Fish in the Bay – April 2019, UC Davis Trawls – April is baby fish month (Part 1).

Happy April!  I trawled with the Hobbs team twice this month, so far: Otter trawls conducted on 6 April, and then again for 20mm net trawls on 13 April.  … And, I am fleshing out a hypothesis that numbers of baby fish in Lower South Bay surge in April.  So far, conclusions are based on only six years of observational record. 

(“Baby Fish” and “Baby Fish Month” are my own terms. They are not part of the UC Davis or Hobbs Lab official lexicon.)

It is getting warmer and saltier at all stations.  That’s what happens in spring.  Only station Art1 had salinity at less than 1ppt, and that is immediately downstream of the SJ-SC RWF discharge point where tertiary-treated wastewater flows into Artesian Slough.  Water temperatures rose at least 5 degrees since March and continue to climb.  No surprises there.

Juvenile Herring and Anchovies less than 40mm are easily confused.  I indicated in RED, in the table far above, instances where very young Pacific Herring were initially misidentified as Anchovies in the field.  Later lab examination correctly identified them.

1. Baby Fish

News Alert:  Longfin Smelt larvae were collected by Dr. Hobbs on 14 April 2019.  This is the second documented successful spawning in Alviso Marsh Complex. The first successful spawn was recorded in early 2017. 

But, Longfin spawning and recruitment is just a small piece of the overall baby fish ecology in Lower South Bay.      

Longfin Smelt are just one of many types of baby fish in the Alviso Marsh Complex.  Longfins hatch and recruit alongside large numbers of Northern Anchovies and various types of gobies at the very least.  Drifting larval Herring further complicate the picture.  Hopefully, regular use of the 20mm net from now on will provide scientific quantification of our Baby Fish Phenomenon.

Is April the baby fish month in LSB?  I have pondered this question since 2014.  That year, we caught 350 tiny fish too small to be identified.  They were listed as “Unidentified Gobies” because they looked more like gobies than anything else.  But, the baby fish record has been a little spotty. 

• Unlike any other month, five of the last six Aprils had notable abundance of baby fish.  It made April fish counts rather tedious. 
• In April 2018, 1386 baby Staghorn Sculpin were large enough to be identified as Staghorns in addition to 11 ‘unidentified gobies.’  There may have also been a “Delayed Baby Fish Effect” with 1001 additional ‘unidentified gobies’ counted in July.
• All catches shown above were collected by coarse Otter net which may have substantially undercounted baby fish.  Use of a finer 20mm net began in 2018. 
• Until this year, little attempt was made to identify baby fish other than larval Longfin Smelt. Most of the rest are recorded as “Unidentified Gobies.”

Baby Fish are hard to identify. There is a technical divide between larval, juvenile, and adult fish.  Baby fish fall somewhere in the larval to juvenile stages of development.  Unlike adults, baby fish are tiny and their identifying characteristics are often under-developed.  To make matters worse, identification keys tend to be based on preserved specimens that are usually pickled in ethanol. Fresh, live baby fish can appear slightly to significantly different. 

Pacific Herring are a significant factor during baby fish month in wet years.  Herring lay huge masses of eggs in estuaries along the West Coast around March.  The egg-laying is notable in more northern portions of SF Bay.  We see a peak in juvenile herring in March or April, especially after extended rain.

Good news!  246 Pacific Herring were caught in April Otter trawls.  All were juveniles, as shown above.  (Tiny larval herring caught in the 20mm net are not included in Otter trawl numbers.)

Young Pacific Herring in Lower South Bay straddle the Baby Fish divide in recent records.  After hatching, egg-sack larvae drift all over the Bay by the millions.  By the time we see them near the Alviso Marsh Complex, they have mostly, or entirely, metamorphosized to juveniles.  They grow quickly before they scoot out to the ocean.  The dozens to few hundreds of fingerlings we catch in Otter nets each March or April were recorded as “Pacific Herring,” not as “Baby Fish” per se.

Short-bodied baby fish from Otter trawls are invariably classified as “Unidientified Gobies.”  In most instances that is probably the correct call.  However, even a cursory close examination would probably tease out Staghorn Sculpin, Prickly Sculpin, and Longjaw Mudsucker babies from the total count at the very least.  

Furthermore, even amongst the generic “Gobids” it would someday be helpful to know how many are Yellowfin versus Shokihaze, Shimofuri, Arrow, Bay, etc.

Of greater interest are “Long-Skinny” larvae.  Longfin Smelt, Pacific Herring, and Northern Anchovy larvae appear long and skinny.  All three species are ecologically important.  All three hatch and/or recruit sometime between around November through April.  Albeit, Anchovy spawning may also occur randomly around the year in LSB.

