Archive for striped bass

Fish numbers in San Francisco Bay Delta remain low

Fishing in the Delta

February 2 is World Wetlands Day, a chance to raise awareness about the importance and value of wetlands. Unfortunately,  the results from the 2013 California Department of Fish and Wildlife (CDFW) Fall Midwater Trawl present a grim diagnosis of the health of California’s largest wetland ecosystem, the San Francisco Bay Delta. With the exception of a few years (1974 and 1979), the Fall Midwater Trawl has been conducted annually from 1967-2013 at approximately 122 stations throughout the Delta. Each station is sampled monthly from September to December, and station locations encompass San Pablo Bay and both the Sacramento River (upstream to Hood) and San Joaquin River (upstream to Stockton). Six fish species documented since 1967 include striped bass (Morone saxatilis), American shad (Alosa sapidissima), threadfin shad (Dorosoma petenense), delta smelt (Hypomesus transpacificus), longfin smelt (Spirinchus thaleichthys), and Sacramento splittail (Pogonichthys macrolepidotus).

Based on population indices reported by CDFW for the Fall Midwater Trawl, all six fish species exhibited low abundance in 2013, and many show continued declining abundance trends (Figure 1). Despite a slight increase in 2011, delta smelt abundance appears to remain low. Low abundance of multiple species may be indicative of the “continuing biological collapse” of the Bay Delta ecosystem, as stated by the California Sportfishing Protection Alliance. Population indices for all surveyed fish species have declined by more than 90 percent since surveys began. Care should be taken in interpreting such calculated indices and extrapolating these trends to a population as a whole, because a survey may not necessarily be representative of an entire population. However, it’s hard to deny that many Bay Delta fish populations have suffered dramatic losses in recent decades.Midwater Trawl Data

Fish declines in the Bay Delta have been linked to poor water quality, predation by non-native fishes, entrainment, and habitat loss (CDWR 2013). Striped bass, American shad, and threadfin shad are non-native to California, while the delta smelt, longfin smelt, and Sacramento splittail are native species. The delta smelt and longfin smelt are both listed as endangered under the Endangered Species Act, and the Sacramento splittail was delisted in 2003. Non-native fishes, such as the striped bass are known to prey upon juvenile salmon, and likely upon many other fishes (Stevens 1966, Nobriga et al. 2013). Striped bass and American shad have been present in the Delta since the late 19th century (Moyle 2002), and threadfin shad were introduced as a forage fish to the Sacramento-San Joaquin drainage in 1959 (CDWR 2013). Non-native fishes can also compete for food and habitat resources with native species, and the threadfin shad likely competes with the native delta smelt (CSWEM 2010). Declining fish population indices are a symptom of a complex barrage of environmental changes that currently threaten California’s major freshwater habitats.

This post featured in our weekly e-newsletter, the Fish Report. You can subscribe to the Fish Report here.


The latest catch: striped bass fyke trap study results

Striped bass catchThis past spring, FISHBIO used a pair of large fyke traps to target striped bass migrating from the Sacramento-San Joaquin Delta into the San Joaquin River as part of a mark-recapture abundance feasibility study (See Counting striped bass). Specifically, we wanted to evaluate trap catch rates, tagging procedures, and trap deployment locations. FISHBIO fabrication experts constructed two massive fyke traps, similar in design to traps that have been used by the Department of Fish and Wildlife (DFW) in the Sacramento River for decades (See What the fyke). After a three-week deployment, the results are in, and demonstrate the effectiveness of fyke traps for this purpose. However, more effort would be needed to mount a full-scale striped bass abundance survey.

