September 2024 Part 2: Goby Faces, Halibut Eyes, Clupeiform Colors, etc.

September report continued …

1. Gobies & Sculpin.

Something odd is happening in Goby World.  All numbers were down compared to historical averages, plus there are signs of an autumn second spawn we have only seen once before.

Longjaw Mudsucker count = 1.  This was only the third Mudsucker caught in 2024.  

Prickly Sculpin count = 2.  The year-to-date Prickly count is 17 – a bit low.  Pricklys depend on rainwater flushing and access to fresher upstream waters.

Shimofuri Goby count = 5.  Year-to-date: 345. The 2024 Shimo count is the lowest since their population exploded in 2020. 

• The top Shimo is showing the lighter striped “watermelon” body color. The darker Shimo below is showing the “snakeskin” pattern.  
• Literature says that mature male Shimos (and closely related Chameleon Gobies) turn dark when defending mating burrow. Could this pair be emblematic of a breeding couple?

Yellowfin Goby count = 50.  Year to date: 921.  Yellowfin numbers are also low.

Red faces.  Faces of male Yellowfins redden during their mating season and the jaws broaden.  This seems to be consistent with the male’s mission to excavate and defend a mating burrow.    

• In this example: The top Yellowfin has a slightly reddish face and broader jaw.  The bottom fish may be a female.
• This is not Yellowfin spawning season! The main spawning time for Yellowfins is January through March. What is going on here?

2. Halibut Eyes.

California Halibut count = 32.  The Halibut recruits of 2024 are growing bigger month-by-month. 

We noticed something interesting in August: Some Halibut have brown eyes, others have vivid blue-green, or teal-colored eyes!

Why do Halibut eyes come in different colors? 

• Our first hypothesis: Maybe Halibut eyes turn green or brown based on salinity – like Clupeiform dorsal colors. If true, upstream Halibut would be mostly brown-eyed and downstream Halibut would have green eyes. 
• Second hypothesis: Maybe Halibut eyes adjust to light intensity or water clarity.  Green eyes might act like headlights in clear dark water.  Brown eyes may work better in high turbidity???

Alas, we quickly learned that green and brown Halibut eyes seem to be equally common and randomly distributed.  (The observed sample size is still very small.  N = 20 or so.)  This mystery remains unsolved.

3. Clupeiform Colors.

American Shad count = 2.  Shad are cool weather fishes in the San Francisco Estuary. We catch very few of them in warm months.

The honest Clupeiform.  American Shad dorsal colors almost always match ambient salinity with excellent consistency.  

• In this example, this Shad was likely hanging out in cooler/saltier water at the bottom of the channel, hence a predominantly Mélange Green dorsal color. The holding tub was filled with surface water at the end of the trawl (2.9 ppt) a minute or two before the first photo.  The second photo was taken a minute later as large golden and brown splotches spread.
• Rule of thumb: It takes around three minutes for a Clupeiform to transition from high salinity = full blue, to low salinity = full brown. (High salinity = >20 ppt.  Low salinity =  <10 ppt.)     

Threadfin Shad count = 20.  Threadfins are smaller cousins of American Shad.  They grow to a maximum length of about 5 inches.  They were transplanted to California to serve as ‘forage fish’ for Striped Bass.  It is an unfortunate history behind this attractive and otherwise pleasant fish.

The shiny Clupeiform.  Threadfins display a confusing mirror sheen across their dorsal sides. The sheen obscures salinity-induced color changes.

Pro tip: Slowly tilt the fish across its longitudinal axis with respect to light source to view the underlying color.  At certain angles, the mirror sheen largely disappears, and the underlying dorsal color can be seen.

Northern Anchovy count = 312.  2024 still stands as a particularly weak year for Anchovies.  

The tricky Clupeiform.  Anchovies are bluer on the color spectrum compared to other Clupeiforms, but they are tricky.  Their dorsal colors can vary enormously at any given level of salinity.

