Fish in the Bay – December 2018 UC Davis Trawls – Crangon 2018: Year of the Crangon!

Happy New Year!  Welcome to 2019

Good News:  We wrapped up December with an unbelievable Crangon brooding event.  This was the capstone on an unprecedented Crangon year.  Even the folks at Laine’s Bait Shop in Alviso ( tell us that this was the biggest shrimp year they have seen in at least 15 years!

2018 was also a banner year for American Shad, Threadfin Shad, Pacific Herring, Longfin Smelt, Staghorn Sculpin, and pretty much any other critter that appreciates the last few wet winters. 

 Saturday, 8 December – Bay-side trawls

Sunday, 9 December – upstream and east of Railroad Bridge

First, the shrimp:  The total Crangon catch was 67,052 for 2018!  Previous year Crangon catches were only a fraction of this number.

Also, as I have recently learned, Crangon have an annual migration and spawing event.  Then Pow!  We got to witness it! 

  • In November, we saw massive numbers of Crangon with “yellow saddles” for want of the technical term. 
  • Then in December, we caught buckets-full of “berried” Crangon.  Yes, “berried” is the technical term for female shrimp with eggs.  According to world-wide Crangon shrimp literature, female Crangon swim upstream to release eggs after fertilization.  Males evidently either hang back or simply don’t survive in high numbers.

1. Brooding Crangon

Jim Hobbs sifts through a tub full of Crangon from Coy1 in November.

The Crangon population has also generally migrated from Bay-side stations early in the summer to more creekside locations up Lower Coyote Creek in cooler weather.  

A pair of abstracts and a note help explain Crangon migration:

  • This one, from Netherlands Journal of Sea Research, indicates that berried female Crangon and mating ready males become sensitive to temperature which stimulates an autumn-winter migration to inshore.  Larvae migrate out into deeper Bay during spring and summer. 
  • This abstract discusses a Crangon variety, C. septemspinosa, in Delaware Bay.  With exception of a March-October reproductive cycle (practically opposite of our C. franciscorum), life-span, diet, and importance in the food web seem to be common traits. 
  • I also received a note from Kathy Heib at CFWS in December: “[Crangon franciscorum in SF Bay] migrate downstream from rearing areas as they mature.  Females with eggs are found at highest salinities … Female C. franciscorum with eggs are common in South Bay in winter until flows increase and salinities drop – then they move further downstream, towards and to Central Bay.”

Crangon franciscorum from Coy4 on 25 November.  These have cream or yellowish-colored “saddles” under the carapace behind the eyes.  These are growing egg masses.  A few others, which I suspect are males, have a dark brown spot over the same area.   There is also one reddish palaemon shrimp near the center of the tray.

I read that some types of red cherry shrimp show a “yellow saddle” as eggs develop.  At a later point, female shrimp become “berried.” Crangon appear to go through a similar reproductive phase.

Closeup of crangon from Alv3 with different shades of cream-colored growing egg mass (yellow saddle).
Slightly smaller Crangon from Pond A21 on 25 November.

No yellow saddle.  The shrimp above were a little smaller and had no egg mass at all.  This leads me to believe they are either a younger cohort … or maybe males?   The Crangon in Pond A21 were dramatically different just two weeks later on December 8th.

Crangon in December – berried females!!! 

On December 8th, after we trawled the three stations in Alviso Slough and rounded the bend into Lower Coyote Creek, we encountered a Crangon brooding storm.  Of the 560 Crangon caught at station Coy4, most, if not a huge majority, were berried females. Each one was carrying hundreds to thousands of eggs.  It was a Crangon brooding bonanza! 

Crangon full of eggs at Pond A21 too! 

We caught berried females at all subsequent trawling stations, with biggest numbers in Pond A21.  This was a complete change from just two weeks earlier.  Unfortunately, with only three professional researchers and one photographer on the boat, we could not systematically measure size and reproductive status of each shrimp.  I can only anecdotally report that there were a lot of females with eggs.  These photos are just a few samples.

