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Not many fish species can tolerate both fresh and saltwater. Sure, there are anadromous and catadromous species like salmon, some species of sturgeon, some species of eels, Pacific Lamprey, and even estuarine species that can tolerate large fluctuations in salinity, like the Starry Flounder. There is even a shark species that can tolerate low salinity or fresh water for long periods of time (Bull Shark, Carcharhinus leucas). Despite these few instances, the majority of all fish species are adapted to a specific salinity (or lack thereof) range.
I can relate to this specific adaptation; I have always been interested in marine fishes (yep, that’s plural!) and have had little interest in freshwater fishes. I am specifically interested in fish ecology, or learning about how fish species interact with other organisms and with their environment, and my undergraduate and graduate studies were focused on studying the trophic ecology (“science speak” for the diet of a fish and how it fits into the food web) of marine fishes. After completing my master’s degree at Moss Landing Marine Laboratories, I applied for a California State Sea Grant Fellowship to increase my understanding of how scientific research can be designed with strategic policy goals in mind. So, when I was awarded the fellowship and placed in the Delta Science Program to help the Delta Independent Science Board (ISB) with their upcoming report focusing on the state of the science regarding how riverine and estuarine flows are affecting fish species in the San Francisco Sacramento-San Joaquin Bay-Delta (whew, let’s just call it the Bay-Delta), I had to “adapt” to a new type of environment—working with freshwater and estuarine fishes.
So what do you do when there is so much to learn about freshwater systems? Dive right in, of course! I did a lot of reading those first few months. When I say a lot, I mean A LOT. I familiarized myself with a whole new cast of characters (so many freshwater/estuarine fish species in this region!), wrapped my head around the complex, dynamic, and greatly human-influenced environment in which they lived, and most difficult of all, tried to understand the political climate revolving around water use and management in California. What I found was extremely interesting; it was an entirely different perspective! When I was focused on studying marine fish species, I found that the most important environmental factors that affected the species I was studying were temperature, oceanographic conditions, and prey availability. In the Bay-Delta system, all those factors come into play plus so many more! Since up to half of the water flowing into the Bay-Delta is diverted either through pumping facilities, other water diversions, or for local in-Delta use, I have to think about how “flows” affect fish growth, mortality, and reproduction. Flow is an extremely complex term and has many hydrodynamic components, and in addition, many factors, such as temperature, salinity, and food resources for fish are affected by flow. Thus, understanding how flows affect fish populations is very involved and is becoming increasingly difficult to understand. The ISB’s report will focus on critically examining how the effect of flow on fish species in the Bay-Delta is assessed, looking at both historical and current information. The report will be out for public consumption towards the end of the year or early next year, so if you are interested in learning more, keep an eye out!
This transition from a marine system to an estuarine/freshwater one was not as difficult as I had initially thought, and it’s been more rewarding then I had ever imagined. The Bay-Delta scientist community is outstanding and inspiring, and is very helpful and welcoming to newcomers. Thanks to this fellowship, I have built upon my trophic ecology background and have a newfound appreciation for freshwater/estuarine fish species, as they are often in direct contact with human-induced habitat changes, in addition to fishing pressure and most other risks that marine species experience. And even though I am still not completely willing to give up my salty past (and future), I must admit that the world does not revolve around marine fishes!
Written by Jenny Bigman