Primary production required for fisheries products

My first peer-reviewed article came out a few weeks ago and can be found here, or through my ResearchGate profile here. The article focuses on refining a measure of biotic impact as measured in life cycle assessment. Life cycle assessment attempts to quantify most environmental impacts of a product from ‘cradle-to-grave’. Thus, the greater consideration of biotic impacts is an important step forward for my focus area: fisheries. As we take fish out of the sea, we need to account for the impact on the ecosystem. This has been most commonly done through a measure of the primary production (or photosynthetic activity) that would have had to occur at the bottom of the food chain to produce these higher food chain items. The method used to date to quantify this primary production required (PPR) did not take into account differences in how energy transfers up the food chain in different ecosystems or the total level of primary production in that ecosystem, or some species-specific factors that I’ll get into later.2000px-ecological_pyramid-svg These ecosystem factors are important to consider as some ecosystems are less efficient at transferring photosynthetic energy up to higher trophic levels, and some ecosystems have lower amounts of primary production occurring annually. Taken together, this means some ecosystems will have less energy to begin with (in their annual energy budget if you will), and even less that will make it to higher trophic level species that we often harvest in fisheries for human consumption. From an energetic perspective, some fish represent a much greater proportion of that fisheries annual ‘energy budget’ than other fish.

I addressed this problem by trying to give better consideration to the factors mentioned above. First, I looked into how different ecosystems transfer energy and came across something in ecosystem modeling called transfer efficiency. After completing a biomass model of how an ecosystem functions, transfer efficiency can be one of the products based on how efficiently energy is transferring to higher trophic level organisms in the ecosystem. This ecosystem-specific transfer efficiency for somewhere like the North Sea will give an indication of energy transfers (for the North Sea it is more efficient that the global average of ~10-11%) in this specific ecosystem and make the results of the PPR equation more specific to that ecosystem. For the North Sea, the transfer efficiency is higher than the global average of ~10-11% meaning that based on this alone, harvesting fish biomass in the North Sea will require less base level photosynthetic activity than the global average.

Second, I included the total annual ecosystem primary production of the source

seawifs_global_biosphere
Chlorophyll concentration in the oceans

ecosystems I considered. I could thus relate the removal of fish biomass in the form of primary production to the total ecosystem’s primary production to give an indication of the scale of how much fish biomass we are removing in the context of total energy available in the ecosystem annually. Again, this will make the results more specific to the ecosystem we are considering through contextualizing the impact within the affected ecosystem.

Finally, I explicitly used species-specific energy and fishmeal and oil yields. Different species yield different amounts of fishmeal and especially fish oil depending on their characteristics (mainly the fat content of the fish at the time of processing). While the other improvements consider the ecosystem the species was sourced from, this focuses on the species itself making the results more specific to the species and its attributes.

While all of these factors may seem small, the continual ignoring of them meant that the results of the previous research often did not consider these factors to their full extent. Differences in the species and ecosystem factors mentioned above generate starkly different results. The figure below shows a difference of a factor of 20 for the same species harvested from different ecosystems. All other factors were the same, except the source ecosystem’s transfer efficiency and underlying primary production.

For me, I am a researcher so that the findings may be applied to move humanity towards a more sustainable future. If the previous method cannot distinguish between a 20x difference in ecological impact in one ecosystem compared to another, then the method must be improved. If we demand more from the companies that produce these feeds, we at least need to give them the proper tools to make these decisions. I know that many of these companies take their commitments seriously and have funded research that explores how they can improve their environmental performance. The fact remains that we have been using a system that does not consider all the factors it could, and my improvement to the PPR measure is one such example. There are other areas where we must continue to expand on our research, and this was a small area that I was lucky to be a part of working on.

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