How Sea-Run Fish Connect Ecosystems
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:
- Transport of marine-derived nutrients to freshwater ecosystems by species such as Atlantic salmon
- Removal of fine sediment and higher abundance of aquatic insects in river habitats with sea lamprey spawning
- Predator-prey roles in freshwater systems by species such as rainbow smelt
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.
The Complex Ecology of Sea-Run Fishes
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:
- Atlantic salmon
- Atlantic tomcod
- American conger eel
- American eel
- Rainbow smelt
- River herring (alewife and blueback)
- Sea-run brook trout
- Sea lamprey
- Shads (American and hickory)
- Striped bass
- Sturgeons (Atlantic and shortnose)
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:
- Spiritual experiences
- Recreation, including recreational fisheries
- Aesthetic enjoyment
- Physical and mental health
- Scientific data
- Educational opportunities
Maintenance and Regulation
Maintenance and regulation services regulate the ecological balance and provide the basis for other services by:
- Habitat formation and conditioning for different species
- Retaining biodiversity
- Cycling nutrients
- Predatory interactions and food web control
Provision services include:
- Subsistence and commercial fisheries harvests
- Raw materials to produce medicines, biofuels, pharmaceuticals, and other goods
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.
Identifying Research Gaps
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:
- Better characterization of the ecosystem services by different species (for example, little is known about the roles of rainbow smelt or American eel)
- A better understanding of species interactions within and outside the sea-run fish community, such as predation or protection from predation
- A deeper understanding of the effect of climate change and other human activities on habitats
A Scientific Framework for Ecosystem-Based Fisheries Management Approaches
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.
A Path Forward
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:
- Step 1: Examine what factors affect the spatial structure of the sea-run fish community across all life stages, population abundances, and population and community diversity to achieve our principal goal: to improve ecosystem services delivery, ecosystem resilience,and increase diadromous community productivity.
- Step 2: Evaluate the roots of the problem and explore a multi-solution approach while researching the ramifications of the different solutions along the ecosystem continuum.
- Step 3: Define management objectives, with quantitative targets of diadromous fish abundance, diversity, and distribution to support ecosystem services delivery.
- Step 4: Define management actions coordinated across species, life-cycle stages, and ecosystems, encompassing specific governance boundaries to increase the productivity of all diadromous fishes
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.
Keys to Success
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.
- Mathias J. Collins
- John F. Kocik
- Rory Saunders
- Timothy F. Sheehan
- Matthew B. Ogburn
- Tara Trinko Lake
CICES. 2022. Towards a common classification of ecosystem services. Common International Classification of Ecosystem Services, European Environmental Agency. Available at: https://cices.eu/ [Accessed January 3, 2022].
Cook CN, Mascia MB, Schwartz MW, Possingham HP, Fuller RA. 2013. Achieving conservation science that bridges the knowledge-action boundary. Conserv Biol. 27:669–678. 10.1111/cobi.12050
Cooke SJ, Nguyen VM, Chapman JM, Reid AJ, Landsman SJ, Young N, Hinch SG, Schott S, Mandrak NE, Semeniuk CAD.. 2021. Knowledge co-production: A pathway to effective fisheries management, conservation, and governance. Fisheries 46:2:89–97. 10.1002/fsh.10512
Dias BS, Frisk MG, Jordaan A. 2019. Opening the tap: Increased riverine connectivity strengthens marine food web pathways. PLoS One 14:5:e02170081. 10.1371/journal.pone.0217008
Hall CJ, Jordaan A, Frisk MG. 2012. Centuries of anadromous forage fish loss: Consequences for ecosystem connectivity and productivity. BioScience 62:8:723–731. 10.1525/bio.2012.62.8.5
Hare JA, Morrison WE, Nelson, MW, Stachura M, Teeters EJ, Griffis RB, Alexander MA, Scott JD, Alade L, Bell RF, Chite AS, et. al. 2016. A vulnerability assessment of fish and invertebrates to climate change on the northeast U.S. continental shelf. PLoS One 11:2:e0146756. 10.1371/journal.pone.0146756
Lassalle G., Béguer M, Beaulaton L, Rochard E. 2008. Diadromous fish conservation plans need to consider global warming issues: An approach using biogeographical models. Biol Conserv 141:4:1105–1118. 10.1016/j.biocon.2008.02.010
Limburg KE, Waldman JR. 2009. Dramatic declines in north Atlantic diadromous fishes. BioScience 59:11:955–965. doi: 10.1525/bio.2009.59.11.7. xc
Link JS, Browman HI. 2017. Operationalizing and implementing ecosystem-based management. ICES J Mar Sci 74:1:379–381. 10.1093/icesjms/fsw247
Saunders R, Hachey MA, Fay CW. 2006. Maine’s diadromous fish community: Past, present, and implications for Atlantic salmon recovery. Fisheries 31:11:537–547. 10.1577/1548-8446(2006)31[537:MDFC]2.0.CO;2.
Schindler DE, Armstrong JB, Reed TE. 2015. The portfolio concept in ecology and evolution. Front Ecol and Environ 13:5:257–263. doi: 10.1890/140275
Waldman JR, Quinn TP. 2022. North American diadromous fishes: Drivers of decline and potential for recovery in the Anthropocene. Sci Adv 8:4: eabl5486. 10.1126/sciadv.abl5486
Walter RC, Merritts DJ. 2008. Natural streams and the legacy of water-powered mills. Science (319:5861: 299–304. doi: 10.1126/science.1151716