In a 2013 pilot study, acoustic tags were inserted into two species of river herring, Alewife Alosa pseudoharengus and Blueback Herring Alosa aestivalis. The primary objectives were to identify handling and tagging effects and assess inriver residence time. The secondary objective was to identify postspawn coastal migration patterns. Fish were collected on spawning grounds in the upper portion of the Hudson River, New York. Vemco V7 acoustic transmitters were gastrically inserted into 25 river herring (13 Alewives and 12 Blueback Herring) that were in pre, active, or post spawning conditions. In-river acoustic data were collected from 23 of the 25 river herring. The majority of tagged fish exhibited some level of fallback (downstream migration) after the tagging event, all Blueback Herring and all male Alewives returning to spawning areas. The majority of female Alewives did not return to the spawning area after tagging, and this may be a result of when and where tagging events occurred. Both species of river herring exhibited similar in-river residence times of approximately 2-3 weeks and exited the system 3-6 d after spawning. Information on coastal movements of four Blueback Herring (two females and two males) was also obtained, spanning the south shore of Long Island, New York, to the mouth of Penobscot Bay, Maine. Coastal and in-river tag detections were reported by members of the Atlantic Cooperative Telemetry Network. In conclusion, this experiment can now be repeated with confidence on a larger scale with multiyear tags in order to identify unknown in-river spawning areas, provide information regarding spawning site fidelity, and bolster current knowledge of coastal migration patterns for both species.

N‐mixture models are often employed to estimate latent organismal abundance while concurrently accounting for detection probability. Our study offers a novel means for simultaneously measuring abundance, detection probability, and gear efficiency by focusing on a previously understudied and relatively immobile subject (river herring eggs). Custom‐designed egg mats accommodating two individual collecting surfaces were deployed in two tributaries of the Hudson River (Fall Kill and Black Creek, New York) to collect anadromous river herring eggs during the spawn. Mats were orientated approximately parallel to streamflow under a stratified random sampling design. Strata were defined as three equidistant spatial segments measured from a given tributary's confluence with the main stem of the Hudson River to its first impassable barrier to fish migration. In total, 93 sites were surveyed, with the majority of eggs being detected within the upper two‐thirds of each respective tributary. Throughout the course of the sampling season, an average of 1,585 eggs per egg mat subsampling event was recovered from the upper two strata of Black Creek, and 2,619 eggs per subsampling event were recovered from the upper two strata of the Fall Kill. In Black Creek, an egg density of 568 eggs per 58.1‐cm2 egg mat subsample was observed over an average deployment duration of 3.7 d at a detection rate of 82%. In the Fall Kill, an egg density of 1,222 eggs per 58.1‐cm2 subsample was observed over an average deployment duration of 3.9 d at a detection rate of 92%. The N‐mixture negative binomial model outperformed Poisson and zero‐inflated Poisson N‐mixture models in estimating river herring egg abundance using Akaike's information criterion model comparison indices. In terms of iteration processing time, N‐mixture modeling using the “unmarked” package in R proved to be more efficient than Bayesian‐based hierarchical modeling processed through the “jagsUI” package.