STB with Tag VAKIThe traps were deployed last May at two locations between the head of the Old River near the city of Mossdale, California, and the confluence with the Stanislaus River more than 20 miles upstream. Overall, 45 striped bass and 49 bycatch fishes (Table 1) were captured over the course of 438 trap-hours (total sum of the hours each trap was set). Striped bass catch per trap-hour was calculated for each day-long trap set, and ranged from 0 to 0.94 bass per hour. Forty striped bass were tagged with yellow disk tags and passive integrated transponder (PIT) tags, and were released in good condition. Similar to results of previous DFW monitoring, the male-to-female sex ratio was highly skewed at 19:1. No striped bass were re-captured in the fyke traps, but anglers reported recapturing one tagged striped bass near the city of Stockton, and another in Old River in the South Delta. Additionally, a striped bass bearing a yellow disk tag was visually identified in video footage from the Stanislaus River weir, indicating that at least one tagged striped bass entered the Stanislaus River in June. 

The results of this pilot study demonstrate the successful use of fyke traps to capture and release healthy striped bass in the mainstem of the San Joaquin River. This capture method is less stressful for the fish than gill netting (Hopkins and Cech 1992), and has minimal impacts on other species, such as listed salmonids (all captured salmon were released in good condition). However, the lack of recaptured striped bass indicates that a much greater effort (through increasing the number of traps and the number of hours of sampling) would be needed for a successful mark-recapture study. The mark-recapture of striped bass would not only provide an opportunity to monitor and count individual striped bass in the San Joaquin Basin, but the sampling could also provide a platform for other valuable research on striped bass movements, such as using PIT and acoustic telemetry technologies. For more details on our pilot effort, please see the final report (Ainsley et al. 2013).

Table 1. Fish captured by species in the San Joaquin River fyke trap pilot study.SJR Fyke Trap Table

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Counting bass

Striped bass fyke trap

There are common questions that anglers and fish biologists often ask, such as What kinds of fish are found in this river? and How many are there? It’s often assumed that we have answered such basic questions long ago, but it’s not as easy as it sounds. Many factors can affect the abundance of fish species, including environmental factors like flow, temperature, and contaminants, or ecosystem factors like food supply and predator abundance. Recently, there has been growing interest in how many adult striped bass (Morone saxatilis) migrate into the San Joaquin River during their spring spawning migration.  

Since 1969, the California Department of Fish and Wildlife  (DFW, formerly “Fish and Game”) has been conducting a mark-and- recapture study to monitor the population dynamics of Central Valley striped bass, focusing on the Sacramento River and the Delta (see DFW reports). The estimated population of legal-sized striped bass remained relatively stable early in the study, but then declined in the late 1970s and 80s (Kohlhorst 1999). In response, DFW began a hatchery stocking program, but discontinued it in 1991 due to concerns about predation on endangered salmonids (Harris and Kohlhorst 1996). DFW studies found a subtle shift in the 1960s and 70s in spawner abundance, with fewer fish spawning the San Joaquin River and Delta and more in the Sacramento River, presumably due to poor water quality (e.g., higher salinity) in the San Joaquin (Turner 1976). With so many recent changes in water quality, water flows, and fish species composition in the estuary, people are curious about the current abundance of striped bass in the San Joaquin River basin.

DFW targets striped bass for their population study during the spring spawning migration in the Sacramento River, and uses large fyke traps north of the city of Sacramento. These traps have two internal fykes that funnel fish into the nose of the trap. We at FISHBIO have been curious whether fyke traps could be used for a similar project to estimate the population of striped bass specifically in the San Joaquin River, and decided to assess the feasibility by conducting a pilot study. After visiting traps operated by DFW and the Department of Water Resources, a few weeks of hard work in the Fab Lab (see What the fyke?), and a survey of potential trap sites, we launched two fyke traps into the river in early May.

We fish the traps for 24-hour periods and check them each morning. Several species may be captured on a given day, providing a glimpse into the species composition of the river. To date, we’ve caught American shad, largemouth bass, white catfish, suckers – and many striped bass. We measure all the striped bass, examine them for existing tags or marks, and tag the legal-size fish with a yellow disk tag, following the same methods DFW has used for decades. We also insert a PIT tag into each striped bass. In the future, we could monitor individual striped bass moving into the river’s tributaries using PIT tag antennas attached to weirs throughout the basin. There is a reward for anyone who recaptures these disk-tagged striped bass and provides us with the relevant information. If you fish the San Joaquin River or South Delta, you may want to keep an eye out for our yellow tags. It could be your lucky day!

