Why we need more holistic approaches? An example of Baltic salmon

The concept of ecosystem-based management (EBM) has become popular for marine research and management in recent years. While there is no commonly accepted definition of EBM, “holistic” is one of the common descriptions for such approach[1]. Why do we need a holistic approach? Let us take salmon as an example. Imagine you are a salmon that was born in a river of a Northern Baltic country. What kind of life would that be?

You may live in the river for 1-4 years before you migrate to the sea. After staying at sea for 1-5 years, you would start to swim back to the river for spawning[2]. At first glance, it does not look very complex. But how would you interact with others and the environment? The water temperature may influence how fast you grow and mature[3][4]. Dams may hinder your migration (depending on which river you were born)[5]. When you migrate to the sea, your diet would change gradually from insects and invertebrates to young herring, and further switching to larger herring and sprat[6]. There is also the danger of being eaten by grey seals or being caught by different types of fisheries: offshore fisheries, coastal trap net fishery or angling at the river[7] (Figure 1). Now your life looks more challenging.

Figure 1: Migration routes (black arrows) of Salmon born in the rivers of the Northern Baltic Sea, and salmon fisheries: offshore fisheries (white dash lines), coastal trap net fisheries (triangle icons) or angling at the river (circle icons). Revise from[8].

In summary, salmon’s life relates to three systems: river ecosystems, marine ecosystems, and human systems. Many conflicts exist among these systems. Focusing on the human system alone is complex enough to clarify the conflicts. The amount of fish caught at the sea may affect the fish availability for river catch. Fish caught in the river also affects the number of fish for spawning at the end and further affects the fish availability for marine catch after few years[9][10]. Building dams benefits some people due to the renewable electricity production but may threaten the benefit for fisheries[11]. The fisheries on other species (herring and sprat) may also affect salmon fisheries due to the food web interactions. When there is a crisis in salmon population, focusing only on salmon or only on one of the factors may not able to solve the problem, since the consequences may result from several factors. That is the reason we need a more comprehensive approach.

Figure 2: Food web relations of salmon in the marine ecosystems based on different life stages[12]. Grey seals and human are predators of salmon; herring and sprat are prey for salmon. Reference of photos: salmon (sketched from the photo from NOAA Central Library Historical Fisheries Collection), sprat (Photo by Hans Hillewaert/ CC4.0), grey seal (Photo by the3cats/ CC0 1.0), coastal trap net fishery (Photo by Maija Holma), herring and offshore fisheries (By Tin-Yu Lai).

However, the goal of “holistic management” is hardly achieved by one step. At this moment, stepping forward to the holistic management is still at a beginning stage. In the case of Baltic salmon, some models are able to include different types of salmon fisheries[13], but there is no model that captures salmon’s food web relation yet. Therefore, we are developing a bio-economic model that includes salmon, grey seal, and herring populations, as well as salmon and herring fisheries. As described in the second paragraph, the interactions of salmon with other species are different depending on its life stages (Figure 2). Based on this, our model is extended from single species age structure models so that different types of interactions can be included at different ages of salmon’s life.

By building food web interactions among the species, the model could be used to explore the potential influences that different fisheries may have on each other even for fisheries that are managed separately (e.g., the offshore fisheries target on Bothnian herring and coastal fisheries target on salmon). Such model could serve as a tool to examine the interaction results among the species and fisheries before setting up the “holistic management”.

[1]Long, R.D., Charles, A., Stephenson, R.L., 2015. Key principles of marine ecosystem-based management. Marine Policy 57, 53-60.

[2]ICES, 2015. Report of the Baltic Salmon and Trout Assessment Working Group (WGBAST). ICES CM 2015\ACOM:08, Rostock, Germany, p. 362 pp.

[3]Vikingstad, E., Andersson, E., Hansen, T. J., Norberg, B., Mayer, I., Stefansson, S. O., … Taranger, G. L. ,2016. Effects of temperature on the final stages of sexual maturation in Atlantic salmon (Salmo salar L.). Fish Physiology and Biochemistry, 42(3), 895–907

[4]Jonsson, B., Jonsson, N. & Finstad, A., 2013. Effects of temperature and food quality on age and size at maturity in ectotherms: An experimental test with Atlantic salmon. Journal of Animal Ecology. 82, 2001-210.

[5]Nieminen, E. ,2017. Bioeconomic and game theoretic applications of optimal Baltic Sea fisheries management : Towards a holistic approach. Univeristy of Helsinki.

[6]Salminen, M., 2001. Diet of post-smolt and one-sea-winter Atlantic salmon in the Bothnian Sea, Northern Baltic. Journal of Fish Biology 58, 16-35.

[7]Same as note 2.

[8]Holma, M., Lindroos, M., Oinonen, S., 2014. The economics of conflicting interests: Northern baltic salmon fishery adaption to gray seal abundance. Natural Resource Modeling 27, 275-299.

[9]Holma, M., 2016. Managing Northern Baltic salmon fisheries under social-ecological complexity. Presentation in 2016 IIFET conference, 12th July-15th July, 2016, Aberdeen, UK.

[10]Kulmala, S., Laukkanen, M., Michielsens, C., 2008. Reconciling economic and biological modeling of migratory fish stocks: Optimal management of the Atlantic salmon fishery in the Baltic Sea. Ecological Economics 64, 716-728

[11]Same as note 5.

[12]Lai ,T.Y., Lindroos, M. & Grønbæk, L. 2017. “The role of food web interactions in multispecies fisheries management: an optimal bioeconomic analysis of Baltic salmon”. Presentation at the World Conference on Natural Resource Modeling (WCNRM), Barcelona, Spain, 6-9 June, 2017.

[13]Same as note 9 and note 10

By Tin-Yu Lai
Published Nov. 21, 2017 10:09 AM - Last modified Nov. 23, 2017 12:20 AM