Research

Dynamic aquifer storage contributes to baseflow in streams, especially during dry periods when surface runoff is minimal.

This review defines baseflow resilience as a stream’s ability to maintain stable flow and water quality despite climate extremes and human impacts like water withdrawals and land use changes.

Watershed characteristics can influence resilience in complex ways—for instance, permeable geology may enhance groundwater-stream connectivity but reduce flow during droughts.

Shallow groundwater responds quickly to stress, while deeper sources delay impacts and can carry long-term contamination.

The review also examines how irrigation affects baseflow and summarizes key hydrogeological factors and stressors, along with metrics for evaluating baseflow resilience, using examples from the Delaware River Basin.

Riverine fishes face major challenges like habitat loss and climate change, which impact the productivity of their ecosystems. While factors like water temperature are often studied, the distribution and availability of food—key to fish growth and survival—remain less understood.

This paper expands on the concept of “foodscapes,” focusing on three aspects of food: abundance, accessibility, and quality. It addresses why food availability is hard to estimate, the consequences of uncertainty, and emerging methods to better measure it.

The authors emphasize the critical role of food in fish conservation, particularly as waters warm.

This study examined how surgery and recovery time after acoustic tagging affect the survival and migration of wild Atlantic Salmon smolts through freshwater, estuarine, and marine environments.

Four treatment groups were compared to assess the impacts of hatchery conditions and post-tagging recovery time. Results showed that short recovery times and hatchery captivity reduced survival, especially within the first 5 days or 48 km after release, with lingering effects during the transition to saltwater.

Hatchery fish migrated faster, likely due to larger size, but still experienced reduced survival. These findings highlight the importance of quantifying tagging-related effects in the wild, as such biases can influence conclusions about natural fish behaviour and survival.

The post-smolt stage is a critical period for Atlantic salmon, making it important to identify their migration routes to protect key habitats.

This study used a biophysical model, coupled with a water circulation model (FVCOM), to simulate post-smolt dispersal in Passamaquoddy Bay, New Brunswick. By testing nine behaviours and six swimming speeds against acoustic telemetry data, the study found that certain behaviours—like swimming southwest or showing tide-varying rheotaxis—aligned well with observed routes, while others (e.g., passive drift, salinity or temperature-based orientation) were unlikely.

The approach shows promise for predicting essential habitats and migration paths of wild post-smolts.

Marine survival is a major challenge for Atlantic Salmon conservation and fisheries. A workshop held in Halifax in December 2017 brought together researchers to review current telemetry efforts and develop a coordinated vision for studying North American salmon populations at sea.

Building on NASCO’s SALSEA-Track initiative, participants discussed how emerging technologies and integrated approaches can improve understanding of ocean habitat use, migration timing, and routes.

While large-scale open ocean survival studies remain challenging, advances in acoustic and satellite telemetry, along with new technologies, are expected to offer more detailed and long-term insights.

This report outlines a framework to guide future collaborative research.

This study used acoustic telemetry and otolith microchemistry to examine rainbow trout migration in three Prince Edward Island rivers. Only 6% of tagged fish left coastal embayments, though many entered saline or tidal waters.

Habitat use varied by river, with Montague River fish using more saline estuary areas, while others remained in tidal or freshwater zones, especially in summer. Some trout stayed entirely in freshwater.

Migrants were often larger and more likely to have anadromous mothers, though freshwater mothers also produced migrants. Overall, partial residency with tidal use was the dominant strategy, alongside smaller marine and freshwater contingents.

Infectious agents play a key role in animal ecology and host population dynamics, making it important to understand their diversity and transmission in wild species like Atlantic salmon.

This study used high-throughput qPCR and genome sequencing to examine infectious agents in sub-adult salmon at sea and adults in three eastern Canadian rivers with varying aquaculture exposure. Fourteen agents were identified, including five previously unreported in Eastern Canada.

While phylogenetic analysis of piscine orthoreovirus suggested intercontinental transmission, no link was found between aquaculture and infection in wild adults. Infections varied with environment, life stage, and origin, highlighting areas for further research.

Acoustic telemetry is widely used to track fish survival, but transmitter loss can lead to underestimated survival rates.

This study measured retention and mortality in hatchery Atlantic salmon smolts tagged with different transmitter sizes during their transition to salt water.

Retention ranged from 34–85%, varying by transmitter type and surgeon. Most expulsions occurred 25–65 days post-tagging and were more frequent when transmitters exceeded 7.5% of smolt weight.

Only transmitters over 12% of body weight significantly increased mortality. To avoid biased survival estimates, it’s crucial to account for expulsion, which depends on transmitter size, life stage, and study duration.

Acoustic telemetry can track fish migration and survival, but predation can cause bias if tags remain active inside predators.

This study tested new predator-detecting tags that signal ingestion by sensing pH changes in the predator’s gut. In the first field trial with Atlantic salmon smolts migrating through freshwater and estuarine zones, researchers found that using these tags helped identify and reduce predation bias in survival and timing estimates.

Estimating ocean mortality is challenging, but using pop-up satellite tags on 156 adult Atlantic salmon from 12 rivers revealed 14% predation and 24% undetermined mortality.

Most predation was by endothermic fish, especially in the Gulf of St. Lawrence and near the Irish Shelf. Marine mammals and large ectothermic fish were less common predators.

Mortality rates were highest for salmon from Canada, Ireland, and Spain, suggesting that low ocean survival may contribute to the steep declines seen in southern populations.