This post featured in our weekly e-newsletter, the Fish Report. You can subscribe to the Fish Report here.

Delta rebound for fish cut short

The Stockton Record
By Alex Breitler
January 4, 2013

Fragile fish species in the Delta returned to near-record lows last year, evidence that a promising bump in 2011 was merely a short-term gain.

The notorious Delta smelt – the 3-inch fish whose dramatic downfall forced water cutbacks to cities and farms during the most recent drought – suffered through its seventh-lowest year on record in 2012, according to data released this week by the state Department of Fish and Wildlife.

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Don’t overlook the little guys

Adult striped bass inhabiting the California San Francisco Bay-Delta are known to be significant fish eating predators (piscivorous), but until recently there has been little research on population-level prey demand of sub-adults. Striped bass are anadromous as adults, migrating between the Sacramento and San Joaquin Rivers and the Pacific Ocean, but millions of sub-adults remain in the Bay-Delta estuary to feed and grow. Studying trends in striped bass consumption is not only important to understanding their feeding requirements, but also to assessing the potential impacts on prey species.
Fisheries biologists classify year-1 and year-2 striped bass as sub-adult (<18 inches) and fish year-3 and older as adults. Adult striped bass are largely opportunistic feeders, consuming almost any fish that will fit within their mouths. Juvenile striped bass initially feed on invertebrates (crustacean plankton, mysid shrimp and amphipods), but quickly move to preying on fish as they grow larger. According to a recently published study (Loboschefsky et al. 2012) in which researchers developed a bioenergetics model of sub-adult striped bass, age-2 striped bass consume an estimated 3.22-4.99 kg (7.1-11.0 lbs.) of fish annually. Perhaps the most interesting result of the model was that on a population level sub-adult striped bass, in most years, consume more prey annually than adult bass.  Although adults consume more prey per individual, sub-adults consume more prey at the population level because there are millions of sub-adults residing in the estuary. However, the population level consumption of fish by adults is still estimated to be greater than for sub-adults, since prey fish make up a greater proportion of the adult diet.

Fish and Game Commission denies CDFG’s proposed changes to striped bass angling regulations

Yesterday, by unanimous decision, the California Fish and Game Commission rejected proposed changes to striped bass regulations. To reduce predation on native salmonids and Delta smelt, the California Department of Fish and Game (CDFG) proposed decreasing size restrictions and increasing bag limits of striped bass. The sport fishing regulation changes were intended to reduce the size and abundance of striped bass in the Delta and Central Valley tributaries, and were proposed as part of a settlement agreement to a lawsuit by the Coalition for a Sustainable Delta. No word yet on how this will impact the original lawsuit, but, we think it’s fair to say that this issue is far from over.

Changes to California striped bass regulations on the table

Last Wednesday the California Department of Fish and Game (DFG) hosted a public meeting in Rio Vista to unveil proposed changes to striped bass fishing regulations. The DFG is required to make changes to the regulations under a lawsuit settlement earlier this year. The meeting was heated and emotional at times with approximately 300 in attendance, representing sport fisherman throughout the state. Many expressed their concerns over the impacts the proposed regulation might have on the future of striped bass fishing in California.

The lawsuit by the Coalition for a Sustainable Delta against the DFG was settled in April 2011. Under the settlement, a comprehensive proposal to address striped bass predation in the Delta must be developed by state and federal fishery management agencies. As part of the settlement DFG must make appropriate changes to the bag limit and size limit regulations to reduce striped bass predation on the listed species, develop an adaptive management plan to research and monitor the overall effects on striped bass abundance, and create a $1 million research program focused on predation of protected species.

