


Our conceptual model investigates the ecological role of sea-run fish and the connections they make among different ecosystems.
Sea-run fish migrate between freshwater, estuarine, and marine habitats during their life cycle. As they migrate, these fishes provide important ecological services and connect ecosystems. Most of these species are born in rivers, use freshwater nurseries before they migrate to sea, and return to the river to reproduce. The exception is the American eel which is born at sea, migrates in rivers to grow, and returns to sea for its reproduction.
The abundance of these fish in the Northwest Atlantic is at, or near, all-time lows for most species. A number of stressors have led to the decline: dams, overfishing, pollution, and climate change. With fewer of these fish, researchers believe that the ecosystem services these species once provided have substantially diminished.
For example, at historic abundance levels alewives provided an important source of energy-rich forage for nearshore fish species in the spring. This lost connection may be partially responsible for the current low abundance of other commercial species in nearshore areas in the Gulf of Maine. Other examples of impaired ecosystem services include:
To repair these connections, we urgently need to look at sea-run fish populations as a community and consider the ecosystems they inhabit altogether. We need to consider their combined interactions and the important roles they play in the healthy functioning across the varied ecosystems (freshwater, estuarine, or marine ecosystems) they inhabit. They also face similar challenges that can be solved simultaneously. This would improve our large-scale approach to research and management, and provide information to better communicate the important roles of these species.
Our goal is to improve ecosystem services delivery and ecosystem resilience to increase the productivity of the sea-run fish community.
Our conceptual model, the Diadromous Watersheds-Ocean Continuum (DWOC) synthesizes the key roles of sea-run species as a community to highlight their importance for ecosystems and how they connect them by delivering important ecosystem services. It provides a framework to work collaboratively to make progress toward ecosystem-based management for sea-run fishes. These connections vary in space and time via the migrations paths and habitats occupied by diadromous fishes along the watershed-ocean continuum: from lakes and upper river areas to coastal, estuaries and high sea areas, across regional and international borders.
The Northwest Atlantic coast hosts a diverse sea-run community. We’re focusing on:
We use ecosystem services to summarize the information on the diadromous community. Ecosystem services are separated into three categories: cultural, maintenance and regulatory, and provisioning.
Cultural services are non-material benefits people obtain from nature. These include:
Maintenance and regulation services regulate the ecological balance and provide the basis for other services by:
Provision services include:
Using an ecosystem services approach allows us to use simple language to describe individual or cumulative ecosystem benefits and ecological connections these species provide. Ecosystem services delivered by fish are influenced by the fish’s seasonal abundance, their migration patterns and timing, and the location of the habitats they use along the diadromous watersheds-ocean continuum, which ranges from freshwater to estuarine and marine environments. Through these ecosystem services, sea-run fish also connect terrestrial and aerial ecosystems.
Approaching the sea-run fish community through DWOC provides insight on research gaps we need to address to support management priorities that will increase sea-run fish productivity, ecosystem resilience, and ecosystem services delivery. These research gaps include:
We have highlighted the need for more interdisciplinary research, spanning from headwaters to the ocean and including biology, physiology, geomorphology, climate science, and socio-economics. This way, the ecosystems’ interdependence and the full life cycle of the species can be properly considered.
Using DWOC, we developed a step-by-step approach to progress toward ecosystem-based management for the diadromous community. This approach takes into account social connections between people and ecosystems that influence sentiments toward sea-run fish. Our framework steps are:
In parallel an adaptive management approach needs to be put in place to allow re-evaluation of the root problems, adjustment to management priorities and actions, and monitoring as progress is made.
Clear and transparent communication between all parties involved is key during this entire process. Another key element is to understand the connections between people and sea-run fish in the affected area so we can estimate the expected level of social and community support for management actions. Finally, while planning management actions we need to consider the fact that habitats have been transformed and continue to be transformed due to human activities, which also impact fish species. Additionally, climate change affects all aspects of the sea-run fish community and habitats across spatial scales.
It can be challenging to work at the scale of multiple ecosystems. Our approach shows how advances can be made at smaller scales and on local issues by starting on a smaller suite of ecosystem services for instance, while embedding these steps into that large-scale holistic understanding of the diadromous communities and ecosystem connections. This also to incrementally make progress toward ecosystem-based management of the sea-run fish community.
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