Fish in the Bay – January 2025. Crappie Shaduary!

January 2025 was a very disappointing month for Longfin Smelt.  Longfin spawning season started well enough.  November and December numbers looked promising.  But then, Longfin numbers abruptly turned sour by early January.  (Bay Study Fall Midwater Trawls also reported a Longfin decline, so this appears to have been a Bay-wide phenomenon.)  

Crappie Shaduary:

Oddball Fish of the month = Black Crappie.  We have seen this non-native freshwater fish before.  On rare occasions, individuals stray downstream from freshwater creek habitats and into our trawling range.  They feast on mysids, amphipods, and insects in addition to various other small bugs.  https://en.wikipedia.org/wiki/Black_crappie

Record Shad catch in January 2025 = “Shaduary.”  In 15 years of trawling record, we have never seen so many Shad in a single month:  533 American Shad + 232 Threadfin Shad. 

• Shad numbers steadily increased in Lower South Bay since our records began in 2010, but this is ridiculous! The January 2025 catch already beats the annual total for every previous year except 2018 and 2019!  This year will almost certainly be our biggest Shad year ever.
• Unlike Crappie, Shad tend to filter feed and pick on smaller organisms like copepods and other tiny zooplankton.

Inland/Mississippi Silversides were present at upstream stations and in restored ponds!  This is very bad!  More on that below.

Some Good news:

• Young Halibut continue recruiting at downstream stations.
• Crangon brooding event: Crangon Shrimp mamas with loads of developing eggs showed up this month!
• First baby Bat Ray of 2025! A baby girl Ray; 170 mm length.  She was probably born in the last week of December.

1. Shad & Bigger Fishes.

Shaduary explosion in Artesian Slough.  Winter is Shad spawning season. Shad return to fresher water this time of year. 

• Curiously and as far as we know, Shad do NOT spawn in Lower South Bay creeks and rivers. Yet, these young ones, generally too young for spawning, show up every winter.

Station Art3 was the ‘Shad winner:’ 427 American + 33 Threadfin = 460 Shad. 

• January weekend results suggest that salinity at between 5 and 6 ppt is a “Shad Sweet Spot.”
• Relatively high zooplankton productivity in Artesian Slough likely stimulated this temporary “Shad Sanctuary.”

Striped Bass lurking just downstream???  We counted and released our haul of 460 Shad as we drifted downstream toward station Coy1.  Suddenly our fish-finding sonar began detecting shadows of bigger fishes!  Predators were on alert.

Bigger fish like Striped Bass know that Shad are good food. https://en.wikipedia.org/wiki/American_shad#:~:text=The%20American%20or%20Atlantic%20shad,is%20a%20valued%20food%20fish.   (Always remember: the scientific name for American Shad is “Alosa sapidissima” which translates as “the delicious, or savory, Shad.”)

• It’s a fish-eat-fish world below the surface.

White Sturgeon / River Monsters!  We tallied five Sturgeon images on fish-finding sonar during the weekend, four of which are shown above. 

• Coyote Creek and adjacent sloughs are wintertime Sturgeon feeding zones. Gobies, Anchovies, baby flatfishes, Lampreys, and shrimp are all part of a healthy Sturgeon diet.

2. Longfins & Bad Omens.

Longfin Smelt count = 70.  Alas, this is a tragedy.  The previous December 2024 Longfin count of 264 was good.  A number of particularly large adults were observed.  It seemed a promising start for this current Longfin spawning season.  … Then, it all went wrong.

• Longfins diminished in all parts of SF Bay compared to the most recent years. For Lower South Bay, this was the lowest January count since 2020.  (That may not seem so long ago, but in terms of recovery of this local Longfin Smelt population, this is a major step backwards!)
• Perhaps even more disturbing, Longfins were behaving differently by January. Very few spawners showed up at the typical upstream stations and almost NONE were caught in restored ponds A19 and A21.  (In all the recent good years, the restored ponds provided more than half of our Longfin catch.)  Instead Longfins tended to drift around in the deeper downstream waters of Coyote Creek and at station Alv3.

Sami gently collects Longfin Smelt from the tub Station Alv3 on 4 Jan 2025.

Exact reasons for this Longfin downturn are unknown. Two possible factors:

• An early atmospheric river in November could have triggered early Longfin spawning in SF Bay. https://www.nytimes.com/2024/11/23/us/storm-rain-atmospheric-river-california.html   Then absence of rain throughout December and January might have just as quickly forced big adult Longfins to flee the area.  https://www.newsweek.com/san-francisco-weather-forecast-prediction-january-2025-february-2014932
• El Nino conditions prevailed in coastal waters from early to (at least) mid-2024. Warm sea surface temperatures + low upwelling may have impeded growth and recruitment of the 2024 year class of Longfins, Sculpins, English Sole, and others. …  Maybe?  https://en.wikipedia.org/wiki/2023%E2%80%932024_El_Ni%C3%B1o_event
• Who knows? We can only guess as we cope with crushed hopes at this point.      

