SC/69A/IST/01  

Document Number

SC/69A/IST/01

Full Title

Preliminary Updated Gray Whale Assessment Models and Implications for the Performance of Gray Whale Strike Limit Algorithms

Author

André E. Punt, Jonathan Scordino, John Brandon, Greg Donovan, Tomoharu Eguchi, Geof H. Givens, Aimée R. Lang, Peter Mahoney And David W. Weller

Authors Summary

The Gray Whale SLA and the Makah Management Plan were tested using operating models that were fitting to monitoring data and hypotheses related to future dynamics and data collection. The models developed and fitted during the Gray Whale Rangewide Review formed the basis for evaluating the performances of the Gray Whale SLA and the Makah Management Plan in terms of their ability to achieve the objectives for aboriginal subsistence whaling. These operating models include multiple areas in the North Pacific along with several alternative stock structure hypotheses. Elevated strandings along the eastern North Pacific migration route, and declines in abundance since the completion of the Rangewide Review in 2018 are indicative of a second mortality event starting in 2019 (see also SC/69a/ISTxx). This event may suggest that the set of scenarios used to evaluate the performances of the Gray Whale SLA and the Makah Management Plan may need to be revised in order to take into account new information on the expected magnitude and frequency of such events. Although the need for a revision remains an open question, SC/69a/ISTxx developed new operating models for the eastern North Pacific gray whales that include a mortality event during 2019-2022 (continuing into 2023) for the Northern Feeding Group and new abundance data, including for the Pacific Coast Feeding Group. Trials have been conducted for stock structure hypotheses 4a/3a, 4b/3b, 4c/3c, 4e/3e, 7a/5a, and 6b, with sensitivity explored to changes to assumptions related to the frequency of catastrophic events, and allowance for an additional mortality event for the Pacific Coast Feeding Group. These operating models are used to conduct projections under the Gray Whale SLA and the Makah Management Plan that use the new scenarios related to possible future mortality events.

Publisher

IWC

Keywords

Publication Year

2023

Abstract

The models developed and fitted during the Gray Whale Rangewide Review formed the basis for evaluating the performances of the Gray Whale SLA and the Makah Management Plan in terms of their ability to achieve the objectives for aboriginal subsistence whaling. Elevated strandings along the eastern North Pacific migration route, and declines in abundance since the completion of the Rangewide Review in 2018 are indicative of a second mortality event starting in 2019. This event may suggest that the set of scenarios used to evaluate the performances of the Gray Whale SLA and the Makah Management Plan may need to be revised in order to take into account new information on the expected magnitude and frequency of such events. Although the need for a revision remains an open question, new operating models for the eastern North Pacific gray whales have been developed that include a mortality event during 2019-2022 (continuing into 2023) for the Northern Feeding Group and new abundance data, including for the Pacific Coast Feeding Group. Trials have been conducted for stock structure hypotheses 4a/3a, 4b/3b, 4c/3c, 4e/3e, 7a/5a, and 6b, with sensitivity explored to changes to assumptions related to the frequency of catastrophic events, and allowance for an additional mortality event for the Pacific Coast Feeding Group. These operating models are used to conduct projections under the Gray Whale SLA and the Makah Management Plan that use the new scenarios related to possible future mortality events. These models will also be useful for updating the assessment of gray whales for the Scientific Committee’s Status of Stocks Website project.