# Within‐Ecosystem Comparison of Bigmouth Buffalo Ictiobus cyprinellus and Common Carp Cyprinus carpio Reveals Diverging Population Trajectories, Declining Recruitment, and a Lifespan of 148 Years

## TL;DR

Bigmouth buffalo, a long-lived fish, are declining while invasive common carp are increasing, with bigmouth buffalo showing recruitment gaps longer than any other animal and lifespans up to 148 years.

## Contribution

The study reveals that bigmouth buffalo have the longest recruitment gaps of any animal and a maximum lifespan of 148 years, the longest of any vertebrate.

## Key findings

- Bigmouth buffalo have recruitment gaps longer than any other animal.
- Bigmouth buffalo can live up to 148 years, making them the 11th longest-lived vertebrate.
- Invasive common carp now outnumber bigmouth buffalo by an order of magnitude in the Qu'Appelle watershed.

## Abstract

The bigmouth buffalo
Ictiobus cyprinellus
is a long‐lived, migratory freshwater fish native to North America whose numbers are declining amidst increasing conservation concerns. Recent studies have uncovered long lifespans, delayed maturation, and episodic recruitment of bigmouth buffalo. Building from previous work in the Qu'Appelle watershed of Saskatchewan, here we quantify otolith‐derived population demographics of bigmouth buffalo and invasive common carp
Cyprinus carpio
across multiple sites in the drainage. The common carp (n = 125) and bigmouth buffalo (n = 173) collected from 2018 to 2024 reveal that common carp reach asymptotic size two times faster, live three times shorter lives, and invest significantly more into reproduction while also exhibiting recruitment stability during the water control era (post‐1958). Indeed, invasive common carp now outnumber native bigmouth buffalo in this watershed by at least an order of magnitude. In contrast, only a single year class (1997) was evident for bigmouth buffalo after 1949. Therefore, only one recruitment year was evident for this species since common carp were first detected in the system in 1955. Remarkably, we find that as of 2024 more than 90% of bigmouth buffalo in this system are greater than 75 years old with a known maximum age of 148 years. We now know that the bigmouth buffalo is the 11th longest‐lived vertebrate out of more than 66,000 species, and across diverse systems can have recruitment gaps longer than any other animal. Bigmouth buffalo require immediate conservation reassessment amidst ongoing population declines.

Within‐ecosystem comparison of invasive common carp and native bigmouth buffalo reveals recruitment gaps for bigmouth buffalo longer than any other animal and lifespans approaching 150 years. In the post‐dam era, invasive common carp are increasing in number while native bigmouth buffalo are declining.