Literature tells us that a large 3-year-old female can carry up to several thousand eggs.  The bottom-most photo above shows a likely example.  You can see how the female uses her “pleopods,” the rear 5 pair of legs also known as “swimmerets,” to guard the big mass of eggs.

The Crangon franciscorum Wikipedia page mentions that the Crangon life-cycle depends on freshwater flows.  This leads to boom-and-bust cycles.  Droughts in the late-1970s and late-1980s were bust years.  Wet years are Crangon boom years. 

Kathy Heib’s 1999 report on Caridean Shrimp in SF Bay shows that big El Nino years, 1982-84 and again in the late 1990s, were also boom years for Bay crangon: 

  • The report also mentions that San Francisco Bay Crangon “reproductive season extends from December through June.” P.79.
  •  The Heib paper also discusses other Bay shrimp, including, Crangon nigricauda (p.90) C. nigromaculata (p.102), Palaemon macrodactylus (p. 111), and Heptacarpus stimpsoni, (p.119) which are also shown in photos below.

2. Other shrimp species seen in December.

Crangon nigromaculata, aka: Black-spot Crangon.  (Yes, the spot is actually blue.) 

It has been an unusual treat to see C. nigromaculata. I have so far been unsuccessful in my search to find an explanation for the blue spot.  The spot must confer some survival advantage.  It looks like an eye.  What organism is it supposed to resemble?  What predator gets fooled?  Somehow a population of this spotted shrimp survives and remains distinct from the two other flavors of SF Bay Crangon.

More black-spot Crangon.

It is very rare to see more than one or two black-spots at a time. These were caught at station LSB-2.   Here they are arranged to show off the spots.  The flesh-colored humps on the sided of the top and bottom shrimp are isopod parasites described below.

Three black-spot Crangon in front, with two black-tail Crangon (C. nigricauda) behind.

Shrimp parasite:  The humps on the two foremost shrimp, in this photo and further above, are common shrimp parasites.  The parasite lies under the shrimp’s carapace.   

From internet sources, I learned that the parasites are isopods; suborder Cymothioda, family Bopyridae, and likely genus Asymmetrione.  The two parasites shown above are big fat female isopods.  From different sources I gleaned that the first isopod to infect a shrimp is invariably a female.  The second isopod will always be a smaller male. 

Cymothioda parasites on the web:

Two views of a black-spot Crangon next to a black-tail.

I think black-tail Crangon are slightly larger than black-spots, albeit, the particular black-spot shrimp shown above was small by black-spot standards.

From the profile shot at top, it appears the black-tail may have been a berried female.  Unfortunately, I did not notice her reproductive status until photo examination much later. 

Two black-spot Crangon side by side.

I took the photo above to show the uniformity of the spot itself.  The smaller shrimp may be younger.  Or, could this be a male-female comparison?

Heptacarpus Shrimp. 

Fifteen of these coastal Heptacarpus types of shrimp were caught at LSB2.  Some were identified as Heptacarpus stimpsoni, “Stimpson Coastal Shrimp,” by both Hobbs and Lewis.   

There are many varieties of coastal shrimp.  Even within the Heptacarpus genus alone there are dozens of species.  And, geographic boundaries of many types along the California coast are variable or not precisely known.  Adding to the confusion, there are very few good photographs to aid identification. 

Another type of Heptacarpus shrimp from LSB2.

These shrimp were red.  Also, there are at least three rostral teeth behind the eye-stalk, so this could be a different species.  The top one appears to be female with eggs. 

More photos of Heptacarpus shrimp from LSB2.
Same group of Heptacarpus in the tray.  Are all four of these Stimpson Coastal Shrimp?  Or, are these two different Heptacarpus species?

Heptacarpus shrimp images featured on the web:   

Palaemon shrimp (Oriental Shrimp)  

Palaemon are summer-time brooders: females become “ovigerous,” carrying 500-3000 eggs from May to August in California.  Like most shrimp, females are larger than males. 

