Spatial Variability and Macro‐Scale Drivers of Growth for Native and Introduced Flathead Catfish Populations

Abstract

Quantifying spatial variability in fish growth and identifying large‐scale drivers of growth are fundamental to many conservation and management decisions. Although fish growth studies often focus on a single population, it is becoming increasingly clear that large‐scale studies are likely needed for addressing transboundary management needs. This is particularly true for species with high recreational value and for those with negative ecological consequences when introduced outside of their native range, such as the Flathead Catfish Pylodictis olivaris. This study quantified growth variability of the Flathead Catfish across a large portion of its contemporary range to determine whether growth differences existed between habitat types (i.e., reservoirs and rivers) and between native and introduced populations. Additionally, we investigated whether growth parameters varied as a function of latitude and time since introduction (for introduced populations). Length‐at‐age data from 26 populations across 11 states in the USA were modeled using a Bayesian hierarchical von Bertalanffy growth model. Population‐specific growth trajectories revealed large variation in Flathead Catfish growth and relatively high uncertainty in growth parameters for some populations. Relatively high uncertainty was also evident when comparing populations and when quantifying large‐scale patterns. Growth parameters (Brody growth coefficient [K] and theoretical maximum average length [L∞]) were not different (based on overlapping 90% credible intervals) between habitat types or between native and introduced populations. For populations within the introduced range of Flathead Catfish, latitude was negatively correlated with K. For native populations, we estimated an 85% probability that L∞ estimates were negatively correlated with latitude. Contrary to predictions, time since introduction was not correlated with growth parameters in introduced populations of Flathead Catfish. Results of this study suggest that Flathead Catfish growth patterns are likely shaped more strongly by finer‐scale processes (e.g., exploitation or prey abundances) as opposed to macro‐scale drivers.

Growth and Mortality of Invasive Flathead Catfish in the Tidal James River, Virginia

“…This may also influence the current study where Flathead Catfish were likely introduced 32 y before the first age and growth samples were collected in 1997. Regardless of a lack of simple trends in growth, the current study supports heterogeneity among years, which could be related to annual differences in climatic variables such as sunshine fraction, wind speed, evapotranspiration rates, and flooding (Kwak et al 2006;Schramm and Eggleton 2006;Jones and Noltie 2007;Rypel 2011;Massie et al 2018). Sample sizes may have been too small in some years to observe statistical differences in growth-we found the 2 y with the largest sample sizes were significantly different from all other years we compared.…”

“…Consequently, managing Flathead Catfish is imperative to limit a source of additional mortality to these at-risk fishes. Prior to this study, synthesized information on James River Flathead Catfish was limited to diet information collected opportunistically during a study focused on Blue Catfish (Schmitt et al 2017(Schmitt et al , 2019a and von Bertalanffy parameter estimates derived from a Flathead Catfish growth meta-analysis (Massie et al 2018). The current study provides critical information on population characteristics for use in population assessments to understand fishing levels necessary to reduce Flathead Catfish abundance and potentially reduce predation mortality on at-risk species.…”

“…Several studies have examined the growth of nonnative and native Flathead Catfish, with findings indicating that nonnative populations generally grow faster (Kwak et al 2006;Sakaris et al 2006;Rypel 2014). However, Massie et al (2018) found no difference in L ' Table 4. Matrix of likelihood ratio test results from pairwise comparisons of von Bertalanffy growth models fit to length-atage data collected from 1997 to 2015 for tidal James River Flathead Catfish Pylodictis olivaris in Virginia.…”

“…However, growth rates during establishment may not always follow expected patterns (Masson et al 2016(Masson et al , 2018. Similarly, Massie et al (2018) reported that growth parameters were not related to time since introduction for 13 nonnative Flathead Catfish populations, but the authors suggested they lacked populations early enough in the invasion process to observe differences. This may also influence the current study where Flathead Catfish were likely introduced 32 y before the first age and growth samples were collected in 1997.…”

Ecosystem-specific growth responses to climate pattern by a temperate freshwater fish

“…Climate mediates growth through-among other variables-changes in temperature and growing season length (Neuheimer and Taggart, 2007;Richard and Rypel, 2013). Growth patterns, thus, may emerge among spatially separated populations as a result of within system processes (e.g., variation in age-at-maturity) and broad-scale gradients in climate (Massie et al, 2018;Richard and Rypel, 2013). Assessments of fish growth patterns that consider processes influencing intrinsic and extrinsic variation are, therefore, central to understanding fish responses to climate patterns and to inform fisheries management.…”