More Bad Omens:  Non-native species & the Quarter Moon.

Inland/Mississippi Silverside count = 535.  Non-native Silversides usually bloom during warm months and then largely disappear when it gets cold. However, contrary to the typical pattern, this was the biggest January count of Mississippi Silversides in our trawling record.  

Two types of “Silversides” – Non-native “Mississippi” and native “Topsmelt” in Pond A21.

Even worse, egg-eating demon Silversides were present at most stations where we should expect to see winter-spawning Longfins.

3. Deep Thoughts about Smelt, Silversides, & Moon phases.

(Note.  Unexpectedly bad Longfin catches in early January under a Quarter Moon led me to investigate whether the Moon Phase on our trawling days could have been another factor.  Interestingly, the answer was “Maybe” – Moon phases often regulate spawning behavior in fishes, especially in Smelt and Silversides.”  HOWEVER, low Longfin numbers persisted in subsequent Longfin Smelt Broodstock trawls throughout the month during subsequent phases – Moon Hypothesis Rejected!

Nonetheless, both Sami and Jim Hobbs were aware of this Moon Phase-Smelt Spawning connection.  They both related to me considerable fish lore on this subject.)     

Rule #1:  Not all “Smelt” are true Smelt, and not all “Silversides” are called Silversides.  The names are often used generically to describe varieties of small silvery estuarine and marine fishes around the world.  Biological science says they are two different fish families that are NOT closely related:

1. Atherinopsidae (a.k.a “Silversides”). Examples: Jacksmelt, Topsmelt, Grunion, Mississippi Silversides, Inland Silversides, etc.
2. Osmeridae (a.k.a “True Smelt”). Examples: Longfin Smelt, Delta Smelt, Surf Smelt, Night Smelt, Rainbow Smelt, etc.  https://www.clovegarden.com/ingred/sf_smeltz.html 

Many members of both families time their spawning activity with the phases of the Moon. 

• Atherinopsidae – Grunion & other Silversides.
  • Walker (1949) https://escholarship.org/content/qt1j33928x/qt1j33928x.pdf
    “The first notice given to the fascinating story of the spawning runs of the grunion was published by Hubbs (1916). In discussing Leuresthes tenuis [California Grunion] he quoted a short letter from Mr. J. S. Joplin, of Santa Ana, describing the spawning of these fish. Mr. Joplin remarked that the fish ran during March, April, and May, on the second, third and fourth nights after the full moon, at full tide. He notes their regularity thus: “I have been observing them for thirty years and the time of their coming is so regular that during that time I have rarely missed them”. … 

    Thompson (1919) first considered that the grunion ran only on the descending tide series following the full moon. In a footnote he noted that a light run had occurred on a tide series following the new moon. He felt, however, that the runs following the new moon were light as compared to those associated with the full moon. He concluded that runs come only after the highest tide of a series.Clark (1925) showed that runs of equal intensity follow the full and the new moons. She also believed that grunion run only after the highest tide of a series has been reached. From studies of the ovaries, she concluded that as soon as one batch of eggs is spawned out, another batch begins to develop, matures, and is spawned out about two weeks later. She wrote, “the interval between spawnings is apparently fifteen days instead of two weeks. This condition results in the fishes spawning on later and lower tides during the higher tide series of high tides than on the lower series of high tides.”

• • Grunion on sandy California beaches. https://cdfwmarine.wordpress.com/2019/03/11/grunion-dance-by-the-light-of-the-moon/  “The phases of the moon have a powerful hold on the lives of these small, silvery fish from beginning to end. Scientists think their “internal clock” may detect the tidal changes heralded by the full and new moons and trigger them to begin their runs. …  on full and new moons from early spring through summer, they abandon their secretive ways and swarm onto some of Southern California’s wide, sandy beaches (also down into Baja California). …Female California grunion can return to ‘dance on the beach’ four to eight times per year and may lay over 3,000 eggs every two weeks. That means a single female has the potential to produce tens of thousands of eggs in her short, four-year life span. The eggs incubate under the sand for about 10 days, until the tides are once again high enough to wash out the fully developed embryos.” 

