Recovery Potential Assessment of East Vancouver Island Summer Chinook (Designatable Units 19 and 20)

Abstract

East Vancouver Island (EVI) Stream, Spring Chinook Designatable Unit (DU) 19 and EVI Ocean, Summer, Chinook DU 20 are both assessed as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). This initiated the current DFO process to provide advice needed to meet various requirements of the Species at Risk Act. DU 19 spawns above Second Lake in the upper reaches of the Nanaimo River. DU 20 spawns in the Nanaimo River and the Puntledge River. While data are limited, some summer-run fish are known to spawn in the Cowichan River and Chemainus River systems. Herein, we will refer to these DUs collectively as EVI Summer Chinook. Marine distribution of EVI Summer Chinook ranges from Southeast Alaska in the north to the Puget Sound in the south. There are some indications that there is a high residency within the Strait of Georgia. EVI Summer Chinook are enhanced by hatcheries in the Nanaimo and Puntledge River systems. These two watersheds have consistently monitored annual returns. Adult EVI Summer Chinook enter the Nanaimo River as early as February, and the Puntledge River in April through to August, with the peak of upstream migration happening in June. Main holding pools in Nanaimo River are at the South Fork Junction, downstream of White Rapid Falls, and First and Second Lake. In the Puntledge River, the main holding location is Comox Lake. Impacts to EVI Summer Chinook were assessed by subject matter experts and high-risk threats identified were harvest, human disturbance, system modification, competition and hatchery practices. Limiting factors that were also affecting EVI Summer Chinook are predation and climate change. EVI Summer Chinook have a survival target of 1,000 natural-origin spawners (based on COSEWIC Criterion D). Precautionarily, we have used system-specific survival targets, the target for the Nanaimo River is 1,000 and the target for the Puntledge River is 1,000 natural spawners. The system-specific recovery target for Nanaimo River is 1,785, and the target for Puntledge River is 2,125 natural spawners. On the Puntledge River a portion of juveniles were coded-wire tagged (CWT) and marked (adipose fin removed) each year for estimation of marine survival and exploitation rate (ER) as well as their movement and distribution. A population viability assessment for the Puntledge River component of EVI Summer Chinook was conducted using an age-structured, state-space life cycle model fit to data from 1980-2020, with future projections extending 40 years in the future. We assume that the sensitivity of the Puntledge River component to threats is representative of all EVI Summer Chinook. Forward simulations were run by varying ten parameter and data inputs organized into five categories: harvest rates, hatchery supplementation, freshwater habitat, marine predation and climate. The probabilities of achieving the survival and recovery targets were most sensitive to changes in pre-spawn survival, ocean harvest rates and regional hatchery releases. The population viability analysis (PVA) model indicated that under baseline conditions, the Puntledge River component of EVI Summer Chinook is as likely as not to achieve the survival target and unlikely to achieve the recovery target by 2042. Scenarios that increased pre-spawn survival, decreased ocean harvest and decreased regional hatchery releases resulted in higher probabilities of achieving the survival and recovery targets. While simulations reflecting improvements in freshwater habitat and productivity show improved survival, freshwater habitat improvement alone will not likely achieve the recovery targets. Other than activities that promote survival and recovery of EVI Summer Chinook, all ongoing and future human-induced mortality, along with activities that result in harmful alteration, disruption, or destruction of their habitat, should be prevented. Due to data availability, not all threats to EVI Summer Chinook could be modelled. There is a need for improved monitoring for compliance (e.g., illegal harvest, forestry, water use, hydroelectric dams), effectiveness of changes (e.g., mitigation, hatchery practice), and ecological populations (e.g., seal predation). First Nations food, social, and ceremonial (FSC) harvest, such as practiced by Snuneymuxw and K’omoks First Nations, is guided by traditional ecological knowledge and aligns with natural cycles. FSC harvest are not considered within the scenarios that considered changes to human-induced fishing mortality. A balanced and culturally informed approach to allowable harm would include FSC harvest as part of the natural system.