Baby fish + mysids!  Dr. Levi Lewis examining the 20mm net catch from station Alv3 above.  The hoop-shaped 20mm net is in the background.  This 5-minute trawl caught too many tiny critters for one jar.  Some juvenile herring, gobies, and mysids are clearly visible. 

Baby fish closeup, again from Alv3.  The largest fish and most of the smaller ones in this photo appear to be Herring.  How many are still larval, versus juvenile, versus young adult?  How carefully should we document our annual fin-fish production in the Alviso Marsh Complex?

Reminder: Because these were caught in the 20mm net, these fish are not counted in the tables far above. 

Herring and Anchovies are fairly closely related as fish go.  Both are members of the Cluipeiformes order https://en.wikipedia.org/wiki/Clupeiformes.  So, it is not surprising that their larval forms are almost indistinguishable.  (Shad and Sardines are also part of this order which could further complicate our local baby fish picture if we ever start detecting them sometime in the future.)

In addition to head shape and ventral melanophores, the guide book says that Northern Anchovies have 40-46 myomers (skeletal muscle fibers that also correspond to adult vertebrae).  Pacific Herring have 45-55 myomers. 

Also to my eye, Pacific Herring have a long straight tapering gut.  The Anchovy gut is rounder and lumpier.

But, baby fish identification gets extremely tricky when the fish is less than about 30mm long.

Sculpin and mudsuckers develop distinctive pigmentation at a very young age.  This makes them easy to distinguish from other types of gobies.

Juvenile Sculpin are even easier to identify.  1386 baby Staghorn Sculpin were counted in April 2018.  That was by far the highest monthly Sculpin count in Hobbs records.  The April 2019 sculpin count was a much more modest, but still respectable, 143.  Similar to Herring, Sculpin tend to straddle the Baby Fish divide because most of the young tend to be field-identified, and hence, not recorded as generic “Baby Fish,” e.g. “Unidentified Gobies.”

2. Adult Fish

Seventeen adult Longfins were caught in April.  These continue to show the silver-purplish breeding colors even though temperature are well above the Longfin spawning threshold. Longfins live 2 to 3 years, so these adults will either migrate back to salty waters or die.  https://www.dfg.ca.gov/delta/data/longfinsmelt/documents/LongfinsmeltFactSheet_July09.pdf

If we can’t save them, no one will:  https://www.biologicaldiversity.org/species/fish/longfin_smelt/

Starry Flounder.  It is still early in the year for Starries.  Three were caught in April.  Zero to a few is normal for April.  This one had the sandpapery tubercles on the skin indicating mating readiness even though it is still a fairly small fish. 

Striped Bass arrived to celebrate baby fish month in their own particular way.  We would probably see more baby fish were it not for these voracious predators.

Striped Bass exert enormous pressure on local fish populations.

 Fat bellies!  Dr. Hobbs thought about slicing open one of these bass to see what they are eating.  Then he reconsidered.  What’s the point?  They are full of baby fish! …

On the other hand, there are probably some Longfins in those bellies too!  To slice, or not to slice …

Let’s move on for now!  (We did not slice.)

Sixty Shokihaze Gobies were counted in April. Shokihazes occasionally outnumber larger Yellowfin Gobies.  We should presume all these non-native gobies also consume vast quantities of mysids and baby fish.  At some point, we may want to further investigate their effect on the local ecosystem.

Shimofuri Gobies were not as numerous in April but had disturbingly fat bellies as well.

Bay Pipefish were NOT caught in April Otter trawls on 6-7 April.  But, we did catch a few in the 20mm net trawls the following week (13-14 April).

(Note to self:  I sense a potential under-count of Bay Pipefish in our records.  The finer 20mm net is probably more effective at catching pipefish, but pipefish are usually manually rejected from 20mm net larval samples!  Rejected pipefish are recorded separately, but not necessarily reunited into the historical record.)

I like pipefish, so I track them no matter how they are caught.

3. Mysids!

Mysids were abundant at most stations.  But, extremely dense concentrations of these tiny shrimp-like bugs are ephemeral. 

Dr. Hobbs speculated that mysids might be responsive to spring-versus-neap tide cycles.  Then, he and Dr. Lewis encountered this bug bonanza on April 14^th upstream in Coyote Creek.  This yet again overturned our unwritten mysid conceptual models.  We must understand the local life-cycle of this important bug.  Someday soon, we shall!

Next up:  Baby Fish Month – Part 2.