Argulus from the Pascagoula River, MS, USA, with an Emphasis on Those of the Threatened Gulf Sturgeon, Acipenser oxyrinchus desotoi

Species of Argulus (Branchiura Thorell, 1864) are common ectoparasites of freshwater, estuarine, and marine fishes. Argulid identification and taxonomy is often confusing because many species are reported to parasitize multiple host species, have similar morphological characters, and come from various salinity regimes. Gulf sturgeon is an anadromous fish natal to drainages in the north-central Gulf of Mexico, and as with many endangered species, has a poorly documented parasite community. During Gulf sturgeon tagging and monitoring studies (2016–2019) in the Pascagoula River, MS, USA, species of Argulus were collected from Gulf sturgeon as well as other incidentally captured fishes. Argulus flavescens Wilson, 1916 was found on Gulf sturgeon and flathead catfish, Argulus americanus Wilson, 1902 on bowfin, and Argulus bicolor Bere, 1936 on Atlantic stingray. We provide morphological details and measurements for these species as well as the first confirmed 28S rDNA molecular data. Argulus flavescens was more abundant and prevalent on larger Gulf sturgeon and on sturgeon captured in freshwater rather than estuarine habitats. Our results indicate that A. flacescens may not tolerate estuarine salinities and that the anadromous life-history pattern of Gulf sturgeon could help rid them of A. flavescens when they emigrate from their riverine habitats.

State-space models to infer movements and behavior of fish detected in a spatial array of acoustic receivers

We developed state-space models for inferring movements and behaviors of fish implanted with acoustic transmitters and detected within a spatial array of stationary acoustic receivers. In these models, fish movements and behavior switching are specified using a hidden Markov model of the changes in an individual’s latent activity center. The observed number of detections at each acoustic receiver is modeled as a function of the distance between the receiver and a fish’s activity center. To illustrate these models, we analyzed the detections of individual Gulf sturgeon (Acipenser oxyrinchus desotoi) that moved within a spatial array of acoustic receivers placed in the Suwannee River, Florida. Our models of these detections provided estimates of the locations of individual sturgeon and the periods when individuals switched between spawning and resting behaviors. We anticipate that these models will be used to analyze acoustic surveys of other species and help design new surveys.

Empirical, spatially explicit natural mortality and movement rate estimates for the threatened Gulf sturgeon (Acipenser oxyrinchus desotoi)

Understanding mortality rates and movement patterns across a species’ distribution can provide key insight necessary for developing effective conservation, recovery, and management plans. We directly estimated site fidelity and natural mortality rates for the threatened Gulf sturgeon (Acipenser oxyrinchus desotoi) across a large portion of their range in the northern Gulf of Mexico using acoustic telemetry methods and a simulation-tested, multistate mark–recapture model. Our results suggest that fidelity rates to riverine habitats used during spring and summer are high, but natural mortality rates vary widely. Our results are highly relevant for managing this species. The high fidelity rates, coupled with supporting genetic analyses, suggest that management of individual riverine populations of Gulf sturgeon should be considered. The need for individual river-based management is exacerbated by the variation in natural mortality rates among rivers. The reasons for these differences in mortality are unclear, but are an important area of future research because higher mortality rates may impede recovery of some Gulf sturgeon populations to stated management targets.