Fish are friends, not foes

By Mollie McCulloch

At the mid-term conservation science conference on Tuesday 1st November 2016, Robert Giesler highlighted his concern towards the controversial issue of the endangered delta smelt (Hypomesus transpacificus); a fish native to California’s delta. Over 80% of the State of California is currently experiencing moderate drought conditions which is the basis for the controversy; fish vs farmers.


Map of the extent of drought across California on 10/11/2016. You can check out the most up-to-date figures right here:

To overcome this drought, people (like the guy below) are arguing that the need for the redirection of rivers is crucial to irrigate fields to keeps crops alive for human consumption and to maximise profits. On the other hand, the diversion of water negatively impacts the ecosystems within the delta. The delta smelt may be small in size (5 to 7 inches) but they play a big role in stabilising community composition. To conserve or not conserve, that is the question.

Protest in Fresno city where farmers and farmworkers rallied to turn the pumps on in the delta to allow irrigation to the farms in the western Central Valley of California.
(Photo credit:
The California Delta and its endemic species, the delta smelt.

The Sacramento-San Joaquin Delta encompasses 57 islands and a collection of fresh water channels. The delta is an essential source of fresh water for the surrounding agricultural area. The delta smelt is endemic to the area and has seen severe population reductions, raising concern to conservationists. The IUCN has listed the species as critically endangered.


The decline of the delta smelt from 1967 to 2015 [1]
The decline in population is due to the pumping of water away from the delta to overcome the problems caused by drought in other areas of California [2]. So why is this species so important to conserve?

A small fish with big impacts;

Protecting the delta smelt has caused some controversy, mainly amongst farmers who are more concerned about their crop yield. Farmers support the decision that water should be redirected towards their farms to ensure the growth of crops and therefore profits. Farmers are even more frustrated with the fact that water restrictions to help conserve the smelt have diverted in the opposite direction; population numbers continue to decline year after year [1]. Despite all the arguments against the protection of the smelt, this little fish plays a big role in ecosystem stability.

The protection of the delta smelt does not just concern itself but can help to protect the wider ecosystem. The smelt is a good indicator species, providing information on the health of the ecosystem [3]. The extinction of the delta smelt would affect the balance of food webs as it is a key species in trophic interactions. The delta is a biodiversity hotspot in the eyes of conservationists [4], therefore has a high priority in conservation strategies to help maintain a high biodiversity. A key feature of conservation goals is to preserve biodiversity, therefore protecting the California delta must be considered in order to achieve this.

Fish or farmers; who wins?

This issue still causes controversy among California. In the eyes of conservationists, the California delta’s ecosystem is too precious to loose in terms of biodiversity but for farmers it is hard to see the importance of species protection, especially a fish as small as the delta smelt. For progress to be made, increased understanding of this important conservation issue is key to protecting the Sacramento-San Joaquin Delta, California.


  1. (2016). Monthly Abundance Indices. [online] Available at: [Accessed 10 Nov. 2016].
  1. Moyle, P., Herbold, B., Stevens, D. and Miller, L. (1992). Life History and Status of Delta Smelt in the Sacramento-San Joaquin Estuary, California. Transactions of the American Fisheries Society, 121(1), pp.67-77.
  2. Hasenbein, M., Komoroske, L., Connon, R., Geist, J. and Fangue, N. (2013). Turbidity and Salinity Affect Feeding Performance and Physiological Stress in the Endangered Delta Smelt. Integrative and Comparative Biology, 53(4), pp.620-634.
  3. Myers, N., Mittermeier, R.A., Mittermeier, C.G., Da Fonseca, G.A. and Kent, J. (2000). Biodiversity hotspots for conservation priorities. Nature, 403(6772), pp.853-858.



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