Improving strategies for coastal river restoration: Tracking anadromous river herring in a coastal Massachusetts stream

Background/Question/Methods

Restoration of coastal ecosystems is a high priority to which substantial resources are allocated. Anadromous fish are considered one indicator of a healthy system and are a current focus of coastal restoration efforts. In the northeastern United States, the closely related blueback herring (Alosa aestivalis) and alewife (A. pseudoharengus), collectively referred to as river herring, have historically been an important component of coastal rivers. Populations have been declining since the 1970’s coast wide. Here we evaluate two aspects of anadromous river herring restoration: movements of spawning adult river herring in the Ipswich River, MA, and the outcome of three translocation strategies. We tagged (Lotek Nanotags NTC-6-1) 36 alewives trapped while naturally migrating upstream in the Ipswich River (defined here as natal fish), and 52 stocked alewives. Fish movements were tracked with an array of 9 stationary Lotek SRX_400 receivers placed throughout the lower 30km. To examine transport-and-release location effects and the implications for restoration, we performed a manipulative reciprocal stocking experiment. Natal fish were tagged, and then released at the downstream intercept site (River km 6) or at the upstream stocking site (Rkm 25). Tagged stocked fish were transported from a donor river and also released at both sites.

Results/Conclusions

Natal fish released at the point of capture and those transferred upstream (n=15) both spent an average of 8 days within the receiver array, with 19% and 26%, respectively, exiting the river in less than 48 hours. Stocked fish released upstream (n=40) remained an average of 5 days in the receiver array with 48% exiting in less than 48 hours, while those released downstream (n=13) spent an average of 1.6 days, with 76% of the fish exiting in less than 48 hours. Regardless of release site, duration of the natal fish spawning migration was similar and telemetry data indicated selection of the same habitat types. Stocked fish released upstream exhibited the most variation, with some fish located in habitats used by natal fish, and others rapidly exiting the telemetry array. The short duration for stocked fish released downstream may indicate stress caused by stocking or an inability to acclimate and respond to migration cues. Restocking of rivers cannot, by itself, address the challenge of restoring a severely depleted fish population, but within the context of understanding fish behavior, protecting habitat, and providing regulatory restrictions on the fishery, restocking may contribute to broader management and restoration goals.