Thirteen novel ideas and underutilised resources to support progress towards a range‐wide American eel stock assessment

Abstract

A robust assessment of the American eel (Anguilla rostrata) stock, required to guide conservation efforts, is challenged by the species’ vast range, high variability in demographic parameters and data inadequacies. Novel ideas and underutilised resources that may assist both analytic assessments and spatially oriented modelling include (1) species and environmental databases; (2) mining of data from scattered sources; (3) infilling of data gaps by spatial analysis; (4) age estimation from measurements of DNA methylation; evaluation of eel abundance by (5) larval, (6) glass‐bottom boat, (7) net enclosure and (8) eDNA surveys; (9) accounting for dam‐induced habitat increases in eel watercourse modelling; (10) spatially oriented modelling with and without temporal components; (11) geographically nested modelling of glass eel recruitment; (12) spawner per recruit modelling and (13) life cycle modelling to examine larval allocation effects. Eel biologists are too few to gather the required assessment data across all of the species’ range. Public posting of electrofishing and eDNA metabarcoding data sets and the use of machine learning techniques to comprehensively inventory small dams will help meet some data needs. These approaches address only a small proportion of the assessment challenges that face American eels. Worldwide collaboration amongst Anguilla scientists is a key enabler of progress towards stock assessment goals.

Patterns in longitudinal distribution of American Eel (Anguilla rostrata) population characteristics in rivers of Puerto Rico

“…Previous species assessments have relied heavily on information from northern portions of the species' range where American Eel have declined (ASMFC, 2017; COSEWIC, 2012; Jacoby et al, 2017; Shepard, 2015). However, evaluating this species across its entire distribution is necessary because it is a single, panmictic population (Cairns et al, 2022). Our findings provide new information on the potential reproductive contribution and status of American Eel from the Caribbean region, which could be used for future range‐wide models and analytic assessments (ASMFC, 2017; Cairns et al, 2022).…”

“…Our findings provide new information on the potential reproductive contribution and status of American Eel from the Caribbean region, which could be used for future rangewide models and analytic assessments (ASMFC, 2017;Cairns et al, 2022). Possible truncated patterns in American Eel in urban river basins and the importance of upstream habitats revealed by our study could inform international cooperation among environmental, dam, and fisheries managers, to highlight the importance of instream passage for this species (ASMFC, 2017;Cairns et al, 2022;MacGregor et al, 2008). Prioritizing stream connectivity and habitat conservation in the Caribbean could contribute to the persistence of the entire American Eel population by ensuring the production of abundant female eel in close proximity to the global spawning location.…”

“…Despite these known risks, species assessments in North America determined that the species did not warrant protection (Shepard, 2015). Range-wide assessments are needed to understand overall trends and conservation needs of the species (Cairns et al, 2022), but there are knowledge gaps from southern parts of its distribution.…”

Panmixia in the American eel extends to its tropical range of distribution: Biological implications and policymaking challenges

“…Eel research is scarce in Latin America and the Caribbean (Benchetrit & McCleave, 2016; Kwak et al., 2019; Roghair et al., 2014; Torres‐Molinari et al., 2023; Wang & Tzeng, 1998) and data throughout that region are sometimes unreliable. Similarly, data are sparse, fairly recent, and inconsistent across all Gulf of Mexico rivers, and even the North American Atlantic data are uneven depending on locations (Cairns, 2020; Cairns et al., 2022; Cornic et al., 2021). Moreover, growth habitats, river continuum, and contamination by organic and elemental pollutants should be carefully taken into account to manage the species, as suggested in recent studies (e.g., Bourillon et al., 2020, 2022; Miller et al., 2016; Righton et al., 2021).…”

Development and validation of two environmental DNA assays for American Eel (Anguilla rostrata)

“…Currently, point or transect‐based electrofishing strategies (Reid, 2011) are used by a variety of American Eel monitoring programs (e.g., Laffaille et al, 2005; Newhard et al, 2021); however, American Eels have been shown to be highly susceptible to injury from these methods (Reynolds & Holliman, 2004). Recently Cairns et al (2022) highlighted the importance of eDNA for American Eel monitoring and Chin et al (2021) showed that American Eel eDNA concentration can be used to predict abundance; however, there is still no validated eDNA assay for this organism. Therefore, the goal of our study was to develop and validate two eDNA assays for the American Eel that could serve as a noninvasive method to aid in conservation efforts of the species (e.g., determination of fish passage and reintroduction success).…”