• In this example, Two Anchovies of similar age, size, guanine crystal coverage, and identical salinity concentration, display slightly different dorsal colors: Thermal Spring versus Lounge Green. Salinity did not vary much during the entire trawl:  ~ 13.4 ppt +/- 0.5. 

Bluing Up.  The green-to-blue threshold for Anchovies is roughly 18 ppt. Above that threshold, they turn blue.  Below 18, they are green … usually.

In this example:  The two Anchovies at top on the far left show vivid green color on their dorsums except just behind the head where chromatophores are beginning to turn blue.  Salinity was 2 to 3 ppt higher at the end of the trawl. They were gradually “bluing up” while we watched.

• All but the top Anchovy have lost almost all guanine in their chromatophores. Lack of guanine makes their dorsums look translucent.

Browning Down.  Below about 10 ppt, Anchovies and Shad turn gold or brown. 

In this example, Anchovy gold is a combination of golden guanine crystals (in chromatophore cells) and the underlying flesh color as the guanine disappears completely.  The Threadfin Shad, shown in the top panel, does not lose guanine and expresses the browner shade of “Different Gold” (#4). 

Anchovies transition from green to golden at salinity slightly below 10 ppt.

In this example, all five Anchovies shown here were “Mélange Green” where salinity was almost exactly 10 ppt over the entire trawl.  

Tricky Anchovies #1.  Anchovies look clear, pinkish, or brown when guanine is gone. 

Pro tip: For Anchovies, always look for traces of crystal color. Don’t be fooled by flesh tones as guanine crystals disappear in low salinity. In this example, most Anchovies appear very brown (“Bengal Grass” or perhaps even “Best Bronze”), but their chromatophores are indicating green: “Nurture Green” or “Lounge Green”.  

Anchovies and invasive Silversides in Pond A19.

Tricky Anchovies #2. 

In this example, most Anchovies here look golden because they lack guanine crystals.  I think most of these were young-of-year.  The few Anchovies that were expressing some guanine color (along their lateral lines) again show hues of “Nurture Green” and “Lounge Green.” 

• This is puzzling. With end salinity of 15 to 18 ppt, we would expect Anchovy crystals to express at least “Thermal Spring’ or bluer. Anchovies are tricky Clupeiforms! 

4. Pelicans.

American White Pelicans visit SF Bay for half the year from mid-summer until early winter.  While here, they spend most days alternately roosting in Pond A17 and feasting on small fishes in adjacent ponds.

We spotted the flock loafing on a mud bank just south of station Coy1.  Rising tide finally nudged them to seek higher ground.    

• American White Pelican, Pelicanus erithrorhynchos https://tgreybirds.com/Pages/AmericanWhitePelicanp.html#:~:text=American%20White%20Pelicans%20winter%20in,beginning%20their%20return%20in%20July.
  “American White Pelicans winter in large numbers in and around San Francisco Bay. They nest in some fifty large colonies on inland lakes in the prairie and basin states and provinces of the US and Canada, departing from their wintering grounds starting in February, and beginning their return in July.” 

Brown Pelicans are deep water plunge-divers.  If we see them, they are almost always cruising over, and/or plunge-diving into waters near LSB1 or LSB2.  Needless to say, Pelicans depend on Anchovies as a major food source. 

It is strangely satisfying to examine a tray full of Anchovies, measure them, check for eggs, evaluate colors, quickly release them —  and then look up to see the brown birds who eat them soaring overhead.  It’s a life-imitating-art-depicting-life kind of moment.   

M. C. Escher: the Dutch artist famous for creating woodcut tessellations featuring birds and fish. His art features many other interesting and abstract things.

• M. C. Escher: https://mcescher.com/
• Fish and Bird Experiments: https://www.escherinhetpaleis.nl/escher-today/experimenting-fishes-birds/?lang=en
• Sky and Water I: https://en.wikipedia.org/wiki/Sky_and_Water_I