. Smaller values indicate periods when cool habitat is compressed onshore, heightening whale entanglement risk.

Habitat Compression Index (HCI) values - central CA 

HCI Maps

Oceanographic Indicators

A combination of basin and regional scale indicators used to inform the seasonal development and variability of coastal upwelling, particularly in the spring. For example, the winter North Pacific High (NPH) monitors the area and intensity of atmospheric pressure, indicating whether strong upwelling conditions and krill populations are likely in the spring.

Upwelling Index - CUTI 39N monthly

North Pacific High (NPH)

Oceanic Nino Index

Whale Abundance

NOAA Fisheries prepares stock assessment reports for all marine mammals in U.S. waters; population size estimates are derived from shipboard surveys and mark-recapture methods.

Humpback whale - abundance

Humpback whale - relative abundance, central CA

Humpback whale - stock assessment report

Gray whale - stock assessment report

Blue whale - stock assessment report

Whale Entanglement Data

Whale entanglement data is compiled by NOAA Fisheries West Coast Region. An Interactive Map can also be used to view the spatial distribution of entanglement records by species, gear type, and year.

Humpback Whale

Gray Whale

Blue Whale

Other/Unid Whale

Total Whales

Prey Abundance

Prey indices provide information on the abundance of krill and forage fish, key forage species for whales, and provide context for whether predators may concentrate in particular feeding grounds where these species are likely present. Increased coastal abundance of forage species can heighten whale entanglement risk.

Krill - central CA

YOY anchovy - central CA

Adult anchovy - central CA

Fixed Gear Fishery - Landings

On the U.S. West Coast, whales have been documented entangled with gear and debris associated with numerous fishery and non-fishery sources (Saez et al. 2020). The most common source of entanglements is Dungeness crab gear, but other documented sources include pot/trap gear targeting CA spot prawn, sablefish, spiny lobster, coonstripe shrimp, and rock crab, as well as gillnets targeting highly migratory species, salmon, and other fishes.

Dungeness crab landings (US West Coast)

California Dungeness crab landings

Oregon Dungeness crab landings

Washington Dungeness crab landings

understanding whale entanglements
Figure 1: Factors contributing to whale entanglements in fishing gear. (Click for larger version with additional details)
Figure 2: Graphic depicting how seasonal patterns of climate / ocean conditions, ecological processes, and human activities interact to enhance risk of whale entanglement in the central California Current. (Click for larger version)