Bait — Grass Shrimp

Ken Jones

Staff member
Grass Shrimp. These small shrimp are important bait in the San Francisco Bay Area. However, the name is somewhat of a misnomer since they are actually bay shrimp, and there are three different types of shrimp. The most common are the California bay shrimp, Cragon franciscorum. This is the shrimp that supported the commercial shrimp fleets, in places like China Camp, from the 1870s to the 1930s. In its peak year, 1935, the fishery saw over three million pounds of shrimp landed, most of which was dried and then used as food. Following the mid ‘30s a decrease began in the catch, which continues somewhat to this day (see reasons below).


Grass Shrimp

Most years now see less than 100,000 pounds a year landed, all of which is sold to bait shops. Common throughout both San Pablo and Suisun Bay, the shrimp are typically found off of Pittsburg from June to August, and then off the Martinez-Port Chicago area from September to November.

In addition to the true California bay shrimp, the smaller blacktail bay shrimp, Cragon nigricauda, and the increasingly common oriental shrimp, sometimes called the Korean or pile shrimp, Palaemon macrodactylus, are also found in these waters and frequently are mixed in with the other shrimp as bait. The oriental shrimp was apparently introduced accidentally from the ballast of ships returning from Asia during the Korean War and today is reported by some sources as more common than Cragon franciscorum.

Grass shrimp are sold live at most Bay Area bait shops. Although sold by the pound, generally a quarter of a pound per person will last all day and they will stay alive if kept cool. They are excellent bait in the bay for many species including perch, white croaker (kingfish), and flatfish like the starry flounder. They are one of the better baits for sturgeon, and are common bait for striped bass. They are much less productive in oceanfront waters.

Usually they are hooked from the head down to the tail with the barb of the hook exposed near the tail (although many hook them in an opposite tail to head manner). You may also put several on your hook (if they are small) and, by just barely hooking them in the side; they will stay alive on the hook for a considerable length of time.

You can of course try to catch your own shrimp. The most common method is to use one of the commercially available shrimp traps that are baited and then lowered down into likely looking neighborhoods for the shrimp. Although California bay shrimp tend to be in somewhat deeper waters, the other two species are frequently caught in traps. Blacktail bay shrimp, with their salt-and-pepper markings, are most commonly found in sand flat areas, often in pools in the sand or buried in the sand, and are also netted by shrimp boats down to a depth of several fathoms. Oriental shrimp are a brackish-water species most common to the streams of Marin County but also moving considerably upstream as far as Antioch. The Oriental shrimp is somewhat larger than the native species (reaching about two inches in length) and has more numerous antennae and a long, toothed rostrum.

They can be kept in good condition throughout the day with the use of a chilled bait cooler (which I recommend). However, the bait shops typically put them in a plastic bag, which is then put inside a second bag containing ice. Whatever the method, try to keep them cool.


Grass Shrimp

If at the end of the day you have some left over you can freeze them in a Ziploc (or similar) bag in your freezer. An idea courtesy of Songslinger on PFIC, “freeze them in baggies with a 3:1 ratio of salt to borax. It keeps them white and fresh-like.”

As to why the number of shrimp have decreased? The main factor has been the loss of tidal marsh around San Francisco Bay, marshlands where the shrimp thrive. In 1930 the Bay Area population was about 1.57 million people. In 2010 the population was 7.15 million people. To accommodate the need for additional homes and business, shoreline areas were dredged and reshaped into usable land for humans while making it unusable for native species like shrimp (and many, many other creatures). Luckily today, many groups are working on restoring marshlands to the bay (but it’s a long term project).

In addition, there are the changes to the bay waters themselves, waters that are the home environment to the shrimp. These shrimp prefer brackish water with a salinity level of 14 parts per thousand (ppt) when young to 24 ppt when ready to spawn. (Ocean waters in contrast are around 35ppt.) They also prefer water temperatures around 65 degrees.

To meet these two criteria, the shrimp move around the bay as dictated by changes in the bay water’s salinity and temperature levels. Winter and spring months see increased freshwater entering San Pablo Bay from the Carquinez Strait. It is runoff from winter storms and, as snow melts in the mountains, it is cold-water runoff from inland areas (snow > water > mountain streams > rivers > Sacramento-San Joaquin Delta > Suisun Bay > Carquinez Straits > San Pablo Bay > San Francisco Bay).

As the winter and spring runoff continues, the bottom water levels in San Pablo Bay continue to see their heavier, more dense saltwater, while the less dense freshwater stream on the top can become thicker; the overall mix is less salty water, water too fresh for the shrimp. During those months the shrimp may move into South San Francisco Bay or even into the ocean.

As the inland water flows decrease in late spring, the shrimp move back into San Pablo Bay and, as water becomes saltier and warmer, move up into Suisun Bay. The change in seasons and saltiness of the bay has always existed but state and federal water projects have complicated the situation. By the 1980s, the amount of water entering the bay had decreased by about 60% from historic levels and though the result to the shrimp population is complex to answer, the decrease probably had a somewhat negative affect. In addition, water is controlled and released by the “pumps” in relation to water and temperature levels affecting the Delta smelt; the downriver impact to other creatures such as these shrimp hasn’t, as far as I know, been studied.

There is not doubt that the population fluctuates in dramatic style, decreasing during dry rain years and increasing during wet rain years. It was reported by Bay Nature Magazine that “in 1996, after two wet years, the shrimp population was 20 times larger than it was in 1980, following the severe drought of the late 1970s.” Since then there have been several periods of drought.

A final interesting fact about Cragon franciscorum, is their lifespan. Apparently the males live to an age of about 18 months while the females live to about 30 months. However, some evidence indicates the species may be protandrous hermaphrodites and that surviving males are transformed into females after one year of life. This may account for the longer lifespan of females.