• • Reebs (2011) https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/lunar-rhythms “Many intertidal species spawn only during the high tides that surround the days of new moon and full moon. Examples include the California grunion (Leuresthes tenuis), the Gulf grunion (Leuresthes sardina), the Atlantic silverside (Menidia menidia), the mummichog, the inanga, the surf smelt (Hypomesus pretiosus), and the foureye (Anableps microlepis). The eggs are deposited high on the shore on spring tides, and, during the following 2 weeks, they remain in wet sand, uncovered by water and thus unexposed to marine predators. They hatch only during the next series of spring tides, which will take the larvae away.” 

• Osmeridae – True Smelt.
  • Delta Smelt. Bennet (2005) https://www.waterboards.ca.gov/waterrights/water_issues/programs/bay_delta/deltaflow/docs/exhibits/sfwc/spprt_docs/sfwc_exh3_bennett_crit_assess_deltasmelt.pdf
    “Spawning success appears to be timed to lunar periods within a water temperature range of about 15 to 20°C.” … Lunar phase can also be an important cue for spawning, particularly for fish depositing eggs in tidal or intertidal habitat (Moyle and Cech 1996). For example, spawning is closely tied to lunar phases in coastal silversides (Atherinidae), most notably for grunion (Leuresthes tenuis) that spawn en-masse at night on California coastal beaches. Peak spawning in H. japonicus also occurs at night during full moons (Hirose and Kawaguchi 1998a), whereas surf smelt are reported by local fishermen to spawn on beaches at night during new moons (Bennett, pers.obs.)

• • Surf Smelt. Therriault et al. (2002) https://publications.gc.ca/collections/collection_2015/mpo-dfo/Fs70-5-2002-115-eng.pdf 
    “Spawning activity has been observed and described extensively (Schaefer 1936; Thompson et al. 1936; Loosanoff 1937; Yap-Chiongco 1941).  Spawning time is affected by tidal and lunar cycles with marked increases in the number of spawners during high evening tides during full moons (Levy 1985).  During the spawning season, surf smelt concentrate just offshore, adjacent to spawning beaches of fine to coarse gravel (1-7mm in diameter) (Schaefer 1936; Penttila 1978; 2001). Approximately one to two hours prior to high tide, single ripe females begin swimming onshore (0-5cm depths).  Several males pursue each female and position themselves … This process takes less than 20 seconds with each female repeating the process over several days until all eggs have been spent.”

• • Rainbow Smelt – on East Coast. https://www.pressherald.com/2011/04/24/peepers-a-sign-that-smelt-are-set-to-spawn_2011-04-24/ 
    “At night, often influenced by the large, full moon tides, smelt will come to the head of the tide area in rivers and congregate as they prepare to spawn. This can be as much as up to two hours on either side of high tide. In fresh water, smelt travel at night and spawn at the base of falls or rapids that they can not pass. … The fertilized eggs are extremely sticky and will adhere to almost anything, including gravel, sand, rocks and weeds.”

• • Japanese Surf Smelt. Hirose and Kawaguchi (1998). https://link.springer.com/article/10.1023/A:1007477705726
    “Spawning occurred from late March to early May with its peak at the spring tide period during full moon in April. Before dark, fish gathered to school from 1–3 m depth, and 10–20 m off the shoreline of the spawning beach. Just before dark, they repeatedly approached the shoreline and stayed near the shoreline to spawn just after dark.” 

Do Moon phases similarly regulate Longfin Smelt spawning?  Investigation continues.

4. Halibut.

California Halibut count = 25.  This was our third best January Halibut catch in LSB.  (January 2016 was #1, with 85.  January 2024 was #2, with 31.)   These are young El Nino-year recruits. 

• Halibut are ambush predators that lay on the bottom. When small silvery fishes to drift within range, the Halibut lunges upward.  Jaws flash open and snap. 
• This predator is also prey. Adult Halibut are very popular game fishes for human anglers.  They taste way better than Striped Bass or Sturgeon IMO, and they are safer for consumption.   https://www.sfei.org/sites/default/files/users/antonytran/SFBay%20Advisory%20Kiosk.pdf      

Another Halibut at Alv2 as he/she was being released.

Warning: Keep your fingers away from those needle-sharp teeth!  Even small Halibuts can bite you!  … The bite doesn’t cause much lasting damage, but it hurts a lot.

As for Longfins …

• Finally, some relief? https://weatherwest.com/archives/43287  “NorCal January dry spell ends on last day of the month …”   (This still could be too late to salvage the current spawning season.)
• Egg-eating Mississippi/Inland Silversides must be recognized as destructive non-native threats to our Longfin spawn.   
• I still cling to the “Bad Moon Hypothesis” despite phases that change weekly and logic telling me it makes no sense.

Bad Moon Rising – Creedence Clearwater Revival (HQ – 5.1 Studio )  https://www.youtube.com/watch?v=w6iRNVwslM4