The striped bass regulations include raising the daily bag limit for striped bass from 2 to 6 fish with a possession limit of 12, and lowering the minimum size for striped bass from 18 to 12 inches. There will also be a “hot spot” for striped bass fishing at Clifton Court Forebay with a daily bag limit of 20 fish, a possession limit of 40 fish and no size limit. Fishing the hot spot will require a report card to be filled out and deposited it in an iron ranger or similar receptacle.

These proposed regulations are not designed to extirpate the striped bass population in California, but are expected to help reduce predation pressure by striped bass on native salmonids and Delta smelt. There are multiple factors, such as diversion facilities, loss of habitat, water quality and predation that have adverse effects on endangered fish in the Delta. In order to address recent declines in salmonid and Delta smelt populations various changes in management practices have been implemented. These practices include, the Biological Opinions on the long-term operations of the Central Valley Project and State Water Project, the Central Valley Project Improvement Act (CVPIA), Total Maximum Daily Load (TMDL) requirements and state and federal fishing regulations. The proposed striped bass reduction plan would join the line up of controversial policies aimed at minimizing the effects of these potential stressors.

Fall-run striped bass!?

For many years most anglers and fisheries biologist had a rough idea of striped bass (Morone saxatilis) movements between the fresh water Delta and tributaries, and marine waters of the San Francisco Bay and beyond. Conventional wisdom tells us that the majority of striped bass move from saltwater into the lower reaches of the Sacramento and San Joaquin Rivers in the spring to spawn, then move to the lower Delta during the summer before migrating back out through the San Francisco Bay to the ocean in late summer and early fall. However, with advances in fisheries technology results from recent research are beginning to challenge the conventional wisdom.

As you can see from this video captured from a Vaki Riverwatcher electronic fish counting system installed at the weir on the lower Tuolumne River, striped bass of all age classes can and do migrate upriver during the fall. It is not clear whether the bass we have detected moving upstream in the fall are migrating, or if they are resident fish that are present year round and are just moving throughout their range. This fish counting weir was installed on September 9, 2010 and has detected 17 striped bass through September 20, 2010 migrating upstream.

Video source: FISHBIO

Low tech fish tag


In this era when fish tags send instant messages to researchers and emit sound waves to communicate with receivers to track fish over long distances, it’s ironic that we rely on this old-school Floy tag as a backup to our expensive high-tech devices. This tag was recently inserted into the back of a striped bass to serve as a means of identifying this fish upon recapture, either upon the failure of the primary electronic tag, or after the tag’s battery life expires.

Photo source: FISHBIO


environmental consulting and environmental research predator tagging bassSurprisingly, although striped bass (Morone saxatilis) are one of the Delta’s most popular sportfish, little is known about their fine-scale migration behavior throughout California. Until recently we believed, for instance, that stripers generally move towards open-water (i.e. bay and ocean) during the winter months, then migrate upstream into lower tributary reaches to spawn in spring, the same time many juvenile salmon and steelhead are migrating downstream. However, sampling in tributaries over the last few years has revealed that a significant number of stripers may reside year-round in freshwater, rather than annually migrating between freshwater and the bay/ocean. This would be an important finding because it would change our current model of freshwater fish communities in lower river reaches throughout California’s Central Valley.

environmental consulting and environmental research field crew tagging predator bass

This striped bass is being tagged with an acoustic transmitter to evaluate its fine-scale (i.e. within freshwater) migration characteristics. This tagged fish, along with many others just like it, will help us evaluate the spatial and temporal distribution of stripers in freshwater, and how variables such as time of year, water temperature, and river flow influence their behavior. The tag is an HTI X-type tag that is secured under the dorsal fin with thin coated cable, inserted through the fish with the help of two 14 gage hypodermic needles. A yellow Floy Tag with our contact info is also placed on the fish in case the fish is captured by an angler, and to help us visually identify the fish during snorkel surveys.

environmental consulting and environmental research field crew tagging predator bass