  • An Ashelby, Grave, and Johnson (2013) paper “The global invader Palaemon macrodactylus … an interrogation of records and synthesis of data,” describes the world-wide invasion of Palaemon shrimp over the past several decades.  (Unfortunately, no link can be provided, but the paper can be googled.)
  • An early Scripps Institute news column gave 1954 as the year of introduction of Palaemon shrimp to SF Bay: 
Exopalaemon shrimp (Siberian Prawn).

Exopalaemons are a non-native freshwater shrimp now common in upstream areas.  And, it’s even more common now, because 2018 was also a record year for Exopalaemons as discussed further below.

Exopalaemon Invasion:  A Brown and Kathy Heib paper tells us that E. modestus probably invaded in the late-1990s.  It was first caught in Lower Sacramento River in Sept 2000.  By 2003, Exos had spread to freshwater and brackish areas in Suisun Bay and the Delta.  By 2004, they were recorded in San Pablo Bay. 

Crangon Table

Above table shows past five years of Crangon tallies from 13 of the 20 LSB stations. The data comes directly from Hobbs Lab archives – with permission from Dr. Hobbs.  The 13 stations were selected to best show month-by-month migration patterns (if any) from Lower South Bay to upstream stations in Lower Coyote Creek. 

  • A sharp increase in Crangon can be seen in months after the very wet winter of 2016-2017.  It is still hard to discern a migration pattern from only four years of comparable trawling record (two dry years, two wet years). 
  • January through perhaps April are Crangon lull periods, and one might conclude that more shrimp are seen in upstream stations near mid-year and perhaps year-end, but the pattern is still pretty fuzzy. 
Palaemon and Exopalaemon Tables.

I made similar tables to show monthly spatial distribution of the other two predominant types of shrimp.  Until now, I had presumed that:

  • Crangon shrimp were in direct competition with the other two types: ie, an increase in Crangon numbers would be matched by declines in Palaemon and Exopalaemon and vice-versa.
  • Palaemon shrimp might tend to predominate downstream/Bay-side stations.
  • Exopalaemon shrimp should nearly monopolize freshwater creek and river stations.

I was WRONG!  TOTALLY WRONG!  Raw numbers of Palaemon are about as high as ever (10,752 from 13 stations in 2018) and the Exopalaemon catch exploded (a record 5,085 shrimp) even as the Crangon bloomed.  2017 and 2018 were simply good years for each type of shrimp!

  3. Sculpin and Gobies.

2018 was also a banner year for Staghorn Sculpin.  Year-end count was 1674, compared to 350 to 500 in previous three years.

Sculpin eat the shrimp.  The above photo collage shows Bonehead Sculpin (top) and Staghorn Sculpin (middle) with shrimp antennae coming out their mouths.  Also, same Staghorn, bottom photo, with full belly.  These were just a few examples.  Sculpin can eat a variety of things. but during the big shrimp year, sculpin were feasting on shrimp.  

Shokihaze gobies (banded) and Shimofuri gobies (striped) from LSB2. 

Coincidentally, an extraordinary number of young Shokihaze and Shimofuri gobies were caught at LSB2 in December.  At roughly 200 each, this was the biggest single catch on record for both species.  Most were very tiny and likely resulted from a Shoki/Shimo spawning event.  I also noticed very young Shokihazis at other stations in both November and December, so I assume this was their recruitment season. 

4. Some pelagic fishes from December.

Top: Pacific Herring & American Shad. Bottom, American Shad.

Shad and Herring are returning. 

  • Top photo by Levi Lewis shows a Pacific Herring and American Shad caught at Coy1 on 9 December.  Both fish are showing the brown riverine back color.
  • Bottom photo shows an American Shad from Alv3.  Note the big filter-feeding mouth agape.

2018 was our biggest year for American Shad, Threadfin Shad, and Pacific Herring.  From September 2017 through June 2018 shad numbers surged.  After June there was a lull, and I presumed that the shad boom was over.  But then, American Shad came roaring back with 170 caught in December.  It still appears that extreme flushing in early 2017 drove most of the shad boom, but hopefully we will see similar recruitment continuing.

