Efforts continue to gain approval for releasing hatchery-raised delta smelt in the San Francisco Bay-Delta Estuary. However, given a poor prognosis for a successful introduction, the chances of approval are not good.1 The biggest obstacle is the absence of a location to release the hatchery-raised fish that will allow their survival and thus contribute to the species’ recovery. Another problem is the potential detrimental effect on the remaining wild smelt from genetic compromise.
To me, the answer to the second issue is clear. With few if any “wild” delta smelt left on Earth, it is essential to get as many hatchery smelt out into the wild as soon as possible to save the species. Let the genetics get worked out later by Mother Nature.
Two locations for release of hatchery smelt seem most plausible: the low salinity zone in the west Delta/eastern Suisun Bay and the Deep-Water Shipping Channel in the north Delta. These are primary late spring and early summer nursery areas that are most likely to have the right habitat conditions (water temperature and low salinity) and food supply. These two locations were the last known concentrations of juvenile delta smelt (Figure 1) from the last strong adult spawn in 2012 (Figure 2).
The better of the two sites is the eastern-Bay/west-Delta location, because the ship-channel gets too warm by summer (Figure 3). In contrast, the region between Collinsville in eastern Suisun Bay and Decker Island in the west Delta is cooler and within the low salinity zone (Figures 4 and 5). A nighttime near-bottom release into cooler, deeper channel waters would give the hatchery smelt at least a minimum opportunity to acclimate to the warm Bay-Delta waters.2
- https://watershed.ucdavis.edu/shed/lund/papers/FuturesForDeltaSmeltDecember2019.pdf , https://www.americanbar.org/groups/environment_energy_resources/publications/es/202000526-hatcheries-in-lieu-of-habitat/ , https://whyy.org/segments/a-tiny-fish-is-on-the-brink-of-extinction-does-it-matter-that-another-just-like-it-is-thriving/ , https://www.recordnet.com/story/sports/outdoors/fishing/2021/01/12/cdfw-fall-trawl-survey-yields-no-delta-smelt-third-year/6642023002/ ↩
- 20ºC is the likely limit for releasing hatchery smelt into the wild: (https://academic.oup.com/conphys/article/7/1/coy076/5334620) ↩