Shad Mahlum

• Doctor of Philosophy
• Quantitative Freshwater Ecologist at National Institute of Water and Atmospheric Research

Anthropogenic barriers to fish passage, such as culverts and dams, are major factors impeding the persistence and recovery of aquatic species. Considerable work has focused on mitigating these impacts; however, activities associated with measuring and restoring connectivity of aquatic ecosystems often face challenges in determining the passability...

The effects of sea lice on the marine survival of wild salmonids are widely debated. In Norway this debate has reached a crescendo as the Norwegian government has recently ratified a management system where the growth in the salmonid aquaculture industry will be conditional on regional estimated impact of salmon lice on wild fish. Sea lice have thu...

Recent advances in the ability to quantify longitudinal connectivity of riverine systems is enabling a better understanding of how connectivity affects fish assemblages. However, the role of connectivity relative to other factors, such as land use, in structuring biological assemblages is just emerging. We assessed the relevance of a structural con...

The restoration of four partial stream barriers was evaluated in watersheds of Terra Nova National Park, Newfoundland, Canada from 2009 to 2011. Brook trout (n = 462) were tagged and tracked moving through our study sites using PIT telemetry and the restoration actions were assessed using three different measures: passage success rates; the range o...

Walleye (Sander vitreus) are an ecologically important species managed for recreational, tribal, and commercial harvest. Walleye prefer cool water and low light conditions, and therefore changing water temperature and clarity potentially impacts walleye habitat and populations across the landscape. Using survey data collected from 1993 to 2018 from...

Walleye Sander vitreus and Yellow Perch Perca flavescens are culturally, economically, and ecologically significant fish species in North America that are affected by drivers of global change. Here, we review and synthesize the published literature documenting the effects of ecosystem changes on Walleye and Yellow Perch. We focus on four drivers: c...

Atlantic salmon is often a focal species of restoration efforts throughout the north Atlantic and it is therefore an excellent case study for how best to design programmes to address and mitigate threats and correct population declines. This perspective is written to promote the work that has been accomplished towards restoration of Atlantic salmon...

A systematic review and meta-analysis was conducted to evaluate the appropriate tag:fish size ratio when tagging juvenile salmonids (genera Oncorhynchus, Salmo, and Salvelinus). The review yielded 18 publications with 211 control and treatment groups reporting results from laboratory studies on the effects of passive integrated transponder (PIT) ta...

The production of Atlantic salmon in aquaculture has grown substantially over the last 40 years. The unintentional release of domesticated salmon poses a significant risk to the long‐term persistence of wild Atlantic salmon populations through ecological interactions and genetic introgression. Our ability to link aquaculture production to farmed es...

Escaped farmed Atlantic salmon Salmo salar interbreeding with wild conspecifics represents a threat to the genetic integrity and viability of wild populations. Therefore, it is necessary to accurately quantify escapees in riverine systems to monitor and mitigate interactions with wild conspecifics. Drift diving surveys are presently used in Norway...

The habitat use of adult Atlantic salmon was evaluated in a fjord complex in western Norway. A representative sample of 9 wild and 29 hatchery origin Atlantic salmon were tagged with acoustic tags and tracked with 28 stationary receivers from June 2012 to river entry. Using a movement-based kernel density estimation, we identified near shore habita...

Floating passive‐integrated transponder (PIT) antennae and smolt traps were used to study the time of sea entry and relative recapture of wild and hatchery‐reared Atlantic salmon Salmo salar smolt released below and above a lake formed in the Vosso River. In total, 8.4 and 4.1% of the tagged wild and hatchery fish, respectively, were detected leavi...

To be able to design effective management to alleviate wild fish from infestation pressure from fish farms, it is pivotal to understand when post-smolts migrate past areas of potential exposure to salmon lice. Here, data from release groups of coded-wire-tagged Atlantic salmon smolts and their subsequent recaptures in a trap net in the outer fjord...

Migration behaviour and estuarine mortality of cultivated Atlantic salmon Salmo salar smolts in a 16 km long estuary were studied using two methods: (1) acoustic telemetry and (2) group tagging in combination with trap nets. Progression rates of surviving individuals through the estuary were relatively slow using both methods [0·38 LT (total length...

Aquatic connectivity is an ecological process that is impacted by anthropogenic activity and has been implicated in the decline of many aquatic species. This has lead to the development of numerous theoretical applications to evaluate connectivity in river systems and optimize barrier restoration. Such tools are attractive as they can be less depen...

Despite heightened levels of protection, impacts of river fragmentation are widespread in Canada's National Parks. Fragmentation associated with dams and culverts is a pervasive stressor that impacts Species at Risk and/or culturally important species such as Atlantic salmon and American eel. While this ecological problem is tractable and efforts a...

Habitat connectivity has one of the most significant effects on the persistence and/or recovery of aquatic species. The modification of stream barriers is a critical step towards the reconnection of movement corridors for fish species. One important aspect in the improvement of stream barriers is an understanding of how barriers affect the movement...

Wildfire is a common natural disturbance that can influence stream ecosystems. Of particular concern are increases in water temperature during and following fires, but studies of these phenomena are uncommon. We examined effects of wildfires in 2000 on maximum water temperature for a suite of second- to fourth-order streams with a range of burn sev...