Northern Anchovy blue-backs in December.

The above fish are true blue-backs.  But, the colorful backs have faded either in response low salinity, or less sunlight in a turbid bay. (I almost speculated that winter low temperature may fade them, but that doesn’t make sense.  The deep blue Pacific is plenty cold year-round.)  I don’t think any of the above individuals would ever turn green or brown.  And, if not, then they must represent a separate Anchovy population. 

  • Anchovy at top:  You can see how bright blue color has completely faded from the top of the back even as the crown and some area above the lateral line remain blue.   
  • Anchovies at bottom:  This pair was similarly colored and faded.  The profile shot shows how skinny and underfed blue-backs appear by December.  I noted the same thing this time last year.

Riddle me this!  Why would an ocean-going blue-back Anchovy swim all the way into Lower South SF Bay in summer to end up looking emaciated by winter?  Evidently, they are not making this trip to fatten-up. 

Literature says that Northern Anchovies spawn miles off the coast.  Some studies acknowledge that a minority of spawning may occur in bays and estuaries.  I am always curious if these skinny blue-backs represent a distinct inshore migrating subgroup and to what extent they interbreed with the Bay’s year-round-resident anchovies.

Northern Anchovy young ones.  These two are showing both blue and green iridophore formation.

They say that iridophores, and chromatophores generally, develop in the neural crest of vertebrates as an embryo.  Then the cells soon migrate to other parts of the body.  These Anchovies are young, but far past embryonic stage of development.  So supposedly, all iridophores should be in place by now.  Yet, these young-of-year fish are only starting to express color!  And, why are some iridophores blue and others green? 

Young green-back Anchovy?

Meanwhile at one of the same stations, this young anchovy is expressing nearly all green iridophores. How do Northern Anchovies “choose” what color they want to be?   If fish age, location, and environmental factors are all identical, this must be a genetic thing!

5. Odds and ends.

Northern Harrier in Pond A21.

This is the classic “Marsh Hawk.”  This bird is sitting on a block of gypsum crystal on pond levee.  The dark brown color tells me she is female?  Males are supposed to be gray on the back, but I have not noticed this difference in the field.  

Harriers hover and swoop over marshes hunting for mice and voles more than anything else. They have an indented “owl-like” face that accentuates hearing during the hunt. 

A tale of two crabs.

Crab Report.  I mentioned before that we don’t see as many Harris Mud Crabs as were seen in the 1980s.  So, I took few minutes this month to briefly compare crab counts from recent Hobbs trawls against similar trawls conducted in the 1980s: 

Harris Mud Crab from Pond A21 at top.  Rhithropanopeus harrisii.  This one is an old invader from the Atlantic Coast first noted in SF Bay in 1937.  Harris crabs have been around so long we tend to consider them as more-or-less native now.

Yellow Shore Crab from Coy4 at bottom.  Hemigrapsus oregonensis or “Heemi.”  These are one of the most common shore crabs on the West Coast from the bottom tip of Alaska to Baja.  Being true natives, I assume we like yellow crabs more., also:

  • Long ago.  From late-1981 through 1986 (5 years) otter trawls at stations near Coy2 and Coy1 caught 462 Harris Mud Crabsas the most common invertebrate, compared to 138 Yellow Shore Crabs.
  • From 2012 to mid-2017 (5.6 years) modern-era Hobbs trawls, at up to 20 stations, yielded only 66 Harris Mud Crabs.  This compares to 2121 Yellow Shore Crabs over same period, albeit more stations and a much broader geographic area.   
  • Clearly, Yellow Shore Crabs are winning the modern crab wars, for better or for worse!  
  • I cannot explain why Synodotea isopods did not dominate invertebrate counts in the 1980s like they do today.    
Harbor seal at Calavaras Point.

Harbor Seal at Calaveras Point.  This goofy seal did not realize that high tide had flooded his mud flat.  I suppose he will wake by the time the water level reaches his nostrils. 

Happy New Year.  It’s time to get moving!

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